documents: block checks read as drawn; alert, fence and box edges kept

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -13,7 +13,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - Web views: `wry` 0.57 (Apache-2.0 OR MIT, default features off, macOS only) lays a child WKWebView over the window.
 - Terminal: `alacritty_terminal` 0.26 (Apache-2.0, default features off, native only) for the grid, its parser and the pseudo-terminal; `futures` carries its events. `vte` 0.15 (Apache-2.0 OR MIT), the parser it re-exports, reads `AnsiText`'s codes alone, so colored output builds for wasm32.
 - Diffs: `similar` 3.2 (Apache-2.0) for line and word diffs and three-way merges; its `unicode` feature splits words at punctuation.
-- Markdown: `markdown` 1.0.0 (markdown-rs, MIT) reads GitHub's flavor and math into a syntax tree with byte positions for `MarkdownRenderer`, `MarkdownEditor`, the highlights, block ranges and outline. `MarkdownRenderer` draws display math through `typography::Latex`, a ```` ```mermaid ```` block through `documents::Diagram`, and pictures from the owner's folder (`base`) or `data:` addresses (`base64` 0.22, MIT OR Apache-2.0); web pictures stay unloaded. Inline math shows as TeX: gpui text carries no inline pictures. Inline it reads as Typora's defaults: `:shortcode:` turns to its emoji as GitHub reads it (the `emojis` crate's names, GitHub's today, so `:cricket:` is the insect; read after escapes and references, so `\:smile:` turns too; inside an autolink or `<code>` it stays text; within one DOM text node, which filtered tags do not split, the first `:name:`-shaped run decides for all: blank text or a space before it turns every shortcode, else none, so `x:smile: :smile:` stays), inline HTML's `u`, `b`/`strong`, `i`/`em`, `s`/`del`/`strike`, `code`/`kbd`, `mark`, `br` and `a href` draw as what they mean GFM's filtered tags (`script`, `style`, `title`, `textarea`, `iframe`, `xmp`, `noembed`, `noframes`, `plaintext`) show as text, and other tags, hyphenated names too, vanish, leaving their text; a tag's name runs to white space or `/`, as HTML5 reads it; attribute values split on ASCII whitespace alone and decode as HTML decodes them; each Markdown container is the element GitHub writes (`em`, `strong`, `del`, `a`), on one stack with the tags and repaired as HTML5 repairs: an end tag closes the innermost element of its name and all above it, of which only formatting elements (`a`, `b`, `code`, `em`, `i`, `s`, `strike`, `strong`, `u`) reopen, a new `a` ends the open one and an `a` without `href` links nothing; other tags are not tracked, and `</br>` breaks as `<br>` does; and a footnote reference is its number in superscript, numbered by first reference, as its definition is; one `~` still strikes. At the root, blocks read as GitHub shows them: a quote whose first line is plain text reading `[!NOTE]`, `[!TIP]`, `[!IMPORTANT]`, `[!WARNING]` or `[!CAUTION]` in any case, after escapes and references, spaces and tabs around it, with more after it, is an alert under its title (Important in the palette's violet, `syntax.keyword`, read at 4.5:1); a paragraph that is `[toc]` alone, as Typora reads it, lists every heading by depth, and a press on one reveals it as a link press does (`MarkdownDocument`'s `reveal`), the heading found where `CodeEditor` anchors carried it through each edit since the read, gone if an edit or an undo took it, and a secondary press acts on press, since a block writing back moves the list; front matter shows in a box without its fences; an HTML block shows its text with the inline tags above, white space collapsed and owed as a browser lays it, block elements breaking lines and closing what opened inside them, HTML5's start tags ending an open `p`, `fieldset` and `menu` too, and an `li` start an `li`, a `dd` or `dt` start either, as HTML5 ends them, comments dropped, the filtered tags shown as text, and an unclosed tag dropping the rest; a rule is a 2px `border_strong` line; bullets go •, ◦, ▪ by list depth, ordered lists counted. Exports read a tree as the drawing does through `MarkdownReader` (`block` gives its `MarkdownBlock`s, `inline` its text, `note` and `label` its footnotes, `headings` the `[toc]` list), one fresh stack per paragraph, heading or cell. `MarkdownDocument` holds a whole file in one `CodeEditor` (text and undo, colored by `CodeEditor::highlighter` with `markdown_highlights`): visual draws the file's top-level blocks in a gpui `list`, a pressed block opening as its source in a `TextInput` whose typing is the document's text at once and whose write-back is one undo step; source is the editor; preview draws without presses. A written-back block, a mode switch or a new text is read at once up to 128 KiB, longer ones on the background executor; typing in source or split reads 300 ms after the last key, off the main thread (markdown-rs grows with the square of its nodes, not its bytes: in release, 128 KiB of one-letter paragraphs takes 1.7 s, 16 KiB 42 ms, while 128 KiB of prose takes 20 ms; a block-heavy text under the cutoff can still hold the UI thread past 100 ms, a known limit). Texts past `LARGEST_READ` (2 MiB) are never read: no blocks, no outline. A new read keeps the list's blocks alike at both ends. One caret serves every mode: the editor's selection, which a written-back block moves; `set_caret` and `set_top_line` set caret and view apart; a top line asked (numbered, so a late frame callback finishes only its own ask; new text places it again, clamped to the text as it then is) waits for the read, lands on its block, then a frame later at its share of the block's height; `reveal` is such an ask with the caret at its line; a switch between source and the listLine truncated
+- Markdown: `markdown` 1.0.0 (markdown-rs, MIT) reads GitHub's flavor and math into a syntax tree with byte positions for `MarkdownRenderer`, `MarkdownEditor`, the highlights, block ranges and outline. `MarkdownRenderer` draws display math through `typography::Latex`, a ```` ```mermaid ```` block through `documents::Diagram`, and pictures from the owner's folder (`base`) or `data:` addresses (`base64` 0.22, MIT OR Apache-2.0); web pictures stay unloaded. Inline math shows as TeX: gpui text carries no inline pictures. Inline it reads as Typora's defaults: `:shortcode:` turns to its emoji as GitHub reads it (the `emojis` crate's names, GitHub's today, so `:cricket:` is the insect; read after escapes and references, so `\:smile:` turns too; inside an autolink or `<code>` it stays text; within one DOM text node, which filtered tags do not split, the first `:name:`-shaped run decides for all: blank text or a space before it turns every shortcode, else none, so `x:smile: :smile:` stays), inline HTML's `u`, `b`/`strong`, `i`/`em`, `s`/`del`/`strike`, `code`/`kbd`, `mark`, `br` and `a href` draw as what they mean GFM's filtered tags (`script`, `style`, `title`, `textarea`, `iframe`, `xmp`, `noembed`, `noframes`, `plaintext`) show as text, and other tags, hyphenated names too, vanish, leaving their text; a tag's name runs to white space or `/`, as HTML5 reads it; attribute values split on ASCII whitespace alone and decode as HTML decodes them; each Markdown container is the element GitHub writes (`em`, `strong`, `del`, `a`), on one stack with the tags and repaired as HTML5 repairs: an end tag closes the innermost element of its name and all above it, of which only formatting elements (`a`, `b`, `code`, `em`, `i`, `s`, `strike`, `strong`, `u`) reopen, a new `a` ends the open one and an `a` without `href` links nothing; other tags are not tracked, and `</br>` breaks as `<br>` does; and a footnote reference is its number in superscript, numbered by first reference, as its definition is; one `~` still strikes. At the root, blocks read as GitHub shows them: a quote whose first line is plain text reading `[!NOTE]`, `[!TIP]`, `[!IMPORTANT]`, `[!WARNING]` or `[!CAUTION]` in any case, after escapes and references, spaces and tabs around it, with more after it, is an alert under its title (Important in the palette's violet, `syntax.keyword`, read at 4.5:1); a paragraph that is `[toc]` alone, as Typora reads it, lists every heading by depth, and a press on one reveals it as a link press does (`MarkdownDocument`'s `reveal`), the heading found where `CodeEditor` anchors carried it through each edit since the read, gone if an edit or an undo took it, and a secondary press acts on press, since a block writing back moves the list; front matter shows in a box without its fences; an HTML block shows its text with the inline tags above, white space collapsed and owed as a browser lays it, block elements breaking lines and closing what opened inside them, HTML5's start tags ending an open `p`, `fieldset` and `menu` too, and an `li` start an `li`, a `dd` or `dt` start either, as HTML5 ends them, comments dropped, the filtered tags shown as text, and an unclosed tag dropping the rest; a rule is a 2px `border_strong` line; bullets go •, ◦, ▪ by list depth, ordered lists counted. Exports read a tree as the drawing does through `MarkdownReader` (`block` gives its `MarkdownBlock`s, `inline` its text, `note` and `label` its footnotes, `headings` the `[toc]` list), one fresh stack per paragraph, heading or cell. `MarkdownDocument` holds a whole file in one `CodeEditor` (text and undo, colored by `CodeEditor::highlighter` with `markdown_highlights`): visual draws the file's top-level blocks in a gpui `list`, a pressed block opening as its source in a `TextInput` whose typing is the document's text at once and whose write-back is one undo step; source is the editor; preview draws without presses. A written-back block, a mode switch or a new text is read at once up to 128 KiB, longer ones on the background executor; typing in source or split reads 300 ms after the last key, off the main thread (markdown-rs grows with the square of its nodes, not its bytes: in release, 128 KiB of one-letter paragraphs takes 1.7 s, 16 KiB 42 ms, while 128 KiB of prose takes 20 ms; a block-heavy text under the cutoff can still hold the UI thread past 100 ms, a known limit). Texts past `LARGEST_READ` (2 MiB) are never read: no blocks, no outline. A new read keeps the list's blocks alike at both ends. One caret serves every mode: the editor's selection, which a written-back block moves; `set_caret` and `set_top_line` set caret and view apart; a top line asked (numbered, so a late frame callback finishes only its own ask; new text places it again, clamped to the text as it then is) waits for the read, lands on its block, then a frame later at its share of the block's height; `reveal` is such an ask with the caret at its line; a switch between source and the listLine truncated
 - Pictures: `image` 0.25 (MIT OR Apache-2.0), the crate gpui decodes with, default features off; it turns decoded frames and rims map tiles.
 - Math and diagrams: RaTeX 0.1.14 (`ratex-parser`, `ratex-layout`, `ratex-svg` with `embed-fonts`, `ratex-types`; MIT, KaTeX's fonts OFL) typesets `Latex` to SVG with outlined glyphs; `mermaid-rs-renderer` 0.3.1 (MIT, default features off) draws `Diagram`. Both go through gpui's `SvgRenderer` at the window's scale, loaded as gpui assets off the main thread; `usvg` 0.46, gpui's own, reads a diagram's size. A RaTeX or Mermaid panic on parsed input becomes the element's error. Each element holds its picture through `primitives::held`: a new source, or the element leaving the window, removes the old asset from gpui's cache and drops its image from the atlas after the frame.
 - Maps: Natural Earth's 110m countries (public domain). `assets/maps/countries.geojson`, trimmed by `scripts/countries.py` to an ISO code, a name and positions to 0.01°, backs `maps::WorldMap`; the gallery's tiles are cut from the same file, z0 to z3, by `scripts/tiles.py` with Pillow.

src/documents/document/apart.rs

@@ -0,0 +1,165 @@
+//! Edits read off the UI thread: formats and block commands.
+
+use std::ops::Range;
+
+use gpui::{AppContext as _, Context};
+
+use super::{
+    DocumentEvent, LARGEST_READ, MarkdownDocument,
+    block::{self, BlockCommand},
+    format::{Change, EditRefusal, InlineFormat, toggle},
+};
+use crate::documents::{MarkdownMode, modes::joint};
+
+/// The text read, the open block's offset, the selection.
+type Snapshot = (String, usize, Range<usize>);
+
+impl MarkdownDocument {
+    /// `format` at the selection, read apart; refusals by event.
+    pub fn format(
+        &mut self,
+        format: InlineFormat,
+        cx: &mut Context<Self>,
+    ) -> Result<(), EditRefusal> {
+        self.apart(
+            format!("format {format:?}"),
+            move |full, selection| toggle(full, selection, format),
+            cx,
+        )
+    }
+
+    /// `command` at the caret, read apart; refusals by event.
+    pub fn block(
+        &mut self,
+        command: BlockCommand,
+        cx: &mut Context<Self>,
+    ) -> Result<(), EditRefusal> {
+        self.apart(
+            format!("block {command:?}"),
+            move |full, selection| block::run(full, selection, command),
+            cx,
+        )
+    }
+
+    /// Reads `read` off the UI thread, then writes its change.
+    fn apart(
+        &mut self,
+        name: String,
+        read: impl FnOnce(&str, Range<usize>) -> Result<Change, EditRefusal> + Send + 'static,
+        cx: &mut Context<Self>,
+    ) -> Result<(), EditRefusal> {
+        if self.mode == MarkdownMode::Preview {
+            return Err(EditRefusal::Preview);
+        }
+        let (full, offset, selection) = self.snapshot(cx);
+        if full.len() > LARGEST_READ {
+            log::info!("markdown document: {name} refused: {} bytes", full.len());
+            return Err(EditRefusal::TooLong);
+        }
+        if self.editing {
+            log::info!("markdown document: {name} refused: one runs");
+            return Err(EditRefusal::Busy);
+        }
+        log::info!("markdown document: {name} reads {} bytes apart", full.len());
+        let taken = (full.clone(), offset, selection.clone());
+        self.editing = true;
+        cx.spawn(async move |document, cx| {
+            let change = cx
+                .background_spawn(async move { read(&full, selection) })
+                .await;
+            document
+                .update(cx, |document, cx| {
+                    document.editing = false;
+                    let done = if document.mode == MarkdownMode::Preview {
+                        Err(EditRefusal::Preview)
+                    } else if document.snapshot(cx) != taken {
+                        Err(EditRefusal::Changed)
+                    } else {
+                        change
+                            .and_then(|change| document.apply(&name, change, &taken.0, taken.1, cx))
+                    };
+                    if let Err(why) = done {
+                        log::info!("markdown document: {name} refused: {why:?}");
+                        cx.emit(DocumentEvent::EditRefused(why));
+                    }
+                })
+                .ok();
+        })
+        .detach();
+        Ok(())
+    }
+
+    /// The text an edit reads: the open block's in place.
+    fn snapshot(&self, cx: &Context<Self>) -> Snapshot {
+        let text = self.editor.read(cx).text();
+        let Some(open) = &self.open else {
+            return (text.to_string(), 0, self.editor.read(cx).primary().range());
+        };
+        let input = open.input.read(cx);
+        let (before, after) = match open.append {
+            true => (format!("{text}{}", joint(text)), ""),
+            false => (
+                text[..open.range.start].to_string(),
+                &text[open.range.end..],
+            ),
+        };
+        let picked = input.selection();
+        let offset = before.len();
+        let full = format!("{before}{}{after}", input.text());
+        (full, offset, offset + picked.start..offset + picked.end)
+    }
+
+    /// Writes `change`: into the open block while it stays inside.
+    fn apply(
+        &mut self,
+        name: &str,
+        (edits, selected): Change,
+        full: &str,
+        offset: usize,
+        cx: &mut Context<Self>,
+    ) -> Result<(), EditRefusal> {
+        log::info!("markdown document: {name}");
+        if let Some(open) = &self.open {
+            let end = offset + open.input.read(cx).text().len();
+            let grown = (edits.iter().map(|(_, with)| with.len()).sum::<usize>() + end)
+                .checked_sub(edits.iter().map(|(range, _)| range.len()).sum::<usize>());
+            let inside = edits
+                .iter()
+                .all(|(range, _)| offset <= range.start && range.end <= end)
+                && grown.is_some_and(|grown| offset <= selected.start && selected.end <= grown);
+            if inside {
+                let (Some(from), Some(to)) = (
+                    edits.iter().map(|(range, _)| range.start).min(),
+                    edits.iter().map(|(range, _)| range.end).max(),
+                ) else {
+                    return Ok(());
+                };
+                let mut written = String::new();
+                let mut at = from;
+                for (range, with) in &edits {
+                    written.push_str(&full[at..range.start]);
+                    written.push_str(with);
+                    at = range.end;
+                }
+                written.push_str(&full[at..to]);
+                open.input.update(cx, |input, cx| {
+                    input.select(from - offset..to - offset, cx);
+                    input.insert(&written, cx);
+                    input.select(selected.start - offset..selected.end - offset, cx);
+                });
+                return Ok(());
+            }
+            log::info!("markdown document: {name} reaches past the open block");
+            self.commit(cx);
+            if self.editor.read(cx).text() != full {
+                log::error!("markdown document: {name}: the write-back is not the text read");
+                return Err(EditRefusal::Changed);
+            }
+        }
+        self.editor.update(cx, |editor, cx| {
+            editor.edit(edits, cx);
+            editor.select(std::iter::once(selected), cx);
+        });
+        Ok(())
+    }
+}

src/documents/document/block.rs

@@ -0,0 +1,446 @@
+//! Block commands at the caret, as Typora's Paragraph menu (R4.7).
+
+mod check;
+mod heading;
+mod insert;
+mod list;
+mod quote;
+mod split;
+
+use std::ops::Range;
+
+use markdown::mdast::Node;
+
+use super::format::{Change, EditRefusal};
+use crate::documents::markdown::{file_tree, span, walk};
+
+/// A command of Typora's Paragraph menu.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum BlockCommand {
+    /// Levels 1 to 6.
+    Heading(u8),
+    Paragraph,
+    /// A level up; a paragraph turns level 6.
+    Promote,
+    /// A level down; level 6 turns a paragraph.
+    Demote,
+    Quote,
+    OrderedList,
+    BulletList,
+    TaskList,
+    Rule,
+    CodeBlock,
+    MathBlock,
+    Toc,
+    FrontMatter,
+    Footnote,
+    LinkDefinition,
+    ParagraphBefore,
+    ParagraphAfter,
+    Delete,
+}
+
+/// `command` at `selection` in `text`, or why not.
+pub(super) fn run(
+    text: &str,
+    selection: Range<usize>,
+    command: BlockCommand,
+) -> Result<Change, EditRefusal> {
+    let root = file_tree(text);
+    let here = Here::new(text, &root, selection);
+    match command {
+        BlockCommand::Heading(_)
+        | BlockCommand::Paragraph
+        | BlockCommand::Promote
+        | BlockCommand::Demote => heading::run(&here, command),
+        BlockCommand::Quote => quote::run(&here),
+        BlockCommand::OrderedList | BlockCommand::BulletList | BlockCommand::TaskList => {
+            list::run(&here, command)
+        }
+        BlockCommand::FrontMatter => insert::front_matter(&here),
+        BlockCommand::ParagraphBefore => insert::paragraph(&here, true),
+        BlockCommand::ParagraphAfter => insert::paragraph(&here, false),
+        BlockCommand::Delete => insert::delete(&here),
+        _ => insert::run(&here, command),
+    }
+}
+
+/// The caret's place in the parsed text.
+pub(super) struct Here<'a> {
+    pub(super) text: &'a str,
+    pub(super) selection: Range<usize>,
+    /// Root down to the deepest block at the selection's start.
+    pub(super) path: Vec<&'a Node>,
+    pub(super) root: &'a Node,
+    /// Every node, in document order.
+    pub(super) nodes: Vec<&'a Node>,
+}
+
+impl<'a> Here<'a> {
+    fn new(text: &'a str, root: &'a Node, selection: Range<usize>) -> Self {
+        let mut nodes = Vec::new();
+        walk(root, &mut nodes);
+        Here {
+            text,
+            path: path(text, root, selection.start),
+            selection,
+            root,
+            nodes,
+        }
+    }
+
+    /// The caret's block, unless the path ends on a container.
+    pub(super) fn leaf(&self) -> Option<&'a Node> {
+        let last = *self.path.last()?;
+        (!holds(last)).then_some(last)
+    }
+
+    /// The containers around `path[..upto]`.
+    pub(super) fn containers(&self, upto: usize) -> Vec<&'a Node> {
+        self.path[..upto]
+            .iter()
+            .copied()
+            .filter(|node| container(node))
+            .collect()
+    }
+
+    /// Whether the caret's line holds nothing past its prefix.
+    pub(super) fn blank(&self) -> bool {
+        let line = line_start(self.text, self.selection.start);
+        let containers = self.containers(self.path.len());
+        inside(self.text, line, &containers)
+            .is_some_and(|at| self.text[at..line_end(self.text, line)].trim().is_empty())
+    }
+
+    /// Root down to the deepest block at `at`.
+    pub(super) fn path_at(&self, at: usize) -> Vec<&'a Node> {
+        path(self.text, self.root, at)
+    }
+
+    /// The common holder's index and the blocks the selection touches.
+    pub(super) fn blocks(&self) -> Option<(usize, Vec<&'a Node>)> {
+        let end = self.path_at(self.selection.end);
+        let mut k = 0;
+        while k + 1 < self.path.len()
+            && k + 1 < end.len()
+            && std::ptr::eq(self.path[k + 1], end[k + 1])
+        {
+            k += 1;
+        }
+        if !holds(self.path[k]) {
+            return Some((k - 1, vec![self.path[k]]));
+        }
+        let (s, e) = (self.selection.start, self.selection.end);
+        let kids: Vec<&Node> = (self.path[k].children().map(Vec::as_slice))
+            .unwrap_or_default()
+            .iter()
+            .filter(|kid| span(kid).start <= e && s <= span(kid).end)
+            .collect();
+        (!kids.is_empty()).then_some((k, kids))
+    }
+
+    /// Whether a paragraph ending on the line before joins `block`.
+    pub(super) fn joins_before(&self, block: &Range<usize>, gone: &[&Node]) -> bool {
+        let line = line_start(self.text, block.start);
+        let Some(previous) = prev_line(self.text, line) else {
+            return false;
+        };
+        let ended = (self.nodes.iter()).any(|node| {
+            matches!(node, Node::Paragraph(_)) && line_start(self.text, span(node).end) == previous
+        });
+        ended && !self.opens(line, gone)
+    }
+
+    /// Whether the line after `block` would join it as text.
+    pub(super) fn joins_after(&self, block: &Range<usize>) -> bool {
+        let Some(next) = next_line(self.text, block.end) else {
+            return false;
+        };
+        let starts = (self.nodes.iter()).any(|node| {
+            let at = span(node).start;
+            line_start(self.text, at) == next
+                && match node {
+                    Node::Paragraph(_) => true,
+                    Node::ThematicBreak(_) => self.text[at..].starts_with('-'),
+                    _ => false,
+                }
+        });
+        starts && !self.opens(next, &[])
+    }
+
+    /// Whether `line` opens a container that stays and interrupts.
+    fn opens(&self, line: usize, gone: &[&Node]) -> bool {
+        let on = |node: &Node| line_start(self.text, span(node).start) == line;
+        let left = |node: &Node| !gone.iter().any(|gone| std::ptr::eq(*gone, node));
+        (self.nodes.iter()).any(|node| match node {
+            Node::List(list) if left(node) => list
+                .children
+                .iter()
+                .any(|item| on(item) && (!list.ordered || list.start == Some(1))),
+            Node::Blockquote(_) => on(node) && left(node),
+            _ => false,
+        })
+    }
+}
+
+/// Blockquotes, list items and footnote definitions.
+pub(super) fn container(node: &Node) -> bool {
+    matches!(
+        node,
+        Node::Blockquote(_) | Node::ListItem(_) | Node::FootnoteDefinition(_)
+    )
+}
+
+/// Whether `node` is task item `holder`'s first text.
+pub(super) fn task_head(holder: &Node, node: &Node) -> bool {
+    matches!(holder, Node::ListItem(item)
+        if item.checked.is_some()
+            && item.children.first().is_some_and(|kid| std::ptr::eq(kid, node)))
+}
+
+/// Where a heading-closing `#` run starts in `line`.
+pub(super) fn closing(line: &str) -> Option<usize> {
+    let line = line.trim_end_matches([' ', '\t']);
+    let kept = line.trim_end_matches('#');
+    (kept.len() < line.len() && kept.ends_with([' ', '\t'])).then_some(kept.len())
+}
+
+/// The byte to escape so `line` reads as prose.
+pub(super) fn unblocked(line: &str) -> Result<Option<usize>, EditRefusal> {
+    let prose = |line: &str| {
+        let root = file_tree(line);
+        matches!(
+            root.children().and_then(|kids| kids.first()),
+            Some(Node::Paragraph(_))
+        )
+    };
+    if prose(line) {
+        return Ok(None);
+    }
+    let mark = line.find(|ch: char| ch.is_ascii_punctuation());
+    match mark.filter(|mark| prose(&format!("{}\\{}", &line[..*mark], &line[*mark..]))) {
+        Some(mark) => Ok(Some(mark)),
+        None => Err(check::misread("a line stays a block")),
+    }
+}
+
+/// Whether the path goes on below `node`.
+fn holds(node: &Node) -> bool {
+    container(node) || matches!(node, Node::Root(_) | Node::List(_))
+}
+
+/// Root down to the deepest block at `at`.
+fn path<'a>(text: &str, root: &'a Node, at: usize) -> Vec<&'a Node> {
+    let mut path = vec![root];
+    while let Some(node) = path.last().copied().filter(|node| holds(node)) {
+        let kids = node.children().map(Vec::as_slice).unwrap_or_default();
+        let found = (kids.iter())
+            .find(|kid| span(kid).contains(&at) || span(kid).end == at)
+            .or_else(|| {
+                // A caret before a block on its line is inside.
+                (kids.iter()).find(|kid| {
+                    let start = span(kid).start;
+                    at < start && !text[at..start].contains(['\n', '\r'])
+                })
+            });
+        let Some(kid) = found else {
+            break;
+        };
+        path.push(kid);
+    }
+    path
+}
+
+pub(super) fn line_start(text: &str, at: usize) -> usize {
+    text[..at].rfind(['\n', '\r']).map_or(0, |at| at + 1)
+}
+
+pub(super) fn line_end(text: &str, at: usize) -> usize {
+    at + text[at..].find(['\n', '\r']).unwrap_or(text.len() - at)
+}
+
+/// The start of the line after `at`'s.
+pub(super) fn next_line(text: &str, at: usize) -> Option<usize> {
+    let end = line_end(text, at);
+    let rest = &text[end..];
+    let ending = if rest.starts_with("\r\n") { 2 } else { 1 };
+    (end < text.len()).then_some(end + ending)
+}
+
+/// The start of the line before `at`'s.
+pub(super) fn prev_line(text: &str, at: usize) -> Option<usize> {
+    let start = line_start(text, at);
+    let ending = if text[..start].ends_with("\r\n") {
+        2
+    } else {
+        1
+    };
+    (start > 0).then(|| line_start(text, start - ending))
+}
+
+/// The text's own line ending.
+pub(super) fn eol(text: &str) -> &'static str {
+    match (text.contains("\r\n"), text.contains('\r')) {
+        (true, _) => "\r\n",
+        (false, true) => "\r",
+        _ => "\n",
+    }
+}
+
+/// Columns before `at` on its line, tabs stopping at four.
+pub(super) fn column(text: &str, at: usize) -> usize {
+    advance(0, &text[line_start(text, at)..at])
+}
+
+fn advance(col: usize, run: &str) -> usize {
+    run.chars().fold(col, |col, ch| match ch {
+        '\t' => col / 4 * 4 + 4,
+        _ => col + 1,
+    })
+}
+
+/// A list marker's or footnote label's bytes, then its spaces.
+pub(super) fn marker(text: &str, node: &Node) -> (usize, usize) {
+    let start = span(node).start;
+    let line = &text[start..line_end(text, start)];
+    let mark = match node {
+        Node::FootnoteDefinition(_) => line.find("]:").map_or(line.len(), |at| at + 2),
+        _ if line.starts_with(['-', '*', '+']) => 1,
+        _ => line.find(['.', ')']).map_or(line.len(), |at| at + 1),
+    };
+    let after = &line[mark..];
+    let spaces = after.len() - after.trim_start_matches([' ', '\t']).len();
+    (mark, spaces)
+}
+
+/// The column a container's continuation lines start at.
+pub(super) fn indent(text: &str, node: &Node) -> usize {
+    let start = span(node).start;
+    let base = column(text, start);
+    let (mark, spaces) = marker(text, node);
+    if matches!(node, Node::FootnoteDefinition(_)) {
+        return base + 4;
+    }
+    let after = advance(base + mark, &text[start + mark..start + mark + spaces]) - base - mark;
+    let blank = text[start + mark..line_end(text, start)].trim().is_empty();
+    match blank || !(1..=4).contains(&after) {
+        true => base + mark + 1,
+        false => base + mark + after,
+    }
+}
+
+/// Where a container's text starts on its first line.
+pub(super) fn opener(text: &str, node: &Node) -> usize {
+    let start = span(node).start;
+    let (mark, spaces) = marker(text, node);
+    let width = advance(
+        column(text, start + mark),
+        &text[start + mark..start + mark + spaces],
+    ) - column(text, start + mark);
+    match (1..=4).contains(&width) {
+        true => start + mark + spaces,
+        false => start + mark + spaces.min(1),
+    }
+}
+
+/// Where `line`'s text starts inside `containers`; none when lazy.
+pub(super) fn inside(text: &str, line: usize, containers: &[&Node]) -> Option<usize> {
+    let end = line_end(text, line);
+    let mut at = line;
+    for node in containers {
+        if text[at..end].trim().is_empty() {
+            return Some(end);
+        }
+        if matches!(node, Node::Blockquote(_)) {
+            let lead = text[at..end].len() - text[at..end].trim_start_matches(' ').len();
+            if lead > 3 || !text[at + lead..end].starts_with('>') {
+                return None;
+            }
+            at += lead + 1;
+            at += usize::from(text[at..end].starts_with([' ', '\t']));
+            continue;
+        }
+        let start = span(node).start;
+        if line <= start && start < end {
+            at = opener(text, node);
+            continue;
+        }
+        let want = indent(text, node);
+        let mut col = column(text, at);
+        while col < want {
+            let ch = text[at..end]
+                .chars()
+                .next()
+                .filter(|ch| matches!(ch, ' ' | '\t'))?;
+            col = advance(col, &text[at..at + 1]);
+            at += ch.len_utf8();
+        }
+    }
+    Some(at)
+}
+
+/// The prefix a new line takes inside `containers`.
+pub(super) fn prefix(text: &str, containers: &[&Node]) -> String {
+    let mut out = String::new();
+    for (ix, node) in containers.iter().enumerate() {
+        if matches!(node, Node::Blockquote(_)) {
+            out.push_str("> ");
+            continue;
+        }
+        let start = span(node).start;
+        let outer = inside(text, line_start(text, start), &containers[..ix]).unwrap_or(start);
+        let width = indent(text, node).saturating_sub(column(text, outer.min(start)));
+        out.push_str(&" ".repeat(width));
+    }
+    out
+}
+
+/// Where byte `at` lies once `edits`, sorted, are written.
+pub(super) fn shifted(at: usize, edits: &[(Range<usize>, String)]) -> usize {
+    let mut moved = at;
+    for (range, with) in edits {
+        if range.end <= at {
+            moved = moved + with.len() - range.len();
+        } else if range.start < at {
+            moved -= at - range.start;
+        }
+    }
+    moved
+}
+
+/// `edits`, sorted, and the caret mapped through them.
+pub(super) fn change(mut edits: Vec<(Range<usize>, String)>, caret: Range<usize>) -> Change {
+    edits.sort_by_key(|(range, _)| range.start);
+    assert!(
+        edits
+            .windows(2)
+            .all(|pair| pair[0].0.end <= pair[1].0.start),
+        "block edits overlap"
+    );
+    let caret = shifted(caret.start, &edits)..shifted(caret.end, &edits);
+    (edits, caret)
+}
+
+/// `edits`, sorted, with the caret already where it lands.
+pub(super) fn placed(mut edits: Vec<(Range<usize>, String)>, caret: usize) -> Change {
+    edits.sort_by_key(|(range, _)| range.start);
+    assert!(
+        edits
+            .windows(2)
+            .all(|pair| pair[0].0.end <= pair[1].0.start),
+        "block edits overlap"
+    );
+    (edits, caret..caret)
+}
+
+/// Why `node` takes no block command at the caret.
+pub(super) fn refusal(node: &Node) -> EditRefusal {
+    match node {
+        Node::Code(_) => EditRefusal::Code,
+        Node::Math(_) => EditRefusal::Math,
+        Node::Html(_) => EditRefusal::Html,
+        Node::Table(_) => EditRefusal::Table,
+        Node::Yaml(_) | Node::Toml(_) => EditRefusal::FrontMatter,
+        _ => EditRefusal::Outside,
+    }
+}

src/documents/document/block/check.rs

@@ -0,0 +1,109 @@
+//! A command's result read back: its text and formats kept.
+
+use std::ops::Range;
+
+use markdown::mdast::Node;
+
+use crate::documents::{
+    MarkdownReader, Style,
+    document::format::EditRefusal,
+    markdown::{file_tree, span, walk},
+};
+
+const KEPT: u16 = bit(Style::Code) | bit(Style::Math);
+const CODE: u16 = 1 << 9;
+const MATH: u16 = 1 << 10;
+const HTML: u16 = 1 << 11;
+
+/// Refuses a result that reads as something else.
+pub(super) fn misread(why: &str) -> EditRefusal {
+    log::warn!("block command: {why}");
+    EditRefusal::Misread
+}
+
+/// `text` with sorted `edits` written, and its parse.
+pub(super) fn reread(text: &str, edits: &[(Range<usize>, String)]) -> (String, Node) {
+    let mut out = String::with_capacity(text.len());
+    let mut at = 0;
+    for (range, with) in edits {
+        out.push_str(&text[at..range.start]);
+        out.push_str(with);
+        at = range.end;
+    }
+    out.push_str(&text[at..]);
+    let root = file_tree(&out);
+    (out, root)
+}
+
+const fn bit(style: Style) -> u16 {
+    1 << style as u16
+}
+
+/// A parsed document read as the drawing reads it.
+pub(super) struct Shown<'a> {
+    root: &'a Node,
+    reader: MarkdownReader<'a>,
+}
+
+impl<'a> Shown<'a> {
+    pub(super) fn new(source: &'a str, root: &'a Node) -> Self {
+        let reader = MarkdownReader::new(source, root);
+        Self { root, reader }
+    }
+
+    /// Each shown character, with its formats.
+    pub(super) fn all(&self) -> Vec<(char, u16)> {
+        let mut out = Vec::new();
+        self.read(self.root, &mut out);
+        out
+    }
+
+    fn read(&self, node: &Node, out: &mut Vec<(char, u16)>) {
+        let (value, format) = match node {
+            Node::Paragraph(_) | Node::Heading(_) | Node::TableCell(_) => {
+                return out.extend(self.inline(node));
+            }
+            Node::Code(code) => (code.value.as_str(), CODE),
+            Node::Math(math) => (math.value.as_str(), MATH),
+            Node::Html(html) => (html.value.as_str(), HTML),
+            _ => {
+                for kid in node.children().map(Vec::as_slice).unwrap_or_default() {
+                    self.read(kid, out);
+                }
+                return;
+            }
+        };
+        out.extend(value.chars().map(|ch| (ch, format)));
+    }
+
+    /// `node`'s drawn text; white space counts only in code.
+    pub(super) fn inline(&self, node: &Node) -> Vec<(char, u16)> {
+        let kids = node.children().map(Vec::as_slice).unwrap_or_default();
+        let inline = self.reader.inline(kids);
+        let mut formats = vec![0u16; inline.text.len()];
+        for (range, style) in &inline.styles {
+            for format in &mut formats[range.clone()] {
+                *format |= bit(*style);
+            }
+        }
+        (inline.text.char_indices())
+            .map(|(at, ch)| (ch, formats[at]))
+            .filter(|(ch, format)| !ch.is_whitespace() || format & KEPT != 0)
+            .collect()
+    }
+
+    /// The level (0 a paragraph) and characters at `at`.
+    pub(super) fn at(&self, at: usize) -> Option<(u8, Vec<(char, u16)>)> {
+        let mut nodes = Vec::new();
+        walk(self.root, &mut nodes);
+        nodes.into_iter().find_map(|node| {
+            let level = match node {
+                Node::Paragraph(_) => 0,
+                Node::Heading(heading) => heading.depth,
+                _ => return None,
+            };
+            let whole = span(node);
+            (whole.start <= at && at <= whole.end).then(|| (level, self.inline(node)))
+        })
+    }
+}

src/documents/document/block/heading.rs

@@ -0,0 +1,221 @@
+//! Heading levels and paragraphs, as Typora's `changeBlock`.
+
+use std::ops::Range;
+
+use markdown::mdast::Node;
+
+use super::{
+    BlockCommand, Here, change, check, closing, eol, insert, inside, line_end, line_start,
+    next_line, prefix, prev_line, refusal, unblocked,
+};
+use crate::documents::{
+    document::format::{Change, EditRefusal},
+    markdown::span,
+};
+
+/// The level `command` asks at `level`; 0 is a paragraph.
+fn target(level: u8, command: BlockCommand) -> u8 {
+    match command {
+        BlockCommand::Heading(n) => {
+            assert!((1..=6).contains(&n), "a heading level is 1 to 6");
+            n
+        }
+        BlockCommand::Promote if level == 0 => 6,
+        BlockCommand::Promote => (level - 1).max(1),
+        BlockCommand::Demote if level == 0 || level == 6 => 0,
+        BlockCommand::Demote => level + 1,
+        _ => 0,
+    }
+}
+
+pub(super) fn run(here: &Here, command: BlockCommand) -> Result<Change, EditRefusal> {
+    let text = here.text;
+    let caret = here.selection.clone();
+    let leaf = here.leaf();
+    let level = match leaf {
+        Some(Node::Paragraph(_)) => 0,
+        Some(Node::Heading(heading)) => heading.depth,
+        Some(node @ (Node::Math(_) | Node::Html(_) | Node::Table(_)))
+            if !matches!(command, BlockCommand::Promote | BlockCommand::Demote) =>
+        {
+            // Typora gives these an empty paragraph after.
+            log::info!("block command: {:?} takes a paragraph after", refusal(node));
+            return insert::paragraph(here, false);
+        }
+        Some(node) => return Err(refusal(node)),
+        None if here.blank() => 0,
+        None => return Err(EditRefusal::Outside),
+    };
+    let goal = target(level, command);
+    if goal == level {
+        return Ok((Vec::new(), caret));
+    }
+    let containers = here.containers(here.path.len());
+    let hashes = "#".repeat(usize::from(goal)) + " ";
+    let Some(node) = leaf else {
+        let line = line_start(text, caret.start);
+        let at = inside(text, line, &containers).expect("a blank line holds its prefix");
+        return Ok(change(vec![(at..at, hashes)], caret));
+    };
+    let whole = span(node);
+    let edits = match (level, goal) {
+        (0, _) if task_head(here, &whole) => return Err(EditRefusal::Outside),
+        (0, _) => to_heading(here, &containers, &whole, hashes),
+        (_, 0) => to_paragraph(here, node, &containers)?,
+        _ => relevel(here, node, &containers, goal),
+    };
+    let change = change(edits, caret);
+    // Every shown character stays; the caret's block is `goal`.
+    let (written, after) = check::reread(text, &change.0);
+    let before = check::Shown::new(text, here.root);
+    let now = check::Shown::new(&written, &after);
+    let placed = match now.at(change.1.start) {
+        Some((level, _)) => level == goal,
+        // An empty paragraph has no node.
+        None => goal == 0 && before.inline(node).is_empty(),
+    };
+    let kept = placed && now.all() == before.all();
+    match kept {
+        true => Ok(change),
+        false => Err(check::misread("a heading change would reread otherwise")),
+    }
+}
+
+/// Whether `node` is an ATX heading, `#` led.
+fn atx(text: &str, node: &Node) -> bool {
+    text[span(node)].trim_start().starts_with('#')
+}
+
+/// Whether the caret is on a task item's first line.
+fn task_head(here: &Here, whole: &Range<usize>) -> bool {
+    let first = line_start(here.text, whole.start) == line_start(here.text, here.selection.start);
+    let leaf = here.path[here.path.len() - 1];
+    first && super::task_head(here.path[here.path.len() - 2], leaf)
+}
+
+/// The caret's line led by `hashes`; lazy lines kept in.
+fn to_heading(
+    here: &Here,
+    containers: &[&Node],
+    whole: &Range<usize>,
+    hashes: String,
+) -> Vec<(Range<usize>, String)> {
+    let text = here.text;
+    let lead = prefix(text, containers);
+    let first = line_start(text, here.selection.start);
+    let mut edits = Vec::new();
+    let mut line = first;
+    loop {
+        let at = match line_start(text, whole.start) == line {
+            true => Some(whole.start),
+            false => inside(text, line, containers),
+        };
+        let content = |from: usize| {
+            from + text[from..].len() - text[from..].trim_start_matches([' ', '\t']).len()
+        };
+        let (at, lazy) = match at {
+            Some(at) => (content(at), ""),
+            None => (content(line), lead.as_str()),
+        };
+        if line == first {
+            edits.push((at..at, format!("{lazy}{hashes}")));
+            if let Some(run) = closing(&text[at..line_end(text, at)]) {
+                edits.push((at + run..at + run, "\\".to_string()));
+            }
+        } else if !lazy.is_empty() {
+            edits.push((at..at, lazy.to_string()));
+        }
+        match next_line(text, line) {
+            Some(next) if next < whole.end => line = next,
+            _ => break,
+        }
+    }
+    edits
+}
+
+/// A heading's marks off; a blank line where text joins.
+fn to_paragraph(
+    here: &Here,
+    node: &Node,
+    containers: &[&Node],
+) -> Result<Vec<(Range<usize>, String)>, EditRefusal> {
+    let text = here.text;
+    let whole = span(node);
+    let blank = format!("{}{}", prefix(text, containers).trim_end(), eol(text));
+    let mut edits = Vec::new();
+    if here.joins_before(&whole, &[]) {
+        let line = line_start(text, whole.start);
+        edits.push((line..line, blank.clone()));
+    }
+    let kids = node.children().map(Vec::as_slice).unwrap_or_default();
+    match atx(text, node) {
+        true => match (kids.first(), kids.last()) {
+            (Some(first), Some(last)) => {
+                let start = span(first).start;
+                edits.push((whole.start..start, String::new()));
+                // The body kept: closing hashes go.
+                let end = line_end(text, start).min(span(last).end);
+                if let Some(mark) = unblocked(&text[start..end])? {
+                    edits.push((start + mark..start + mark, "\\".to_string()));
+                }
+                edits.push((span(last).end..whole.end, String::new()));
+            }
+            _ => edits.push((whole.clone(), String::new())),
+        },
+        false => {
+            // The underline line goes with the break before it.
+            let under = line_start(text, whole.end);
+            let ending = text[..under].len() - text[..under].trim_end_matches(['\r', '\n']).len();
+            edits.push((under - ending.min(2)..whole.end, String::new()));
+        }
+    }
+    if here.joins_after(&whole) {
+        let next = next_line(text, whole.end).expect("a joining line follows");
+        edits.push((next..next, blank.clone()));
+    }
+    Ok(edits)
+}
+
+/// A heading moved to level `goal`.
+fn relevel(
+    here: &Here,
+    node: &Node,
+    containers: &[&Node],
+    goal: u8,
+) -> Vec<(Range<usize>, String)> {
+    let text = here.text;
+    let whole = span(node);
+    if atx(text, node) {
+        let at = whole.start + text[whole.clone()].find('#').expect("an ATX heading has #");
+        let run = text[at..].len() - text[at..].trim_start_matches('#').len();
+        return vec![(at..at + run, "#".repeat(usize::from(goal)))];
+    }
+    let under = line_start(text, whole.end);
+    let marks = &text[under..whole.end];
+    let at = under + marks.find(['=', '-']).expect("a setext underline");
+    let run = marks.trim_end().len() - (at - under);
+    if goal <= 2 {
+        let mark = if goal == 1 { "=" } else { "-" };
+        return vec![(at..at + run, mark.repeat(run))];
+    }
+    // Levels past 2 are ATX: one line, the underline gone.
+    let mut edits = vec![(
+        whole.start..whole.start,
+        "#".repeat(usize::from(goal)) + " ",
+    )];
+    let mut line = line_start(text, whole.start);
+    while let Some(next) = next_line(text, line).filter(|next| *next < under) {
+        let end = line_end(text, line);
+        let from = inside(text, next, containers).unwrap_or(next);
+        let from = from + text[from..].len() - text[from..].trim_start_matches([' ', '\t']).len();
+        edits.push((end..from, " ".to_string()));
+        line = next;
+    }
+    let last = prev_line(text, under).expect("a setext heading has text");
+    if let Some(run) = closing(&text[last..line_end(text, last)]) {
+        edits.push((last + run..last + run, "\\".to_string()));
+    }
+    let ending = text[..under].len() - text[..under].trim_end_matches(['\r', '\n']).len();
+    edits.push((under - ending.min(2)..whole.end, String::new()));
+    edits
+}

src/documents/document/block/insert.rs

@@ -0,0 +1,319 @@
+//! Blocks put in and taken out, as Typora's `insertBlock`.
+
+use std::collections::HashSet;
+
+use markdown::mdast::Node;
+
+use super::{
+    BlockCommand, Here, container, eol, inside, line_end, line_start, next_line, placed, prefix,
+    prev_line, refusal,
+    split::{Room, content, split},
+    task_head,
+};
+use crate::documents::{
+    document::format::{Change, EditRefusal},
+    markdown::span,
+};
+
+/// Whether `line` holds text past `containers`' prefix.
+fn text_on(text: &str, line: usize, containers: &[&Node]) -> bool {
+    let at = content(text, line, containers);
+    at < line_end(text, line)
+}
+
+/// The selection's text, line by line, prefixes cut.
+fn picked(here: &Here, containers: &[&Node]) -> Vec<String> {
+    let text = here.text;
+    let (s, e) = (here.selection.start, here.selection.end);
+    let mut out = Vec::new();
+    let mut at = s;
+    while at < e {
+        out.push(text[at..line_end(text, at).min(e)].to_string());
+        match next_line(text, at).filter(|next| *next < e) {
+            Some(next) => at = inside(text, next, containers).unwrap_or(next).min(e),
+            None => break,
+        }
+    }
+    out
+}
+
+/// The smallest footnote number not taken.
+fn free_note(here: &Here) -> usize {
+    let used: HashSet<&str> = (here.nodes.iter())
+        .filter_map(|node| match node {
+            Node::FootnoteDefinition(note) => Some(note.identifier.as_str()),
+            Node::FootnoteReference(note) => Some(note.identifier.as_str()),
+            _ => None,
+        })
+        .collect();
+    (1..)
+        .find(|n: &usize| !used.contains(n.to_string().as_str()))
+        .expect("a free number")
+}
+
+/// `command`'s lines and the caret's line and byte.
+fn lines(
+    here: &Here,
+    command: BlockCommand,
+    body: Vec<String>,
+) -> (Vec<String>, Option<(usize, usize)>) {
+    let fenced = |fence: String, body: Vec<String>| {
+        let mut lines = vec![fence.clone()];
+        lines.extend(if body.is_empty() {
+            vec![String::new()]
+        } else {
+            body
+        });
+        lines.push(fence);
+        (lines, Some((1, 0)))
+    };
+    match command {
+        BlockCommand::CodeBlock => {
+            let longest = (body.iter())
+                .flat_map(|line| line.split(|ch| ch != '`'))
+                .map(str::len)
+                .max()
+                .unwrap_or(0);
+            fenced("`".repeat(longest.max(2) + 1), body)
+        }
+        BlockCommand::MathBlock => fenced("$$".to_string(), body),
+        BlockCommand::Toc => (vec!["[toc]".to_string()], Some((0, 5))),
+        BlockCommand::Footnote => {
+            let line = format!("[^{}]: ", free_note(here));
+            let end = line.len();
+            (vec![line], Some((0, end)))
+        }
+        BlockCommand::LinkDefinition => {
+            let first = body.first().map_or("", |line| line.trim());
+            if first.contains(['/', '\\']) {
+                let address: String = first.chars().take(160).collect();
+                return (vec![format!("[]: {address}")], Some((0, 1)));
+            }
+            let label: String = (first.split_whitespace().next().unwrap_or_default())
+                .chars()
+                .take(20)
+                .collect();
+            let line = format!("[{label}]: ");
+            let caret = if label.is_empty() { 1 } else { line.len() };
+            (vec![line], Some((0, caret)))
+        }
+        _ => (vec!["---".to_string()], None),
+    }
+}
+
+/// `lines` joined inside `lead`, and the caret's byte in them.
+fn joined(
+    lines: &[String],
+    caret: Option<(usize, usize)>,
+    nl: &str,
+    lead: &str,
+) -> (String, Option<usize>) {
+    let mut out = String::new();
+    let mut at = None;
+    for (ix, line) in lines.iter().enumerate() {
+        if ix > 0 {
+            out.push_str(nl);
+            out.push_str(lead);
+        }
+        if let Some((row, byte)) = caret
+            && row == ix
+        {
+            at = Some(out.len() + byte);
+        }
+        out.push_str(line);
+    }
+    (out, at)
+}
+
+/// Whether a paragraph or ATX heading splits at the caret.
+fn splits(text: &str, node: &Node) -> bool {
+    match node {
+        Node::Paragraph(_) => true,
+        Node::Heading(_) => text[span(node)].trim_start().starts_with('#'),
+        _ => false,
+    }
+}
+
+pub(super) fn run(here: &Here, command: BlockCommand) -> Result<Change, EditRefusal> {
+    let text = here.text;
+    let leaf = here.leaf();
+    let containers = here.containers(here.path.len() - usize::from(leaf.is_some()));
+    let lead = prefix(text, &containers);
+    let room = Room {
+        nl: eol(text),
+        blank: lead.trim_end().to_string(),
+        lead,
+        containers,
+    };
+    let (lines, caret) = lines(here, command, picked(here, &room.containers));
+    let (block, inner) = joined(&lines, caret, room.nl, &room.lead);
+    let rule = inner.is_none();
+    match leaf {
+        Some(node) if splits(text, node) => {
+            if here.selection.end > span(node).end {
+                return Err(EditRefusal::Across);
+            }
+            split(here, node, &room, &block, inner)
+        }
+        Some(node) if !here.selection.is_empty() => Err(refusal(node)),
+        Some(node) => {
+            let at = line_end(text, span(node).end);
+            let next =
+                next_line(text, at).is_some_and(|next| text_on(text, next, &room.containers));
+            let gap = room.gap();
+            let tail = match rule {
+                true => gap.clone(),
+                false => String::new(),
+            };
+            let sep = if next {
+                format!("{}{}", room.nl, room.blank)
+            } else {
+                String::new()
+            };
+            let caret = at + gap.len() + inner.unwrap_or(block.len() + tail.len());
+            Ok(placed(
+                vec![(at..at, format!("{gap}{block}{tail}{sep}"))],
+                caret,
+            ))
+        }
+        None if here.blank() && here.selection.is_empty() => {
+            let line = line_start(text, here.selection.start);
+            let at = inside(text, line, &room.containers).expect("a blank line holds its prefix");
+            let end = line_end(text, line);
+            let prev =
+                prev_line(text, line).is_some_and(|prev| text_on(text, prev, &room.containers));
+            let next =
+                next_line(text, line).is_some_and(|next| text_on(text, next, &room.containers));
+            let head = if prev {
+                format!("{}{}", room.nl, room.lead)
+            } else {
+                String::new()
+            };
+            let tail = if rule { room.gap() } else { String::new() };
+            let sep = if next {
+                format!("{}{}", room.nl, room.blank)
+            } else {
+                String::new()
+            };
+            let caret = at + head.len() + inner.unwrap_or(block.len() + tail.len());
+            Ok(placed(
+                vec![(at..end, format!("{head}{block}{tail}{sep}"))],
+                caret,
+            ))
+        }
+        None => Err(EditRefusal::Outside),
+    }
+}
+
+/// An empty line before or after the caret's block.
+pub(super) fn paragraph(here: &Here, before: bool) -> Result<Change, EditRefusal> {
+    let text = here.text;
+    let leaf = here.leaf().ok_or(EditRefusal::Outside)?;
+    let whole = span(leaf);
+    let containers = here.containers(here.path.len() - 1);
+    let lead = prefix(text, &containers);
+    let room = Room {
+        nl: eol(text),
+        blank: lead.trim_end().to_string(),
+        lead,
+        containers,
+    };
+    let gap = room.gap();
+    let holder = here.path[here.path.len() - 2];
+    if before && task_head(holder, leaf) {
+        return Err(EditRefusal::Outside);
+    }
+    // A holder's first line keeps its opener: text moves down.
+    if before
+        && container(holder)
+        && !matches!(holder, Node::Blockquote(_))
+        && line_start(text, span(holder).start) == line_start(text, whole.start)
+    {
+        let down = format!("{}{}", room.nl, room.lead);
+        return Ok(placed(vec![(whole.start..whole.start, down)], whole.start));
+    }
+    if before {
+        let mut edits = Vec::new();
+        let mut shift = 0;
+        if here.joins_before(&whole, &[]) {
+            let line = line_start(text, whole.start);
+            let blank = format!("{}{}", room.blank, room.nl);
+            shift = blank.len();
+            edits.push((line..line, blank));
+        }
+        edits.push((whole.start..whole.start, gap));
+        return Ok(placed(edits, whole.start + shift));
+    }
+    let at = line_end(text, whole.end);
+    let next = next_line(text, at).is_some_and(|next| text_on(text, next, &room.containers));
+    let sep = if next {
+        format!("{}{}", room.nl, room.blank)
+    } else {
+        String::new()
+    };
+    Ok(placed(
+        vec![(at..at, format!("{gap}{sep}"))],
+        at + gap.len(),
+    ))
+}
+
+/// Front matter at the top, unless there is some.
+pub(super) fn front_matter(here: &Here) -> Result<Change, EditRefusal> {
+    let first = here.root.children().and_then(|kids| kids.first());
+    if matches!(first, Some(Node::Yaml(_) | Node::Toml(_))) {
+        return Err(EditRefusal::Present);
+    }
+    let nl = eol(here.text);
+    let tail = match here.text.is_empty() || here.text.starts_with(['\n', '\r']) {
+        true => "",
+        false => nl,
+    };
+    Ok(placed(
+        vec![(0..0, format!("---{nl}{nl}---{nl}{tail}"))],
+        3 + nl.len(),
+    ))
+}
+
+/// The caret's block gone; a lone paragraph takes its holder.
+pub(super) fn delete(here: &Here) -> Result<Change, EditRefusal> {
+    let text = here.text;
+    let leaf = here.leaf().ok_or(EditRefusal::Outside)?;
+    let mut ix = here.path.len() - 1;
+    if matches!(leaf, Node::Paragraph(_))
+        && let Some(parent) = here.path.get(ix - 1)
+        && container(parent)
+        && parent.children().is_some_and(|kids| kids.len() == 1)
+    {
+        ix -= 1;
+    }
+    let whole = span(here.path[ix]);
+    let line = line_start(text, whole.start);
+    if !text[line..whole.start]
+        .chars()
+        .all(|ch| matches!(ch, ' ' | '\t' | '>'))
+    {
+        return Ok(placed(vec![(whole.clone(), String::new())], whole.start));
+    }
+    // Containers wholly on the lines go too.
+    let last = line_end(text, whole.end);
+    let top = (1..=ix)
+        .find(|j| {
+            let held = span(here.path[*j]);
+            line <= held.start && held.end <= last
+        })
+        .expect("the block lies on its lines");
+    let gone = &here.path[top..=ix];
+    let outer = here.containers(top);
+    let mut end = next_line(text, whole.end).unwrap_or(text.len());
+    let blank_above = prev_line(text, line).is_none_or(|prev| !text_on(text, prev, &outer));
+    if blank_above && end < text.len() && !text_on(text, end, &outer) {
+        end = next_line(text, end).unwrap_or(text.len());
+    }
+    // Neighbors that would join keep a blank line between.
+    let joins = here.joins_before(&whole, gone) && here.joins_after(&whole);
+    let with = match joins {
+        true => format!("{}{}", prefix(text, &outer).trim_end(), eol(text)),
+        false => String::new(),
+    };
+    Ok(placed(vec![(line..end, with)], line))
+}

src/documents/document/block/list.rs

@@ -0,0 +1,315 @@
+//! Lists on, off and retyped, as Typora's `toggleIndent`.
+
+use std::ops::Range;
+
+use markdown::mdast::{Code, List, Node};
+
+use super::{
+    BlockCommand, Here, change, column, eol, indent, inside, line_end, line_start, next_line,
+    opener, prefix, refusal, unblocked,
+};
+use crate::documents::{
+    document::format::{Change, EditRefusal},
+    markdown::span,
+};
+
+fn kind(list: &List) -> BlockCommand {
+    match (list.ordered, list.children.first()) {
+        (true, _) => BlockCommand::OrderedList,
+        (false, Some(Node::ListItem(item))) if item.checked.is_some() => BlockCommand::TaskList,
+        _ => BlockCommand::BulletList,
+    }
+}
+
+/// The marker an item takes: number `n` or the bullet.
+fn marker(kind: BlockCommand, n: u32, bullet: char) -> String {
+    match kind {
+        BlockCommand::OrderedList => format!("{n}. "),
+        BlockCommand::TaskList => format!("{bullet} [ ] "),
+        _ => format!("{bullet} "),
+    }
+}
+
+/// A marker's width for continuation lines; boxes add none.
+fn width(kind: BlockCommand, n: u32) -> usize {
+    match kind {
+        BlockCommand::OrderedList => format!("{n}. ").len(),
+        _ => 2,
+    }
+}
+
+pub(super) fn run(here: &Here, command: BlockCommand) -> Result<Change, EditRefusal> {
+    let caret = here.selection.clone();
+    let path = &here.path;
+    let item = match here.leaf() {
+        Some(leaf) => path.len().checked_sub(2).filter(|ix| match path[*ix] {
+            Node::ListItem(item) => {
+                !caret.is_empty()
+                    || item
+                        .children
+                        .first()
+                        .is_some_and(|kid| std::ptr::eq(kid, leaf))
+            }
+            _ => false,
+        }),
+        None => Some(path.len() - 1).filter(|ix| matches!(path[*ix], Node::ListItem(_))),
+    };
+    // A selection past the list takes every touched sibling.
+    if let Some(ix) = item
+        && let Node::List(list) = path[ix - 1]
+        && (here.path_at(caret.end).iter()).any(|node| std::ptr::eq(*node, path[ix - 1]))
+    {
+        let edits = match kind(list) == command {
+            true => unwrap(here, ix - 1, list)?,
+            false => {
+                let start = if list.ordered {
+                    list.start.unwrap_or(1)
+                } else {
+                    1
+                };
+                let outer = here.containers(ix - 1);
+                retype(here.text, path[ix - 1], list, &outer, command, start)?
+            }
+        };
+        return Ok(change(edits, caret));
+    }
+    if here.leaf().is_none() && caret.is_empty() {
+        if !here.blank() {
+            return Err(EditRefusal::Outside);
+        }
+        let line = line_start(here.text, caret.start);
+        let at = inside(here.text, line, &here.containers(path.len()))
+            .expect("a blank line holds its prefix");
+        return Ok(change(vec![(at..at, marker(command, 1, '-'))], caret));
+    }
+    let (k, blocks) = here.blocks().ok_or(EditRefusal::Outside)?;
+    Ok(change(wrap(here, k, &blocks, command)?, caret))
+}
+
+/// Indent from `at` to column `want`: its end, columns past.
+fn indented(text: &str, at: usize, want: usize) -> Option<(usize, usize)> {
+    let end = line_end(text, at);
+    let mut cut = at;
+    let mut col = column(text, at);
+    while col < want {
+        let ch = text[cut..end]
+            .chars()
+            .next()
+            .filter(|ch| matches!(ch, ' ' | '\t'))?;
+        col = if ch == '\t' { col / 4 * 4 + 4 } else { col + 1 };
+        cut += 1;
+    }
+    Some((cut, col - want))
+}
+
+/// Each non-lazy line of `item` after its first, with indent.
+fn continued<'a>(
+    text: &'a str,
+    item: &Node,
+    outer: &'a [&Node],
+) -> impl Iterator<Item = (usize, usize, usize)> + 'a {
+    let whole = span(item);
+    let want = indent(text, item);
+    std::iter::successors(next_line(text, whole.start), move |line| {
+        next_line(text, *line)
+    })
+    .take_while(move |line| *line < whole.end)
+    .filter_map(move |line| {
+        let at = inside(text, line, outer)?;
+        if text[at..line_end(text, line)].trim().is_empty() {
+            return None;
+        }
+        let (cut, past) = indented(text, at, want)?;
+        Some((at, cut, past))
+    })
+}
+
+/// Every item's marker off, its lines out one level.
+fn unwrap(here: &Here, ix: usize, list: &List) -> Result<Vec<(Range<usize>, String)>, EditRefusal> {
+    let text = here.text;
+    let outer = here.containers(ix);
+    let blank = format!("{}{}", prefix(text, &outer).trim_end(), eol(text));
+    let whole = span(here.path[ix]);
+    let mut edits = Vec::new();
+    for (n, item) in list.children.iter().enumerate() {
+        let start = span(item).start;
+        let line = line_start(text, start);
+        let joins = match n {
+            0 => here.joins_before(&whole, &[here.path[ix]]),
+            _ => prev_text(text, line, &outer),
+        };
+        if joins {
+            edits.push((line..line, blank.clone()));
+        }
+        let first = item.children().and_then(|kids| kids.first()).map(span);
+        let boxed = matches!(item, Node::ListItem(item) if item.checked.is_some());
+        match &first {
+            Some(kid) if !text[start..kid.start].contains(['\n', '\r']) => {
+                edits.push((start..kid.start, String::new()));
+            }
+            Some(kid) => {
+                let next = next_line(text, start).expect("an item's text lies below");
+                edits.push((line..next, String::new()));
+                if boxed {
+                    edits.push((unbox(text, kid.start), String::new()));
+                }
+            }
+            None => edits.push((start..line_end(text, start), String::new())),
+        }
+        if boxed && let Some(kid) = first {
+            edits.extend(escaped(text, kid.start)?);
+        }
+        for (at, cut, past) in continued(text, item, &outer) {
+            edits.push((at..cut, " ".repeat(past)));
+        }
+    }
+    if here.joins_after(&whole) {
+        let next = next_line(text, whole.end).expect("a joining line follows");
+        edits.push((next..next, blank.clone()));
+    }
+    Ok(edits)
+}
+
+/// The task box before the text at `kid`.
+fn unbox(text: &str, kid: usize) -> Range<usize> {
+    let line = line_start(text, kid);
+    line + text[line..kid].rfind('[').expect("a task's box")..kid
+}
+
+/// A backslash where text at `at`, unboxed, opens a block.
+fn escaped(text: &str, at: usize) -> Result<Option<(Range<usize>, String)>, EditRefusal> {
+    let mark = unblocked(&text[at..line_end(text, at)])?;
+    Ok(mark.map(|mark| (at + mark..at + mark, "\\".to_string())))
+}
+
+/// Whether `node`, holding `code`, is fenced in the source.
+fn fenced(text: &str, node: &Node, code: &Code) -> bool {
+    code.lang.is_some()
+        || code.value.is_empty()
+        || text[span(node)].lines().count() > code.value.lines().count()
+}
+
+/// Whether the line before `line` holds text inside `outer`.
+fn prev_text(text: &str, line: usize, outer: &[&Node]) -> bool {
+    super::prev_line(text, line).is_some_and(|prev| {
+        inside(text, prev, outer).is_none_or(|at| !text[at..line_end(text, prev)].trim().is_empty())
+    })
+}
+
+/// Each marker as `kind`'s from `start`; lines follow.
+fn retype(
+    text: &str,
+    node: &Node,
+    list: &List,
+    outer: &[&Node],
+    kind: BlockCommand,
+    start: u32,
+) -> Result<Vec<(Range<usize>, String)>, EditRefusal> {
+    let bullet = match list.ordered {
+        true => '-',
+        false => text[span(node).start..].chars().next().unwrap_or('-'),
+    };
+    let mut edits = Vec::new();
+    let task = kind == BlockCommand::TaskList;
+    for (n, item) in list.children.iter().enumerate() {
+        let number = start + n as u32;
+        let at = span(item).start;
+        let (mark, spaces) = super::marker(text, item);
+        let first = item.children().and_then(|kids| kids.first());
+        let boxed = matches!(item, Node::ListItem(item) if item.checked.is_some());
+        let body = at + mark + spaces;
+        let blank = body == line_end(text, at);
+        if boxed {
+            // A box stays when the kind keeps boxes.
+            let kind = if task { BlockCommand::BulletList } else { kind };
+            let end = if blank { opener(text, item) } else { body };
+            edits.push((at..end, marker(kind, number, bullet)));
+            if !task {
+                let kid = span(first.expect("a boxed item has text")).start;
+                edits.push((unbox(text, kid), String::new()));
+                edits.extend(escaped(text, kid)?);
+            }
+        } else if task && let Some(kid) = first.filter(|kid| !matches!(kid, Node::Paragraph(_))) {
+            // GFM boxes only a paragraph.
+            return Err(refusal(kid));
+        } else if blank {
+            edits.push((at..opener(text, item), marker(kind, number, bullet)));
+        } else {
+            // Indented code is written again from its value.
+            let pad = match first {
+                Some(kid @ Node::Code(code)) if !fenced(text, kid, code) => {
+                    let line = code.value.lines().next().unwrap_or_default();
+                    4 + line.len() - line.trim_start_matches(' ').len()
+                }
+                _ => 0,
+            };
+            edits.push((at..body, marker(kind, number, bullet) + &" ".repeat(pad)));
+        }
+        let want = column(text, at) + width(kind, number);
+        for (from, cut, past) in continued(text, item, outer) {
+            let pad = want.saturating_sub(column(text, from)) + past;
+            edits.push((from..cut, " ".repeat(pad)));
+        }
+    }
+    Ok(edits)
+}
+
+/// Each paragraph line, and each other block, made an item.
+fn wrap(
+    here: &Here,
+    k: usize,
+    blocks: &[&Node],
+    command: BlockCommand,
+) -> Result<Vec<(Range<usize>, String)>, EditRefusal> {
+    let text = here.text;
+    let outer = here.containers(k + 1);
+    let lead = prefix(text, &outer);
+    let mut edits = Vec::new();
+    let mut n = 1;
+    for block in blocks {
+        if let Node::List(list) = block {
+            if kind(list) != command {
+                edits.extend(retype(text, block, list, &outer, command, n)?);
+            }
+            n += list.children.len() as u32;
+            continue;
+        }
+        if command == BlockCommand::TaskList && !matches!(block, Node::Paragraph(_)) {
+            return Err(refusal(block));
+        }
+        let whole = span(block);
+        let mut line = line_start(text, whole.start);
+        while line <= whole.end {
+            let first = line == line_start(text, whole.start);
+            let (at, lazy) = match first {
+                true => (Some(whole.start), ""),
+                false => match inside(text, line, &outer) {
+                    Some(at) => (Some(at), ""),
+                    None => (None, lead.as_str()),
+                },
+            };
+            let at = at.unwrap_or(line);
+            let content = at + text[at..].len() - text[at..].trim_start_matches([' ', '\t']).len();
+            if !text[at..line_end(text, line)].trim().is_empty() {
+                let mark = match first || matches!(block, Node::Paragraph(_)) {
+                    true => {
+                        n += 1;
+                        marker(command, n - 1, '-')
+                    }
+                    false => " ".repeat(width(command, n - 1)),
+                };
+                let at = if matches!(block, Node::Paragraph(_)) {
+                    content
+                } else {
+                    at
+                };
+                edits.push((at..at, format!("{lazy}{mark}")));
+            }
+            match next_line(text, line) {
+                Some(next) => line = next,
+                None => break,
+            }
+        }
+    }
+    Ok(edits)
+}

src/documents/document/block/quote.rs

@@ -0,0 +1,166 @@
+//! Quotes on and off, as Typora's `toggleIndent`.
+
+use std::ops::Range;
+
+use markdown::mdast::Node;
+
+use super::{
+    Here, change, check, eol, inside, line_end, line_start, next_line, prefix, split::content,
+    task_head,
+};
+use crate::documents::{
+    alert,
+    document::format::{Change, EditRefusal},
+    markdown::{file_tree, span},
+};
+
+pub(super) fn run(here: &Here) -> Result<Change, EditRefusal> {
+    let caret = here.selection.clone();
+    let ix = match here.leaf() {
+        Some(_) => here.path.len() - 2,
+        None => here.path.len() - 1,
+    };
+    if let Node::Blockquote(_) = here.path[ix]
+        && whole(here, ix)
+    {
+        return unwrap(here, ix).map(|edits| change(edits, caret));
+    }
+    if here.leaf().is_none() && here.selection.is_empty() {
+        if !here.blank() {
+            return Err(EditRefusal::Outside);
+        }
+        let line = line_start(here.text, caret.start);
+        let at = inside(here.text, line, &here.containers(here.path.len()))
+            .expect("a blank line holds its prefix");
+        return Ok(change(vec![(at..at, "> ".to_string())], caret));
+    }
+    let (k, blocks) = here.blocks().ok_or(EditRefusal::Outside)?;
+    // GFM reads a task's first line as text.
+    if task_head(here.path[k], blocks[0]) {
+        return Err(EditRefusal::Outside);
+    }
+    Ok(change(wrap(here, k, &blocks), caret))
+}
+
+/// Whether the selection takes in the whole quote at `ix`.
+fn whole(here: &Here, ix: usize) -> bool {
+    if here.selection.is_empty() {
+        return true;
+    }
+    let quote = here.path[ix];
+    let end = here.path_at(here.selection.end);
+    let kids = quote.children().map(Vec::as_slice).unwrap_or_default();
+    let first = here.path.get(ix + 1).copied();
+    let last = end.get(ix + 1).copied();
+    end.get(ix).is_some_and(|node| std::ptr::eq(*node, quote))
+        && first.is_some_and(|first| kids.first().is_some_and(|kid| std::ptr::eq(kid, first)))
+        && last.is_some_and(|last| kids.last().is_some_and(|kid| std::ptr::eq(kid, last)))
+}
+
+/// One `>` off each line of the quote at `ix`.
+fn unwrap(here: &Here, ix: usize) -> Result<Vec<(Range<usize>, String)>, EditRefusal> {
+    let text = here.text;
+    let quote = here.path[ix];
+    let whole = span(quote);
+    let outer = here.containers(ix);
+    let blank = format!("{}{}", prefix(text, &outer).trim_end(), eol(text));
+    let mut edits = Vec::new();
+    let mut line = line_start(text, whole.start);
+    if here.joins_before(&whole, &[quote]) {
+        edits.push((line..line, blank.clone()));
+    }
+    if let Node::Blockquote(inner) = quote
+        && alert(inner).is_some()
+    {
+        if !marker_only(&text[whole.start..line_end(text, line)]) {
+            return Err(check::misread("an alert marker shares its line"));
+        }
+        // A body block keeps its indent; text sheds it.
+        let continues = inner
+            .children
+            .first()
+            .is_some_and(|head| span(head).end > line_end(text, line));
+        // The marker goes with blank lines; an outer opener stays.
+        let (mut cut, mut rest) = (whole.end, whole.end);
+        let mut next = next_line(text, line);
+        while let Some(at) = next.filter(|at| *at < whole.end) {
+            let lead = match mark(text, at, &outer) {
+                Some(mark) => mark.end,
+                None => content(text, at, &outer),
+            };
+            let body =
+                lead + text[lead..].len() - text[lead..].trim_start_matches([' ', '\t']).len();
+            if body < line_end(text, at) {
+                cut = if continues { body } else { lead };
+                rest = next_line(text, at).unwrap_or(text.len());
+                break;
+            }
+            next = next_line(text, at);
+        }
+        edits.push((whole.start..cut, String::new()));
+        line = rest;
+    }
+    while line < whole.end {
+        if let Some(mark) = mark(text, line, &outer) {
+            edits.push((mark, String::new()));
+        }
+        match next_line(text, line) {
+            Some(next) => line = next,
+            None => break,
+        }
+    }
+    if here.joins_after(&whole) {
+        let next = next_line(text, whole.end).expect("a joining line follows");
+        edits.push((next..next, blank.clone()));
+    }
+    Ok(edits)
+}
+
+/// Whether `line`, a quote's first, holds only an alert marker.
+fn marker_only(line: &str) -> bool {
+    let root = file_tree(&format!("{line}\n> x"));
+    let Some(Node::Blockquote(quote)) = root.children().and_then(|kids| kids.first()) else {
+        return false;
+    };
+    matches!(alert(quote), Some((_, body)) if matches!(&body[..],
+        [Node::Paragraph(head)] if matches!(&head.children[..],
+            [Node::Text(text)] if text.value == "x")))
+}
+
+/// `line`'s `>` and one space after, inside `outer`.
+fn mark(text: &str, line: usize, outer: &[&Node]) -> Option<Range<usize>> {
+    let at = inside(text, line, outer)?;
+    let end = line_end(text, line);
+    let lead = text[at..end].len() - text[at..end].trim_start_matches(' ').len();
+    let mark = at + lead;
+    (lead <= 3 && text[mark..end].starts_with('>')).then(|| {
+        let space = usize::from(text[mark + 1..end].starts_with([' ', '\t']));
+        mark..mark + 1 + space
+    })
+}
+
+/// `> ` before each line of `blocks`, held by `path[k]`.
+fn wrap(here: &Here, k: usize, blocks: &[&Node]) -> Vec<(Range<usize>, String)> {
+    let text = here.text;
+    let outer = here.containers(k + 1);
+    let first = span(blocks[0]).start;
+    let last = span(blocks[blocks.len() - 1]).end;
+    let mut edits = Vec::new();
+    let mut line = line_start(text, first);
+    while line <= last {
+        let at = match line == line_start(text, first) {
+            true => Some(first),
+            false => inside(text, line, &outer),
+        };
+        // A lazy line stays in its paragraph.
+        if let Some(at) = at {
+            let blank = text[at..line_end(text, line)].trim().is_empty();
+            edits.push((at..at, if blank { ">" } else { "> " }.to_string()));
+        }
+        match next_line(text, line) {
+            Some(next) => line = next,
+            None => break,
+        }
+    }
+    edits
+}

src/documents/document/block/split.rs

@@ -0,0 +1,229 @@
+//! A paragraph or heading split, as Typora's `splitAt`.
+
+use std::ops::Range;
+
+use markdown::mdast::Node;
+
+use super::{
+    Here, check, closing, inside, line_end, line_start, next_line, placed, prev_line, shifted,
+    task_head, unblocked,
+};
+use crate::documents::{
+    document::format::{Change, EditRefusal, marks},
+    markdown::span,
+};
+
+/// Where the new block's text goes, ending the edit.
+pub(super) struct Room<'a> {
+    pub(super) nl: &'static str,
+    pub(super) lead: String,
+    pub(super) blank: String,
+    pub(super) containers: Vec<&'a Node>,
+}
+
+impl Room<'_> {
+    /// A blank line, then a new line's prefix.
+    pub(super) fn gap(&self) -> String {
+        format!("{}{}{}{}", self.nl, self.blank, self.nl, self.lead)
+    }
+}
+
+/// Where `line`'s text starts inside `containers`; a lazy line's own.
+pub(super) fn content(text: &str, line: usize, containers: &[&Node]) -> usize {
+    let at = inside(text, line, containers).unwrap_or(line);
+    at + text[at..].len() - text[at..].trim_start_matches([' ', '\t']).len()
+}
+
+/// Back from `at` over blanks and prefixes, to `floor`.
+fn back(text: &str, mut at: usize, floor: usize, containers: &[&Node]) -> usize {
+    loop {
+        let line = line_start(text, at).max(floor);
+        at = line + text[line..at].trim_end_matches([' ', '\t']).len();
+        if line == floor || at > content(text, line, containers) {
+            return at;
+        }
+        at = line_end(text, prev_line(text, line).expect("a line above the floor"));
+    }
+}
+
+/// On from `at` over blanks and prefixes, to `ceil`.
+fn forth(text: &str, mut at: usize, ceil: usize, containers: &[&Node]) -> usize {
+    loop {
+        let end = line_end(text, at).min(ceil);
+        at = end - text[at..end].trim_start_matches([' ', '\t']).len();
+        if at < end {
+            return at;
+        }
+        match next_line(text, at) {
+            Some(next) if next < ceil => at = content(text, next, containers),
+            _ => return ceil,
+        }
+    }
+}
+
+/// Inline nodes with no text to cut.
+fn sealed(node: &Node) -> bool {
+    matches!(
+        node,
+        Node::InlineMath(_) | Node::Html(_) | Node::FootnoteReference(_)
+    )
+}
+
+/// `at` off inline edges; marks to close, then reopen.
+fn seam(here: &Here, mut at: usize) -> Result<(usize, String, String), EditRefusal> {
+    let text = here.text;
+    let marked: Vec<(&Node, [Range<usize>; 2])> = (here.nodes.iter())
+        .filter_map(|node| Some((*node, marks(node, text)?)))
+        .collect();
+    while let Some([open, _]) = (marked.iter())
+        .map(|(_, holes)| holes)
+        .find(|[open, _]| open.start < at && open.end == at)
+    {
+        at = open.start;
+    }
+    while let Some([_, close]) = (marked.iter())
+        .map(|(_, holes)| holes)
+        .find(|[_, close]| close.start == at && at < close.end)
+    {
+        at = close.end;
+    }
+    let strictly = |range: Range<usize>| range.start < at && at < range.end;
+    let mut cut: Vec<&(&Node, [Range<usize>; 2])> = (marked.iter())
+        .filter(|(node, _)| strictly(span(node)))
+        .collect();
+    let paired =
+        |node: &Node| matches!(node, Node::Strong(_) | Node::Emphasis(_) | Node::Delete(_));
+    let unsafe_cut = (here.nodes.iter()).any(|node| sealed(node) && strictly(span(node)))
+        || (cut.iter()).any(|(node, [open, close])| {
+            !paired(node) || strictly(open.clone()) || strictly(close.clone())
+        });
+    if unsafe_cut {
+        return Err(EditRefusal::Across);
+    }
+    cut.sort_by_key(|(node, _)| span(node).start);
+    let close = (cut.iter().rev()).map(|(_, [_, close])| &text[close.clone()]);
+    let open = cut.iter().map(|(_, [open, _])| &text[open.clone()]);
+    Ok((at, close.collect(), open.collect()))
+}
+
+/// `block` put where the selection splits `node`.
+pub(super) fn split(
+    here: &Here,
+    node: &Node,
+    room: &Room,
+    block: &str,
+    inner: Option<usize>,
+) -> Result<Change, EditRefusal> {
+    let text = here.text;
+    let whole = span(node);
+    let kids = node.children().map(Vec::as_slice).unwrap_or_default();
+    let (marks, body) = match node {
+        Node::Heading(heading) => (
+            "#".repeat(usize::from(heading.depth)) + " ",
+            kids.first().map_or(whole.end, |kid| span(kid).start)
+                ..kids.last().map_or(whole.end, |kid| span(kid).end),
+        ),
+        _ => (String::new(), whole.clone()),
+    };
+    // A caret in heading marks takes the text's edge.
+    let s = here.selection.start.clamp(body.start, body.end);
+    let e = here.selection.end.clamp(body.start, body.end);
+    let (s, close, _) = seam(here, s)?;
+    let (e, _, open) = seam(here, e)?;
+    let containers = &room.containers;
+    let mut from = back(text, s, body.start, containers);
+    let after = forth(text, e, body.end, containers);
+    let before = from > body.start;
+    let follows = after < body.end;
+    // GFM reads a task's first line as text.
+    if !before && task_head(here.path[here.path.len() - 2], node) {
+        return Err(EditRefusal::Outside);
+    }
+    if !before {
+        from = whole.start;
+    }
+    let to = if follows { after } else { whole.end };
+    let gap = room.gap();
+    let mut written = String::new();
+    if before {
+        written.push_str(&close);
+        written.push_str(&gap);
+    }
+    let start = written.len();
+    written.push_str(block);
+    let lead = if follows { marks.len() + open.len() } else { 0 };
+    let caret = match inner {
+        Some(inner) => start + inner,
+        None => {
+            written.push_str(&gap);
+            written.len() + lead
+        }
+    };
+    if follows {
+        if inner.is_some() {
+            written.push_str(&gap);
+        }
+        written.push_str(&marks);
+        written.push_str(&open);
+    }
+    let mut edits = Vec::new();
+    let mut shift = 0;
+    if !before && here.joins_before(&whole, &[]) {
+        let line = line_start(text, whole.start);
+        let blank = format!("{}{}", room.blank, room.nl);
+        shift = blank.len();
+        edits.push((line..line, blank));
+    }
+    edits.push((from..to, written));
+    // A heading's cut end must not close it.
+    let line = line_start(text, from);
+    if before
+        && close.is_empty()
+        && matches!(node, Node::Heading(_))
+        && let Some(run) = closing(&text[line..from])
+    {
+        edits.push((line + run..line + run, "\\".to_string()));
+        shift += 1;
+    }
+    // The rest must not open a block.
+    if follows
+        && marks.is_empty()
+        && open.is_empty()
+        && let Some(mark) = unblocked(&text[after..line_end(text, after)])?
+    {
+        edits.push((after + mark..after + mark, "\\".to_string()));
+    }
+    let change = placed(edits, from + shift + caret);
+    let edits = &change.0;
+    let (written, after_root) = check::reread(text, edits);
+    let now = check::Shown::new(&written, &after_root);
+    let level = match node {
+        Node::Heading(heading) => heading.depth,
+        _ => 0,
+    };
+    let piece = |at: usize| {
+        now.at(shifted(at, edits))
+            .and_then(|(got, chars)| (got == level).then_some(chars))
+    };
+    let head = if before {
+        piece(from - 1)
+    } else {
+        Some(Vec::new())
+    };
+    let tail = if follows { piece(to) } else { Some(Vec::new()) };
+    let want = check::Shown::new(text, here.root).inline(node);
+    let kept = head
+        .zip(tail)
+        .is_some_and(|(head, tail)| match here.selection.is_empty() {
+            true => [head, tail].concat() == want,
+            false => {
+                want.starts_with(&head)
+                    && want.ends_with(&tail)
+                    && head.len() + tail.len() <= want.len()
+            }
+        });
+    match kept {
+        true => Ok(change),
+        false => Err(check::misread("a split would reread otherwise")),
+    }
+}

src/documents/document/format.rs

@@ -1,6 +1,5 @@
 //! Inline formats toggle at the selection, as Typora's (R4.6).
 
-mod apply;
 mod clear;
 
 use std::ops::Range;
@@ -26,9 +25,9 @@ pub enum InlineFormat {
     Clear,
 }
 
-/// Why a format did not happen.
+/// Why a format or block command did not happen.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum FormatRefusal {
+pub enum EditRefusal {
     /// Preview takes no edits.
     Preview,
     Code,
@@ -37,14 +36,20 @@ pub enum FormatRefusal {
     FrontMatter,
     /// No paragraph, heading or cell at the caret.
     Outside,
+    /// A table holds the caret.
+    Table,
+    /// Front matter is there already.
+    Present,
     /// The selection crosses a block or another mark.
     Across,
     /// Past the largest read: source alone.
     TooLong,
-    /// A long format still runs.
+    /// Another edit is still read.
     Busy,
-    /// The text changed before a long format finished.
+    /// The text changed before the edit was read.
     Changed,
+    /// The result would read as other text or blocks.
+    Misread,
 }
 
 /// The edits and the selection after them.
@@ -94,7 +99,7 @@ fn block(node: &Node) -> bool {
 }
 
 /// A styled node's two marks, kept text between.
-fn marks(node: &Node, text: &str) -> Option<[Range<usize>; 2]> {
+pub(super) fn marks(node: &Node, text: &str) -> Option<[Range<usize>; 2]> {
     let whole = span(node);
     let inner = match node {
         Node::Strong(_) | Node::Emphasis(_) | Node::Delete(_) => content(node),
@@ -160,7 +165,7 @@ fn verbatim(
     nodes: &[&Node],
     selection: &Range<usize>,
     format: InlineFormat,
-) -> Result<(), FormatRefusal> {
+) -> Result<(), EditRefusal> {
     let mut blocks: Vec<Range<usize>> = nodes
         .iter()
         .filter(|node| block(node))
@@ -180,14 +185,14 @@ fn verbatim(
         // Clear takes a block's inline code and tags too.
         let held = format != InlineFormat::Clear && touches(false);
         let why = match node {
-            Node::Code(_) if touches(true) => FormatRefusal::Code,
-            Node::Math(_) if touches(true) => FormatRefusal::Math,
-            Node::Yaml(_) | Node::Toml(_) if touches(true) => FormatRefusal::FrontMatter,
-            Node::InlineCode(_) if format != InlineFormat::Code && held => FormatRefusal::Code,
-            Node::InlineMath(_) if held => FormatRefusal::Math,
+            Node::Code(_) if touches(true) => EditRefusal::Code,
+            Node::Math(_) if touches(true) => EditRefusal::Math,
+            Node::Yaml(_) | Node::Toml(_) if touches(true) => EditRefusal::FrontMatter,
+            Node::InlineCode(_) if format != InlineFormat::Code && held => EditRefusal::Code,
+            Node::InlineMath(_) if held => EditRefusal::Math,
             Node::Html(_) => match holder(&blocks, &whole).is_some() {
-                true if held => FormatRefusal::Html,
-                false if touches(true) => FormatRefusal::Html,
+                true if held => EditRefusal::Html,
+                false if touches(true) => EditRefusal::Html,
                 _ => continue,
             },
             _ => continue,
@@ -233,7 +238,7 @@ pub(super) fn toggle(
     text: &str,
     selection: Range<usize>,
     format: InlineFormat,
-) -> Result<Change, FormatRefusal> {
+) -> Result<Change, EditRefusal> {
     toggle_tree(text, &file_tree(text), selection, format)
 }
 
@@ -243,7 +248,7 @@ pub(super) fn toggle_tree(
     root: &Node,
     selection: Range<usize>,
     format: InlineFormat,
-) -> Result<Change, FormatRefusal> {
+) -> Result<Change, EditRefusal> {
     let mut nodes = Vec::new();
     walk(root, &mut nodes);
     verbatim(&nodes, &selection, format)?;
@@ -287,8 +292,8 @@ pub(super) fn toggle_tree(
         if s != e {
             let touched = (rooms.iter()).any(|range| range.start <= e && s <= range.end);
             return Err(match touched {
-                true => FormatRefusal::Across,
-                false => FormatRefusal::Outside,
+                true => EditRefusal::Across,
+                false => EditRefusal::Outside,
             });
         }
         let line = text[..s]
@@ -299,7 +304,7 @@ pub(super) fn toggle_tree(
             + text[s..].split(['\r', '\n']).next().unwrap_or_default();
         return match line.trim().is_empty() {
             true => Ok(pair(s, format)),
-            false => Err(FormatRefusal::Outside),
+            false => Err(EditRefusal::Outside),
         };
     };
     if format == InlineFormat::Underline
@@ -377,7 +382,7 @@ fn crossed(
     s: usize,
     e: usize,
     format: InlineFormat,
-) -> Result<(), FormatRefusal> {
+) -> Result<(), EditRefusal> {
     for node in nodes {
         let whole = span(node);
         if matches!(node, Node::Text(_)) || whole.start < within.start || whole.end > within.end {
@@ -398,7 +403,7 @@ fn crossed(
         // A same style cut is taken in whole.
         let same = merges(format) && styled(format, node);
         if strictly(s) || strictly(e) || (overlaps && !holds_all && !same) {
-            return Err(FormatRefusal::Across);
+            return Err(EditRefusal::Across);
         }
     }
     Ok(())
@@ -412,7 +417,7 @@ fn wrap(
     mut s: usize,
     mut e: usize,
     format: InlineFormat,
-) -> Result<Change, FormatRefusal> {
+) -> Result<Change, EditRefusal> {
     crossed(text, nodes, within, s, e, format)?;
     if merges(format) {
         for node in nodes.iter().filter(|node| styled(format, node)) {

src/documents/document/format/apply.rs

@@ -1,138 +0,0 @@
-//! The document's format command.
-
-use std::ops::Range;
-
-use gpui::{AppContext as _, Context};
-
-use super::{Change, FormatRefusal, InlineFormat, toggle};
-use crate::documents::{
-    MarkdownMode,
-    document::{DocumentEvent, LARGEST_READ, MarkdownDocument},
-    modes::joint,
-};
-
-/// The text formatted, the open block's offset, the selection.
-type Snapshot = (String, usize, Range<usize>);
-
-impl MarkdownDocument {
-    /// `format` at the selection, read apart; refusals by event.
-    pub fn format(
-        &mut self,
-        format: InlineFormat,
-        cx: &mut Context<Self>,
-    ) -> Result<(), FormatRefusal> {
-        if self.mode == MarkdownMode::Preview {
-            return Err(FormatRefusal::Preview);
-        }
-        let (full, offset, selection) = self.snapshot(cx);
-        if full.len() > LARGEST_READ {
-            log::info!(
-                "markdown document: format {format:?} refused: {} bytes",
-                full.len()
-            );
-            return Err(FormatRefusal::TooLong);
-        }
-        if self.formatting {
-            log::info!("markdown document: format {format:?} refused: one runs");
-            return Err(FormatRefusal::Busy);
-        }
-        log::info!(
-            "markdown document: format {format:?} reads {} bytes apart",
-            full.len()
-        );
-        let taken = (full.clone(), offset, selection.clone());
-        self.formatting = true;
-        cx.spawn(async move |document, cx| {
-            let change = cx
-                .background_spawn(async move { toggle(&full, selection, format) })
-                .await;
-            document
-                .update(cx, |document, cx| {
-                    document.formatting = false;
-                    let done = if document.mode == MarkdownMode::Preview {
-                        Err(FormatRefusal::Preview)
-                    } else if document.snapshot(cx) != taken {
-                        Err(FormatRefusal::Changed)
-                    } else {
-                        change.and_then(|change| {
-                            document.apply(format, change, &taken.0, taken.1, cx)
-                        })
-                    };
-                    if let Err(why) = done {
-                        log::info!("markdown document: format {format:?} refused: {why:?}");
-                        cx.emit(DocumentEvent::FormatRefused(why));
-                    }
-                })
-                .ok();
-        })
-        .detach();
-        Ok(())
-    }
-
-    /// The text a format reads: the open block's in place.
-    fn snapshot(&self, cx: &Context<Self>) -> Snapshot {
-        let text = self.editor.read(cx).text();
-        let Some(open) = &self.open else {
-            return (text.to_string(), 0, self.editor.read(cx).primary().range());
-        };
-        let input = open.input.read(cx);
-        let (before, after) = match open.append {
-            true => (format!("{text}{}", joint(text)), ""),
-            false => (
-                text[..open.range.start].to_string(),
-                &text[open.range.end..],
-            ),
-        };
-        let picked = input.selection();
-        let offset = before.len();
-        let full = format!("{before}{}{after}", input.text());
-        (full, offset, offset + picked.start..offset + picked.end)
-    }
-
-    /// Writes `change`, into the open block if one is.
-    fn apply(
-        &mut self,
-        format: InlineFormat,
-        (edits, selected): Change,
-        full: &str,
-        offset: usize,
-        cx: &mut Context<Self>,
-    ) -> Result<(), FormatRefusal> {
-        log::info!("markdown document: format {format:?}");
-        let Some(open) = &self.open else {
-            self.editor.update(cx, |editor, cx| {
-                editor.edit(edits, cx);
-                editor.select(std::iter::once(selected), cx);
-            });
-            return Ok(());
-        };
-        let end = offset + open.input.read(cx).text().len();
-        if !edits
-            .iter()
-            .all(|(range, _)| offset <= range.start && range.end <= end)
-        {
-            log::warn!("markdown document: format {format:?} reaches past the open block");
-            return Err(FormatRefusal::Across);
-        }
-        let (Some(from), Some(to)) = (
-            edits.iter().map(|(range, _)| range.start).min(),
-            edits.iter().map(|(range, _)| range.end).max(),
-        ) else {
-            return Ok(());
-        };
-        let mut written = String::new();
-        let mut at = from;
-        for (range, with) in &edits {
-            written.push_str(&full[at..range.start]);
-            written.push_str(with);
-            at = range.end;
-        }
-        written.push_str(&full[at..to]);
-        open.input.update(cx, |input, cx| {
-            input.select(from - offset..to - offset, cx);
-            input.insert(&written, cx);
-            input.select(selected.start - offset..selected.end - offset, cx);
-        });
-        Ok(())
-    }
-}

src/documents/document/format/clear.rs

@@ -4,7 +4,7 @@ use std::ops::Range;
 
 use markdown::mdast::Node;
 
-use super::{Change, FormatRefusal, after, block, cut, holder, marks, room};
+use super::{Change, EditRefusal, after, block, cut, holder, marks, room};
 use crate::documents::{markdown::span, tree::inside};
 
 /// The backslashes of escapes in a text node's span.
@@ -46,14 +46,14 @@ pub(super) fn clear(
     text: &str,
     nodes: &[&Node],
     selection: Range<usize>,
-) -> Result<Change, FormatRefusal> {
+) -> Result<Change, EditRefusal> {
     let mut blocks: Vec<Range<usize>> = (nodes.iter())
         .filter(|node| block(node))
         .map(|node| room(node, text))
         .filter(|range| range.start <= selection.end && selection.start <= range.end)
         .collect();
     if blocks.is_empty() {
-        return Err(FormatRefusal::Outside);
+        return Err(EditRefusal::Outside);
     }
     blocks.sort_by_key(|block| block.start);
     let mut autolinks: Vec<Range<usize>> = (nodes.iter())

src/documents/document/mod.rs

@@ -1,4 +1,6 @@
+mod apart;
 mod attach;
+mod block;
 mod edit;
 mod finding;
 mod format;
@@ -23,7 +25,8 @@ use gpui::{
 
 pub use crate::documents::tree::DocumentHeading;
 pub use attach::Attachment;
-pub use format::{FormatRefusal, InlineFormat};
+pub use block::BlockCommand;
+pub use format::{EditRefusal, InlineFormat};
 pub use look::DocumentLook;
 use parse::{Parsed, alike, parsed};
 pub use point::{DocumentTarget, TargetBlock};
@@ -59,7 +62,7 @@ pub enum DocumentEvent {
     /// A secondary press moved the caret onto this.
     Pointed(DocumentTarget),
     /// A long format, accepted, did not happen.
-    FormatRefused(FormatRefusal),
+    EditRefused(EditRefusal),
 }
 
 /// A top line asked, numbered so late callbacks know theirs.
@@ -89,7 +92,7 @@ pub struct MarkdownDocument {
     /// Text changes counted; a read of an older one lapses.
     edits: u64,
     _parsing: Option<Task<()>>,
-    formatting: bool,
+    editing: bool,
     list: ListState,
     open: Option<Open>,
     /// A top line asked for, until the view holds it.
@@ -161,7 +164,7 @@ impl MarkdownDocument {
             parsed: Arc::default(),
             edits: 0,
             _parsing: None,
-            formatting: false,
+            editing: false,
             list: ListState::new(1, ListAlignment::Top, overdraw),
             open: None,
             top: None,

src/documents/document/tests/block.rs

@@ -0,0 +1,374 @@
+//! Block commands as Typora's Paragraph menu (R4.7).
+
+use gpui::{Modifiers, TestAppContext};
+use markdown::mdast::Node;
+
+use super::{open, opened, press, text};
+use crate::documents::{
+    BlockCommand, EditRefusal, MarkdownMode, document::block::run, markdown::file_tree,
+};
+
+/// `marked` after `command`: `‸` is the caret, `⟨…⟩` the selection.
+pub(super) fn ran(marked: &str, command: BlockCommand) -> Result<String, EditRefusal> {
+    let caret = marked.find('‸');
+    let text: String = marked.chars().filter(|ch| !"‸⟨⟩".contains(*ch)).collect();
+    let selection = match caret {
+        Some(at) => at..at,
+        None => {
+            let start = marked.find('⟨').expect("a selection");
+            start..marked.find('⟩').expect("its end") - '⟨'.len_utf8()
+        }
+    };
+    let (edits, selected) = run(&text, selection, command)?;
+    let mut out = text.clone();
+    for (range, with) in edits.into_iter().rev() {
+        out.replace_range(range, &with);
+    }
+    Ok(match selected.is_empty() {
+        true => format!("{}‸{}", &out[..selected.start], &out[selected.start..]),
+        false => format!(
+            "{}⟨{}⟩{}",
+            &out[..selected.start],
+            &out[selected.clone()],
+            &out[selected.end..]
+        ),
+    })
+}
+
+pub(super) fn ok(marked: &str, command: BlockCommand) -> String {
+    ran(marked, command).expect("ran")
+}
+
+/// The top-level blocks `text` reads as.
+pub(super) fn kinds(text: &str) -> Vec<&'static str> {
+    let text: String = text.chars().filter(|ch| !"‸⟨⟩".contains(*ch)).collect();
+    let root = file_tree(&text);
+    let kids = root.children().map(Vec::as_slice).unwrap_or_default();
+    (kids.iter())
+        .map(|kid| match kid {
+            Node::Paragraph(_) => "p",
+            Node::Heading(_) => "h",
+            Node::Blockquote(_) => "quote",
+            Node::List(_) => "list",
+            Node::Code(_) => "code",
+            Node::Math(_) => "math",
+            Node::ThematicBreak(_) => "rule",
+            Node::Yaml(_) => "yaml",
+            Node::Definition(_) => "definition",
+            Node::FootnoteDefinition(_) => "note",
+            _ => "other",
+        })
+        .collect()
+}
+
+#[test]
+fn headings_set_as_typoras_menu() {
+    use BlockCommand::*;
+    assert_eq!(ok("a‸b", Heading(2)), "## a‸b");
+    assert_eq!(ok("## a‸b", Heading(2)), "## a‸b");
+    assert_eq!(ok("## a‸b", Heading(3)), "### a‸b");
+    assert_eq!(ok("a‸", Promote), "###### a‸");
+    assert_eq!(ok("# a‸", Promote), "# a‸");
+    assert_eq!(ok("## a‸", Promote), "# a‸");
+    assert_eq!(ok("###### a‸", Demote), "a‸");
+    assert_eq!(ok("a‸", Demote), "a‸");
+    assert_eq!(ok("a\n\n‸\n\nb", Heading(2)), "a\n\n## ‸\n\nb");
+}
+
+#[test]
+fn a_paragraph_line_becomes_the_heading_alone() {
+    let out = ok("a\nb‸\nc", BlockCommand::Heading(1));
+    assert_eq!(out, "a\n# b‸\nc");
+    assert_eq!(kinds(&out), ["p", "h", "p"]);
+    assert_eq!(ok("> a\nb‸", BlockCommand::Heading(1)), "> a\n> # b‸");
+    assert_eq!(ok("> a‸\nb", BlockCommand::Heading(1)), "> # a‸\n> b");
+}
+
+#[test]
+fn setext_headings_relevel_and_go_atx_past_two() {
+    use BlockCommand::*;
+    assert_eq!(ok("a‸\n===", Heading(2)), "a‸\n---");
+    assert_eq!(ok("a‸\n===", Heading(3)), "### a‸");
+    assert_eq!(ok("a\nb‸\n---", Heading(4)), "#### a b‸");
+    assert_eq!(ok("a‸\n===", Paragraph), "a‸");
+}
+
+#[test]
+fn a_heading_made_text_keeps_apart_from_its_neighbors() {
+    use BlockCommand::Paragraph;
+    assert_eq!(ok("a\n# h‸", Paragraph), "a\n\nh‸");
+    assert_eq!(ok("# h‸\nb", Paragraph), "h‸\n\nb");
+    let out = ok("# h‸\n---", Paragraph);
+    assert_eq!(kinds(&out), ["p", "rule"]);
+    assert_eq!(ok("- a\n- # h‸", Paragraph), "- a\n- h‸");
+    let out = ok("> # h‸\nb", Paragraph);
+    assert_eq!(kinds(&out), ["quote", "p"]);
+}
+
+#[test]
+fn heading_commands_refuse_or_add_a_paragraph_as_typora() {
+    use BlockCommand::*;
+    assert_eq!(ran("```\na‸\n```", Heading(1)), Err(EditRefusal::Code));
+    assert_eq!(ran("$$\na‸\n$$", Promote), Err(EditRefusal::Math));
+    assert_eq!(ok("$$\na‸\n$$", Heading(1)), "$$\na\n$$\n\n‸");
+    assert_eq!(
+        ran("---\nt: a‸\n---\n", Heading(1)),
+        Err(EditRefusal::FrontMatter)
+    );
+    assert_eq!(ran("- [ ] a‸", Heading(1)), Err(EditRefusal::Outside));
+}
+
+#[test]
+fn quotes_wrap_and_unwrap() {
+    use BlockCommand::Quote;
+    assert_eq!(ok("a‸", Quote), "> a‸");
+    assert_eq!(ok("> a‸", Quote), "a‸");
+    assert_eq!(ok("> a\n> b‸", Quote), "a\nb‸");
+    assert_eq!(ok("> a\nb‸", Quote), "a\nb‸");
+    assert_eq!(ok("⟨a\n\nb⟩", Quote), "> ⟨a\n>\n> b⟩");
+    assert_eq!(ok("x\n> a‸", Quote), "x\n\na‸");
+    assert_eq!(ok("> [!NOTE]\n> a‸", Quote), "a‸");
+    assert_eq!(ok("- a‸", Quote), "- > a‸");
+    assert_eq!(ok("> a\n>\n> ⟨b⟩", Quote), "> a\n>\n> > ⟨b⟩");
+}
+
+#[test]
+fn lists_wrap_each_line() {
+    use BlockCommand::*;
+    assert_eq!(ok("a‸", BulletList), "- a‸");
+    assert_eq!(ok("a‸", OrderedList), "1. a‸");
+    assert_eq!(ok("a‸", TaskList), "- [ ] a‸");
+    assert_eq!(ok("⟨a\nb⟩", OrderedList), "1. ⟨a\n2. b⟩");
+    assert_eq!(ok("> a‸", BulletList), "> - a‸");
+    assert_eq!(ok("- a\n\n  b‸", BulletList), "- a\n\n  - b‸");
+}
+
+#[test]
+fn a_list_of_the_kind_unwraps_and_another_retypes() {
+    use BlockCommand::*;
+    let out = ok("- a\n- b‸", BulletList);
+    assert_eq!(out, "a\n\nb‸");
+    assert_eq!(kinds(&out), ["p", "p"]);
+    assert_eq!(ok("- a\n- b‸", OrderedList), "1. a\n2. b‸");
+    assert_eq!(ok("- a\n  b‸", OrderedList), "1. a\n   b‸");
+    assert_eq!(ok("- [ ] a‸", BulletList), "- a‸");
+    assert_eq!(ok("* a‸", TaskList), "* [ ] a‸");
+    assert_eq!(ok("3. a\n4. b‸", BulletList), "- a\n- b‸");
+}
+
+#[test]
+fn inserts_split_the_paragraph_at_the_caret() {
+    use BlockCommand::*;
+    assert_eq!(ok("ab‸cd", Rule), "ab\n\n---\n\n‸cd");
+    assert_eq!(ok("ab‸", CodeBlock), "ab\n\n```\n‸\n```");
+    assert_eq!(ok("a ⟨b⟩", CodeBlock), "a\n\n```\n‸b\n```");
+    assert_eq!(ok("‸ab", Toc), "[toc]‸\n\nab");
+    assert_eq!(ok("# ab‸cd", Rule), "# ab\n\n---\n\n# ‸cd");
+    assert_eq!(ok("- ab‸", Rule), "- ab\n\n  ---\n\n  ‸");
+    assert_eq!(ok("```\na‸\n```", Rule), "```\na\n```\n\n---\n\n‸");
+    assert_eq!(ok("a\n\n‸\n\nb", Rule), "a\n\n---\n\n‸\n\nb");
+    assert_eq!(ran("⟨a\n\nb⟩", Rule), Err(EditRefusal::Across));
+}
+
+#[test]
+fn notes_and_definitions_take_free_names() {
+    use BlockCommand::*;
+    let out = ok("x[^1]\n\n[^1]: y\n\nab‸", Footnote);
+    assert_eq!(out, "x[^1]\n\n[^1]: y\n\nab\n\n[^2]: ‸");
+    assert_eq!(ok("‸", LinkDefinition), "[‸]: ");
+    assert_eq!(ok("⟨see⟩", LinkDefinition), "[see]: ‸");
+    assert_eq!(ok("⟨a/b.md⟩", LinkDefinition), "[‸]: a/b.md");
+    let out = ok("ab‸", MathBlock);
+    assert_eq!(kinds(&out), ["p", "math"]);
+}
+
+#[test]
+fn empty_paragraphs_come_before_and_after() {
+    use BlockCommand::*;
+    assert_eq!(ok("a‸", ParagraphAfter), "a\n\n‸");
+    assert_eq!(ok("# a‸\nb", ParagraphAfter), "# a\n\n‸\n\nb");
+    assert_eq!(ok("a\n\nb‸", ParagraphBefore), "a\n\n‸\n\nb");
+    assert_eq!(ok("a\n# h‸", ParagraphBefore), "a\n\n‸\n\n# h");
+    let out = ok("- a‸", ParagraphBefore);
+    assert_eq!(out, "- ‸\n  a");
+    assert_eq!(kinds(&out), ["list"]);
+    let out = ok("x[^1]\n\n[^1]: a‸", ParagraphBefore);
+    assert_eq!(out, "x[^1]\n\n[^1]: ‸\n    a");
+    assert_eq!(kinds(&out), ["p", "note"]);
+}
+
+#[test]
+fn front_matter_goes_on_top_once() {
+    let out = ok("a‸", BlockCommand::FrontMatter);
+    assert_eq!(out, "---\n‸\n---\n\na");
+    assert_eq!(kinds(&out), ["yaml", "p"]);
+    assert_eq!(
+        ran("---\nt: 1\n---\n\na‸", BlockCommand::FrontMatter),
+        Err(EditRefusal::Present)
+    );
+}
+
+#[test]
+fn delete_takes_the_block_or_its_lone_holder() {
+    use BlockCommand::Delete;
+    assert_eq!(ok("a\n\nb‸\n\nc", Delete), "a\n\n‸c");
+    assert_eq!(ok("x\n\n> b‸\n\nc", Delete), "x\n\n‸c");
+    assert_eq!(ok("- a\n- b‸\n- c", Delete), "- a\n‸- c");
+    assert_eq!(ok("- a‸\n\n  b", Delete), "- ‸\n\n  b");
+}
+
+#[test]
+fn line_endings_follow_the_text() {
+    assert_eq!(
+        ok("ab‸\r\n", BlockCommand::ParagraphAfter),
+        "ab\r\n\r\n‸\r\n"
+    );
+}
+
+#[gpui::test]
+fn a_source_command_is_one_undo_step(cx: &mut TestAppContext) {
+    let (document, cx) = open("alpha\n", MarkdownMode::Source, cx);
+    document.update(cx, |document, cx| {
+        document
+            .editor
+            .update(cx, |editor, cx| editor.select(std::iter::once(2..2), cx));
+        document.block(BlockCommand::Heading(2), cx).expect("taken");
+    });
+    cx.run_until_parked();
+    assert_eq!(text(&document, cx), "## alpha\n");
+    document.update(cx, |document, cx| {
+        document.editor.update(cx, |editor, cx| editor.undo(cx));
+    });
+    assert_eq!(text(&document, cx), "alpha\n");
+}
+
+#[gpui::test]
+fn an_open_block_takes_a_command_and_stays_open(cx: &mut TestAppContext) {
+    let (document, cx) = open("alpha\n", MarkdownMode::Visual, cx);
+    press(0, Modifiers::none(), cx);
+    document.update(cx, |document, cx| {
+        document.block(BlockCommand::Quote, cx).expect("taken");
+    });
+    cx.run_until_parked();
+    assert_eq!(opened(&document, cx), "> alpha", "still open to type in");
+}
+
+#[gpui::test]
+fn a_command_past_the_open_block_writes_it_back_first(cx: &mut TestAppContext) {
+    let (document, cx) = open("first\n\nalpha\n", MarkdownMode::Visual, cx);
+    press(1, Modifiers::none(), cx);
+    document.update(cx, |document, cx| {
+        let open = document.open.as_ref().expect("opened");
+        open.input.update(cx, |input, cx| input.insert("x", cx));
+        document
+            .block(BlockCommand::FrontMatter, cx)
+            .expect("taken");
+    });
+    cx.run_until_parked();
+    let written = text(&document, cx);
+    assert!(written.starts_with("---\n\n---\n"), "{written:?}");
+    assert!(
+        written.contains("alpha") && written.contains('x'),
+        "{written:?}"
+    );
+    document.read_with(cx, |document, _| assert!(document.open.is_none()));
+}
+
+/// The one list's items, each as its blocks' kinds.
+fn items(text: &str) -> Vec<Vec<&'static str>> {
+    let text: String = text.chars().filter(|ch| !"‸⟨⟩".contains(*ch)).collect();
+    let root = file_tree(&text);
+    let Some(Node::List(list)) = root.children().and_then(|kids| kids.first()) else {
+        panic!("a list first");
+    };
+    (list.children.iter())
+        .map(|item| {
+            (item
+                .children()
+                .map(Vec::as_slice)
+                .unwrap_or_default()
+                .iter())
+            .map(|kid| match kid {
+                Node::Paragraph(_) => "p",
+                Node::Code(_) => "code",
+                _ => "other",
+            })
+            .collect()
+        })
+        .collect()
+}
+
+#[test]
+fn a_caret_in_heading_marks_splits_at_the_text() {
+    use BlockCommand::Rule;
+    assert_eq!(ok("‸# alpha", Rule), "---\n\n# ‸alpha");
+    let out = ok("# alpha #‸##", Rule);
+    assert_eq!(kinds(&out), ["h", "rule"]);
+}
+
+#[test]
+fn a_task_list_keeps_checked_boxes() {
+    assert_eq!(
+        ok("- a\n- [x] b‸", BlockCommand::TaskList),
+        "- [ ] a\n- [x] b‸"
+    );
+}
+
+#[test]
+fn an_alert_in_an_item_keeps_the_item() {
+    let out = ok("- > [!NOTE]\n  > a‸\n- b", BlockCommand::Quote);
+    assert_eq!(out, "- a‸\n- b");
+    assert_eq!(items(&out), [vec!["p"], vec!["p"]]);
+}
+
+#[test]
+fn a_split_closes_and_reopens_inline_marks() {
+    use BlockCommand::Rule;
+    let out = ok("**ab‸cd**", Rule);
+    assert_eq!(out, "**ab**\n\n---\n\n**‸cd**");
+    assert_eq!(kinds(&out), ["p", "rule", "p"]);
+    assert_eq!(ran("[a‸b](u)", Rule), Err(EditRefusal::Across));
+    assert_eq!(ran("`a‸b`", Rule), Err(EditRefusal::Across));
+}
+
+#[test]
+fn a_retyped_item_keeps_its_code_indent() {
+    let out = ok("-     code‸", BlockCommand::OrderedList);
+    assert_eq!(out, "1.     code‸");
+    assert_eq!(items(&out), [vec!["code"]]);
+}
+
+#[test]
+fn deleting_keeps_neighbors_apart() {
+    let out = ok("p\n# h‸\nq", BlockCommand::Delete);
+    assert_eq!(out, "p\n‸\nq");
+    assert_eq!(kinds(&out), ["p", "p"]);
+}
+
+#[test]
+fn heading_marks_keep_their_text() {
+    use BlockCommand::*;
+    let out = ok("alpha #‸", Heading(1));
+    assert_eq!(out, "# alpha \\#‸");
+    assert_eq!(kinds(&out), ["h"]);
+    let out = ok("# - alpha‸", Paragraph);
+    assert_eq!(out, "\\- alpha‸");
+    assert_eq!(kinds(&out), ["p"]);
+    assert_eq!(kinds(&ok("# 1. a‸", Paragraph)), ["p"]);
+}
+
+#[test]
+fn a_tasks_first_text_takes_no_block() {
+    use BlockCommand::*;
+    assert_eq!(ran("- [ ] a‸", Quote), Err(EditRefusal::Outside));
+    assert_eq!(ran("- [ ] ‸ab", Rule), Err(EditRefusal::Outside));
+    assert_eq!(ran("- [ ] ‸ab", CodeBlock), Err(EditRefusal::Outside));
+    assert_eq!(ran("- [ ] a‸", ParagraphBefore), Err(EditRefusal::Outside));
+}
+
+#[test]
+fn a_selection_past_a_list_takes_its_siblings() {
+    let out = ok("- ⟨a\n\nb⟩", BlockCommand::OrderedList);
+    assert_eq!(out, "1. ⟨a\n\n2. b⟩");
+    assert_eq!(kinds(&out), ["list"]);
+}

src/documents/document/tests/block_edges.rs

@@ -0,0 +1,223 @@
+//! Block commands whose results reread as written.
+
+use markdown::mdast::Node;
+
+use super::block::{kinds, ok, ran};
+use crate::documents::{BlockCommand, EditRefusal, markdown::file_tree};
+
+fn plain(marked: &str) -> String {
+    marked.chars().filter(|ch| !"‸⟨⟩".contains(*ch)).collect()
+}
+
+/// Every node of `text`, in document order.
+fn nodes(text: &str, keep: &mut dyn FnMut(&Node)) {
+    fn walk(node: &Node, keep: &mut dyn FnMut(&Node)) {
+        keep(node);
+        for kid in node.children().map(Vec::as_slice).unwrap_or_default() {
+            walk(kid, keep);
+        }
+    }
+    walk(&file_tree(text), keep);
+}
+
+fn checks(text: &str) -> Vec<Option<bool>> {
+    let mut out = Vec::new();
+    nodes(text, &mut |node| {
+        if let Node::ListItem(item) = node {
+            out.push(item.checked);
+        }
+    });
+    out
+}
+
+fn codes(text: &str) -> Vec<String> {
+    let mut out = Vec::new();
+    nodes(text, &mut |node| {
+        if let Node::Code(code) = node {
+            out.push(code.value.clone());
+        }
+    });
+    out
+}
+
+fn texts(text: &str) -> Vec<String> {
+    let mut out = Vec::new();
+    nodes(text, &mut |node| {
+        if let Node::Text(text) = node {
+            out.push(text.value.clone());
+        }
+    });
+    out
+}
+
+#[test]
+fn a_split_that_would_reread_otherwise_refuses() {
+    assert_eq!(
+        ran("~~ab‸~cd~~", BlockCommand::Rule),
+        Err(EditRefusal::Misread)
+    );
+    assert_eq!(
+        ran("__ab‸_cd__", BlockCommand::Rule),
+        Err(EditRefusal::Misread)
+    );
+}
+
+#[test]
+fn a_split_rest_that_would_open_a_block_is_escaped() {
+    let out = plain(&ok("a ‸- b", BlockCommand::Rule));
+    assert_eq!(out, "a\n\n---\n\n\\- b");
+    assert_eq!(kinds(&out), ["p", "rule", "p"]);
+}
+
+#[test]
+fn closing_hashes_stay_text_wherever_a_heading_line_ends() {
+    let out = plain(&ok("alpha #‸\n===", BlockCommand::Heading(3)));
+    assert_eq!(out, "### alpha \\#");
+    assert_eq!(texts(&out), ["alpha #"]);
+    let out = plain(&ok("# a #‸ b", BlockCommand::Rule));
+    assert_eq!(kinds(&out), ["h", "rule", "h"]);
+    assert_eq!(texts(&out), ["a #", "b"]);
+}
+
+#[test]
+fn a_paragraph_reads_the_heading_body_without_closing_hashes() {
+    let out = plain(&ok("# ---‸ ###", BlockCommand::Paragraph));
+    assert_eq!(out, "\\---");
+    assert_eq!(kinds(&out), ["p"]);
+    let out = plain(&ok("# [x]: /u‸ ###", BlockCommand::Paragraph));
+    assert_eq!(kinds(&out), ["p"]);
+    assert_eq!(texts(&out).concat(), "[x]: /u");
+}
+
+#[test]
+fn a_task_box_below_its_marker_stays_checked() {
+    let out = plain(&ok("1.‸\n   [x] a", BlockCommand::TaskList));
+    assert_eq!(checks(&out), [Some(true)]);
+    assert_eq!(texts(&out), ["a"]);
+}
+
+#[test]
+fn retyping_keeps_code_columns_past_tabs() {
+    let source = "-\t\t‸code";
+    let out = plain(&ok(source, BlockCommand::OrderedList));
+    assert_eq!(codes(&out), codes(&plain(source)));
+    assert_eq!(codes(&out).len(), 1);
+}
+
+#[test]
+fn a_task_cannot_box_code() {
+    assert_eq!(
+        ran("-     ‸a", BlockCommand::TaskList),
+        Err(EditRefusal::Code)
+    );
+}
+
+#[test]
+fn an_alert_unwraps_into_its_holder() {
+    assert_eq!(
+        plain(&ok("- > [!NOTE]‸\n    a", BlockCommand::Quote)),
+        "- a"
+    );
+    assert_eq!(
+        plain(&ok("> > [!NOTE]‸\n>   a", BlockCommand::Quote)),
+        "> a"
+    );
+    let out = plain(&ok("- > [!NOTE]‸\n  >\n  >\n  > a", BlockCommand::Quote));
+    assert_eq!(out, "- a");
+    assert_eq!(kinds(&out), ["list"]);
+}
+
+#[test]
+fn an_alert_marker_sharing_its_line_refuses() {
+    assert_eq!(
+        ran("> [!NOTE]&#10;a‸", BlockCommand::Quote),
+        Err(EditRefusal::Misread)
+    );
+}
+
+#[test]
+fn delete_keeps_neighbors_apart_past_gone_openers() {
+    let out = plain(&ok("p\n> # ‸h\nq", BlockCommand::Delete));
+    assert_eq!(out, "p\n\nq");
+    assert_eq!(kinds(&out), ["p", "p"]);
+}
+
+fn inline_codes(text: &str) -> Vec<String> {
+    let mut out = Vec::new();
+    nodes(text, &mut |node| {
+        if let Node::InlineCode(code) = node {
+            out.push(code.value.clone());
+        }
+    });
+    out
+}
+
+#[test]
+fn a_heading_join_keeps_white_space_in_code() {
+    let source = "a `x\n  y`‸\n===";
+    match ran(source, BlockCommand::Heading(3)) {
+        Err(EditRefusal::Misread) => {}
+        Ok(out) => assert_eq!(inline_codes(&plain(&out)), inline_codes(&plain(source))),
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn a_split_that_draws_otherwise_refuses() {
+    for (source, command) in [
+        ("<u>ab‸cd</u>", BlockCommand::Rule),
+        ("<u>a‸\nb</u>", BlockCommand::Heading(1)),
+        ("x:smile: ‸:smile:", BlockCommand::Rule),
+    ] {
+        assert_eq!(ran(source, command), Err(EditRefusal::Misread), "{source}");
+    }
+}
+
+#[test]
+fn an_alert_body_block_keeps_its_indent() {
+    let out = plain(&ok("> [!NOTE]\n>\n>     co‸de", BlockCommand::Quote));
+    assert_eq!(
+        (kinds(&out), codes(&out)),
+        (vec!["code"], vec!["code".to_string()])
+    );
+    let out = plain(&ok(
+        "> [!NOTE]\n>\n>   ```\n>   co‸de\n>   ```",
+        BlockCommand::Quote,
+    ));
+    assert_eq!(
+        (kinds(&out), codes(&out)),
+        (vec!["code"], vec!["code".to_string()])
+    );
+}
+
+#[test]
+fn retyping_reads_a_fence_from_its_source() {
+    let out = plain(&ok("-     ```lang‸", BlockCommand::OrderedList));
+    assert_eq!(codes(&out), vec!["```lang".to_string()]);
+    let out = plain(&ok("-     \u{a0}code‸", BlockCommand::OrderedList));
+    assert_eq!(codes(&out), vec!["\u{a0}code".to_string()]);
+}
+
+#[test]
+fn a_removed_box_leaves_text() {
+    assert_eq!(
+        plain(&ok("- [x] ---‸", BlockCommand::BulletList)),
+        "- \\---"
+    );
+    assert_eq!(
+        plain(&ok("- [x] # h‸", BlockCommand::BulletList)),
+        "- \\# h"
+    );
+    assert_eq!(plain(&ok("-\n  [x] a‸", BlockCommand::TaskList)), "a");
+    assert_eq!(plain(&ok("- [x] # h‸", BlockCommand::TaskList)), "\\# h");
+}
+
+#[test]
+fn an_empty_heading_becomes_an_empty_paragraph() {
+    assert!(ran("# ‸", BlockCommand::Paragraph).is_ok());
+}
+
+#[test]
+fn an_escaped_alert_marker_on_its_own_line_unwraps() {
+    assert_eq!(plain(&ok("> \\[!NOTE]\n> a‸", BlockCommand::Quote)), "a");
+}

src/documents/document/tests/format.rs

@@ -8,7 +8,7 @@ use web_time::Instant;
 
 use super::{open, opened, press, text};
 use crate::documents::{
-    DocumentEvent, FormatRefusal, InlineFormat, LARGEST_READ, MarkdownDocument, MarkdownMode,
+    DocumentEvent, EditRefusal, InlineFormat, LARGEST_READ, MarkdownDocument, MarkdownMode,
     document::{
         format::{toggle, toggle_tree},
         visual,
@@ -17,7 +17,7 @@ use crate::documents::{
 };
 
 /// `marked` toggled: `‸` is the caret, `⟨…⟩` the selection.
-fn toggled(marked: &str, format: InlineFormat) -> Result<String, FormatRefusal> {
+fn toggled(marked: &str, format: InlineFormat) -> Result<String, EditRefusal> {
     let caret = marked.find('‸');
     let text: String = marked.chars().filter(|ch| !"‸⟨⟩".contains(*ch)).collect();
     let selection = match caret {
@@ -109,7 +109,7 @@ fn clear_takes_every_mark_off_the_touched_blocks() {
 
 #[test]
 fn code_math_html_and_front_matter_refuse() {
-    use FormatRefusal as Why;
+    use EditRefusal as Why;
     use InlineFormat::*;
     assert_eq!(toggled("```\nco‸de\n```", Strong), Err(Why::Code));
     assert_eq!(toggled("x `co‸de` y", Strong), Err(Why::Code));
@@ -126,12 +126,9 @@ fn code_math_html_and_front_matter_refuse() {
 #[test]
 fn a_selection_across_a_link_or_into_its_address_refuses() {
     use InlineFormat::*;
-    assert_eq!(toggled("[a ⟨b](u) c⟩", Strong), Err(FormatRefusal::Across));
-    assert_eq!(
-        toggled("[a](ht‸tp://x)", Strong),
-        Err(FormatRefusal::Across)
-    );
-    assert_eq!(toggled("a\n\n> ‸", Strong), Err(FormatRefusal::Outside));
+    assert_eq!(toggled("[a ⟨b](u) c⟩", Strong), Err(EditRefusal::Across));
+    assert_eq!(toggled("[a](ht‸tp://x)", Strong), Err(EditRefusal::Across));
+    assert_eq!(toggled("a\n\n> ‸", Strong), Err(EditRefusal::Outside));
 }
 
 #[gpui::test]
@@ -185,14 +182,14 @@ fn the_source_takes_a_format_as_one_step(cx: &mut TestAppContext) {
 fn preview_refuses_a_format(cx: &mut TestAppContext) {
     let (document, cx) = open("alpha\n", MarkdownMode::Preview, cx);
     let refused = document.update(cx, |document, cx| document.format(InlineFormat::Strong, cx));
-    assert_eq!(refused, Err(FormatRefusal::Preview));
+    assert_eq!(refused, Err(EditRefusal::Preview));
     assert_eq!(text(&document, cx), "alpha\n");
 }
 
 #[test]
 fn an_end_in_marks_or_an_address_refuses() {
     use InlineFormat::*;
-    let across = Err(FormatRefusal::Across);
+    let across = Err(EditRefusal::Across);
     assert_eq!(toggled("a *‸*bold** z", Strong), across);
     assert_eq!(toggled("[a](ht‸tps://example.com)", Link), across);
     assert_eq!(toggled("a *⟨*b** c⟩", Strong), across);
@@ -283,12 +280,12 @@ fn a_format_lapses_when_the_text_moves(cx: &mut TestAppContext) {
 fn refusals(
     document: &Entity<MarkdownDocument>,
     cx: &mut VisualTestContext,
-) -> Rc<RefCell<Vec<FormatRefusal>>> {
+) -> Rc<RefCell<Vec<EditRefusal>>> {
     let heard = Rc::new(RefCell::new(Vec::new()));
     let kept = heard.clone();
     cx.update(|_, cx| {
         cx.subscribe(document, move |_, event: &DocumentEvent, _| {
-            if let DocumentEvent::FormatRefused(why) = event {
+            if let DocumentEvent::EditRefused(why) = event {
                 kept.borrow_mut().push(*why);
             }
         })
@@ -308,13 +305,13 @@ fn a_lapse_comes_by_event(cx: &mut TestAppContext) {
             .update(cx, |editor, cx| editor.edit([(0..0, "y".to_string())], cx));
     });
     cx.run_until_parked();
-    assert_eq!(*heard.borrow(), [FormatRefusal::Changed]);
+    assert_eq!(*heard.borrow(), [EditRefusal::Changed]);
 }
 
 #[test]
 fn an_unwrap_refuses_an_end_in_nested_marks() {
     use InlineFormat::*;
-    let across = Err(FormatRefusal::Across);
+    let across = Err(EditRefusal::Across);
     assert_eq!(toggled("**[a](ht‸tps://x)**", Strong), across);
     assert_eq!(toggled("**~~a~‸~**", Strong), across);
     assert_eq!(toggled("<u>[a](ht‸tps://x)</u>", Underline), across);
@@ -359,7 +356,7 @@ fn a_second_format_refuses_while_one_runs(cx: &mut TestAppContext) {
         document.format(InlineFormat::Strong, cx).expect("taken");
         document.format(InlineFormat::Emphasis, cx)
     });
-    assert_eq!(second, Err(FormatRefusal::Busy));
+    assert_eq!(second, Err(EditRefusal::Busy));
     cx.run_until_parked();
     document.update(cx, |document, cx| {
         document.format(InlineFormat::Emphasis, cx).expect("taken")
@@ -386,7 +383,7 @@ fn a_refusal_comes_by_event(cx: &mut TestAppContext) {
     });
     assert_eq!(taken, Ok(()));
     cx.run_until_parked();
-    assert_eq!(*heard.borrow(), [FormatRefusal::Code]);
+    assert_eq!(*heard.borrow(), [EditRefusal::Code]);
     assert_eq!(text(&document, cx), source);
 }
 
@@ -400,14 +397,14 @@ fn a_format_drops_once_preview_shows(cx: &mut TestAppContext) {
     });
     cx.run_until_parked();
     assert!(text(&document, cx).starts_with("xx"));
-    assert_eq!(*heard.borrow(), [FormatRefusal::Preview]);
+    assert_eq!(*heard.borrow(), [EditRefusal::Preview]);
 }
 
 #[gpui::test]
 fn a_text_past_the_largest_read_refuses(cx: &mut TestAppContext) {
     let (document, cx) = word(cx, LARGEST_READ + 1);
     let refused = document.update(cx, |document, cx| document.format(InlineFormat::Strong, cx));
-    assert_eq!(refused, Err(FormatRefusal::TooLong));
+    assert_eq!(refused, Err(EditRefusal::TooLong));
 }
 
 #[gpui::test]

src/documents/document/tests/mod.rs

@@ -366,6 +366,8 @@ fn a_press_after_a_write_back_waits_for_the_long_read(cx: &mut TestAppContext) {
 }
 
 mod attach;
+mod block;
+mod block_edges;
 mod format;
 mod history;
 mod links;

src/documents/mod.rs

@@ -36,8 +36,9 @@ pub use counts::{ReadingTime, WordCount};
 pub use diagram::{Diagram, diagram_svg};
 pub(crate) use diagram::{flatten, options as svg_options};
 pub use document::{
-    Attachment, DocumentEvent, DocumentHeading, DocumentLook, DocumentTarget, FormatRefusal,
-    InlineFormat, LARGEST_READ, MarkdownDocument, TableEdit, TableRefusal, TargetBlock,
+    Attachment, BlockCommand, DocumentEvent, DocumentHeading, DocumentLook, DocumentTarget,
+    EditRefusal, InlineFormat, LARGEST_READ, MarkdownDocument, TableEdit, TableRefusal,
+    TargetBlock,
 };
 pub use epub::{Chapter, EpubReader};
 pub use format::{Format, format};