Documents: \( pairs stay in one paragraph and off addresses; formulas place at wraps

- Pairs pair inside one paragraph, heading or cell; links' addresses,
  images, code and <code>/<kbd> text stay literal.
- Adjacent formulas stay two; a parting space is dropped after parsing.
- Stray and escaped dollars, in or out of a formula, stay dollars.
- A formula's node spans its delimiters; its value is the written TeX.
- A formula wrapped whole draws at its own line's start.
- A failed inline formula shows its reason after the TeX.

Co-Authored-By: Claude <noreply@anthropic.com>

src/documents/markdown.rs

@@ -1,4 +1,6 @@
-use std::{borrow::Cow, ops::Range};
+use std::ops::Range;
+
+mod tex;
 
 use gpui::App;
 use markdown::{Constructs, ParseOptions, mdast};
@@ -24,68 +26,11 @@ pub(crate) fn tree(text: &str) -> mdast::Node {
 }
 
 fn parsed(text: &str, options: &ParseOptions) -> mdast::Node {
-    let text = tex_math(text, options);
+    let swapped = tex::swapped(text, options);
-    markdown::to_mdast(&text, options).expect("markdown without MDX always parses")
+    let mut root =
-}
+        markdown::to_mdast(&swapped.text, options).expect("markdown without MDX always parses");
-
+    tex::mend(&mut root, &swapped);
-/// `\(` and `\[` delimiters as `$`, byte for byte.
+    root
-fn tex_math<'a>(text: &'a str, options: &ParseOptions) -> Cow<'a, str> {
-    if !text.contains("\\(") && !text.contains("\\[") {
-        return Cow::Borrowed(text);
-    }
-    let root = markdown::to_mdast(text, options).expect("markdown without MDX always parses");
-    let mut nodes = Vec::new();
-    walk(&root, &mut nodes);
-    let mut kept = vec![false; text.len()];
-    for node in nodes {
-        use mdast::Node::{Code, Html, InlineCode, InlineMath, Math, Toml, Yaml};
-        if matches!(
-            node,
-            Code(_) | InlineCode(_) | Math(_) | InlineMath(_) | Html(_) | Yaml(_) | Toml(_)
-        ) {
-            kept[span(node)].fill(true);
-        }
-    }
-    let bytes = text.as_bytes();
-    let mut out = bytes.to_vec();
-    let mut open: Option<(usize, u8)> = None;
-    let mut at = 0;
-    while at + 1 < bytes.len() {
-        match bytes[at] {
-            // A blank line ends a paragraph and its formula.
-            b'\n' if blank_after(&bytes[at + 1..]) => open = None,
-            b'\\' if !kept[at] => {
-                match (bytes[at + 1], open) {
-                    (b'(', None) => open = Some((at, b')')),
-                    (b'[', None) => open = Some((at, b']')),
-                    (close, Some((start, wanted)))
-                        if close == wanted && at > start + 2 && !text[start..at].contains('$') =>
-                    {
-                        out[start..start + 2].copy_from_slice(b"$ ");
-                        out[at..at + 2].copy_from_slice(b" $");
-                        open = None;
-                    }
-                    _ => {}
-                }
-                // An escaped backslash escapes nothing after it.
-                at += 2;
-                continue;
-            }
-            _ => {}
-        }
-        at += 1;
-    }
-    match out == bytes {
-        true => Cow::Borrowed(text),
-        false => Cow::Owned(String::from_utf8(out).expect("ASCII swaps keep UTF-8")),
-    }
-}
-
-/// Whether the line `rest` starts holds only white space.
-fn blank_after(rest: &[u8]) -> bool {
-    rest.iter()
-        .take_while(|byte| **byte != b'\n')
-        .all(u8::is_ascii_whitespace)
 }
 
 /// An inline formula's TeX: inside `$` runs or `\(` pairs.

src/documents/markdown/tex.rs

@@ -0,0 +1,266 @@
+//! `\(…\)` and `\[…\]` read as math between dollars.
+
+use std::{borrow::Cow, ops::Range};
+
+use markdown::{ParseOptions, mdast, unist::Position};
+
+use super::{span, walk};
+use crate::documents::tree::{Style, html};
+
+/// Bytes a literal dollar may stand in as while parsing.
+const STAND_INS: std::ops::RangeInclusive<u8> = 0x01..=0x08;
+
+/// One pair's delimiters as written.
+pub(super) struct Pair {
+    open: Range<usize>,
+    close: Range<usize>,
+}
+
+/// The swapped text and what to put back after parsing.
+pub(super) struct Swapped<'a> {
+    pub text: Cow<'a, str>,
+    pairs: Vec<Pair>,
+    /// Spaces that only part two dollars.
+    gaps: Vec<usize>,
+    /// The byte every other dollar was written as.
+    stand_in: u8,
+}
+
+/// `text` with each pair's delimiters as dollars, byte for byte.
+pub(super) fn swapped<'a>(text: &'a str, options: &ParseOptions) -> Swapped<'a> {
+    let stand_in = STAND_INS
+        .clone()
+        .find(|byte| !text.as_bytes().contains(byte));
+    let none = || Swapped {
+        text: Cow::Borrowed(text),
+        pairs: Vec::new(),
+        gaps: Vec::new(),
+        stand_in: 0,
+    };
+    if !text.contains("\\(") && !text.contains("\\[") {
+        return none();
+    }
+    let Some(stand_in) = stand_in else {
+        log::warn!("markdown: \\( reads as text; every stand-in byte is used");
+        return none();
+    };
+    let root = markdown::to_mdast(text, options).expect("markdown without MDX always parses");
+    let mut nodes = Vec::new();
+    walk(&root, &mut nodes);
+    let mut kept = vec![false; text.len()];
+    let (mut pairs, mut dollars) = (Vec::new(), Vec::new());
+    for node in nodes {
+        use mdast::Node::{Heading, Paragraph, TableCell};
+        if matches!(node, Paragraph(_) | Heading(_) | TableCell(_)) {
+            keep(node, text, &mut kept);
+            paired(text, span(node), &kept, &mut pairs, &mut dollars);
+        }
+    }
+    if pairs.is_empty() {
+        return none();
+    }
+    let (out, gaps) = written(text, &pairs, &dollars, stand_in);
+    Swapped {
+        text: Cow::Owned(String::from_utf8(out).expect("ASCII swaps keep UTF-8")),
+        pairs,
+        gaps,
+        stand_in,
+    }
+}
+
+/// Marks what in `container` is not prose: code, tags, addresses.
+fn keep(container: &mdast::Node, text: &str, kept: &mut [bool]) {
+    let mut nodes = Vec::new();
+    walk(container, &mut nodes);
+    let mut code: Option<(String, usize)> = None;
+    for node in &nodes[1..] {
+        use mdast::Node::*;
+        let whole = span(node);
+        match node {
+            InlineCode(_) | InlineMath(_) | Image(_) | ImageReference(_) | FootnoteReference(_) => {
+                kept[whole].fill(true)
+            }
+            Link(_) | LinkReference(_) => {
+                kept[whole.clone()].fill(true);
+                // Bracketed text is prose; its address is not.
+                let last = node.children().and_then(|children| children.last());
+                if text[whole.clone()].starts_with('[')
+                    && let Some(last) = last
+                {
+                    // A text's span skips a leading escape: start at `[`.
+                    kept[whole.start + 1..span(last).end].fill(false);
+                }
+            }
+            Html(_) => {
+                kept[whole.clone()].fill(true);
+                let Some(tag) = html::tag(&text[whole.clone()]) else {
+                    continue;
+                };
+                match &code {
+                    Some((name, from)) if tag.closing && tag.name == *name => {
+                        kept[*from..whole.start].fill(true);
+                        code = None;
+                    }
+                    None if !tag.closing && html::inline_style(&tag.name) == Some(Style::Code) => {
+                        code = Some((tag.name, whole.end));
+                    }
+                    _ => {}
+                }
+            }
+            _ => {}
+        }
+    }
+    // An unclosed `<code>` runs to its block's end.
+    if let Some((_, from)) = code {
+        kept[from..span(container).end].fill(true);
+    }
+}
+
+/// Pairs and bare dollars in `within`; pairs cross nothing kept.
+fn paired(
+    text: &str,
+    within: Range<usize>,
+    kept: &[bool],
+    pairs: &mut Vec<Pair>,
+    dollars: &mut Vec<usize>,
+) {
+    let bytes = text.as_bytes();
+    let mut open: Option<(usize, u8)> = None;
+    let mut at = within.start;
+    while at < within.end {
+        if kept[at] {
+            open = None;
+        } else if bytes[at] == b'$' {
+            dollars.push(at);
+        } else if bytes[at] == b'\\' && at + 1 < within.end {
+            match (bytes[at + 1], open) {
+                (b'(', None) => open = Some((at, b')')),
+                (b'[', None) => open = Some((at, b']')),
+                (close, Some((start, wanted))) if close == wanted && !kept[at + 1] => {
+                    if !bytes[start + 2..at].iter().all(u8::is_ascii_whitespace) {
+                        pairs.push(Pair {
+                            open: start..start + 2,
+                            close: at..at + 2,
+                        });
+                    }
+                    open = None;
+                }
+                _ => {}
+            }
+            // An escaped byte escapes nothing after it.
+            at += 2;
+            continue;
+        }
+        at += 1;
+    }
+}
+
+/// The swapped bytes; a space parts dollars that would touch.
+fn written(text: &str, pairs: &[Pair], dollars: &[usize], stand_in: u8) -> (Vec<u8>, Vec<usize>) {
+    let mut out = text.as_bytes().to_vec();
+    for at in dollars {
+        out[*at] = stand_in;
+    }
+    let mut gaps = Vec::new();
+    for (ix, pair) in pairs.iter().enumerate() {
+        for byte in &mut out[pair.open.end..pair.close.start] {
+            if *byte == b'$' {
+                *byte = stand_in;
+            }
+        }
+        let open = match pair.open.start.checked_sub(1).map(|before| out[before]) {
+            Some(b'$') => {
+                gaps.push(pair.open.start);
+                *b" $"
+            }
+            _ => *b"$ ",
+        };
+        out[pair.open.clone()].copy_from_slice(&open);
+        let after = pair.close.end;
+        let opens_next = pairs
+            .get(ix + 1)
+            .is_some_and(|next| next.open.start == after);
+        let close = match opens_next || out.get(after) == Some(&b'$') {
+            true => {
+                gaps.push(pair.close.start + 1);
+                *b"$ "
+            }
+            false => *b" $",
+        };
+        out[pair.close.clone()].copy_from_slice(&close);
+    }
+    (out, gaps)
+}
+
+/// Puts TeX, spans and dollars back; drops parting spaces.
+pub(super) fn mend(root: &mut mdast::Node, swapped: &Swapped) {
+    if swapped.pairs.is_empty() {
+        return;
+    }
+    if let mdast::Node::InlineMath(math) = root
+        && let Some(position) = &mut math.position
+        && let Some(pair) =
+            (swapped.pairs.iter()).find(|pair| pair.open.contains(&position.start.offset))
+    {
+        math.value = written_tex(&math.value, pair, swapped, position);
+        position.start.column -= position.start.offset - pair.open.start;
+        position.start.offset = pair.open.start;
+        position.end.column += pair.close.end - position.end.offset;
+        position.end.offset = pair.close.end;
+    }
+    if let Some(children) = root.children_mut() {
+        children.iter_mut().for_each(|child| trim(child, swapped));
+        children.retain(|child| !matches!(child, mdast::Node::Text(text) if text.value.is_empty()));
+        children.iter_mut().for_each(|child| mend(child, swapped));
+    }
+}
+
+/// The TeX as written, from the value markdown-rs read.
+fn written_tex(value: &str, pair: &Pair, swapped: &Swapped, at: &Position) -> String {
+    let bytes = swapped.text.as_bytes();
+    // A pad: the space a delimiter writes inside its dollar.
+    let pads = (
+        at.start.offset == pair.open.start,
+        at.end.offset == pair.close.end,
+    );
+    let ends = (
+        pads.0 || bytes[pair.open.end] == b' ',
+        pads.1 || bytes[pair.close.start - 1] == b' ',
+    );
+    // With spaces at both ends, markdown-rs trimmed one each.
+    let mut tex = match ends {
+        (true, true) => format!(" {value} "),
+        _ => value.to_string(),
+    };
+    if pads.1 {
+        tex.pop();
+    }
+    if pads.0 {
+        tex.remove(0);
+    }
+    tex.replace(char::from(swapped.stand_in), "$")
+}
+
+/// Restores a text's dollars; drops a parting space at its ends.
+fn trim(node: &mut mdast::Node, swapped: &Swapped) {
+    let mdast::Node::Text(text) = node else {
+        return;
+    };
+    text.value = text.value.replace(char::from(swapped.stand_in), "$");
+    let Some(position) = &mut text.position else {
+        return;
+    };
+    if swapped.gaps.contains(&position.start.offset) && text.value.starts_with(' ') {
+        text.value.remove(0);
+        position.start.offset += 1;
+        position.start.column += 1;
+    }
+    if swapped.gaps.contains(&(position.end.offset - 1)) && text.value.ends_with(' ') {
+        text.value.pop();
+        position.end.offset -= 1;
+        position.end.column -= 1;
+    }
+}
+
+#[cfg(test)]
+mod tests;

src/documents/markdown/tex/tests.rs

@@ -0,0 +1,99 @@
+use markdown::mdast::Node;
+
+use crate::documents::markdown::{options, span, tree, walk};
+
+/// Each formula's TeX and span, and the text left.
+fn read(source: &str) -> (Vec<(String, std::ops::Range<usize>)>, String) {
+    let root = tree(source);
+    let mut nodes = Vec::new();
+    walk(&root, &mut nodes);
+    let mut maths = Vec::new();
+    let mut text = String::new();
+    for node in nodes {
+        match node {
+            Node::InlineMath(math) => maths.push((math.value.clone(), span(node))),
+            Node::Text(written) => text.push_str(&written.value),
+            _ => {}
+        }
+    }
+    (maths, text)
+}
+
+fn tex(source: &str) -> Vec<String> {
+    read(source).0.into_iter().map(|(tex, _)| tex).collect()
+}
+
+fn untouched(source: &str) {
+    let plain = markdown::to_mdast(source, &options()).unwrap();
+    assert_eq!(tree(source), plain, "{source:?}");
+}
+
+#[test]
+fn a_pair_spans_its_delimiters_and_keeps_its_tex() {
+    assert_eq!(
+        read(r"a \(x\) b"),
+        (vec![("x".into(), 2..7)], "a  b".into())
+    );
+    assert_eq!(tex(r"\( x \)"), [" x "]);
+    assert_eq!(tex(r"\(x \)\(y\)"), ["x ", "y"]);
+}
+
+#[test]
+fn adjacent_formulas_stay_two() {
+    for (source, maths) in [
+        (r"\(x\)\(y\)", vec!["x", "y"]),
+        (r"$x$\(y\)", vec!["x", "y"]),
+        (r"\(y\)$x$", vec!["y", "x"]),
+        (r"\[x\]\(y\)", vec!["x", "y"]),
+    ] {
+        let (found, text) = read(source);
+        let found: Vec<_> = found.into_iter().map(|(tex, _)| tex).collect();
+        assert_eq!(found, maths, "{source:?}");
+        assert_eq!(text, "", "no parting space shows: {source:?}");
+    }
+}
+
+#[test]
+fn dollars_stay_dollars() {
+    assert_eq!(tex(r"\(\$5\)"), [r"\$5"]);
+    assert_eq!(tex(r"\[a \$ b\]"), [r"a \$ b"]);
+    assert_eq!(tex(r"\(a$b\)"), ["a$b"]);
+    assert_eq!(
+        read(r"costs $5 and \(x\)"),
+        (vec![("x".into(), 13..18)], "costs $5 and ".into()),
+        "a stray dollar does not pair with a formula"
+    );
+    assert_eq!(read(r"\$\(x\)").1, "$", "an escaped dollar before");
+    assert_eq!(read(r"\(x\)\$").1, "$", "an escaped dollar after");
+}
+
+#[test]
+fn addresses_keep_their_parentheses() {
+    let link = r"[go](https://e.test/\(x\))";
+    untouched(link);
+    untouched(r"![p](pics/\(x\).png)");
+    untouched("[go][a\\(x\\)]\n\n[a\\(x\\)]: /u");
+    untouched(r"<https://e.test/\(x\)>");
+    assert_eq!(tex(r"[\(x\)](https://e.test)"), ["x"], "link text is prose");
+    untouched(r"[a\(b](c)\)");
+}
+
+#[test]
+fn code_and_tags_stay_literal() {
+    untouched(r"a <code>\(x\)</code> b");
+    untouched(r"a <kbd>\(x\)</kbd> b");
+    untouched(r"a <code>\(x\) b");
+    untouched(r"`\(x\)`");
+    untouched(r"\(a `b` c\)");
+    assert_eq!(tex(r"<b>\(x\)</b>"), ["x"], "other tags hold prose");
+}
+
+#[test]
+fn a_pair_stays_in_one_block() {
+    untouched("- \\(a\n- b\\)");
+    untouched("\\(a\r\rb\\)");
+    untouched("\\(a\r\n\r\nb\\)");
+    untouched("# \\(a\nb\\)");
+    untouched("| \\(a | b\\) |\n| - | - |");
+    assert_eq!(tex("> \\(a\n> b\\)"), ["a\nb"], "a quote's lines");
+}

src/documents/render.rs

@@ -1,4 +1,4 @@
-use std::{path::Path, rc::Rc, sync::Arc};
+use std::{ops::Range, path::Path, rc::Rc, sync::Arc};
 
 use gpui::{
     AnyElement, App, ElementId, Entity, FontStyle, FontWeight, HighlightStyle, InteractiveText,
@@ -171,10 +171,13 @@ fn highlight(style: &Style, colors: &Palette, rule: Pixels) -> HighlightStyle {
     }
 }
 
-/// `inline` as text; `hidden` ranges lose their highlight.
+/// Highlights laid over a text's own.
+type Over = Vec<(Range<usize>, HighlightStyle)>;
+
+/// `inline` as text; hidden ranges lose highlight, `over` adds some.
 fn drawn_text(
     inline: &Inline,
-    hidden: &[std::ops::Range<usize>],
+    (hidden, over): (&[Range<usize>], Over),
     links: Option<ElementId>,
     on_link: &Option<OnLink>,
     cx: &App,
@@ -185,6 +188,7 @@ fn drawn_text(
     let styles: Vec<_> = (inline.styles.iter())
         .filter(|(range, _)| !hidden.contains(range))
         .map(|(range, style)| (range.clone(), highlight(style, colors, rule)))
+        .chain(over)
         .collect();
     let styled = StyledText::new(inline.text.clone()).with_highlights(crate::editor::stack(styles));
     let layout = styled.layout().clone();
@@ -233,7 +237,8 @@ impl Draw<'_> {
     fn inline(&self, inline: &Inline, cx: &App) -> AnyElement {
         let links = (!inline.links.is_empty()).then(|| self.key("links"));
         if !inline.styles.iter().any(|(_, style)| *style == Style::Math) {
-            let (drawn, layout) = drawn_text(inline, &[], links, self.hooks.on_link, cx);
+            let (drawn, layout) =
+                drawn_text(inline, (&[], Vec::new()), links, self.hooks.on_link, cx);
             let at = move |position| {
                 layout
                     .index_for_position(position)

src/documents/render/math_text.rs

@@ -3,14 +3,15 @@
 use std::{cell::RefCell, ops::Range, rc::Rc, sync::Arc};
 
 use gpui::{
-    AnyElement, App, Bounds, Corners, Element, ElementId, GlobalElementId, InspectorElementId,
+    AnyElement, App, Bounds, Corners, Element, ElementId, GlobalElementId, HighlightStyle,
-    IntoElement, LayoutId, Pixels, Point, RenderImage, SharedString, Size, TextLayout,
+    InspectorElementId, IntoElement, LayoutId, Pixels, Point, RenderImage, SharedString, Size,
-    TextStyleRefinement, Window, point,
+    TextLayout, TextStyleRefinement, Window, point,
 };
 
 use super::{OnLink, drawn_text};
 use crate::{
     documents::tree::{Inline, Style},
+    theme::ActiveTheme,
     typography::typeset,
 };
 
@@ -36,6 +37,8 @@ pub(super) struct MathText {
     text: Option<AnyElement>,
     /// Each picture, its size, and the drawn span it covers.
     pictures: Vec<(Arc<RenderImage>, Size<Pixels>, Range<usize>)>,
+    /// One glue character's width.
+    glue: Pixels,
 }
 
 impl MathText {
@@ -65,6 +68,7 @@ impl MathText {
             shown,
             text: None,
             pictures: Vec::new(),
+            glue: Pixels::ZERO,
         };
         (text, at)
     }
@@ -100,14 +104,14 @@ fn back(swaps: &[Swap], at: usize) -> usize {
     (at as isize + shift) as usize
 }
 
-/// `inline` with each swapped span drawn as `glue[ix]` glue.
+/// `inline` with each swapped span drawn as `drawn_as[ix]`.
-fn shown(inline: &Inline, swaps: &mut [Swap], glue: &[usize]) -> Inline {
+fn shown(inline: &Inline, swaps: &mut [Swap], drawn_as: &[String]) -> Inline {
     let mut text = String::new();
     let mut from = 0;
-    for ((written, drawn), count) in swaps.iter_mut().zip(glue) {
+    for ((written, drawn), with) in swaps.iter_mut().zip(drawn_as) {
         text.push_str(&inline.text[from..written.start]);
         let start = text.len();
-        text.extend(std::iter::repeat_n(GLUE, *count));
+        text.push_str(with);
         *drawn = start..text.len();
         from = written.end;
     }
@@ -166,9 +170,8 @@ impl Element for MathText {
             .map(|(range, _)| range.clone())
             .collect();
         maths.sort_by_key(|range| range.start);
-        let mut swaps = Vec::new();
+        let (mut swaps, mut drawn_as) = (Vec::new(), Vec::new());
-        let mut counts = Vec::new();
+        let (mut pictures, mut errors) = (Vec::new(), Vec::new());
-        let mut pictures = Vec::new();
         for (ix, range) in maths.into_iter().enumerate() {
             let source = SharedString::from(self.inline.text[range.clone()].to_string());
             match typeset(
@@ -179,22 +182,42 @@ impl Element for MathText {
                 cx,
             ) {
                 Some(Ok((image, size))) => {
-                    counts.push((size.width / width).ceil().max(1.0) as usize);
+                    let count = (size.width / width).ceil().max(1.0) as usize;
-                    pictures.push((image, size));
+                    drawn_as.push(GLUE.to_string().repeat(count));
+                    pictures.push((image, size, swaps.len()));
                     swaps.push((range, 0..0));
                 }
                 // The formula is the user's text: not logged.
-                Some(Err(_)) => log::warn!("markdown: an inline formula shows as TeX, unset"),
+                Some(Err(error)) => {
+                    log::warn!("markdown: an inline formula shows as TeX, unset");
+                    drawn_as.push(format!(" ({error})"));
+                    errors.push(swaps.len());
+                    swaps.push((range.end..range.end, 0..0));
+                }
                 None => {}
             }
         }
-        let inline = shown(&self.inline, &mut swaps, &counts);
+        let inline = shown(&self.inline, &mut swaps, &drawn_as);
-        let hidden: Vec<Range<usize>> = swaps.iter().map(|(_, drawn)| drawn.clone()).collect();
+        let hidden: Vec<Range<usize>> = (pictures.iter())
-        let (mut text, layout) =
+            .map(|(_, _, ix)| swaps[*ix].1.clone())
-            drawn_text(&inline, &hidden, self.links.clone(), &self.on_link, cx);
+            .collect();
+        let danger = HighlightStyle {
+            color: Some(cx.theme().colors.danger),
+            ..HighlightStyle::default()
+        };
+        let said = (errors.iter())
+            .map(|ix| (swaps[*ix].1.clone(), danger))
+            .collect();
+        let (mut text, layout) = drawn_text(
+            &inline,
+            (&hidden, said),
+            self.links.clone(),
+            &self.on_link,
+            cx,
+        );
         let tallest = pictures
             .iter()
-            .map(|(_, size)| size.height)
+            .map(|(_, size, _)| size.height)
             .fold(Pixels::ZERO, Pixels::max);
         // A tall formula opens the paragraph's lines.
         let taller = (tallest > style.line_height_in_pixels(rem)).then(|| TextStyleRefinement {
@@ -202,9 +225,10 @@ impl Element for MathText {
             ..TextStyleRefinement::default()
         });
         let id = window.with_text_style(taller, |window| text.request_layout(window, cx));
-        self.pictures = (pictures.into_iter().zip(&hidden))
+        self.pictures = (pictures.into_iter().zip(hidden))
-            .map(|((image, size), drawn)| (image, size, drawn.clone()))
+            .map(|((image, size, _), drawn)| (image, size, drawn))
             .collect();
+        self.glue = width;
         *self.shown.borrow_mut() = Some(Shown { layout, swaps });
         self.text = Some(text);
         (id, ())
@@ -244,18 +268,9 @@ impl Element for MathText {
         };
         let line = layout.line_height();
         for (image, size, drawn) in &self.pictures {
-            let (Some(start), Some(end)) = (
+            let Some((start, room)) = place(layout, drawn, self.glue) else {
-                layout.position_for_index(drawn.start),
-                layout.position_for_index(drawn.end),
-            ) else {
                 continue;
             };
-            // Glue at a line's end ends there.
-            let room = if end.y == start.y {
-                end.x - start.x
-            } else {
-                size.width
-            };
             let origin = start + point((room - size.width) / 2.0, (line - size.height) / 2.0);
             let bounds = Bounds {
                 origin,
@@ -270,6 +285,22 @@ impl Element for MathText {
     }
 }
 
+/// Where glue `drawn` starts, and how wide it runs.
+fn place(
+    layout: &TextLayout,
+    drawn: &Range<usize>,
+    glue: Pixels,
+) -> Option<(Point<Pixels>, Pixels)> {
+    let last = layout.position_for_index(drawn.end - GLUE.len_utf8())?;
+    let first = layout.position_for_index(drawn.start)?;
+    // A wrap's index reads as the previous line's end.
+    let start = match first.y == last.y {
+        true => first,
+        false => point(layout.bounds().origin.x, last.y),
+    };
+    Some((start, last.x + glue - start.x))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -282,7 +313,7 @@ mod tests {
             ..Inline::default()
         };
         let mut swaps = vec![(2..5, 0..0)];
-        let drawn = shown(&inline, &mut swaps, &[4]);
+        let drawn = shown(&inline, &mut swaps, &[GLUE.to_string().repeat(4)]);
         assert_eq!(drawn.text, format!("a {} b", GLUE.to_string().repeat(4)));
         let glue = GLUE.len_utf8() * 4;
         assert_eq!(swaps[0].1, 2..2 + glue);
@@ -296,60 +327,107 @@ mod tests {
         assert_eq!(forward(&swaps, 6), 3 + glue);
     }
 
-    type Found = Rc<
+    type Read = Box<dyn Fn(Point<Pixels>) -> usize>;
-        RefCell<
+    type Found = Rc<RefCell<Option<(Rc<RefCell<Option<Shown>>>, Read)>>>;
-            Option<(
-                Rc<RefCell<Option<Shown>>>,
-                Box<dyn Fn(Point<Pixels>) -> usize>,
-            )>,
-        >,
-    >;
 
-    struct Probe(Found);
+    /// Draws `text` with `math` a formula, `width` wide.
+    struct Probe {
+        text: &'static str,
+        math: Range<usize>,
+        width: f32,
+        found: Found,
+    }
 
     impl gpui::Render for Probe {
         fn render(&mut self, _: &mut Window, _: &mut gpui::Context<Self>) -> impl IntoElement {
             use gpui::{ParentElement as _, Styled as _};
             let inline = Inline {
-                text: "a x^2 b".into(),
+                text: self.text.into(),
-                styles: vec![(2..5, Style::Math)],
+                styles: vec![(self.math.clone(), Style::Math)],
                 ..Inline::default()
             };
             let (text, at) = MathText::new("probe".into(), inline, None, None);
-            *self.0.borrow_mut() = Some((text.shown.clone(), Box::new(at)));
+            *self.found.borrow_mut() = Some((text.shown.clone(), Box::new(at)));
-            gpui::div().text_size(gpui::px(16.0)).child(text)
+            let shell = gpui::div()
+                .w(gpui::px(self.width))
+                .text_size(gpui::px(16.0));
+            shell.child(text)
         }
     }
 
-    #[gpui::test]
+    fn laid(
-    fn a_formula_draws_over_glue_and_reads_back(cx: &mut gpui::TestAppContext) {
+        text: &'static str,
+        math: Range<usize>,
+        width: f32,
+        cx: &mut gpui::TestAppContext,
+    ) -> Found {
         cx.update(crate::theme::Theme::init);
         let found = Found::default();
         let held = found.clone();
-        let (_, cx) = cx.add_window_view(move |_, _| Probe(held));
+        let (_, cx) = cx.add_window_view(move |_, _| Probe {
+            text,
+            math,
+            width,
+            found: held,
+        });
         for _ in 0..4 {
             cx.run_until_parked();
             cx.update(|window, _| window.refresh());
         }
+        found
+    }
+
+    #[gpui::test]
+    fn a_formula_draws_over_glue_and_reads_back(cx: &mut gpui::TestAppContext) {
+        let found = laid("a x^2 b", 2..5, 400.0, cx);
         let found = found.borrow();
         let (shown, at) = found.as_ref().expect("drawn");
         let shown = shown.borrow();
         let Shown { layout, swaps } = shown.as_ref().expect("laid out");
         assert_eq!(swaps.len(), 1, "the formula typeset in place");
-        let drawn = swaps[0].1.clone();
+        let drawn = &swaps[0].1;
-        let (start, end) = (
+        let at_x = |ix| layout.position_for_index(ix).expect("on its line").x;
-            layout.position_for_index(drawn.start),
+        let glue = at_x(drawn.end) - at_x(drawn.end - GLUE.len_utf8());
-            layout.position_for_index(drawn.end),
+        let (start, room) = place(layout, drawn, glue).expect("placed");
-        );
+        assert!(room > gpui::px(10.0), "glue holds the picture's width");
-        let (start, end) = (start.expect("its start"), end.expect("its end"));
+        let middle = point(start.x + room / 2.0, start.y + layout.line_height() / 2.0);
-        assert!(
-            end.x - start.x > gpui::px(10.0),
-            "glue holds the picture's width"
-        );
-        let middle = point(
-            (start.x + end.x) / 2.0,
-            start.y + layout.line_height() / 2.0,
-        );
         assert_eq!(at(middle), 2, "a press on the picture is the formula");
     }
+
+    #[gpui::test]
+    fn a_formula_wrapped_whole_draws_on_its_line(cx: &mut gpui::TestAppContext) {
+        let text = "aaaaaaaaaa x^2+y^2=r^2 tail";
+        let found = laid(text, 11..22, 160.0, cx);
+        let found = found.borrow();
+        let (shown, at) = found.as_ref().expect("drawn");
+        let shown = shown.borrow();
+        let Shown { layout, swaps } = shown.as_ref().expect("laid out");
+        let drawn = &swaps[0].1;
+        let line = layout.line_height();
+        let last = layout.position_for_index(drawn.end - GLUE.len_utf8());
+        assert_eq!(last.expect("its glue").y, layout.bounds().top() + line);
+        let (start, _) = place(layout, drawn, gpui::px(0.0)).expect("placed");
+        assert_eq!(
+            start,
+            point(layout.bounds().left(), layout.bounds().top() + line),
+            "the picture starts the second line"
+        );
+        assert_eq!(at(start + point(gpui::px(2.0), line / 2.0)), 11);
+    }
+
+    #[gpui::test]
+    fn a_failed_formula_says_why_after_its_tex(cx: &mut gpui::TestAppContext) {
+        let found = laid("a x^2^3 b", 2..7, 400.0, cx);
+        let found = found.borrow();
+        let (shown, _) = found.as_ref().expect("drawn");
+        let shown = shown.borrow();
+        let Shown { layout, swaps } = shown.as_ref().expect("laid out");
+        assert_eq!(swaps[0].0, 7..7, "the TeX stays; the reason follows");
+        let text = layout.wrapped_text();
+        assert!(
+            text.starts_with("a x^2^3 (") && text.ends_with(") b"),
+            "{text:?}"
+        );
+        assert!(text.contains(" at "), "where RaTeX stopped: {text:?}");
+    }
 }

src/documents/tree/mod.rs

@@ -6,7 +6,7 @@ use super::markdown::{span, tree, walk};
 
 mod blocks;
 mod emoji;
-mod html;
+pub(crate) mod html;
 mod html_block;
 mod sources;
 mod stack;
@@ -318,7 +318,7 @@ impl<'a> Reader<'a> {
         }
     }
 
-    /// Text split at its images; lone `$$` or `\[` math is block.
+    /// Text splits at images; a lone formula is block.
     fn paragraph(&self, node: &mdast::Node, children: &[mdast::Node], out: &mut Vec<Node>) {
         if let [mdast::Node::InlineMath(math)] = children
             && ["$$", "\\["]

src/typography/math.rs

@@ -193,7 +193,7 @@ fn framed(svg: &str, width: f32, height: f32) -> Result<(String, Size<Pixels>),
     Ok((wrapped(svg, [left, top, w, h])?, size(px(w), px(h))))
 }
 
-/// `svg`'s drawing under a root viewing `[left, top, w, h]` in px.
+/// `svg` drawn in a px root viewing `[left, top, w, h]`.
 fn wrapped(svg: &str, [left, top, w, h]: [f32; 4]) -> Result<String, MathError> {
     let open = svg
         .find('>')