documents: lists go on, block lines shift, tables change, matches show, fences color by language

The document carries Markdown's editing tools for ElyMark (MARK-06):
Enter continues a list item or ends an empty one, Tab and Shift-Tab
shift an open block's lines, table rows and columns come and go as
one undo step, a match shows in any mode, replacements are one step,
and a fenced block colors by its language.

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

src/documents/document/finding.rs

@@ -0,0 +1,57 @@
+//! Matches shown in any mode; replacements in one step.
+
+use std::ops::Range;
+
+use gpui::{Context, Window};
+
+use super::MarkdownDocument;
+use crate::documents::MarkdownMode;
+
+impl MarkdownDocument {
+    /// `range` in view: selected, or in its opened block.
+    pub fn show_match(&mut self, range: Range<usize>, window: &mut Window, cx: &mut Context<Self>) {
+        let line = |document: &Self, cx: &Context<Self>| {
+            document.editor.read(cx).text()[..range.start]
+                .matches('\n')
+                .count()
+        };
+        match self.mode {
+            MarkdownMode::Source | MarkdownMode::Split => {
+                self.editor
+                    .update(cx, |editor, cx| editor.select(std::iter::once(range), cx));
+            }
+            MarkdownMode::Preview => self.reveal(line(self, cx), window, cx),
+            MarkdownMode::Visual => {
+                if self.commit(cx).is_some() {
+                    self.reparse(true, cx);
+                }
+                if !self.read_now(cx) {
+                    return log::warn!("markdown document: a match shown while the text is read");
+                }
+                let ix = self.block_at(range.start);
+                let held = self.parsed.blocks.get(ix).map(|block| block.range.clone());
+                let Some(block) =
+                    held.filter(|block| block.start <= range.start && range.end <= block.end)
+                else {
+                    // Outside one block: its line.
+                    return self.reveal(line(self, cx), window, cx);
+                };
+                let start = block.start;
+                self.open(Some(ix), false, window, cx);
+                self.list.scroll_to_reveal_item(ix);
+                if let Some(open) = &self.open {
+                    let input = open.input.clone();
+                    let inside = range.start - start..range.end - start;
+                    input.update(cx, |input, cx| input.select(inside, cx));
+                }
+            }
+        }
+    }
+
+    /// `edits` to the text as one undo step.
+    pub fn replace(&mut self, edits: Vec<(Range<usize>, String)>, cx: &mut Context<Self>) {
+        self.commit(cx);
+        log::info!("markdown document: {} replaced", edits.len());
+        self.editor.update(cx, |editor, cx| editor.edit(edits, cx));
+    }
+}