MarkdownDocument: one caret for every mode, pressed blocks kept across write-backs, preview read only, keyboard reach, history capped on every path

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

src/editor/edit.rs

@@ -336,6 +336,7 @@ impl CodeEditor {
         }
         if let Some(previous) = self.history.undo(self.snapshot()) {
             self.restore(previous, cx);
+            self.cap_history();
         }
     }
 
@@ -345,6 +346,7 @@ impl CodeEditor {
         }
         if let Some(next) = self.history.redo(self.snapshot()) {
             self.restore(next, cx);
+            self.cap_history();
         }
     }
 

src/editor/ime.rs

@@ -67,6 +67,7 @@ impl CodeEditor {
             && start.text != self.buffer.text()
         {
             self.history.record(start, false);
+            self.cap_history();
         }
     }
 

src/editor/prose.rs

@@ -46,6 +46,16 @@ impl CodeEditor {
         self.restart_blink(cx);
     }
 
+    /// Keeps undo within its byte budget, logging what went.
+    pub(crate) fn cap_history(&mut self) {
+        let dropped = self
+            .history
+            .trim(self.history_bytes, |step| step.text.len());
+        if dropped > 0 {
+            log::info!("code editor: {dropped} far undo steps dropped");
+        }
+    }
+
     /// A line's colors, as the owner or as code.
     pub(crate) fn line_colors(&self, text: &str, cx: &App) -> Vec<(Range<usize>, HighlightStyle)> {
         let Some(LineHighlighter(highlight)) = &self.options.highlighter else {

src/editor/state.rs

@@ -103,6 +103,8 @@ pub struct CodeEditor {
     pub(crate) buffer: Buffer,
     pub(crate) selections: Vec<Selection>,
     pub(crate) history: History<Snapshot>,
+    /// Undo keeps at most this many bytes of text.
+    pub(crate) history_bytes: usize,
     pub(crate) focus: FocusHandle,
     pub(crate) scroll: UniformListScrollHandle,
     pub(crate) folded: BTreeSet<usize>,
@@ -172,6 +174,7 @@ impl CodeEditor {
             buffer: Buffer::new(text),
             selections: vec![Selection::caret(0)],
             history: History::default(),
+            history_bytes: super::prose::HISTORY_BYTES,
             focus,
             scroll: UniformListScrollHandle::new(),
             folded: BTreeSet::new(),
@@ -432,12 +435,7 @@ impl CodeEditor {
         if before.text != self.buffer.text() {
             if self.composing.is_none() {
                 self.history.record(before, typing);
-                let dropped = self
-                    .history
-                    .trim(super::prose::HISTORY_BYTES, |step| step.text.len());
-                if dropped > 0 {
-                    log::info!("code editor: {dropped} oldest undo steps dropped");
-                }
+                self.cap_history();
             }
             self.marks.ghost = None;
             self.folded.retain(|line| *line < self.buffer.lines());

src/editor/tests/history.rs

@@ -0,0 +1,34 @@
+use gpui::{EntityInputHandler, TestAppContext};
+
+use super::editor;
+
+/// Bytes of text all undo and redo steps hold.
+fn held(editor: &super::CodeEditor) -> usize {
+    editor.history.held(|step| step.text.len())
+}
+
+#[gpui::test]
+fn compositions_keep_undo_within_its_budget(cx: &mut TestAppContext) {
+    let (editor, cx) = editor(&"x".repeat(100), cx);
+    editor.update_in(cx, |editor, window, cx| {
+        editor.history_bytes = 250;
+        for word in ["a", "b", "c", "d"] {
+            editor.replace_and_mark_text_in_range(None, word, None, window, cx);
+            editor.unmark_text(window, cx);
+        }
+        assert!(held(editor) <= 250, "{} bytes held", held(editor));
+        assert!(editor.history.can_undo(), "the nearest steps stay");
+    });
+}
+
+#[gpui::test]
+fn undo_keeps_redo_within_its_budget(cx: &mut TestAppContext) {
+    let (editor, cx) = editor("small", cx);
+    editor.update(cx, |editor, cx| {
+        editor.history_bytes = 50;
+        editor.edit([(0..5, "y".repeat(80))], cx);
+        editor.undo(cx);
+        assert_eq!(editor.text(), "small");
+        assert!(!editor.history.can_redo(), "a redo past the budget went");
+    });
+}

src/editor/tests/mod.rs

@@ -1,3 +1,4 @@
+mod history;
 mod stale;
 
 use std::{cell::Cell, rc::Rc, time::Duration};