macOS ⌘⌫: match Zed editor::DeleteToBeginningOfLine

[chasehuh]

Summary

On macOS, ⌘⌫ (Cmd+Backspace) in the CodeMirror 6 note editor must match Zed’s default Editor binding exactly: editor::DeleteToBeginningOfLine (hard / logical line start — not soft-wrap boundary, not full DeleteLine).

Why This Matters

Line-kill chords are high-frequency when editing notes. After the CM6 cutover, ⌘⌫ feels wrong vs Zed. This is an explicit product keymap decision with Zed as the single source of truth — not “macOS TextEdit vaguely” and not CM’s stock soft-wrap-aware default.

Conversation Context

• Repo: chasehuh/memo; editor: CM6 from CodeMirror 6 inline Markdown image widgets #8.
• User (macOS): wants ⌘⌫ to behave like Zed (where it “works correctly”); earlier wording (“한 줄이 통째로 사라지길”) described the feel of clearing a line from EOL, not Zed’s separate full-line-delete chord.
• Companion layout bug (gutter/wrap): CM6 gutter/content vertical desync with soft wrap (scroll-beyond padding) #9 — still retest with wrap on, but desired semantics are hard-line (so soft-wrap boundary bugs must not redefine the product rule).
• App-level window shortcuts in memo-app.tsx only handle ⌘N / ⌘B / ⌘\ — they do not intercept Backspace.

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Source of truth: Zed (locked)

Verified against zed-industries/zed@7cf50a771f54427f76b4584030c7b3b66f4e39f5 (main at research time).

Default macOS keymap (Editor context)

Chord	Action	File
⌘⌫ cmd-backspace	editor::DeleteToBeginningOfLine	assets/keymaps/default-macos.json L74
⌘⌦ cmd-delete	editor::DeleteToEndOfLine	L75
⌥⌫ alt-backspace	editor::DeleteToPreviousWordStart (ignore_newlines: false)	L76
⇧⌘K cmd-shift-k	editor::DeleteLine (full hard-line remove — different chord)	L580

Do not conflate: JetBrains keymap in Zed maps cmd-backspace → editor::DeleteLine (assets/keymaps/macos/jetbrains.json). That is not the default. Memo follows default-macos, not JetBrains.

Action implementation

DeleteToBeginningOfLine — doc: “Deletes from the cursor to the beginning of the current line.” Field stop_at_indent defaults to false; default keymap binds the action with no args.

Implementation delete_to_beginning_of_line:

1. Mark each selection reversed = true
2. select_to_beginning_of_line with stop_at_soft_wraps: false (hardcoded) and stop_at_indent: action.stop_at_indent (default false)
3. backspace (deletes the resulting selection; if still empty, deletes one unit left — typically the preceding newline)

Line target uses indented_line_beginning / line_beginning: with stop_at_soft_boundaries: false, the target is always the logical / hard line start, never a soft-wrap visual boundary.

Covering tests: test_beginning_end_of_line, test_delete_to_line_boundary (selection cases), soft-wrap ignore behavior for the same movement flags in test_beginning_end_of_line_ignore_soft_wrap.

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Desired Behavior (Zed-locked — supersedes earlier waffle)

Previous “Needs verification / recommended default / alternative bind ⌘⌫ to deleteLine” language is superseded. Product choice is fixed:

⌘⌫ → Zed editor::DeleteToBeginningOfLine

Exact semantic rules:

1. Hard line only. Ignore soft-wrap visual boundaries. From mid-wrap, delete through to the logical line start (column 0 of that hard line), not the start of the current visual wrap row.
2. No indent stop. Default binding does not stop at first non-whitespace (stop_at_indent: false). Indentation before the cursor is deleted too.
3. Cursor mid-line / at EOL. Delete all text from hard BOL → cursor; leave an empty hard line; cursor at BOL. From EOL this clears the whole line’s text (empty line remains) — the “line went away” feel without removing the linebreak.
4. Cursor already at hard BOL (empty selection). Do not no-op: delete one unit backward (normally the preceding \n), joining with the previous line. At document start, nothing left to delete.
5. Non-empty selection (Zed-specific). Do not only delete the selected span. Zed reverses the selection, extends the head to hard BOL, then deletes → effectively hard BOL → selection’s right edge. Example from Zed’s test: "one «two three» four" + action → " four".
6. Multiple cursors. Apply per selection/cursor (Zed tests exercise multi-cursor delete-to-BOL).
7. Newlines. Only crossed when already at hard BOL (join) or when a multi-line selection’s right edge is past newlines after the BOL expansion. Mid-line ⌘⌫ does not delete into the previous line.
8. Undo. One transactional undo step for the kill (Zed wraps in transact).

Related chords (do not overload onto ⌘⌫)

Chord	Memo target	Notes
⇧⌘K	CM deleteLine ≈ Zed editor::DeleteLine	Removes entire hard line including linebreak; line literally disappears. Cursor lands on following (or previous) line.
⌥⌫	CM deleteGroupBackward ≈ Zed DeleteToPreviousWordStart	Word/group delete; ignore_newlines: false in Zed default.
⌘⌦	Optional parity: delete to hard EOL	Zed DeleteToEndOfLine also uses stop_at_soft_wraps: false. Nice-to-have, not required to close this issue.

Observable contract (QA)

• Mid-line + ⌘⌫ → text BOL..cursor gone; empty remainder of line kept.
• EOL + ⌘⌫ → line text cleared; empty hard line remains.
• Empty line / caret at BOL + ⌘⌫ → join with previous line (line “removed”).
• Soft-wrap on + caret mid visual wrap → still deletes to hard BOL (may clear text across multiple visual rows of one hard line).
• Selection "one two three four" with "two three" selected + ⌘⌫ → " four" (BOL→selection end), not "one four".
• ⇧⌘K still full line delete; ⌥⌫ still word/group; ⌘N/⌘B/⌘\ unaffected.
• Hangul IME: while view.composing, do not corrupt composition.

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Current Behavior (memo / CM today)

What CodeMirror ships

From @codemirror/commands standardKeymap / defaultKeymap:

Chord (macOS)	Command	Effect vs Zed
⌘⌫	deleteLineBoundaryBackward	Soft-wrap–aware boundary via view.moveToLineBoundary. Mismatch with Zed hard-line rule.
—	deleteToLineStart (exported, not bound to ⌘⌫)	Uses lineBlockAt(head).from (hard line for normal text). Closer for empty cursors; see gaps below.
⌥⌫	deleteGroupBackward	OK keep.
⇧⌘K	deleteLine	Matches Zed’s separate full-line delete chord.

CM deleteBy (used by both delete helpers): non-empty selection → delete selection only. That diverges from Zed rule (5) above.

What memo does today

components/codemirror-editor.tsx installs filtered defaultKeymap (Tab overridden). macOS { mac: "Mod-Backspace", run: deleteLineBoundaryBackward } is kept — so memo currently follows CM soft-wrap boundary, not Zed.

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CodeMirror mapping (implementation guidance)

Approach	Empty cursor / hard line	Soft wrap	Non-empty selection	Verdict
Stock deleteLineBoundaryBackward	Soft-wrap boundary	Soft	Delete selection only	Reject — not Zed
Stock deleteToLineStart	Hard line start + BOL→join	Hard (via line block)	Delete selection only	Close for caret-only; fails Zed selection expansion
Custom command (required for exact parity)	doc.lineAt(head).from → head; if at from, delete from-1	Hard	Expand each range to line.from .. range.to then delete (mirror Zed reverse+select-to-BOL)	Required for SoT

Recommendation: implement a small custom command (e.g. zedDeleteToBeginningOfLine) + Prec.high macOS binding for Mod-Backspace with preventDefault: true. Keep CM deleteLine on ⇧⌘K. Optionally leave or remove the stock mac-only deleteLineBoundaryBackward binding so it cannot win on precedence.

Suggested module (optional):

// lib/editor/line-kill.ts
export function memoLineKillKeymap(): Extension
// Prec.high:
// - Mod-Backspace → zedDeleteToBeginningOfLine (custom)
// - Shift-Mod-k → deleteLine (ensure present)

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Implementation Notes

Likely files

• components/codemirror-editor.tsx — Prec.high(keymap.of([…])) for macOS line-kill.
• lib/editor/line-kill.ts (new) — custom Zed-parity command.
• README — document ⌘⌫ = delete to hard line start (Zed); ⇧⌘K = delete line.

Flow

1. Reproduce current CM soft-wrap / selection behavior.
2. Add custom command + high-precedence binding.
3. QA matrix below; retest after CM6 gutter/content vertical desync with soft wrap (scroll-beyond padding) #9 if wrap geometry was misleading during debugging.

Tests

• Manual checklist in PR (required), including selection case from Zed’s test.
• Optional unit test of pure “compute delete range(s)” helper.

Edge Cases And Risks

• Soft wrap on: must still target hard BOL (product rule).
• Multi-selections: apply per range like Zed.
• Image widget / markdown lines: deleting line text / joining must keep decorations consistent.
• IME composition: skip or no-op safely while composing.
• Do not bind ⌘⌫ to deleteLine (that is ⇧⌘K / JetBrains-keymap territory).

Non-Goals

• Full Zed keymap port.
• Binding ⌘⌫ to editor::DeleteLine.
• Fixing gutter desync in the same PR (CM6 gutter/content vertical desync with soft wrap (scroll-beyond padding) #9) unless it blocks QA.

Acceptance Criteria

• ⌘⌫ matches Zed DeleteToBeginningOfLine rules (1)–(8) above, including hard-line + selection expands to BOL.
• PR cites Zed default-macos + input.rs implementation (or this issue’s SoT section).
• ⇧⌘K remains full hard-line deleteLine.
• ⌥⌫ remains word/group delete.
• App shortcuts ⌘N / ⌘B / ⌘\ still work.
• Undo restores the kill in one step when possible.
• Soft-wrap on: no soft-wrap-boundary-only deletes for ⌘⌫.
• Empty line / caret at BOL + ⌘⌫ joins as documented.

QA Plan

1. Worktree from latest main; pnpm dev.
2. Matrix: wrap on/off × caret at BOL / mid / EOL × empty vs non-empty × ASCII vs Hangul.
3. Selection case: one two three four with two three selected → expect four.
4. Soft-wrap: long hard line wrapped; caret on 2nd visual row → ⌘⌫ clears back to hard BOL (may clear text from prior visual rows of same hard line).
5. ⇧⌘K removes the hard line entirely; compare to ⌘⌫ clearing text only.
6. Regression: paste image, arrow ligatures, Tab spaces, save/sync.

Suggested PR Scope

S — “fix macOS ⌘⌫ to match Zed DeleteToBeginningOfLine”. Link #9 for wrap QA.

[chasehuh]

Companion layout issue: #9 (gutter↔content desync). Retest ⌘⌫ after that fix if soft-wrap boundaries are involved.

[chasehuh]

Research update (Zed SoT locked)

Desired Behavior in the issue body is now locked to Zed default macOS Editor behavior — not CM stock, not JetBrains keymap, not full-line delete.

• Binding: cmd-backspace → editor::DeleteToBeginningOfLine
  https://github.com/zed-industries/zed/blob/7cf50a771f54427f76b4584030c7b3b66f4e39f5/assets/keymaps/default-macos.json#L74
• Impl: hard-line only (stop_at_soft_wraps: false), stop_at_indent: false by default
  https://github.com/zed-industries/zed/blob/7cf50a771f54427f76b4584030c7b3b66f4e39f5/crates/editor/src/input.rs#L1106-L1133
• Full line delete is separate: cmd-shift-k → editor::DeleteLine (do not put this on ⌘⌫)
• CM mapping: stock deleteLineBoundaryBackward ≠ Zed; deleteToLineStart is close for empty carets but wrong on non-empty selection — custom command required for exact parity.

Earlier “needs verification / optional bind ⌘⌫ to deleteLine” guidance in this issue is superseded by the rewritten body.