kte/docs/audits/claude-findings-20260923.md

Bug and Performance Audit

Project: kte (Kyle's Text Editor) Date: 2026-09-23 Auditor: Claude Code (automated review, four parallel reviewers plus spot verification) Baseline: d8d2ae8 (debug build clean, kte_tests 0 failures)

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Method

The tree was split into four review areas: core text model (PieceTable, Buffer, OptimizedSearch), undo and swap (UndoSystem/Tree/Node, Swap, ErrorRecovery, SyscallWrappers), commands (Command.cc, KKeymap), and frontends/syntax (Terminal, ImGui, Qt, Editor, syntax/). Every finding below was traced to a concrete scenario. Findings marked [repro] were reproduced with a small test program; the rest were confirmed by reading the code.

Finding IDs are stable and are referenced by fix commits:

• M — memory safety (crash, out-of-bounds, use-after-free, data race)
• D — data integrity (undo, swap journal, text corruption)
• B — incorrect behaviour
• P — performance

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M — Memory safety

M1. PieceTable assignment keeps a stale line index [repro]

PieceTable.cc:47-98. Copy and move assignment copy pieces_, add_, and total_size_, but leave the destination's line_index_ and line_index_dirty_ untouched. Editor::CloseBuffer erases from std::vector<Buffer>, which move-assigns every later buffer into the previous slot.

Scenario: open A ("line1\nline2\nline3\n"), open B ("x"), render both, close A. Slot 0 now holds B's text with A's index: LineCount() returns 4 and GetLineView(1) builds a view over bytes 6–12 of a 1-byte buffer.

Fix: mark the line index dirty (and clear it) in both assignment operators.

M2. Background highlighter thread races buffer mutation

syntax/HighlighterEngine.cc:184-249. PrefetchViewport (called from the terminal and ImGui renderers) queues rows for a worker thread which calls buf.GetLineString, walking pieces_ and reading add_. The main thread's PieceTable::Insert/Delete mutate both without any shared lock; add_.append may reallocate. The worker also stores a raw Buffer* (pending_.buf) which dangles when AddBuffer's push_back reallocates or CloseBuffer's erase shifts buffers.

Fix: remove the background warm-up, or feed it an immutable snapshot.

M3. Per-window SwapManager leaves dangling recorders (ImGui multi-window)

ImGuiFrontend.cc:381-385, Editor.cc:205-213. Each window's Editor owns its own SwapManager but shares the buffer vector. A buffer created from a secondary window keeps a swap_rec_ pointing into that window's manager; closing the window destroys it, and the next edit in the main window calls into freed memory. Rehome from the wrong manager also returns nullptr, silently disabling journaling for the primary's buffers.

Fix: share one SwapManager across windows, and detach every buffer an Editor attached when that Editor is destroyed.

M4. Recursive undo-tree free overflows the stack [repro]

UndoTree.cc:12 (free_node_graph), also UndoSystem.cc:354 (is_descendant, dfs_find_parent). Recursion depth equals history length. About 300k nodes segfaults a debug build on an 8 MB stack; replace-all over ~150k matches (two nodes each) followed by close or reload is enough.

Fix: free iteratively with an explicit stack.

M5. Jump-to-mark places the cursor past the end of the buffer

Command.cc:3720. Marks are not adjusted on edits and cmd_jump_to_mark does not clamp. After deleting lines below a mark, C-k j puts the cursor on a nonexistent row; cmd_move_left and cmd_move_up (:3866, :3988) then index rows[y] out of bounds.

Fix: clamp in cmd_jump_to_mark and in compute_mark_region.

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D — Data integrity

D1. Smart-newline undo deletes the wrong text [repro]

Command.cc:3139-3146. The indent is inserted and the cursor moved past it before u->Begin(UndoType::Insert); UndoSystem::Begin records the cursor position, so the node is placed indent.size() columns too far right. " foobar" + SmartNewline + two undos yields " foo next" (the following line's text is spliced in and bar is lost).

Fix: Begin at new_x, then insert, then move the cursor; group the newline and the indent.

D2. Cursor column left past end-of-line corrupts undo

cmd_scroll_up/cmd_scroll_down (Command.cc:4178, :4215, bound to the mouse wheel), replace-all's cursor restore (:2580), and cmd_jump_to_mark call SetCursor without clamping x. delete_text does not clamp; it treats the excess as crossing the newline. Backspace then joins lines with an empty (dropped) undo node, and typing followed by undo deletes a newline instead of the typed character.

Fix: clamp x to the line length in Buffer::SetCursor.

D3. delete_row on a final line without trailing newline leaves a stray \n

Buffer.cc:803. Affects delete_region (C-w, M-d, M-Backspace), regex replace (Command.cc:2996), reflow (:4884), and the kill ring. "foo\nbar" + M-d at end of foo yields "foo\n".

D4. Phantom empty row after a trailing newline

PieceTable::LineCount() counts the empty row after a final \n. C-k C-d on that row records a DeleteRow("") whose undo inserts a line (Command.cc:3516); regex replace of ^ matches it and appends an extra line (:2985).

D5. Missing or wrong undo grouping

• Plain replace-all (Command.cc:2537-2577) has no group: N replacements need 2N undos, and the final Insert stays pending so the next typed characters coalesce into it.
• Visual-line newline (:3043-3075) records no undo at all.

D6. Reflow on a blank line merges the adjacent paragraphs

Command.cc:4592. "aaa\n\nbbb" with the cursor on the blank line and ESC q gives "aaa bbb".

D7. Swap journal is fragile exactly where it matters

• Swap.cc:1344-1373: a torn final record (the power-loss case) makes the whole file unreadable instead of replaying the valid prefix.
• Swap.cc:1134-1157, :1187, :1224: after any dropped record (breaker open, >16 MB payload, partial write) later records still replay against a different base state; a partial write leaves bytes that later records are appended behind.
• Swap.cc:1040 vs :1187: checkpoints allow 4 GB but the record length is 24 bits; buffers over 16 MB are never checkpointed and the journal grows without bound.
• Swap.cc:644, :708: a failed header write leaves an fd with no header; answering N to "delete corrupt swap?" appends new edits to the corrupt file.

D8. Circuit breaker failure window never expires

ErrorRecovery.cc:77. last_failure_time_ is updated before IsWindowExpired() reads it, so elapsed time is always zero; five failures hours apart still open the breaker.

D9. Stale syntax highlighting after undo-to-clean or reload

Buffer.h:391-400. version_ is bumped only in SetDirty(true). Undo back to the saved node calls SetDirty(false), and OpenFromFile (reload) never bumps it, so HighlighterEngine keeps serving spans for the old text.

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B — Behaviour

B1. set_escdelay is compiled out

TerminalFrontend.cc:46. set_escdelay is a function in ncurses, not a macro, so #ifdef set_escdelay is always false and ESC waits the 1000 ms default.

B2. Terminal resize runs C-g

TerminalInputHandler.cc:167-171 maps KEY_RESIZE to CommandId::Refresh, the cancel handler: it clears the mark, cancels prompts (including the swap-recovery prompt, so the file is never opened), and resets the universal argument.

B3. ESC-as-Meta flag is not cleared on most paths

TerminalInputHandler.cc:56-279. ESC followed by an arrow, Enter, Tab, or a control chord leaves esc_meta set; the next plain d runs M-d. Same in ImGuiInputHandler.cc:43-73.

B4. C-h shadows Backspace in the terminal

The generic control lookup (TerminalInputHandler.cc:264) maps ^H to SearchReplace before the Backspace branch (:307) runs.

B5. Byte-based editing splits UTF-8

Command.cc:3259, :3352, :3861-3947. Backspace, delete, and horizontal motion step by byte: Backspace on é leaves a lone 0xC3, and C-b/C-f land inside code points.

B6. Horizontal scroll counts bytes, renderer counts cells

compute_render_x (Command.cc:52-60) counts bytes while TerminalRenderer.cc:269-322 skips display cells: a long CJK line scrolls to blank with the cursor off-screen.

B7. GUI draws non-ASCII text as replacement glyphs

Highlighters emit one span per non-ASCII byte and ImGuiRenderer.cc (~510) / QtFrontend.cc (~333) decode each span separately.

B8. ImGui drops the character after Ctrl+V

ImGuiInputHandler.cc:362, :382, :401 set a suppress-next-text flag for chords that produce no text event.

B9. Control characters mis-measured in the terminal

TerminalRenderer.cc:314, :364, :413 count C0 controls as width 1; ncurses draws them as ^X.

B10. Qt tab width disagrees with the command layer

QtFrontend.cc:138 uses 4; Command.cc uses 8.

B11. Smart newline edits the old buffer while a prompt is open

Command.cc:3131. With a prompt active, cmd_newline accepts it and the saved indent is inserted through a possibly stale Buffer*.

B12. Line count stale after merged appends [repro]

PieceTable.cc:220-260. addPieceBack/addPieceFront merge paths skip InvalidateLineIndex(). Latent today.

B13. Syntax highlighter edge cases

Go raw strings and Rust multi-line strings do not carry state across lines; shell $# is highlighted as a comment; a C++ #define line opening /* does not carry the comment.

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P — Performance

P1. Whole-file Rows() rebuild per frame

Renderers call buf->Rows() every frame (TerminalRenderer.cc:45, ImGuiRenderer.cc:69, QtFrontend.cc:477), and ensure_cursor_visible (Command.cc:91) after every command. After an edit this rebuilds a std::string per line, each via two GetRange calls.

P2. Whole-buffer materialization for one line

Buffer::GetLineView (Buffer.cc:633) calls content_.Data(), which copies the entire file; the line index is rebuilt byte-by-byte after every edit.

P3. Re-highlight from row 0 on every keystroke

SetDirty(true) calls InvalidateFrom(0); stateful highlighters then re-lex from the top of the file to the viewport.

P4. Quadratic region commands

Replace-all, delete_region, indent/unindent, reflow, and repeated backspace re-fetch Rows() after each mutation inside their loops.

P5. Opening a file checkpoints into a journal that is then deleted

Swap.cc:493 snapshots, writes, and fsyncs the whole file into unnamed-N.swp before removing it.

P6. Boyer–Moore bad-character shift degenerates to 1

OptimizedSearch.cc:63, :96: when the mismatched byte is absent from the pattern the shift is 1 instead of j. Test-only today.

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Recommended order

1. M1 (one-line fix)
2. M2 (remove or snapshot the warm-up thread)
3. D2 + M5 (clamp in SetCursor and jump-to-mark)
4. D1 (smart-newline undo order)
5. D7 (accept a torn final swap record)
6. P1/P2 (Nrows() + GetLineString in hot paths)

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Fix status

Updated as fixes land on claude/funny-fermat-gj2vm5.

ID	Status
M1	fixed: assignment operators invalidate the line index
M2	fixed: background warm-up thread removed; visible rows highlighted synchronously
M3	fixed: editors sharing buffers share the owner's SwapManager
M4	fixed: iterative free/search; clear() also leaked root siblings, now frees all
M5	fixed: jump-to-mark clamps; move up/down clamp the row (move-down also underflowed)
D1	fixed: Begin before the cursor moves; newline + indent grouped
D2	fixed for scroll up/down and replace-all restore
D3	fixed: kill-region, regex replace, reflow and kill-line edit byte ranges in place
D4	fixed: regex replace skips the row after a final newline (a zero-width pattern used to hang the editor); kill-line there is a no-op
D5	fixed: replace-all one undo group; visual-line newline recorded as one group
D6	fixed: reflow on a blank line is a no-op
D7	fixed: torn tail replays the valid prefix; lost records mark a gap resynced by checkpoint; partial writes truncated; header failure closes; large inserts split; oversize checkpoints skipped; declined corrupt swap moved to .corrupt
D8	fixed: window checked before recording the failure
D9	fixed: every text mutation bumps the version (including undo to the saved state); reload and replace also clear undo/highlighting
B1	fixed: guard on NCURSES_VERSION
B2	fixed: KEY_RESIZE issues no command
B3	fixed: ESC-meta flag consumed on every key; ESC ^H and ESC Enter reach their bindings
B4	not changed: C-h is a deliberate binding (search & replace); terminals whose terminfo kbs is ^H are translated to KEY_BACKSPACE by ncurses
B5	fixed: backspace/delete/left/right step over whole UTF-8 characters; up/down snap to a boundary
B6	fixed: horizontal scroll and mouse column use display cells (mbrtowc/wcwidth)
B7–B10, B13	open (GUI-only or highlighter edge cases)
B11	fixed: SmartNewline with a prompt open delegates to Newline
B12	fixed: merged appends invalidate the line index
P1	fixed: ensure_cursor_visible and the terminal/ImGui renderers no longer call Rows()
P2	fixed: line index updated in place on insert/delete (14.7 ms -> 0.28 ms per keystroke on a 38 MB buffer)
P3	fixed: highlighting invalidated from the edited row (46 ms -> 0.14 ms per keystroke near the end of a 100k-line C++ file)
P4	replace-all and delete-region fixed; indent/unindent loops unchanged
P5	fixed: no throwaway checkpoint on filename change
P6	open (test-only code)

Regression tests: tests/test_audit_regressions.cc. Each test fails on the unfixed code (M4 by crashing).