diff --git a/docs/superpowers/specs/2026-08-07-diff-side-by-side-design.md b/docs/superpowers/specs/2026-08-07-diff-side-by-side-design.md new file mode 100644 index 00000000..f9c40fef --- /dev/null +++ b/docs/superpowers/specs/2026-08-07-diff-side-by-side-design.md @@ -0,0 +1,225 @@ +# Diff Viewer: Side-by-Side, Syntax Highlighting, Word Diff + +Date: 2026-08-07 +Status: approved (design), not implemented + +## Problem + +The diff viewer renders every change as a flat unified stream. Reading what actually changed +inside a modified line means mentally aligning a `−` row with a `+` row several rows below it. +The user reads diffs faster side by side. + +Three gaps, all in the same surface: + +1. No side-by-side mode. +2. No syntax highlighting — the merge editor (`ConflictResolverView`) already has it via + TextMate, the diff viewer does not. +3. No intra-line (word) highlighting, so a one-character change looks like a whole-line rewrite. + +## Current state + +| Concern | Where | +|---|---| +| Parsing | `src/ClaudeDo.Ui/ViewModels/Modals/UnifiedDiffParser.cs` → `DiffFileViewModel.Lines` | +| Models | `src/ClaudeDo.Ui/ViewModels/Modals/DiffModels.cs` (`DiffLineViewModel{Kind,OldNo,NewNo,Text}`, `DiffLineKind{Add,Del,Ctx,File}`) | +| Rendering | `src/ClaudeDo.Ui/Views/Controls/DiffLinesView.axaml` — non-virtualized `ItemsControl`, one `Border`+`Grid`+4 `TextBlock`s per line, `TextWrapping="NoWrap"` | +| Host | `src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml` — Files mode (line 154, `SelectedFile.Lines`) and Planning mode (line 162, flattened `DiffLines` across all files) | +| Highlighting reference | `src/ClaudeDo.Ui/Views/Conflicts/ConflictResolverView.axaml.cs:80-83` — `RegistryOptions(ThemeName.DarkPlus)` + `InstallTextMate` + `SetGrammar` by file extension | + +`Avalonia.AvaloniaEdit`, `AvaloniaEdit.TextMate` and `TextMateSharp.Grammars` are already +referenced in `ClaudeDo.Ui.csproj`. + +## Decision + +Replace `DiffLinesView` with an AvaloniaEdit-based control. TextMate highlighting is bound to +the `TextEditor` control; it cannot be lifted into `TextBlock` inlines without reimplementing +the scope→brush layer that `AvaloniaEdit.TextMate` already provides. Building split/wrap/word +diff on the `TextBlock` model first and swapping the renderer later would be throwaway work. + +Side effect worth having: AvaloniaEdit virtualizes, which removes the current non-virtualized +`ItemsControl` as a scaling limit on large diffs. + +Rejected: keeping the `ItemsControl` and hand-rolling highlighting from `TextMateSharp` +tokenization — same output, materially more code, and a second highlighting path to maintain +alongside the merge editor's. + +## Layout semantics + +Left pane is the **old** state, right pane is the **new** state — each side carries the complete +version of the hunk, not "removals here, additions there". + +``` + LEFT (old) RIGHT (new) + 12 public void Save() 12 public void Save() + 13 var x = 1; 13 var x = 2; ← word diff on `1` / `2` + 14 Log("old"); · (filler) + · (filler) 14 Log("new"); + 15 } 15 } +``` + +## Components + +### 1. `DiffAlignment` (new, pure) + +`src/ClaudeDo.Ui/ViewModels/Modals/DiffAlignment.cs` + +Turns `IReadOnlyList` into a render-ready `AlignedDiff`. No Avalonia types, +fully unit-testable. + +```csharp +public enum AlignedSide { Ctx, Del, Add, Filler, Gap } + +public readonly record struct TextSpan(int Start, int Length); + +public sealed record SplitRow( + AlignedSide LeftKind, int? OldNo, string LeftText, IReadOnlyList LeftSpans, + AlignedSide RightKind, int? NewNo, string RightText, IReadOnlyList RightSpans); + +public sealed record UnifiedRow( + AlignedSide Kind, int? OldNo, int? NewNo, string Text, IReadOnlyList Spans); + +public sealed record AlignedDiff( + IReadOnlyList SplitRows, string LeftText, string RightText, + IReadOnlyList UnifiedRows, string UnifiedText); +``` + +Row index `i` maps to document line `i + 1` in the corresponding text. That mapping is the +contract the margin and both renderers depend on. + +**Pairing.** Walk the lines. A `Ctx` run emits rows with the same text on both sides. A change +block (a `Del` run followed by an `Add` run) pairs index-wise up to `min(delCount, addCount)`; +the overhang gets `Filler` rows on the opposite side. + +**Gaps.** The parser drops `@@` headers, so a skipped region shows up as a jump in `OldNo`/`NewNo` +between consecutive lines. `DiffAlignment` detects that jump and inserts a `Gap` row on both +sides. The parser is not touched. + +**Word diff.** Only for `(Del, Add)` rows that are paired 1:1. Tokenize each side into runs of +word characters / whitespace / single punctuation, run an LCS over the tokens, and emit the +changed token runs as character spans per side. + +Two guards, both `const` and both covered by tests: +- Skip when either side exceeds `MaxWordDiffChars = 2000` — LCS cost, and such lines are + unreadable as word diffs anyway. +- Skip when token similarity is below `MinWordDiffSimilarity = 0.5` (common tokens / max token + count). Below that the two lines are unrelated rewrites and per-word tinting is noise. + +### 2. `DiffTextView` (new control, replaces `DiffLinesView`) + +`src/ClaudeDo.Ui/Views/Controls/DiffTextView.axaml` + `.axaml.cs` + +Styled properties: + +| Property | Type | Meaning | +|---|---|---| +| `File` | `DiffFileViewModel?` | Source; the control aligns it and caches the `AlignedDiff` per file instance | +| `Mode` | `DiffViewMode` (`Unified`\|`Split`) | Layout | +| `WrapLines` | `bool` | Bound to each editor's `WordWrap` | + +Two `TextEditor`s in a two-column grid, both `IsReadOnly=true`, `ShowLineNumbers=false`. +`Unified` mode collapses the right editor and spans the left one across both columns, feeding +it `UnifiedText`. `Split` mode shows both, fed `LeftText` / `RightText`. + +Per editor: +- **TextMate**: one shared `RegistryOptions(ThemeName.DarkPlus)`; grammar resolved from + `File.Path`'s extension via `GetLanguageByExtension` → `GetScopeByLanguageId` → `SetGrammar`, + exactly as `ConflictResolverView.ApplyGrammar` does. No extension match → no grammar, plain text. +- **`DiffLineNumberMargin : AbstractMargin`** — draws line numbers from the row list. Split: old + numbers left, new numbers right. Unified: two number columns in one margin. `Filler` and `Gap` + rows draw nothing. +- **`DiffLineBackgroundRenderer : IBackgroundRenderer`** — full-width tint per visual line by + row kind: add / del / filler / gap / ctx. +- **`WordDiffRenderer : IBackgroundRenderer`** — stronger tint over the changed spans, via + `BackgroundGeometryBuilder` at `lineStartOffset + span.Start`. + +Both renderers resolve rows through a single `Func` keyed by document line. + +**Highlighting on fragments.** Only hunks are in the document, not whole files, so TextMate's +line-by-line state can be wrong at a fragment boundary (a line inside a block comment may be +highlighted as code). Accepted — the same is true of every fragment-based diff viewer. + +**Colors.** Line tints stay the existing low-alpha `RunningTintBrush` / `ErrorTintBrush` so +syntax foregrounds remain legible. The per-line foreground recolor from `DiffLinesView` +(green/red text) is dropped — syntax colors take over. `Filler` gets a new dim token brush, +`Gap` renders as a dim `⋯` separator row. + +**Scroll sync** (split only), modeled on `ConflictResolverView.HookScrollSync` — find each +editor's descendant `ScrollViewer`, guard re-entry with a `_syncing` flag: +- `WrapLines = false`: sync `Offset.Y` directly. Line heights match, so alignment is exact. +- `WrapLines = true`: line heights diverge. Sync on the first visible document line instead + (`ScrollToLine`), which keeps the top of the viewport aligned and lets rows drift downward. + +### 3. Host changes + +`DiffViewerView.axaml`: +- Header gains a segmented Unified/Split toggle and a wrap toggle. +- Files mode: `DiffLinesView Lines="{Binding SelectedFile.Lines}"` → `DiffTextView File="{Binding SelectedFile}"`. +- Planning mode: the flattened single-stream `DiffLines` view is replaced by an `ItemsControl` + over the subtask's parsed files, each item a file header plus its own `DiffTextView`. One + editor can only carry one grammar, so per-file editors are required for highlighting to work + at all here. `DiffViewerViewModel` exposes the parsed per-file list for the selected subtask; + `DiffLines` and `UnifiedDiffParser.Flatten` lose their last consumer and are removed. + +`DiffLinesView.axaml` + `.axaml.cs` are deleted once both usages are migrated. + +### 4. Persistence + +`src/ClaudeDo.Ui/AppSettings.cs` (`~/.todo-app/ui.config.json`) already holds UI-only +preferences (`Language`, `AccentPreset`) with plain `Load()`/`Save()`. Two properties are added +there: + +```csharp +public string DiffViewMode { get; set; } = "unified"; // "unified" | "split" +public bool DiffWrapLines { get; set; } +``` + +`DiffViewerViewModel` takes the injected `AppSettings`, seeds its toggles on open and calls +`Save()` when either changes. No database column, no EF migration, no hub method — a view +preference does not belong in `AppSettingsEntity`. + +### 5. Localization + +New keys in both `locales/en.json` and `locales/de.json` (Localization.Tests enforces parity): +`diff.view.unified`, `diff.view.split`, `diff.view.wrap`. + +## Testing + +`tests/ClaudeDo.Ui.Tests` — `DiffAlignment` is pure and carries the logic worth testing: + +- Context-only diff → identical rows on both sides, no fillers. +- Equal-size change block → 1:1 pairing, no fillers. +- Unequal change block (3 del / 5 add) → 3 paired rows + 2 right-side rows with left fillers. +- Add-only and delete-only blocks → fillers on the opposite side throughout. +- Non-contiguous line numbers → exactly one `Gap` row inserted. +- Word diff: single-token change yields one span per side at the right offsets. +- Word diff skipped above `MaxWordDiffChars` and below `MinWordDiffSimilarity`. +- Row index ↔ document line mapping holds for both `SplitRows` and `UnifiedRows`. +- Binary file and empty-content file → empty `AlignedDiff`, no crash. + +`AppSettings` round-trip: persisted mode and wrap survive `Save()`/`Load()`. + +Rendering (margin, both renderers, scroll sync, TextMate colors) is not unit-testable here and +is an explicit manual visual pass — see Open items. + +## Known limitations + +1. **Wrap + split drift.** With wrap on, the two panes align at the top of the viewport but rows + drift apart further down. Per-line vertical alignment as VS Code does it is out of scope. +2. **Fragment highlighting.** See above — highlighting state can be wrong at hunk boundaries. +3. **Editors per file in Planning mode.** A subtask touching many files instantiates one editor + per file. Same cost as viewing those files individually in Files mode; not capped. If it + proves slow, the fix is lazy instantiation on expand, not a silent truncation. + +## Open items (manual verification) + +- Visual pass on both modes: tints legible over DarkPlus syntax colors; line numbers aligned; + filler and gap rows readable. +- Scroll sync with wrap off (exact) and wrap on (top-anchored). +- Planning mode with a multi-file subtask. +- Toggle state survives an app restart. + +## Docs to update on completion + +- `src/ClaudeDo.Ui/CLAUDE.md` — Views/Controls list and the "Diff & Conflicts" section still + name `DiffLinesView`. +- `docs/explore-notes/review-merge.md` — diff stack description + "verified against" commit.