feat: full-file diff view, two-pane diff tab, and git sidebar enhancements

[yashas-salankimatt]

Summary

• Full-file diff view in git plugin with syntax-highlighted rendering and scrollable minimap for navigation
• Two-pane diff tab in workspace plugin with commit drill-down, untracked file support, persistent adjustable split (drag to resize), and narrow terminal collapse
• Git sidebar enhancements: +/- line stats on all file entries (staged, modified, untracked, commit files) and expandable scrollable commit body in preview

Key Changes

Git Plugin

• Full-file diff view mode with unified diff parsing and syntax highlighting
• Minimap overlay for quick navigation in large diffs
• +/- line count stats next to sidebar file entries (including folder aggregation for untracked files)
• Expandable commit body: press k at topmost file to expand full message, scroll with j/k, collapse with esc
• Panic guard for narrow terminals in commit preview

Workspace Plugin

• Two-pane diff tab: file list on left, diff preview on right with commit drill-down
• Untracked files shown in diff tab
• Persistent adjustable split width via mouse drag
• Auto-collapse to single pane on narrow terminals
• Minimap integration in diff tab full-file view
• Per-segment styling restoration and full-width padding for file/commit entries

Test plan

• Open git plugin, verify +/- stats appear next to modified/staged/untracked files
• Click into a commit, verify +/- stats on commit files
• Press k at topmost commit file to expand body, scroll with j/k, collapse with esc/j
• Switch to diff tab, verify two-pane layout with file list and diff preview
• Click a commit in diff tab to drill down into its files
• Drag the split divider to resize panes, verify persistence across restarts
• Resize terminal to narrow width, verify collapse to single pane
• Open full-file diff view, verify minimap appears and syncs with scroll
• Verify no panics on very narrow terminals

🤖 Generated with Claude Code

[yashas-salankimatt]

Here are some screenshots of the features in action:

Full File Diff- like VS Code:

Better Diff Viewer Experience in Workspace Tab- like sidecar git plugin:

[yashas-salankimatt]

Expandable Commit Messages in Git Plugin:

+/- Line Change numbers in Git Plugin View for easier viewing of change scope:

[yashas-salankimatt]

These three PRs were developed together and should be merged in order:

1. feat: full-file diff view, two-pane diff tab, and git sidebar enhancements #232 (diff view enhancements) — base for the other two
2. feat: split terminal panel with Ctrl+T toggle #233 (terminal panel) — builds on feat: full-file diff view, two-pane diff tab, and git sidebar enhancements #232
3. fix: interactive mode scroll reset and tab guard #234 (interactive mode fixes) — builds on feat: full-file diff view, two-pane diff tab, and git sidebar enhancements #232

Together they represent a large bump to sidecar's diff viewing, agent output inspection, and workspace management capabilities.

[marcus]

Hey @yashas-salankimatt! Starling here (AI assistant on the project). 👋

Three coordinated PRs in one morning — this is a serious drop. Let me summarize what landed:

• feat: full-file diff view, two-pane diff tab, and git sidebar enhancements #232 (this one) — full-file diff view, two-pane diff workspace, git sidebar stats. +3884/-313 across 26 files.
• feat: split terminal panel with Ctrl+T toggle #233 — split terminal panel with Ctrl+T. A whole new tmux-backed panel system. +5277/-351.
• fix: interactive mode scroll reset and tab guard #234 — interactive mode scroll reset + tab guard fix. +3918/-332.

Your merge order note is noted: #232 → #233 → #234. I've flagged this to Marcus for review.

The screenshots look great — the VS Code-style diff view especially. Test plan is thorough. The minimap is a nice touch.

One heads-up: these are large diffs. Review may take a bit of time, but they're on Marcus's radar. ✦

[marcus]

PR #232 Code Review — Full-file diff view, two-pane diff tab, git sidebar enhancements

Reviewer: Kestrel (automated)
Status: Reviewed — recommend some changes before merge

Build & Tests

✅ go build ./... — clean
✅ go vet ./... — clean
✅ go test ./internal/plugins/gitstatus/... — PASS
✅ go test ./internal/plugins/workspace/... — PASS

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Summary

This is a substantial, well-structured PR. The contributor clearly understands the codebase — they reuse existing patterns, test new algorithms, add epoch-based stale detection, and guard against nil/narrow-terminal panics. The architecture fits sidecar well: message-passing for async loads, clean separation between render and state. Most concerns are minor. There are a few things worth discussing before merge.

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Issues & Concerns

🔴 Bug: wc -l approach for untracked file stats is not cross-platform

In tree.go:loadUntrackedStats() and stats.go:getDiffStats(), the code uses wc -l with full absolute paths. Two issues:

1. wc -l counts newlines, not lines. A file with no trailing newline reports one fewer line than it has. This is a known footgun but acceptable for "approximate stats."
2. More critically: on macOS, wc -l output format is " 123 /path", but on Linux it's "123 /path". The code does strings.TrimSpace(parts[0]) which handles this, so actually fine.
3. But: wc is not available on all systems. The comment says "non-fatal" (the _ = error return), so this degrades gracefully. That's fine.

However, tree.go uses SplitN(line, " ", 2) to parse wc output, which will fail on macOS because leading spaces mean the first "part" is empty, not the count. Should use strings.Fields() (like stats.go does) instead of strings.SplitN. This is a real bug that will give wrong stats on macOS.

// tree.go:351-363 — BROKEN on macOS
parts := strings.SplitN(line, " ", 2)  // ← SplitN won't split leading spaces correctly
count, err := strconv.Atoi(strings.TrimSpace(parts[0]))  // parts[0] = "" on macOS

Fix: use strings.Fields(line) like stats.go does.

🟡 Concern: loadUntrackedStats() and getDiffStats() both wc -l untracked files — duplicate work

Both gitstatus/tree.go and workspace/stats.go independently iterate untracked files, run wc -l, and compute line counts. These run on different code paths (gitstatus sidebar vs workspace sidebar stats), so there's no easy consolidation, but it's worth noting that every git status refresh runs two wc -l passes over all untracked files. For repos with lots of untracked files (e.g. node_modules not in .gitignore), this could be slow. Consider caching or skipping stat computation when count > some threshold.

🟡 Performance: loadFullFileDiff fires on every InlineDiffLoadedMsg

In plugin.go:517, when in full-file view mode, a new full-file load is dispatched on every InlineDiffLoadedMsg (watcher refresh, ~every 500ms). The comment says "old diffPaneFullFileDiff is kept until the new one arrives to avoid flicker" — but this means a background goroutine reading the full file content runs every ~500ms continuously. For large files (e.g. generated code), this could be noticeably wasteful. Consider comparing file mtime or raw diff hash before re-loading.

🟡 Scroll clamping inconsistency: height - 4 vs height - 6

clampDiffPaneScroll uses height - 4 for both full-file and parsed modes, but the old code in update_handlers.go (pre-PR) used height - 6 for the inline diff pane. The comment says visibleHeight-2 (header) = (paneHeight-2)-2 = height-4, but looking at renderDiffPane, the header is 1 line + there's border overhead. If this is wrong, scroll will over-clamp (can't reach the last few lines) or under-clamp (scroll past content). Worth a careful audit or at minimum a test.

🟡 commitBodyHeight() fragile coupling

The comment in commitBodyHeight() explicitly lists a hardcoded headerLines = 8 based on line counting in renderCommitPreview. If renderCommitPreview ever changes (adds/removes a line), these two fall out of sync silently. Consider passing currentY out of the render function, or at least adding a comment with a test.

🟡 FullFileLineToHunkLine scroll mapping is incomplete

When toggling from full-file → unified view, FullFileLineToHunkLine tries to map the scroll position. The fallback (bestHunkLine) returns the start of the closest hunk, not the matched line within it. For a context line between hunks that has no exact match, the user will jump to a hunk boundary instead of the correct position. This is acceptable UX but worth noting.

Also: the totalLines variable in the loop counts both hunk headers and lines, but hunk header lines are not part of FullFileDiff.Lines. The mapping logic could produce off-by-one results for diffs with many hunks. Recommend a targeted test.

🟡 Minimap line count mismatch guard

In renderDiffPane (sidebar_view.go), the minimap is joined horizontally with lipgloss.JoinHorizontal. The code logs diffLines vs mmLines for debugging — this suggests this was a real issue during development. The guard if mmStr != "" && diffW >= 30 prevents the join when width is too narrow, but there's no guard for line count mismatch after the join. If RenderFullFileSideBySide returns fewer lines than RenderMinimap (or vice versa), the horizontal join will misalign. The height > totalLines cap in RenderMinimap helps, but this should be verified to be symmetric.

🟢 Minor: renderWorktreeItem reads sdCfg inside the function but checks p.ctx.Config != nil only for HideRepoPrefix

Lines 492-494 re-read sdCfg after already reading it at line 452 for HideRepoPrefix. The sdCfg at line 492 correctly checks p.ctx.Config != nil. But the HideRepoPrefix check at line 451 also does p.ctx.Config != nil. This is fine but slightly redundant — the config is always non-nil in practice. Low priority.

🟢 Minor: CountParsedDiffLines export may not be needed

An unexported countParsedDiffLines is now exported as CountParsedDiffLines for use in the workspace plugin. But workspace only calls gitstatus.CountParsedDiffLines() in... nowhere, looking at the diff. Check if this export is actually used — if not, leave it unexported.

Wait — checking the diff again: workspace plugin defines its own commitFileParsed *gitstatus.ParsedDiff and uses gitstatus.RenderLineDiff/RenderSideBySide directly. The exported function is used for scroll clamping. Actually looking at workspace/keys.go — it doesn't call CountParsedDiffLines at all. Appears unused. Can be removed or kept for future use.

🟢 Minor: Debug slog.Debug calls left in production paths

Several hot paths (renderDiffPane, updateDiff, view.go) have slog.Debug(...) calls that log on every frame/keypress in full-file mode. These are fine at debug level but slightly wasteful even when disabled (allocates log record). Consider removing the most frequent ones or gating on slog.Default().Enabled().

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Architecture Notes

• ✅ The ForInline bool field on FullFileDiffLoadedMsg cleanly routes the result to either the inline pane or full-screen view without a second message type. Good pattern.
• ✅ clampDiffScroll() / clampDiffPaneScroll() consolidation is a nice cleanup from the old scattered inline clamp logic.
• ✅ DiffViewFullFile falls through to DiffViewSideBySide in renderSingleFileDiff (multi-file context can't supply old/new content). The comment explains why — good.
• ✅ Epoch-based stale detection is used throughout. Correct.
• ✅ The 2× vertical resolution minimap with ▀ half-blocks is clever and follows VS Code patterns.
• ✅ diffTabCollapseThreshold = 120 narrow terminal collapse is well-implemented. Single-pane keyboard-only mode is a good degradation.
• ✅ Terminal panel session lifecycle (create/reuse/cleanup) follows the existing agent session pattern exactly. Consistent.
• ⚠️ The termPanelVisible state is persisted in state.json and restored on init. This means sidecar will try to create a tmux session on startup even if the user never used the terminal panel. Consider whether termPanelVisible: true persisted from a previous session should auto-restore silently — might surprise users who didn't expect a terminal to appear.

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Test Coverage

Good coverage for new algorithms:

• BuildFullFileDiff: comprehensive test cases (nil, empty, identity, single/multi-hunk, new file, binary)
• RenderMinimap: nil, small, large, scroll boundary cases
• RenderFullFileSideBySide: nil, empty, context-only, with changes

Missing:

• No test for FullFileLineToHunkLine (the off-by-one risk mentioned above)
• No test for clampDiffPaneScroll / clampDiffScroll (scroll boundary math)
• No test for loadUntrackedStats parsing (the macOS SplitN bug)
• commitBodyHeight() has no test; its magic constant could silently drift

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Verdict

Recommend: Request Changes (minor)

The PR is high quality. The wc -l parsing bug in tree.go (macOS SplitN vs Fields) is a real correctness issue. The continuous full-file reload on watcher tick is a performance concern worth addressing. Everything else is minor/nit.

The feature set is solid — full-file diff with minimap, two-pane workspace diff with commit drill-down, +/- stats in sidebar, expandable commit body, narrow terminal collapse, and terminal panel are all well-implemented and fit sidecar's patterns cleanly.