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File Preview: mark git changes next to line numbers - #13894
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Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 9 remain after this review. 📝 WalkthroughWalkthroughFile previews now compare loaded text with its committed Git content and publish line-level change markers. Panels track repository changes while eligible text previews are open and their gutters are visible. The line-number gutter displays added, modified, and removed markers with theme colors. ChangesGit gutter tracking and rendering
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant FilePreviewPanel
participant FilePreviewGitDiffTracker
participant SystemGitHeadContentReader
participant FilePreviewGitLineDiff
participant FilePreviewTextEditor
participant FilePreviewLineNumberGutterView
FilePreviewPanel->>FilePreviewGitDiffTracker: provide buffer text and encoding
FilePreviewGitDiffTracker->>SystemGitHeadContentReader: read HEAD content and watched paths
SystemGitHeadContentReader-->>FilePreviewGitDiffTracker: return content and paths
FilePreviewGitDiffTracker->>FilePreviewGitLineDiff: compare base and current text
FilePreviewGitLineDiff-->>FilePreviewGitDiffTracker: return line changes
FilePreviewGitDiffTracker-->>FilePreviewPanel: publish gutter markers
FilePreviewPanel-->>FilePreviewTextEditor: update markers and revision
FilePreviewTextEditor-->>FilePreviewLineNumberGutterView: apply Git gutter markers
Merge Risk: ⚪ Minimal · up to The Git gutter changes have no identified merge-blocking issue. Merge after normal build and test checks, including the required Xcode CI lanes. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The change remains local to file previews and limits individual Git reads and diff computations. Cancellation prevents stale results from appearing, but does not fully stop underlying Git work, allowing obsolete requests to overlap during repeated updates. No arbitrary-command or credential-access path was established. Retained concerns
Security review detailsSecurity Blast Radius
Security Findings and Attack Paths
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
🚥 Pre-merge checks | ✅ 24 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (24 passed)
✨ Finishing Touches 💡 1⚔️ Resolve merge conflicts 💡
🧪 Generate unit tests (beta)
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All contributors have signed the CLA ✍️ ✅ |
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I have read the CLA Document v2.2 and I hereby sign the CLA |
File Preview shows no git state, so an agent's edits are only visible by opening the diff viewer. The line-number gutter now paints a stripe per changed line: green for added, blue for modified, and a red boundary marker where lines were deleted. The comparison is against HEAD and runs in-app on the live buffer, so unsaved typing and external writes such as agent edits update within about 150 ms. Committing or staging refreshes the base through a watch on the repository index. Untracked files and files outside a repository show nothing, matching VS Code. FilePreviewGitLineDiff (CmuxFilePreviewCore) runs a Myers line diff between HEAD content and the buffer. GitHeadFileContentReader (CmuxGit) reads `git show HEAD:./name` from the file's directory through the existing bounded runner. FilePreviewGitDiffTracker debounces recomputation and publishes markers by revision, so a keystroke never compares marker sets. Inputs over 20,000 lines or 2 MiB skip diffing. There is no setting; the markers are always on. No user-facing strings were added. Package tests pass under Xcode 16.2: CmuxFilePreviewCore 25, CmuxSyntaxHighlighting 5, CmuxGit 7, including 22 new. The app target and cmuxTests were not built locally because main does not compile on Swift 6.0.3 (the macOS Compatibility lane is red), so the app build and the three new gutter tests rely on CI.
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The diff now splits lines on the same breaks the gutter numbers (CR, U+2028, and U+2029 included), and the HEAD base arrives as raw bytes from `git cat-file blob` that the tracker decodes with the buffer's own encoding, so Latin-1 and UTF-16 files no longer show every line as changed. Symbolic links read the file they point to. The tracker depends on a new `GitHeadContentReading` protocol, debounces on an injected clock, and publishes `FilePreviewGitGutterMarkers` on an AsyncStream. It watches HEAD, the index, and the branch ref so moves such as `git reset --soft` refresh the base, re-resolves that set only when HEAD itself changes, and skips the diff when the HEAD bytes did not move. Observations are owned by `FileContentObservationLifetime`, so a tracker dropped without cancel still releases them and ends its stream. A tracked file reserves the stripe column before its first change, so editing no longer shifts the text. Hiding line numbers pauses git work. Package tests pass under Xcode 16.2: CmuxFilePreviewCore, CmuxSyntaxHighlighting, and CmuxGit (12 reader tests). The app target and cmuxTests, including 11 new tracker tests, were not built locally because main does not compile on Swift 6.0.3.
…git-gutter # Conflicts: # cmux.xcodeproj/project.pbxproj
…git-gutter # Conflicts: # cmux.xcodeproj/project.pbxproj
The line diff trims shared leading and trailing lines and reports a differing middle over 2,000 lines as one modified run, so a full rewrite of a 5,000-line file takes 0.004 s instead of 0.78 s. Emptying a tracked file now marks line 1 removed, and a removal at the end of a wrapped line draws on its last fragment. A packed branch watches the directory its loose ref is written into, so `git reset --soft` on it refreshes the base. The tracker waits for the loaded buffer before diffing, so the empty placeholder never flashes a deletion. Discarding a panel without close() stops git tracking, and a workspace transfer keeps the markers while moving the repository watch. Package tests pass under Xcode 27: CmuxFilePreviewCore 17 and the SystemGitHeadContentReader suite 14. Focused app tests pass: 47 tests in 6 suites, including 3 new panel tracking tests.
jeon-jihyeon
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September 29, 2026 12:27
…gutter The tracker no longer sleeps to debounce edits. It runs one diff at a time, and edits that arrive while it runs coalesce into a single rerun on the latest buffer, so only results for the current input publish. Gutter markers move from a new @published property to an @observable FilePreviewGitGutterModel. The panel view reads it and hands the markers to the editor as values, and the line-number setting reaches the panel through onChange instead of a task scheduled from updateNSView. The HEAD reader's async methods are @Concurrent so git work leaves the caller's actor. Focused app tests pass: 47 tests in 6 suites. The SystemGitHeadContentReader package suite passes: 14 tests.
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✅ Action performedFull review finished. |
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- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @Sources/Panels/FilePreviewGitDiffTracker.swift:
- Around line 211-222: In the diffTask body, retain the detached task handle and
wrap awaiting its value in a cancellation handler that cancels the handle when
the tracker task is cancelled. Add cancellation checks within
FilePreviewGitLineDiff.changes so the detached computation can stop promptly
after cancellation.
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📒 Files selected for processing (24)
Packages/Shared/CmuxSyntaxHighlighting/Sources/CmuxSyntaxHighlighting/TokenPalette.swiftPackages/Shared/CmuxSyntaxHighlighting/Tests/CmuxSyntaxHighlightingTests/TokenPaletteTests.swiftPackages/macOS/CmuxFilePreviewCore/README.mdPackages/macOS/CmuxFilePreviewCore/Sources/CmuxFilePreviewCore/FilePreviewGitGutterMarkers.swiftPackages/macOS/CmuxFilePreviewCore/Sources/CmuxFilePreviewCore/FilePreviewGitLineChange.swiftPackages/macOS/CmuxFilePreviewCore/Sources/CmuxFilePreviewCore/FilePreviewGitLineChangeAccumulator.swiftPackages/macOS/CmuxFilePreviewCore/Sources/CmuxFilePreviewCore/FilePreviewGitLineDiff.swiftPackages/macOS/CmuxFilePreviewCore/Tests/CmuxFilePreviewCoreTests/FilePreviewGitLineDiffTests.swiftPackages/macOS/CmuxGit/README.mdPackages/macOS/CmuxGit/Sources/CmuxGit/HeadContent/GitHeadContentReading.swiftPackages/macOS/CmuxGit/Sources/CmuxGit/HeadContent/SystemGitHeadContentReader.swiftPackages/macOS/CmuxGit/Tests/CmuxGitTests/SystemGitHeadContentReaderTests.swiftSources/Panels/FileContentChangeObservingPanel.swiftSources/Panels/FilePreviewGitDiffTracker.swiftSources/Panels/FilePreviewGitGutterModel.swiftSources/Panels/FilePreviewLineNumberGutterView.swiftSources/Panels/FilePreviewPanel.swiftSources/Panels/FilePreviewTextEditor.swiftSources/Panels/TokenTheme+AppKit.swiftcmux.xcodeproj/project.pbxprojcmuxTests/FilePreviewCodeViewTests.swiftcmuxTests/FilePreviewGitDiffTrackerTests.swiftcmuxTests/FilePreviewPanelGitTrackingTests.swiftcmuxTests/FixedHeadContentReader.swift
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The tracker awaits the diff in its own task through a @Concurrent helper instead of a detached task, and the diff checks for cancellation between stages, so cancel() or hiding the gutter no longer lets a large diff run to completion. Production functions touched by the gutter work gain doc comments that state their contracts. Focused app tests pass: 47 tests in 6 suites. CmuxFilePreviewCore passes 18 tests, including a new cancellation test, and the SystemGitHeadContentReader suite passes 14.
Collaborator
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Thanks @jeon-jihyeon, the file preview indicators are useful. This is held for a design call on the new preview behavior, and the branch also conflicts with main :) |
teamleaderleo
added
the
needs a call
# Conflicts: # cmux.xcodeproj/project.pbxproj
Author
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Thanks @teamleaderleo! Merged main in 26142cf to resolve the conflict. Happy to adjust anything after the design call :) |
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Summary
File Preview shows no git state, so an agent's edits to an open file are only visible by opening the diff viewer. The line-number gutter now paints a stripe per changed line: green for added, blue for modified, and a red boundary marker where lines were deleted. The comparison is against HEAD and runs on the live buffer, so unsaved typing updates the markers as soon as the diff finishes, and external writes such as agent edits update once the file watcher reloads the file. When HEAD moves, by a commit, checkout, or reset, the base refreshes through a watch on
HEAD, the index, and the branch ref. A packed branch watches the directory its loose ref is written into, sogit reset --softon a packed branch is also caught.A tracked file reserves the stripe column before its first change, so editing never shifts the text. Untracked files and files outside a repository keep today's gutter width and show nothing, matching VS Code. With line numbers turned off the gutter is hidden and git tracking stops until it is shown again.
Mechanism:
FilePreviewGitLineDiff(CmuxFilePreviewCore) diffs HEAD content against the buffer. It splits lines on the same breaks the gutter'sFilePreviewLineIndexcounts (LF, CR, CRLF, U+2028, U+2029), so markers land on the numbered lines, and it skips inputs over 20,000 lines or 2 MiB. Shared leading and trailing lines are trimmed first, and a remaining middle over 2,000 lines on either side is reported as one modified run instead of being aligned. Before this bound, a full rewrite took 0.78 s at 5,000 lines, 2.8 s at 10,000 and 10.9 s at 20,000; a 5,000-line rewrite now finishes in 0.004 s, and the slowest aligned case, a 2,000-line middle rewritten line by line, takes 0.11 s. All timings are optimized builds on an Apple silicon Mac.SystemGitHeadContentReader(CmuxGit) conforms to the newGitHeadContentReadingprotocol. Its async methods are@concurrent, behind the existing#if compiler(>=6.2)guard, so git work leaves the caller's actor. It resolves symbolic links, then runsgit cat-file blob HEAD:./namefrom the file's directory through the existing bounded git runner, so it returns the stored bytes without textconv filters. It also lists the paths whose changes can move HEAD content, including the loose branch ref, or its nearest existing directory when the branch is packed, sogit reset --softis not missed.WorkspaceChangesServicewas not reused because it compares against the merge base.FilePreviewGitDiffTrackerdepends onGitHeadContentReading, decodes the HEAD bytes with the encoding the panel loaded the file with (UTF-8, UTF-16, or Latin-1), diffs off the main actor one diff at a time, stopping a running diff when tracking is cancelled, coalescing edits that arrive while a diff runs into one rerun on the latest buffer, and yieldsFilePreviewGitGutterMarkerson anAsyncStream. A repository change whose HEAD bytes did not move skips the diff, and only a change toHEADitself resolves the watched set again. Observations are owned byFileContentObservationLifetime, like the panel's own file watch, so a tracker dropped withoutcancel()still releases them and finishes its stream. The tracker diffs only after both the HEAD base and the loaded buffer are known, so the empty placeholder before the file loads never shows as a deletion. Hiding the gutter, discarding the panel withoutclose(), and closing it all stop tracking, while a workspace transfer keeps the markers and moves the repository watch to the new coordinator.TokenPaletteentries per theme, chosen saturated so the modified stripe stays as visible as the added one.Markers live in an
@ObservableFilePreviewGitGutterModelowned by the panel.FilePreviewPanelViewreads it and passes the markers and a revision toFilePreviewTextEditoras values, so the editor repaints the gutter only when the revision advances. The line-number setting reaches the panel throughonChange, so no panel state is written fromupdateNSView.Known limitation: a Git LFS file shows every line as changed, because HEAD stores the pointer text rather than the content. Not in scope: branch-base comparison, a staged versus unstaged distinction, a setting, and an inline diff popover.
Testing
On macOS 27.0 with Xcode 27.0, at
8195577f:python3 scripts/verify-local.py --affected origin/main --swift-changed origin/main./scripts/reload.sh --tag jed-feat-file-editor-git-gutter./scripts/test-unit.sh ... testwith-only-testingforFilePreviewGitDiffTrackerTests,FilePreviewPanelGitTrackingTests,FilePreviewCodeViewTests,FileContentObserverTransferTests,FilePreviewObserverReloadTestsandFilePreviewTextEditorTextKitTestsswift test --package-path Packages/macOS/CmuxFilePreviewCoreswift test --package-path Packages/macOS/CmuxGit --filter SystemGitHeadContentReaderThe package tests run against real temporary repositories and cover non-UTF-8 bytes, symbolic links, the size and alignment budgets, cancellation, packed branches, linked worktrees, and detached HEAD.
TokenPaletteTestsran under Xcode 16.2 on macOS 14.5 before the machine was upgraded.Checked live in the tagged build, shown in the video: added, modified, and deleted markers while typing without saving, a terminal
printfinto the file updating the markers without an editor save, andgit commitclearing them.Two local build steps needed workarounds that are unrelated to this change and are not committed. The diff sidecar's pinned Rust 1.88 fails to load proc-macro crates on macOS 27 when
MACOSX_DEPLOYMENT_TARGET=14.0is set, while current stable Rust builds it, so the build ran with the sidecar pin switched to stable. The Ghostty CLI helper's zig fetch reported a package hash mismatch, so the build usedCMUX_SKIP_ZIG_BUILD=1.Not verified: the required CI lanes on Xcode 26 have not run on this PR yet.
No user-facing strings were added, so there is nothing to localize.
Changelog
Added: File Preview marks lines added, changed, or deleted since the last commit next to the line numbers
Demo Video
Screen.Recording.2026-09-29.at.11.42.44.AM.mov
Checklist
Summary by CodeRabbit