Git - re-read the index base when staging, reverting or unstaging ranges

[soreavis]

Fixes #64027

The bug

Stage a selected range, commit, then stage a second range with nothing in between, and the second stage also stages an exact revert of the just-committed region (it shows up in git diff --cached and gets committed). Reliably reproducible; @joaomoreno diagnosed the mechanism back in 2018 ("VS Code fails to refresh the index version of the file in time for that second stage").

Root cause

_stageChanges/_revertChanges/the two unstage paths build the staged content by applying the selected line changes onto the index/HEAD base, which they obtain via openTextDocument(toGitUri(uri, '~' | 'HEAD')). The git file system provider serves that content fresh (readFile runs git show every time), but the workbench caches the TextDocument, and the provider's invalidation event is @debounce(1100). So within ~1.1s of a commit the cached base is stale — the second stage applies the new hunk onto the pre-commit base and reverts the first commit. workspace.fs.readFile on the same git: URI bypasses the document cache and is always fresh.

The fix

Read the base directly with workspace.fs.readFile + workspace.decode({ encoding: modifiedDocument.encoding }) (the inverse of the workspace.encode({ encoding }) already used on the stage write path), instead of opening a document for it. applyLineChanges now takes the two sides as strings, backed by a small LineIndex helper that provides the lineCount/line-length/getText behaviour it relied on — so the freshly read base can be applied without a TextDocument. Both parameters became strings because the unstage sites pass the git side as the modified argument.

I kept LineIndex rather than reaching for openTextDocument({ content }) deliberately: an untitled document per stage would land in workspace.textDocuments and fire onDidOpenTextDocument to every extension on a frequently-run command, and slicing the string preserves the base bytes/EOL exactly (an untitled doc infers and can normalize EOL). LineIndex is verified byte-identical to the previous TextDocument-based algorithm.

Scope

This changes the four applyLineChanges-based range/hunk commands (stage/revert/unstage selected ranges and the gutter stage/revert/unstage-change actions). The diff-editor toolbar's git.diff.stageHunk/stageSelection path stages a string precomputed by the diff editor and never went through this base read, so it is unaffected.

Tests

• extensions/git/src/test/smoke.test.ts — an end-to-end regression: stage a region, commit, stage a second region, and assert the index contains only the second region. Verified it fails on the current code (stages 1\n… — line 1 reverted) and passes with the fix.
• extensions/git/src/test/staging.test.ts — unit coverage for the applyLineChanges string refactor: mid-file, end-of-file insert/delete (Can't stage empty removed last line #59670), CRLF, and multiple selected changes.

The end-to-end test covers git.stageSelectedRanges (the ~/index base), which is the reliably reproducible case since the working-tree quick diff always keeps that document open. The revert and unstage sites take the identical fresh read against the HEAD base, whose staleness is impractical to drive in an end-to-end test, so they lean on the applyLineChanges byte-parity units plus the shared read path.

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@lszomoru

Matched files:

• extensions/git/src/commands.ts
• extensions/git/src/staging.ts
• extensions/git/src/test/smoke.test.ts
• extensions/git/src/test/staging.test.ts

[Copilot]

Pull request overview

Fixes stale Git index/HEAD reads during range staging, reverting, and unstaging.

Changes:

• Reads Git base content directly from the filesystem provider.
• Refactors line-change application to operate on strings.
• Adds unit and end-to-end regression coverage.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
extensions/git/src/staging.ts	Adds string-based line indexing and change application.
extensions/git/src/commands.ts	Uses fresh base content for range operations.
extensions/git/src/test/staging.test.ts	Tests line application and EOL edge cases.
extensions/git/src/test/smoke.test.ts	Covers the stale-index regression.