feat: Add undo and revert commit functionality to workspace commits

[Ziinc]

Summary

This PR adds two new commit manipulation features to the Commits tab: "Undo commit" and "Revert commit". These operations allow users to modify their workspace commit history with different semantics.

Key Changes

Backend (Rust)

• jj_undo_commit() in src-tauri/src/jj.rs: Implements undoing the latest commit in a workspace's lineage by abandoning it and folding its changes back into the working copy. Validates that:
  • The commit is the current tip (@-), not the working copy itself
  • The commit is not on the target branch
  • Commits must be undone sequentially from the tip backwards
• jj_revert_commit() in src-tauri/src/jj.rs: Creates a new commit that reverses the changes of any target commit (except the working copy) using a 3-way merge strategy. The new commit is created on top of the current tip with a "Revert" prefix in its description.
• Core API wrappers in src-tauri/src/core/commits.rs: Added undo_commit() and revert_commit() functions that handle workspace lookup and path resolution before delegating to jj operations.
• Tauri commands in src-tauri/src/commands/workspace.rs: Exposed undo_commit and revert_commit as async commands callable from the frontend.

Frontend (TypeScript/React)

• API bindings in src/lib/api-extra.ts: Added undoCommit() and revertCommit() functions to invoke the new Tauri commands.
• UI components in src/components/CommitDiffViewer.tsx:
  • Added handleUndo() and handleRevert() handlers with confirmation dialogs
  • "Undo commit" button appears only on the latest workspace commit (isFirst)
  • "Revert commit" button appears on all real commits except the working copy
  • Both operations trigger appropriate toast notifications on success/failure
  • Undo removes the commit with animation; revert refreshes the commit list

Tests

• Unit tests in src/components/CommitDiffViewer.undoRevert.test.tsx: Comprehensive test suite covering:
  • Undo button visibility (only on latest commit)
  • Revert button visibility (all commits except working copy)
  • Successful undo and revert operations with API mocking
  • Cancellation behavior when user declines confirmation
• Integration tests in src-tauri/tests/core_commits_test.rs:
  • test_undo_commit_only_allows_latest_commit_sequentially: Validates sequential undo constraint
  • test_undo_commit_rejects_commit_on_target_branch: Ensures target branch commits cannot be undone
  • test_revert_commit_creates_backout_commit: Verifies revert creates proper backout commit
  • test_revert_commit_rejects_working_copy: Prevents reverting the working copy
• Screenshot/E2E test in scripts/screenshot/specs/undo-revert-commit.spec.tsx: Full user workflow demonstrating creating commits, undoing, reverting, and the resulting state changes.

Notable Implementation Details

• Undo semantics: Implemented as validated abandon—the commit is removed and its changes are folded back into the working copy, exactly reversing the commit operation. Only the tip can be undone to maintain a clear sequential workflow.
• Revert semantics: Creates a new commit using 3-way merge (commit's tree vs. parent tree, merged onto current tip), producing a proper backout commit that can itself be undone if needed.
• Workspace reconciliation: Both operations call reconcile_all_workspaces_after_rewrite() to handle potential working-copy rewrites across all workspaces.
• UI constraints: The "Undo commit" button is only shown on the first (latest) commit in the list, while "Revert commit" is available on all real commits, making the distinction clear
  https://claude.ai/code/session_017D1cm4fRhCRLPAnNNPKRd3

[github-actions]

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