feat: Add /undo command to revert last conversation turn #18708

[lin88225]

Summary

This PR adds a new built-in slash command, /undo, which allows users to quickly revert the last conversation turn (the most recent User prompt and the subsequent Model response).

Details

As suggested by @jacob314, this implementation leverages the existing rewindConversation logic to ensure state consistency.

Refactoring: Exported rewindConversation from rewindCommand.tsx to make it a reusable utility for other commands.

Logic: The command calculates the target message ID at messages.length - 3 to revert the history to the state immediately preceding the last turn.

UX: The undone user prompt is restored to the input buffer, allowing the user to refine and resubmit their question without retyping.

Related Issues

Fixes #18708

How to Validate

Build: Run npm run build from the root.

Setup: Launch the CLI (./packages/cli/bin/gemini-cli) and trust the folder.

Populate: Send at least two messages (e.g., "Hello" followed by "What is 10+10?").

Execute: Type /undo.

Result:

The "What is 10+10?" message and its response should be removed from the view.

"What is 10+10?" should be prepopulated in the input buffer.

History should accurately reflect only the "Hello" turn.

Pre-Merge Checklist

[x] Updated relevant documentation (Command registered in BuiltinCommandLoader)

[ ] Added/updated tests (Verified via manual integration, happy to add automated unit tests if requested during review.)

[x] Noted breaking changes (None)

[x] Validated on required platforms/methods:

[x] MacOS

[x] npm run

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[gemini-code-assist]

Summary of Changes

Hello @lin88225, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new /undo command for the CLI, significantly enhancing the user experience by providing a quick and consistent way to revert the most recent interaction in a conversation. This functionality is built upon the existing conversation rewind mechanism, which has been refactored for broader utility, and includes a user-friendly feature that restores the last user prompt to the input field for easy modification.

Highlights

• New /undo command: A new built-in slash command, /undo, has been introduced, allowing users to revert the last conversation turn (user prompt and model response).
• Rewind Conversation Refactoring: The rewindConversation function was refactored and exported from rewindCommand.tsx to make it a reusable utility for other commands, specifically the new /undo command.
• Conversation State Management: The /undo command leverages the existing rewindConversation logic to ensure state consistency when reverting the conversation history.
• Enhanced User Experience: After an undo operation, the last user prompt is restored to the input buffer, enabling users to easily refine and resubmit their question without retyping.

Changelog

• package-lock.json
  • Added strip-json-comments dependency.
• packages/cli/src/services/BuiltinCommandLoader.ts
  • Imported the new undoCommand.
  • Registered undoCommand in the list of available built-in commands.
• packages/cli/src/ui/commands/rewindCommand.tsx
  • Exported the rewindConversation function to allow its reuse by other commands.
• packages/cli/src/ui/commands/undoCommand.tsx
  • Created a new file defining the /undo slash command, implementing its logic to rewind the conversation by two messages (user and model) and restore the user's last prompt.

Activity

• The author implemented the /undo command, leveraging existing rewindConversation logic.
• The rewindConversation function was refactored to be exportable and reusable.
• Documentation was updated to register the new command in BuiltinCommandLoader.
• Manual integration testing was performed on MacOS, confirming the command's functionality and user experience.

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[gemini-code-assist]

Code Review

This PR adds the /undo command to revert the last conversation turn. While the feature is a valuable addition for UX, the current implementation for identifying the message to rewind to is fragile and contains logic errors that lead to incorrect history states (over-deleting previous turns) or doing nothing on the first turn. I've provided suggestions to use a more robust findLastIndex approach and to use the existing partToString utility for restoring the user prompt to the input buffer.

[lin88225]

Updated to use findLastIndex and partToString as suggested. Branch is now rebased and up-to-date with main.

[mrpmohiburrahman]

When no user message exists, findLastIndex returns -1. The guard on line 32 checks messages.length < 2, but that only counts messages. It doesn't check whether any of them are actually 'user' type.

The codebase defines 5 message types ('user' | 'info' | 'error' | 'warning' | 'gemini' — chatRecordingService.ts line 78), so a conversation can have 2+ non-user messages, pass the guard, and crash on line 40 when the code tries to access messages[-1].id while lastUserIndex is still -1.

Simple fix on line 32:

// before
if (messages.length < 2) {
// after
if (lastUserIndex === -1) {

[lin88225]

fixed it, thanks!