fix(cli-ui): enable Ctrl+Backspace for word deletion in Windows Terminal

[dogukanozen]

Summary

windows terminal sends \x08 (ctrl+h) for ctrl+backspace, which was being treated as a plain backspace. this PR updates KeypressContext to correctly parse it as a ctrl+backspace keypress, enabling word deletion.

Details

Related Issues

Closes #21445

How to Validate

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

[gemini-code-assist]

Summary of Changes

Hello, 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 resolves an issue where the KeypressContext incorrectly interpreted the \x08 character sent by Windows Terminal for Ctrl+Backspace. By updating the keypress parsing logic, the system now accurately recognizes Ctrl+Backspace, allowing users to perform word deletion as expected in Windows Terminal environments.

Highlights

• Windows Terminal Keypress Handling: Correctly parsed the \x08 character, which is sent by Windows Terminal for Ctrl+Backspace, as a Ctrl+Backspace keypress, enabling word deletion functionality.

Changelog

• packages/cli/src/ui/contexts/KeypressContext.tsx
  • Modified the emitKeys generator to distinguish between \b (Ctrl+Backspace) and \x7f (backspace) for improved keypress interpretation.

Activity

• No human activity has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request addresses a Ctrl+Backspace issue in Windows Terminal. The proposed fix, while correctly identifying the \b character for this combination, introduces a critical regression by altering the Backspace functionality in other terminals. To maintain consistency with existing UI behavior across different terminal environments, as per repository guidelines, the fix should be scoped specifically to Windows Terminal using the WT_SESSION environment variable. This prevents unintended UX changes for other users. Additionally, a unit test is recommended to verify the new behavior and prevent future regressions.

[dogukanozen]

@gemini-code-assist please recheck

[gemini-code-assist]

Code Review

This pull request aims to fix an issue where Ctrl+Backspace does not delete a word on Windows Terminal. The proposed change correctly identifies the \b character sequence and interprets it as a Ctrl+Backspace when running inside Windows Terminal. I've kept the original comment highlighting a potential critical regression if the regular Backspace key also sends the \b sequence, as it would break normal backspace functionality. The comment recommends adding a specific test case to prevent such a regression, following the project's testing conventions.

[dogukanozen]

@gemini-code-assist please recheck

[gemini-code-assist]

Thanks for the recheck request, @dogukanozen! I've taken another look at your changes and the new tests.

This is a great first pull request! The solution you've implemented is well-targeted and correctly addresses the issue of Ctrl+Backspace in Windows Terminal. The addition of specific tests for the WT_SESSION environment variable ensures that the fix behaves as expected across different terminal environments without introducing regressions.

Your code is clear, and the new tests demonstrate a good understanding of the problem and how to verify the solution. Excellent work!

I'm happy to confirm that the changes look good and effectively resolve the reported issue. Keep up the great work!

[gemini-cli]

Hi there! Thank you for your interest in contributing to Gemini CLI.

To ensure we maintain high code quality and focus on our prioritized roadmap, we have updated our contribution policy (see Discussion #17383).

We only guarantee review and consideration of pull requests for issues that are explicitly labeled as 'help wanted'. All other community pull requests are subject to closure after 14 days if they do not align with our current focus areas. For this reason, we strongly recommend that contributors only submit pull requests against issues explicitly labeled as 'help-wanted'.

This pull request is being closed as it has been open for 14 days without a 'help wanted' designation. We encourage you to find and contribute to existing 'help wanted' issues in our backlog! Thank you for your understanding and for being part of our community!

[cocosheng-g]

@dogukanozen, apologies for the bot closing this PR! We have reopened it. Please sync your branch to the latest main and we will have someone review it shortly.

[cocosheng-g]

/gemini review

[gemini-code-assist]

Code Review

This pull request updates the keypress handling logic to correctly identify Ctrl+Backspace in Windows Terminal. It specifically checks for the WT_SESSION environment variable when a \b character is received to set the ctrl flag. Corresponding unit tests have been added to verify this behavior across different environment configurations. I have no feedback to provide.

[gemini-code-assist]

Code Review

This pull request improves backspace handling by distinguishing between standard backspace and Ctrl+Backspace in Windows and Windows Terminal environments. Specifically, it updates the BACKSPACE constant to \x7f in test files and modifies KeypressContext.tsx to treat \b as a control key when the OS environment variable is Windows_NT or WT_SESSION is active. New unit tests have been added to ensure correct behavior across various platforms. I have no feedback to provide.

[dogukanozen]

@cocosheng-g i believe the ci tests will pass now. the tests were failing previously because settingsdialog.test.tsx and BaseSettingsDialog.test.tsx were simulating the backspace key with \b, which conflicted with the new Ctrl+Backspace logic introduced in this PR. i have updated those test files to use the standard \x7f character, so everything should process correctly now.

[gemini-code-assist]

Code Review

This pull request updates the backspace handling logic to correctly distinguish between a standard backspace and Ctrl+Backspace in Windows and Windows Terminal environments. It modifies emitKeys in KeypressContext.tsx to treat \b as a control key when OS is Windows_NT or WT_SESSION is present, while \x7f is used for standard backspace. Corresponding updates were made to test constants in SettingsDialog.test.tsx and BaseSettingsDialog.test.tsx, and new test cases were added to KeypressContext.test.tsx to verify the logic across different environments. I have no feedback to provide.

_{Note: Security Review did not run due to the size of the PR.}

[biodbg]

(Windows terminal; Win10) I am experiencing word deletion even without holding "control" with backspace. This is a new behavior in 0.39 that was not in 0.38.2, afaik

[dogukanozen]

Hi @biodbg could you provide a bit more detail?

Environment: Which terminal (Windows Terminal, CMD, PowerShell) and shell (Bash, PowerShell, etc.) are you using?
Reproduction: Does this happen immediately upon starting the CLI, or does it trigger after a long conversation or
a specific event/tool call?
Connection: Are you running the CLI locally, or are you connected to a remote machine via SSH/WSL?
Key Check: What happens when you press Ctrl+H? Does it delete a single character or a whole word?
Terminal Version: If you are using Windows Terminal, could you share the version number?

This information will help me understand why your environment is sending the \b code for a regular backspace.

[biodbg]

Thanks! Here's my info:

Environment: Which terminal (Windows Terminal, CMD, PowerShell) and shell (Bash, PowerShell, etc.) are you using?

Windows terminal w/ cmd.exe, with Gemini-CLI running shell PowerShell commands.
Same behavior with Windows terminal w/ cygwin tcsh, with Gemini-CLI running PowerShell commands.

Reproduction: Does this happen immediately upon starting the CLI, or does it trigger after a long conversation or a specific event/tool call?

Yes- from the start, and on every re-invocation (with v0.39)

Connection: Are you running the CLI locally, or are you connected to a remote machine via SSH/WSL?

Local

Key Check: What happens when you press Ctrl+H? Does it delete a single character or a whole word?

Ctrl-H deletes a single character

Terminal Version: If you are using Windows Terminal, could you share the version number?

Windows Terminal Preview Version: 1.25.923.0

[scidomino]

The bug only seems to happen if you're using node 22. Node 24 works fine. I'm going to revert this for now. We can reexamine later.

[dogukanozen]

The bug only seems to happen if you're using node 22. Node 24 works fine. I'm going to revert this for now. We can reexamine later.

thanks for checking.
i’m using node 24 as well and couldn’t reproduce it on my side.
i also tested this pr across different terminal environments locally and everything looked fine for me.

[scidomino]

node sits between us and keyboard so it makes sense that it could have an effect like this. My guess is in node 24 they introduced some kind of backspace normalization that this PR relies on.

[biodbg]

Thanks for digging into this, and diagnosing the Node dependency so quickly!