Git command execution fails with `cannot spawn : No such file or directory` due to empty `diff.external` configuration

[zbynekwinkler]

What happened?

When Gemini CLI runs git commands in its execution sandbox, git fails with:

cannot spawn : No such file or directory

This is because the platform attempts to override and disable external diff tools by configuring diff.external to an empty string (""). Instead of disabling external diffing, Git's diff engine treats the empty string as the name of an external executable to spawn, causing it to fail.

What did you expect to happen?

Git commands should run successfully using the built-in, standard diff engine without attempting to spawn an empty-string executable.

Client information

Client Information

0.56.0-nightly.20260806.g761f604c1
Windows (win32)

Login information

No response

Anything else we need to know?

Root Cause

The platform injects several default Git configuration overrides through GIT_CONFIG_KEY_<N> and GIT_CONFIG_VALUE_<N> environment variables. Specifically, it maps:

• diff.external -> "" (empty string)

In Git, setting diff.external to an empty string does not disable the setting; instead, it instructs Git to spawn "" as an external diff tool, which fails with cannot spawn : No such file or directory.

Responsible Code

1. packages/core/src/services/shellExecutionService.ts (line 520) in the defaultGitOverrides array:

   ['diff.external', '']

2. packages/core/src/utils/gitUtils.ts (lines 44-45) in getSafeGitEnv():

   GIT_CONFIG_KEY_7: 'diff.external',
   GIT_CONFIG_VALUE_7: '',

Introducing Commit

The regression was introduced in the following commit:

• Commit: c0d192452b4e2df7efb6d62a60385f475bfd6779
• Author: luisfelipe-alt luisfelipe@google.com
• Message: fix(core): normalize git environment and resolve workspace state mismatch (#28792)

Proposed Resolution

Completely remove the diff.external overrides from the default overrides list and safe environment helper, allowing Git to use its built-in engine natively. If you want to make sure no external diff tool is used, call git diff --no-ext-diff.

[gemini-cli]

Effort Analysis:
The issue is caused by the platform incorrectly overriding diff.external to an empty string in packages/core/src/services/shellExecutionService.ts (line 520) and packages/core/src/utils/gitUtils.ts (lines 44-45). This causes Git to attempt to spawn an empty string as an external diff tool, failing with a cannot spawn : No such file or directory error, particularly on Windows (win32) as reported. While the fix itself is a trivial removal of the configuration override, the bug's manifestation is platform-specific and occurs within the execution sandbox. According to the guidelines, bugs that are platform-specific or require cross-environment setups (like the sandbox) must not be rated as effort/small due to the increased overhead of reproduction and testing across different operating systems to ensure the fix doesn't introduce side effects in the Git environment normalization logic.