Executing Flutter CLI commands within Git hooks inside a submodule repository can result in the Dart SDK being corrupted. This issue makes all Flutter/Dart commands unusable, requiring a full reinstallation of the Flutter SDK to recover.

Steps to Reproduce

1. Clone a minimal reproduction repository that contains a submodule where the Flutter project resides:

   git clone [email protected]:Xm798/example-project --recurse-submodules

2. Create a Git pre-commit hook inside the submodule at .git/modules/submodules/example-submodule/hooks/pre-commit and add any Flutter-related commands, such as:

   flutter doctor
   dart format .

3. In the submodule directory (submodules/example-submodule), commit any change to trigger the hook:

   git commit -m "Trigger pre-commit hook"

4. Observe the following error:

   Downloading Darwin arm64 Dart SDK from Flutter engine 780e976079f7c9e9cc1f106566bc155e4fbf0297...
     % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                    Dload  Upload   Total   Spent    Left  Speed
   100   258  100   258    0     0    692      0 --:--:-- --:--:-- --:--:--   693
   [/Users/Cyrus/opt/flutter/bin/cache/dart-sdk-darwin-arm64.zip]
     End-of-central-directory signature not found.  Either this file is not
     a zipfile, or it constitutes one disk of a multi-part archive.  In the
     latter case the central directory and zipfile comment will be found on
     the last disk(s) of this archive.
   unzip:  cannot find zipfile directory in one of /Users/Cyrus/opt/flutter/bin/cache/dart-sdk-darwin-arm64.zip or
           /Users/Cyrus/opt/flutter/bin/cache/dart-sdk-darwin-arm64.zip.zip, and cannot find /Users/Cyrus/opt/flutter/bin/cache/dart-sdk-darwin-arm64.zip.ZIP, period.
   
   It appears that the downloaded file is corrupt; please try again.
   If this problem persists, please report the problem at:
     https://github.com/flutter/flutter/issues/new?template=1_activation.yml
   

5. After this failure, running any Flutter or Dart commands results in:

   $flutter --version
   /Users/Cyrus/opt/flutter/bin/internal/shared.sh: line 268: /Users/Cyrus/opt/flutter/bin/cache/dart-sdk/bin/dart: No such file or directory

6. Checking the Flutter cache directory reveals that the Dart SDK has been entirely removed:

   ls -lah /Users/Cyrus/opt/flutter/bin/cache/dart-sdk/
   drwxr-xr-x@  2 Cyrus  staff    64B  3 18 20:18 .
   drwxr-xr-x@ 31 Cyrus  staff   992B  3 18 20:18 ..

Actual results

The issue originates from the script bin/internal/update_engine_version.sh, which attempts to determine the Flutter branch and engine version using:

BRANCH=$(git -C "$FLUTTER_ROOT" rev-parse --abbrev-ref HEAD)
ENGINE_VERSION=$(git -C "$FLUTTER_ROOT" merge-base HEAD origin/master)

However, when running inside a Git hook in a submodule, git sets the environment variable GIT_DIR to the submodule’s repository. This causes -C "$FLUTTER_ROOT" to be ignored, leading to incorrect values being retrieved. For example, in the error log above, the commit hash 780e976079f7c9e9cc1f106566bc155e4fbf0297 actually belongs to the latest commit in the submodule:

commit 780e976079f7c9e9cc1f106566bc155e4fbf0297 (HEAD -> master, origin/master, origin/HEAD)
Author: Xm798 <[email protected]>
Date:   Tue Mar 18 19:57:44 2025 +0800

Additionally, bin/internal/update_dart_sdk.sh deletes the old Dart SDK before successfully downloading a new one, leading to a completely broken development environment if the download fails.

This issue forces users to completely reinstall Flutter SDK to restore functionality, significantly disrupting development workflows.

Logs

No response

Flutter Doctor output

/Users/Cyrus/opt/flutter/bin/internal/shared.sh: line268: /Users/Cyrus/opt/flutter/bin/cache/dart-sdk/bin/dart: No such file or directory