[ci] Add Gemini Code Assist review config (#9632)

This adds initial configuration files for [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code) in preparation for turing it on for this repository on a trial basis. These config files are based on [the official docs](https://developers.google.com/gemini-code-assist/docs/customize-gemini-behavior-github)

It also adds a note to the PR template to provide some notice/guidance to contributors about how to use automated feedback, to clarify the role of the automated reviews and hopefully minimize potential issues in case the bot leaves incorrect feedback.

Author: stuartmorgan-g

.gemini/config.yaml

@@ -0,0 +1,13 @@
+# Minimize verbosity.
+have_fun: false
+code_review:
+  # For now, use the default of MEDIUM for testing. Based on desired verbosity,
+  # we can change this to LOW or HIGH in the future.
+  comment_severity_threshold: MEDIUM
+  pull_request_opened:
+    # Explicitly set help to false in case the default changes in the future, as
+    # having a help message on every PR would be spammy.
+    help: false
+    # These tend to be verbose, and since we expect PR authors to clearly
+    # describe their PRs this would be at best duplicative.
+    summary: false

.gemini/styleguide.md

@@ -0,0 +1,23 @@
+# Flutter Packages Style Guide
+
+## Introduction
+
+This style guide outlines the coding conventions for contributions to the
+flutter/packages repository.
+
+## Style Guides
+
+Code should follow the relevant style guides, and use the correct
+auto-formatter, for each language, as described in
+[the repository contributing guide's Style section](https://github.com/flutter/packages/blob/main/CONTRIBUTING.md#style).
+
+## Best Practices
+
+- Code should follow the guidance and principles described in
+  [the flutter/packages contribution guide](https://github.com/flutter/flutter/blob/master/docs/ecosystem/contributing/README.md).
+- Code should be tested. Changes to plugin packages, which include code written
+  in C, C++, Java, Kotlin, Objective-C, or Swift, should have appropriate tests
+  as described in [the plugin test guidance](https://github.com/flutter/flutter/blob/master/docs/ecosystem/testing/Plugin-Tests.md).
+- PR descriptions should include the Pre-Review Checklist from
+  [the PR template](https://github.com/flutter/packages/blob/main/.github/PULL_REQUEST_TEMPLATE.md),
+  with all of the steps completed.

.github/PULL_REQUEST_TEMPLATE.md

@@ -18,6 +18,14 @@
 
 If you need help, consider asking for advice on the #hackers-new channel on [Discord].
 
+**Note**: The Flutter team is currently trialing the use of
+[Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code).
+Comments from the `gemini-code-assist` bot should not be taken as authoritative
+feedback from the Flutter team. If you find its comments useful you can
+update your code accordingly, but if you are unsure or disagree with the
+feedback, please feel free to wait for a Flutter team member's review for
+guidance on which automated comments should be addressed.
+
 [^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.
 
 <!-- Links -->

script/tool/lib/src/common/file_filters.dart

@@ -8,21 +8,24 @@
 /// commands that are only affected by package code.
 bool isRepoLevelNonCodeImpactingFile(String path) {
   return <String>[
-    'AUTHORS',
-    'CODEOWNERS',
-    'CONTRIBUTING.md',
-    'LICENSE',
-    'README.md',
-    // This deliberate lists specific files rather than excluding the whole
-    // .github directory since it's better to have false negatives than to
-    // accidentally skip tests if something is later added to the directory
-    // that could affect packages.
-    '.github/PULL_REQUEST_TEMPLATE.md',
-    '.github/dependabot.yml',
-    '.github/labeler.yml',
-    '.github/post_merge_labeler.yml',
-    '.github/workflows/pull_request_label.yml',
-  ].contains(path);
+        'AUTHORS',
+        'CODEOWNERS',
+        'CONTRIBUTING.md',
+        'LICENSE',
+        'README.md',
+        // This deliberate lists specific files rather than excluding the whole
+        // .github directory since it's better to have false negatives than to
+        // accidentally skip tests if something is later added to the directory
+        // that could affect packages.
+        '.github/PULL_REQUEST_TEMPLATE.md',
+        '.github/dependabot.yml',
+        '.github/labeler.yml',
+        '.github/post_merge_labeler.yml',
+        '.github/workflows/pull_request_label.yml',
+      ].contains(path) ||
+      // This directory only affects automated code reviews, so cannot affect
+      // any package tests.
+      path.startsWith('.gemini/');
 }
 
 /// Returns true for native (non-Dart) code files, for use in command-ignored-

script/tool/test/xcode_analyze_command_test.dart

@@ -599,6 +599,7 @@ packages/package_a/$file
         gitProcessRunner.mockProcessesForExecutable['git-diff'] =
             <FakeProcessInfo>[
           FakeProcessInfo(MockProcess(stdout: '''
+.gemini/config.yaml
 README.md
 CODEOWNERS
 packages/package_a/CHANGELOG.md