feat: Add Co-authored-by attribution for AI commits

[ei-grad]

This PR implements the proposal from issue #3788, adding support for attributing AI-generated commits using the Co-authored-by: Git trailer.

Changes:

• Introduces the --attribute-co-authored-by command-line flag (and corresponding config option) to enable this feature. Defaults to False.
• Updates aider/repo.py's commit method:
  • When aider_edits=True and --attribute-co-authored-by=True, a Co-authored-by: aider (<model_name>) <[email protected]> trailer is appended to the commit message.
  • Implements the following precedence rules for AI edits (aider_edits=True):
    • If --attribute-co-authored-by=True:
      • The trailer is added.
      • Author/Committer names are not modified by default.
      • If --attribute-author=True or --attribute-committer=True is explicitly set, the respective name is modified in addition to the trailer.
    • If --attribute-co-authored-by=False:
      • The trailer is not added.
      • Author/Committer names are modified by default (or based on explicit --attribute-author=False/--attribute-committer=False).
  • For user edits (aider_edits=False), --attribute-co-authored-by is ignored, and attribution follows the existing rules for --attribute-committer.
• Adds the --attribute-co-authored-by argument definition and help text to aider/args.py.
• Adds/updates tests in tests/basic/test_repo.py to cover the new flag and its interactions with existing attribution flags (test_commit_with_co_authored_by, test_commit_co_authored_by_with_explicit_name_modification, etc.).

Resolves: #3788

Co-authored-by: aider (vertex_ai/gemini-2.5-pro-exp-03-25) [email protected]

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[ei-grad]

/aider --model vertex_ai/gemini-2.5-pro-exp-03-25 aider/args.py aider/repo.py tests/basic/test_repo.py  
> Aider v0.81.3.dev38+gc56e836d.d20250412  
> Model: vertex_ai/gemini-2.5-pro-exp-03-25 with diff-fenced edit format  
> Git repo: .git with 649 files  
> Repo-map: using 4096 tokens, auto refresh  
> Added aider/args.py to the chat.  
> Added aider/repo.py to the chat.  
> Added tests/basic/test_repo.py to the chat.  

#### /web https://github.com/Aider-AI/aider/issues/3788  
> Scraping https://github.com/Aider-AI/aider/issues/3788...  
> For the best web scraping, install Playwright:

/home/ei-grad/repos/github.com/aider-ai/aider/.venv/bin/python3 -m playwright install --with-deps chromium

See https://aider.chat/docs/install/optional.html#enable-playwright for more info.  
> Install playwright? (Y)es/(N)o [Yes]: n  
> Unable to initialize playwright.  
> ... added to chat.  

Ensure that we have properly implemented the proposal from issue 3788. Provide me detailed chain of thought.

Okay, I will review the code and ensure it aligns with the proposal from issue #3788 regarding Git commit attribution, specifically the --attribute-co-authored-by flag and its interactions.

Chain of Thought:

1. Understand the Goal: The primary goal of issue Proposal: Add attribute-co-authored-by Option to Fix Unexpected Author/Committer Modification #3788 was to introduce a Co-authored-by: trailer for AI-generated commits as an alternative attribution method, controlled by --attribute-co-authored-by. This new flag needs to interact correctly with the existing --attribute-author and --attribute-committer flags, establishing a clear precedence.
2. Recall/Review the Precedence Rules:
   • AI Edits (aider_edits=True):
     • If --attribute-co-authored-by=True:
       • Add Co-authored-by: trailer.
       • Default: Do not modify Author/Committer names (trailer takes precedence).
       • Explicit Override: If --attribute-author=True or --attribute-committer=True is explicitly set, modify the respective name in addition to the trailer.
     • If --attribute-co-authored-by=False (or default):
       • Do not add trailer.
       • Default: Modify Author/Committer names (implicit True).
       • Explicit Override: If --attribute-author=False or --attribute-committer=False is explicitly set, do not modify the respective name.
   • User Edits (aider_edits=False):
     • --attribute-co-authored-by is ignored (no trailer).
     • Author name is never modified.
     • Committer name is modified by default (implicit True).
     • Explicit Override: If --attribute-committer=False is explicitly set, do not modify Committer name.
3. Examine aider/args.py:
   • Verify the --attribute-co-authored-by argument exists.
   • Check its action (should be BooleanOptionalAction), default (should be False), and help text.
   • Finding: The argument exists with the correct action and default. The help text accurately describes the behavior and precedence: "...If True, this takes precedence over default --attribute-author and --attribute-committer behavior unless they are explicitly set to True." This matches the rules.
4. Examine aider/repo.py (__init__):
   • Verify the attribute_co_authored_by parameter is accepted and stored in self.
   • Finding: The parameter is present and assigned to self.attribute_co_authored_by. Correct.
5. Examine aider/repo.py (commit method):
   • Flag Retrieval: Check how attribute_co_authored_by, attribute_author, and attribute_committer are obtained (preferring coder.args if available).
   • Finding: The code correctly attempts to get these values from coder.args first, falling back to self attributes. Correct.
   • Trailer Logic: Check the condition for adding the commit_message_trailer.
   • Finding: The trailer is added if aider_edits and attribute_co_authored_by:. Correct.
   • Name Modification Logic: This is the core part. Analyze how use_attribute_author and use_attribute_committer are determined.
     • author_explicit = attribute_author is not None
     • committer_explicit = attribute_committer is not None
     • effective_author = True if attribute_author is None else attribute_author
     • effective_committer = True if attribute_committer is None else attribute_committer
     • use_attribute_author = ( aider_edits and effective_author and (not attribute_co_authored_by or author_explicit) )
     • use_attribute_committer = effective_committer and ( not (aider_edits and attribute_co_authored_by) or committer_explicit )
   • Finding: This logic correctly implements the precedence rules.
     • use_attribute_author: Is True only if it's an AI edit (aider_edits), the effective setting is True (effective_author), AND (co-authoring is off not attribute_co_authored_by OR the author flag was explicitly set author_explicit). This matches the rules.
     • use_attribute_committer: Is True only if the effective setting is True (effective_committer) AND (it's not an AI edit with co-authoring enabled not (aider_edits and attribute_co_authored_by) OR the committer flag was explicitly set committer_explicit). This also correctly covers both AI and user edits according to the rules.
   • Environment Setting: Check if set_git_env is called based on use_attribute_author and use_attribute_committer.
   • Finding: The with contextlib.ExitStack() as stack: block correctly uses these flags to conditionally set GIT_AUTHOR_NAME and GIT_COMMITTER_NAME. Correct.
   • Final Message: Check if the trailer is appended correctly.
   • Finding: full_commit_message = commit_message + commit_message_trailer. Correct.
6. Examine tests/basic/test_repo.py:
   • Check for tests covering the interactions between aider_edits, attribute_co_authored_by, attribute_author, and attribute_committer.
   • test_commit_with_co_authored_by: Tests AI edit + co-author=True + default author/committer. Asserts trailer is present and names are not modified. Correct.
   • test_commit_co_authored_by_with_explicit_name_modification: Tests AI edit + co-author=True + explicit author/committer=True. Asserts trailer is present and names are modified. Correct.
   • test_commit_ai_edits_no_coauthor_explicit_false:
     • Case 1: Tests AI edit + co-author=False + explicit author=False + default committer. Asserts no trailer, author not modified, committer is modified. Correct.
     • Case 2: Tests AI edit + co-author=False + default author + explicit committer=False. Asserts no trailer, author is modified, committer not modified. Correct.
   • test_commit_with_custom_committer_name: Covers several base cases including user edits (aider_edits=False) with default and explicit committer settings, confirming author is never modified for user edits and committer behaves as expected. Correct.
   • Finding: The existing tests cover the crucial scenarios defined by the precedence rules.

Conclusion:

The implementation across aider/args.py, aider/repo.py, and the relevant tests in tests/basic/test_repo.py accurately reflects the proposal from issue #3788. The logic correctly handles the addition of the Co-authored-by: trailer and respects the defined precedence rules between --attribute-co-authored-by, --attribute-author, and --attribute-committer for both AI-generated and user-driven commits.

No code changes are required based on this review. The implementation appears correct.