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fix: use get_origin() for typing.GenericAlias detection - #3746

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Jihaochang1 wants to merge 2 commits into
modelcontextprotocol:mainfrom
Jihaochang1:fix/typing-dict-annotation-issue-3745
Closed

Jihaochang1 wants to merge 2 commits into
modelcontextprotocol:mainfrom
Jihaochang1:fix/typing-dict-annotation-issue-3745

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Summary

Fixes #3745 by checking the origin of type expressions instead of their class type.

Problem

  • typing.Dict[str, Any] is a typing._GenericAlias, not a types.GenericAlias
  • The check isinstance(type_expr, GenericAlias) failed to match it
  • This caused different output schemas for semantically equivalent annotations
  • Ruff UP006 auto-rewrite could silently break client schema caching

Fix

Changed from:

elif isinstance(type_expr, GenericAlias):

to:

elif get_origin(type_expr) is not None:

This properly handles both typing.Dict and dict annotations consistently.

Impact

Closes #3745

Fixes modelcontextprotocol#3745 by checking the origin of type expressions instead of
their class type. typing.Dict[str, Any] is a typing._GenericAlias,
not a types.GenericAlias, so the previous check failed to match it.

This ensures consistent behavior between typing.Dict and dict annotations,
preventing silent schema changes when Ruff UP006 rewrites old-style
annotations to modern syntax.
@github-actions github-actions Bot added the missing-issue-link Auto-closed: PR needs a linked issue assigned to its author (see CONTRIBUTING.md) label Oct 23, 2026
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This PR has been closed automatically. This repo only keeps pull requests open when they come from a maintainer, or from a contributor a maintainer has assigned to the linked issue, and you aren't currently assigned to #3745.

If a maintainer assigns you to #3745, this PR reopens on its own and there's nothing more you need to do here. Assignment is a maintainer call based on capacity; comments that only ask to be assigned don't factor in. What does help is engaging on the issue itself by confirming the repro, explaining why it matters for your use case, or describing the approach you'd take.

You're welcome to keep pushing commits here (just avoid force-pushing, since GitHub can't reopen a rewritten branch), but that on its own won't get the PR reviewed or the issue assigned, and realistically most auto-closed PRs stay closed. There's no need to open a new PR either way.

CONTRIBUTING.md has the full reasoning, but in short:

  • We're a small team with very little capacity to review community PRs right now.
  • Many recent PRs are AI-generated with little human review, and reviewing one carefully still costs a maintainer as much time as it ever did. A well-described issue is usually more useful to us than the code.

Maintainers: reopen, remove missing-issue-link, or add bypass-issue-check to override.

@github-actions github-actions Bot closed this Oct 23, 2026
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typing.Dict[str, X] return annotation is wrapped in {"result": ...}, unlike dict[str, X]

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