fix: preserve parameter types in tool() and resource() decorators with ParamSpec#2964
Open
Robin1987China wants to merge 1 commit into
Open
Conversation
…h ParamSpec (modelcontextprotocol#1822) Replace the type-erasing _CallableT with ParamSpec for the tool() and resource() decorators, which are pure pass-through and benefit fully from parameter type preservation. This allows type checkers to validate decorated function signatures without # type: ignore. completion() and prompt() keep explicit Callable[..., Any] because they feed into downstream type-constrained APIs where ParamSpec would create false type errors. AI assistance: Fix implemented with AI assistance (opencode). I've reviewed every changed line and validated with pyright + pytest.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Motivation
Fixes #1822
MCPServer decorators (
@server.tool(),@server.resource()) use_CallableT = TypeVar("_CallableT", bound=Callable[..., Any])which erases parameter type information. This forces users to add# type: ignoreand prevents type checkers from validating decorated function signatures.Changes
_CallableTwithParamSpecfortool()andresource()decorators (pure pass-through, full benefit)Callable[..., Any]forcompletion()andprompt()— these feed into downstream type-constrained APIs where ParamSpec creates false type errorsVerification
pyright: 0 errors, 0 warningspytest: 2601 passed (1 pre-existing flaky test unrelated)AI assistance
Fix implemented with AI assistance (opencode). I have reviewed every changed line and validated with pyright + pytest.