fix: handle callable class instances in find_context_parameter() #2042
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When registering a callable class instance as an MCP tool via FastMCP.add_tool(), the ctx: Context parameter was incorrectly exposed as an externally visible tool parameter instead of being injected by the framework. Root cause: typing.get_type_hints() was called on the class instance rather than its __call__ method, so Context type hints were not resolved. Fix: detect non-function/non-method callables and target their __call__ method, mirroring the existing pattern in _is_async_callable(). Fixes modelcontextprotocol#1974
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Summary
Fix
find_context_parameter()to correctly detectContextparameters in callable class instances registered viaFastMCP.add_tool().Motivation and Context
When registering a callable class instance as an MCP tool, the
ctx: Contextparameter is incorrectly exposed as an externally visible tool parameter in the JSON schema instead of being injected by the framework.Root cause:
typing.get_type_hints(fn)is called on the class instance rather than its__call__method, so the Context type hint is not resolved.Fix: Detect non-function/non-method callables and target their
__call__method for type hint resolution. This mirrors the existing pattern in_is_async_callable().Resolves #1974
What Has Been Changed?
src/mcp/server/mcpserver/utilities/context_injection.py: Added callable class instance handling beforeget_type_hints()calltests/server/mcpserver/test_tool_manager.py: Added 3 tests:test_context_parameter_detection_callable_class— sync callable classtest_context_parameter_detection_async_callable_class— async callable classtest_context_injection_callable_class— full injection + schema exclusionHow Has This Been Tested?
test_tool_manager.pypass (including 3 new tests)context_kwargis correctly set to"ctx"ctxis excluded from tool parameters JSON schemaBreaking Changes
No breaking changes.
Types of changes
Checklist