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Fix BaseModel method name conflicts in func_metadata #1123

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Merged
merged 1 commit into from
Jul 14, 2025

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@bhosmer-ant bhosmer-ant commented Jul 10, 2025

Fix BaseModel method name conflicts in func_metadata when function parameters have names that conflict with BaseModel methods.

Motivation and Context

When function parameters have names that conflict with BaseModel methods (e.g., 'model_dump', 'dict', 'json', 'validate'), Pydantic v2 raises warnings about shadowing parent attributes. This prevents users from creating MCP tools with parameter names that match BaseModel method names.

How Has This Been Tested?

  • new tests in test_func_metadata.py:
    • test_basemodel_reserved_names: Verifies schema generation with conflicting parameter names
    • test_basemodel_reserved_names_validation: Tests validation and function calling with reserved names
    • test_basemodel_reserved_names_with_json_preparsing: Tests JSON pre-parsing with reserved names

Breaking Changes

None. This change is fully backward compatible. The aliasing is transparent to users - they continue to use the original parameter names in their function signatures and when calling the functions.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

The solution uses Pydantic's alias system to map conflicting parameter names to prefixed internal fields (field_ prefix) while preserving the original names in the external API. The implementation:

  • Dynamically detects BaseModel method conflicts using hasattr and callable checks
  • Only applies aliases to parameters that actually conflict
  • Updates model_dump_one_level and pre_parse_json to handle aliases correctly
  • Uses by_alias=True in schema generation to ensure correct parameter names in the API

When function parameters have names that conflict with BaseModel methods
(e.g., 'model_dump', 'dict', 'json'), Pydantic v2 warns about shadowing
parent attributes. This fix uses aliases to map conflicting parameter
names to prefixed internal fields while preserving the original names
in the external API.

- Dynamically detect BaseModel method conflicts using hasattr/callable
- Apply aliases only to conflicting parameters
- Update model_dump_one_level and pre_parse_json to handle aliases
- Add by_alias=True to schema generation for correct parameter names
- Add tests for functions with reserved parameter names
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@ihrpr ihrpr left a comment

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LGTM

@ihrpr ihrpr merged commit 49991fd into main Jul 14, 2025
13 checks passed
@ihrpr ihrpr deleted the basil/fastmcp_reserved_param_names branch July 14, 2025 07:29
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2 participants