Python: apply input_variables defaults when rendering prompt templates - #14459
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…riptions build_model_schema() preferred FieldInfo.metadata over FieldInfo.description when deriving field descriptions. In pydantic v2, FieldInfo.metadata is a list of constraint objects (annotated_types.Ge, Gt, ...), so for any field declared with a constraint (e.g. Field(description=..., ge=0)) the real description was replaced by the constraint object. The resulting schema carried a non-string 'description' and json.dumps() of the function-calling tool payload failed with 'TypeError: Object of type Ge is not JSON serializable'. Only treat str and dict-with-'description' entries in metadata as descriptions (these come from Annotated metadata), and fall back to FieldInfo.description otherwise.
The per-variable default was validated and exported as metadata but never consulted at render time, so a missing argument rendered as an empty string instead of the declared default. Seed missing arguments with their defaults before rendering; explicit arguments always win. Signed-off-by: Manohar Paturi <186662190+ManoharPaturi@users.noreply.github.com>
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Fixes #14458.
KernelPromptTemplate.rendernow seeds any missing argument with the declaredinput_variablesdefault before rendering (case-insensitive name check, explicit arguments always win, falsy defaults untouched so the existing empty-string behavior for unset defaults stays).2 regression tests: default applies when the argument is missing, and an explicit argument overrides the default. The default-applies test fails on main. Full prompt_template suite green (13 passed), ruff clean.