next: builtin function type hints block client type checking

[DropD]

Problem

When testing the effect of #2484 on type checking in icon4py, it appears that it enables mypy to check the arguments and return types of builtins like where. Since mypy could not trace them back to their actual definition before, it just quietly ignored them.

This leads to many ( > 100) false positives like below.

model/atmosphere/advection/src/icon4py/model/atmosphere/advection/stencils/compute_ppm4gpu_fractional_flux.py:77:19: error: Argument 1 to "__call__" of "WhereBuiltinFunction" has incompatible type "bool"; expected "Field[Any, Any]"  [arg-type]
model/atmosphere/advection/src/icon4py/model/atmosphere/advection/stencils/compute_ppm4gpu_fractional_flux.py:77:30: error: Argument 2 to "__call__" of "WhereBuiltinFunction" has incompatible type "float"; expected "Field[Any, Any] | tuple[Any, ...]"  [arg-type]
model/atmosphere/advection/src/icon4py/model/atmosphere/advection/stencils/compute_ppm4gpu_fractional_flux.py:77:35: error: Argument 3 to "__call__" of "WhereBuiltinFunction" has incompatible type "float"; expected "Field[Any, Any] | tuple[Any, ...]"  [arg-type]
model/atmosphere/advection/src/icon4py/model/atmosphere/advection/stencils/compute_ppm4gpu_fractional_flux.py:96:85: error: Argument 3 to "__call__" of "WhereBuiltinFunction" has incompatible type "float"; expected "Field[Any, Any] | tuple[Any, ...]"  [arg-type]
model/atmosphere/advection/src/icon4py/model/atmosphere/advection/stencils/compute_ppm4gpu_fractional_flux.py:99:12: error: Incompatible return value type (got "Field[Any, Any] | tuple[Any, ...]", expected "Field[Dims[Any, Any], floating[_64Bit]]")  [return-value]

Solution

Options:

• remove type hints from those builtins in order for mypy to ignore call sites again
• improve type hints (unknown effort but likely non-trivial)
• add a hook to ignore them to the mypy-plugin added in fix[next]: Reduce type ignores in client code #2484