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Don't suggest Foo[...] when Foo(arg=...) is used in annotation #21238

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Merged
JukkaL merged 1 commit into from
Apr 16, 2026
Merged

Don't suggest Foo[...] when Foo(arg=...) is used in annotation #21238

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fix: don't suggest Foo[...] when Foo(arg=...) is used 
When a function call with keyword arguments appears in a type
annotation (e.g. `Foo(sort=True)`), mypy was suggesting to use
`Foo[...]` instead. This suggestion is misleading because
`Foo[sort=True]` is a syntax error -- the user likely intended a
function call, not a type parameterization.

Now, when keyword arguments are present, mypy shows "Cannot use a
function call in a type annotation" instead. The `Foo[...]` suggestion
is preserved for calls with only positional arguments (e.g. `Foo(int)`)
where the user likely meant `Foo[int]`.

Fixes #16506
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@yosofbadr
yosofbadr committed Apr 15, 2026
commit 53cfee2c0dac1c7eeb84be29d2c9fb1e8b178996
5 changes: 4 additions & 1 deletion mypy/fastparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1958,7 +1958,10 @@ def visit_Call(self, e: Call) -> Type:
if not isinstance(self.parent(), ast3.List):
note = None
if constructor:
note = "Suggestion: use {0}[...] instead of {0}(...)".format(constructor)
if e.keywords:
note = "Cannot use a function call in a type annotation"
else:
note = "Suggestion: use {0}[...] instead of {0}(...)".format(constructor)
return self.invalid_type(e, note=note)
if not constructor:
self.fail(message_registry.ARG_CONSTRUCTOR_NAME_EXPECTED, e.lineno, e.col_offset)
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11 changes: 11 additions & 0 deletions test-data/unit/check-fastparse.test
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Original file line number Diff line number Diff line change
Expand Up @@ -207,6 +207,17 @@ def f(a: Foo(int)) -> int:
main:7: error: Invalid type comment or annotation
main:7: note: Suggestion: use Foo[...] instead of Foo(...)

[case testFasterParseCallWithKeywordArgs_no_native_parse]

def Foo(sort: bool) -> type:
return int

def f(a: Foo(sort=True)) -> int:
pass
[out]
main:5: error: Invalid type comment or annotation
main:5: note: Cannot use a function call in a type annotation

[case testFastParseMatMul]

from typing import Any
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