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[red-knot] respect TYPE_CHECKING even if not imported from typing (#16468)

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## Summary

This PR closes #15722.

The change is that if the variable `TYPE_CHECKING` is defined/imported,
the type of the variable is interpreted as `Literal[True]` regardless of
what the value is.
This is compatible with the behavior of other type checkers (e.g. mypy,
pyright).

## Test Plan

I ran the tests with `cargo test -p red_knot_python_semantic` and
confirmed that all tests passed.

---------

Co-authored-by: Carl Meyer <carl@astral.sh>
This commit is contained in:
Shunsuke Shibayama
2025-03-05 00:58:29 +09:00
committed by GitHub
parent c9ab925275
commit 1977dda079
3 changed files with 35 additions and 8 deletions
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8
crates/red_knot_python_semantic/src/symbol.rs
View File

@@ -458,8 +458,12 @@ fn symbol_by_id<'db>(
// a diagnostic if we see it being modified externally. In type inference, we
// can assign a "narrow" type to it even if it is not *declared*. This means, we
// do not have to call [`widen_type_for_undeclared_public_symbol`].
let is_considered_non_modifiable =
symbol_table(db, scope).symbol(symbol_id).name() == "__slots__";
// `TYPE_CHECKING` is a special variable that should only be assigned `False`
// at runtime, but is always considered `True` in type checking.
// See mdtest/known_constants.md#user-defined-type_checking for details.
let is_considered_non_modifiable = symbol_table(db, scope).symbol(symbol_id).name()
== "__slots__"
|| symbol_table(db, scope).symbol(symbol_id).name() == "TYPE_CHECKING";
widen_type_for_undeclared_public_symbol(db, inferred, is_considered_non_modifiable)
.into()

7
crates/red_knot_python_semantic/src/types/infer.rs
View File

@@ -2149,7 +2149,12 @@ impl<'db> TypeInferenceBuilder<'db> {
unpacked.expression_type(name_ast_id)
}
TargetKind::Name => {
if self.in_stub() && value.is_ellipsis_literal_expr() {
// `TYPE_CHECKING` is a special variable that should only be assigned `False`
// at runtime, but is always considered `True` in type checking.
// See mdtest/known_constants.md#user-defined-type_checking for details.
if &name.id == "TYPE_CHECKING" {
Type::BooleanLiteral(true)
} else if self.in_stub() && value.is_ellipsis_literal_expr() {
Type::unknown()
} else {
value_ty