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Fix False positive "Function declared to return Never but is missing an explicit return" #4207

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Fix False positive "Function declared to return Never but is missing an explicit return" #4207

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75553a8
Add a failing test
mwestbroek Jul 19, 2026
b93a9f9
Handle specific case where annotation is Never and there are no expli…
mwestbroek Jul 19, 2026
ac902c2
Run test.py
mwestbroek Jul 19, 2026
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11 changes: 0 additions & 11 deletions conformance/third_party/conformance.exp
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Original file line number Diff line number Diff line change
Expand Up @@ -10830,17 +10830,6 @@
],
"specialtypes_any.py": [],
"specialtypes_never.py": [
{
"code": -2,
"column": 22,
"concise_description": "Function declared to return `NoReturn` but is missing an explicit `return`",
"description": "Function declared to return `NoReturn` but is missing an explicit `return`",
"line": 19,
"name": "bad-return",
"severity": "error",
"stop_column": 30,
"stop_line": 19
},
{
"code": -2,
"column": 21,
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4 changes: 3 additions & 1 deletion conformance/third_party/conformance.result
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Original file line number Diff line number Diff line change
Expand Up @@ -137,7 +137,9 @@
"qualifiers_final_annotation.py": [],
"qualifiers_final_decorator.py": [],
"specialtypes_any.py": [],
"specialtypes_never.py": [],
"specialtypes_never.py": [
"Line 19: Expected 1 errors"
],
"specialtypes_none.py": [],
"specialtypes_promotions.py": [],
"specialtypes_type.py": [],
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12 changes: 6 additions & 6 deletions conformance/third_party/results.json
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Original file line number Diff line number Diff line change
@@ -1,9 +1,9 @@
{
"total": 140,
"pass": 134,
"fail": 6,
"pass_rate": 0.96,
"differences": 13,
"pass": 133,
"fail": 7,
"pass_rate": 0.95,
"differences": 14,
"passing": [
"aliases_explicit.py",
"aliases_implicit.py",
Expand Down Expand Up @@ -117,7 +117,6 @@
"qualifiers_final_annotation.py",
"qualifiers_final_decorator.py",
"specialtypes_any.py",
"specialtypes_never.py",
"specialtypes_none.py",
"specialtypes_promotions.py",
"specialtypes_type.py",
Expand Down Expand Up @@ -146,7 +145,8 @@
"constructors_callable.py": 2,
"dataclasses_descriptors.py": 2,
"exceptions_context_managers.py": 2,
"generics_scoping.py": 4
"generics_scoping.py": 4,
"specialtypes_never.py": 1
},
"comment": "@generated"
}
4 changes: 4 additions & 0 deletions pyrefly/lib/alt/solve.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5435,6 +5435,10 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
);
}
} else {
// If the annotation is `NoReturn` or `Never` and there is no explicit return, there is no need to check further.
if annotation.is_never() && !has_explicit_returns {
return;
}
self.check_type(implicit_return.ty(), annotation, range, errors, &|| {
TypeCheckContext::of_kind(TypeCheckKind::ImplicitFunctionReturn(
has_explicit_returns,
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10 changes: 10 additions & 0 deletions pyrefly/lib/test/returns.rs
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Expand Up @@ -388,6 +388,16 @@ def g():
"#,
);

testcase!(
test_no_explicit_return_if_return_type_is_never,
r#"
from typing import Never

def f() -> Never:
print("hello")
"#,
);

testcase!(
test_return_no_error,
r#"
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