[ty] improve bad specialization results & error messages (#21840)

## Summary

This PR includes the following changes:

* When attempting to specialize a non-generic type (or a type that is
already specialized), the result is `Unknown`. Also, the error message
is improved.
* When an implicit type alias is incorrectly specialized, the result is
`Unknown`. Also, the error message is improved.
* When only some of the type alias bounds and constraints are not
satisfied, not all substitutions are `Unknown`.
* Double specialization is prohibited. e.g. `G[int][int]`

Furthermore, after applying this PR, the fuzzing tests for seeds 1052
and 4419, which panic in main, now pass.
This is because the false recursions on type variables have been
removed.

```python
# name_2[0] => Unknown
class name_1[name_2: name_2[0]]:
    def name_4(name_3: name_2, /):
        if name_3:
            pass

#  (name_5 if unique_name_0 else name_1)[0] => Unknown
def name_4[name_5: (name_5 if unique_name_0 else name_1)[0], **name_1](): ...
```

## Test Plan

New corpus test
mdtest files updated
This commit is contained in:
Shunsuke Shibayama 2025-12-12 12:21:34 +09:00 committed by GitHub
parent ddb7645e9d
commit 5e42926eee
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
10 changed files with 377 additions and 77 deletions

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@ -0,0 +1 @@
def _[T: (T if cond else U)[0], U](): pass

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@ -0,0 +1,4 @@
class _[T: (0, T[0])]:
def _(x: T):
if x:
pass

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@ -283,7 +283,7 @@ reveal_type(OnlyParamSpec[...]().attr) # revealed: (...) -> None
def func(c: Callable[P2, None]):
reveal_type(OnlyParamSpec[P2]().attr) # revealed: (**P2@func) -> None
# TODO: error: paramspec is unbound
# error: [invalid-type-arguments] "ParamSpec `P2` is unbound"
reveal_type(OnlyParamSpec[P2]().attr) # revealed: (...) -> None
# error: [invalid-type-arguments] "No type argument provided for required type variable `P1` of class `OnlyParamSpec`"
@ -327,15 +327,14 @@ reveal_type(TypeVarAndParamSpec[int, [int, str]]().attr) # revealed: (int, str,
reveal_type(TypeVarAndParamSpec[int, [str]]().attr) # revealed: (str, /) -> int
reveal_type(TypeVarAndParamSpec[int, ...]().attr) # revealed: (...) -> int
# TODO: We could still specialize for `T1` as the type is valid which would reveal `(...) -> int`
# TODO: error: paramspec is unbound
reveal_type(TypeVarAndParamSpec[int, P2]().attr) # revealed: (...) -> Unknown
# error: [invalid-type-arguments] "ParamSpec `P2` is unbound"
reveal_type(TypeVarAndParamSpec[int, P2]().attr) # revealed: (...) -> int
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be either a list of types, `ParamSpec`, `Concatenate`, or `...`"
reveal_type(TypeVarAndParamSpec[int, int]().attr) # revealed: (...) -> int
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be"
reveal_type(TypeVarAndParamSpec[int, int]().attr) # revealed: (...) -> Unknown
reveal_type(TypeVarAndParamSpec[int, ()]().attr) # revealed: (...) -> int
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be"
reveal_type(TypeVarAndParamSpec[int, ()]().attr) # revealed: (...) -> Unknown
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be"
reveal_type(TypeVarAndParamSpec[int, (int, str)]().attr) # revealed: (...) -> Unknown
reveal_type(TypeVarAndParamSpec[int, (int, str)]().attr) # revealed: (...) -> int
```
Nor can they be omitted when there are more than one `ParamSpec`s.

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@ -68,13 +68,91 @@ reveal_type(C[int, int]) # revealed: <type alias 'C[Unknown]'>
And non-generic types cannot be specialized:
```py
from typing import TypeVar, Protocol, TypedDict
type B = ...
# error: [non-subscriptable] "Cannot subscript non-generic type alias"
reveal_type(B[int]) # revealed: Unknown
# error: [non-subscriptable] "Cannot subscript non-generic type alias"
def _(b: B[int]): ...
def _(b: B[int]):
reveal_type(b) # revealed: Unknown
type IntOrStr = int | str
# error: [non-subscriptable] "Cannot subscript non-generic type alias"
def _(c: IntOrStr[int]):
reveal_type(c) # revealed: Unknown
type ListOfInts = list[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `list[int]` is already specialized"
def _(l: ListOfInts[int]):
reveal_type(l) # revealed: Unknown
type List[T] = list[T]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: Double specialization is not allowed"
def _(l: List[int][int]):
reveal_type(l) # revealed: Unknown
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'list[T@DoubleSpecialization]'>` is already specialized"
type DoubleSpecialization[T] = list[T][T]
def _(d: DoubleSpecialization[int]):
reveal_type(d) # revealed: Unknown
type Tuple = tuple[int, str]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `tuple[int, str]` is already specialized"
def _(doubly_specialized: Tuple[int]):
reveal_type(doubly_specialized) # revealed: Unknown
T = TypeVar("T")
class LegacyProto(Protocol[T]):
pass
type LegacyProtoInt = LegacyProto[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `LegacyProto[int]` is already specialized"
def _(x: LegacyProtoInt[int]):
reveal_type(x) # revealed: Unknown
class Proto[T](Protocol):
pass
type ProtoInt = Proto[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `Proto[int]` is already specialized"
def _(x: ProtoInt[int]):
reveal_type(x) # revealed: Unknown
# TODO: TypedDict is just a function object at runtime, we should emit an error
class LegacyDict(TypedDict[T]):
x: T
type LegacyDictInt = LegacyDict[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias"
def _(x: LegacyDictInt[int]):
reveal_type(x) # revealed: Unknown
class Dict[T](TypedDict):
x: T
type DictInt = Dict[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `Dict` is already specialized"
def _(x: DictInt[int]):
reveal_type(x) # revealed: Unknown
type Union = list[str] | list[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `list[str] | list[int]` is already specialized"
def _(x: Union[int]):
reveal_type(x) # revealed: Unknown
```
If the type variable has an upper bound, the specialized type must satisfy that bound:
@ -98,6 +176,15 @@ reveal_type(BoundedByUnion[int]) # revealed: <type alias 'BoundedByUnion[int]'>
reveal_type(BoundedByUnion[IntSubclass]) # revealed: <type alias 'BoundedByUnion[IntSubclass]'>
reveal_type(BoundedByUnion[str]) # revealed: <type alias 'BoundedByUnion[str]'>
reveal_type(BoundedByUnion[int | str]) # revealed: <type alias 'BoundedByUnion[int | str]'>
type TupleOfIntAndStr[T: int, U: str] = tuple[T, U]
def _(x: TupleOfIntAndStr[int, str]):
reveal_type(x) # revealed: tuple[int, str]
# error: [invalid-type-arguments] "Type `int` is not assignable to upper bound `str` of type variable `U@TupleOfIntAndStr`"
def _(x: TupleOfIntAndStr[int, int]):
reveal_type(x) # revealed: tuple[int, Unknown]
```
If the type variable is constrained, the specialized type must satisfy those constraints:
@ -119,6 +206,15 @@ reveal_type(Constrained[int | str]) # revealed: <type alias 'Constrained[int |
# error: [invalid-type-arguments] "Type `object` does not satisfy constraints `int`, `str` of type variable `T@Constrained`"
reveal_type(Constrained[object]) # revealed: <type alias 'Constrained[Unknown]'>
type TupleOfIntOrStr[T: (int, str), U: (int, str)] = tuple[T, U]
def _(x: TupleOfIntOrStr[int, str]):
reveal_type(x) # revealed: tuple[int, str]
# error: [invalid-type-arguments] "Type `object` does not satisfy constraints `int`, `str` of type variable `U@TupleOfIntOrStr`"
def _(x: TupleOfIntOrStr[int, object]):
reveal_type(x) # revealed: tuple[int, Unknown]
```
If the type variable has a default, it can be omitted:

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@ -237,7 +237,7 @@ def func[**P2](c: Callable[P2, None]):
P2 = ParamSpec("P2")
# TODO: error: paramspec is unbound
# error: [invalid-type-arguments] "ParamSpec `P2` is unbound"
reveal_type(OnlyParamSpec[P2]().attr) # revealed: (...) -> None
# error: [invalid-type-arguments] "No type argument provided for required type variable `P1` of class `OnlyParamSpec`"
@ -281,14 +281,14 @@ reveal_type(TypeVarAndParamSpec[int, [int, str]]().attr) # revealed: (int, str,
reveal_type(TypeVarAndParamSpec[int, [str]]().attr) # revealed: (str, /) -> int
reveal_type(TypeVarAndParamSpec[int, ...]().attr) # revealed: (...) -> int
# TODO: error: paramspec is unbound
reveal_type(TypeVarAndParamSpec[int, P2]().attr) # revealed: (...) -> Unknown
# error: [invalid-type-arguments] "ParamSpec `P2` is unbound"
reveal_type(TypeVarAndParamSpec[int, P2]().attr) # revealed: (...) -> int
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be"
reveal_type(TypeVarAndParamSpec[int, int]().attr) # revealed: (...) -> Unknown
reveal_type(TypeVarAndParamSpec[int, int]().attr) # revealed: (...) -> int
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be"
reveal_type(TypeVarAndParamSpec[int, ()]().attr) # revealed: (...) -> Unknown
reveal_type(TypeVarAndParamSpec[int, ()]().attr) # revealed: (...) -> int
# error: [invalid-type-arguments] "Type argument for `ParamSpec` must be"
reveal_type(TypeVarAndParamSpec[int, (int, str)]().attr) # revealed: (...) -> Unknown
reveal_type(TypeVarAndParamSpec[int, (int, str)]().attr) # revealed: (...) -> int
```
Nor can they be omitted when there are more than one `ParamSpec`.

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@ -653,13 +653,92 @@ def g(obj: Y[bool, range]):
A generic alias that is already fully specialized cannot be specialized again:
```toml
[environment]
python-version = "3.12"
```
```py
from typing import Protocol, TypeVar, TypedDict
ListOfInts = list[int]
# error: [invalid-type-arguments] "Too many type arguments: expected 0, got 1"
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'list[int]'>` is already specialized"
def _(doubly_specialized: ListOfInts[int]):
# TODO: This should ideally be `list[Unknown]` or `Unknown`
reveal_type(doubly_specialized) # revealed: list[int]
reveal_type(doubly_specialized) # revealed: Unknown
type ListOfInts2 = list[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: `list[int]` is already specialized"
DoublySpecialized = ListOfInts2[int]
def _(doubly_specialized: DoublySpecialized):
reveal_type(doubly_specialized) # revealed: Unknown
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'list[int]'>` is already specialized"
List = list[int][int]
def _(doubly_specialized: List):
reveal_type(doubly_specialized) # revealed: Unknown
Tuple = tuple[int, str]
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'tuple[int, str]'>` is already specialized"
def _(doubly_specialized: Tuple[int]):
reveal_type(doubly_specialized) # revealed: Unknown
T = TypeVar("T")
class LegacyProto(Protocol[T]):
pass
LegacyProtoInt = LegacyProto[int]
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'LegacyProto[int]'>` is already specialized"
def _(doubly_specialized: LegacyProtoInt[int]):
reveal_type(doubly_specialized) # revealed: Unknown
class Proto[T](Protocol):
pass
ProtoInt = Proto[int]
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'Proto[int]'>` is already specialized"
def _(doubly_specialized: ProtoInt[int]):
reveal_type(doubly_specialized) # revealed: Unknown
# TODO: TypedDict is just a function object at runtime, we should emit an error
class LegacyDict(TypedDict[T]):
x: T
# TODO: should be a `non-subscriptable` error
LegacyDictInt = LegacyDict[int]
# TODO: should be a `non-subscriptable` error
def _(doubly_specialized: LegacyDictInt[int]):
# TODO: should be `Unknown`
reveal_type(doubly_specialized) # revealed: @Todo(Inference of subscript on special form)
class Dict[T](TypedDict):
x: T
DictInt = Dict[int]
# error: [non-subscriptable] "Cannot subscript non-generic type: `<class 'Dict[int]'>` is already specialized"
def _(doubly_specialized: DictInt[int]):
reveal_type(doubly_specialized) # revealed: Unknown
Union = list[str] | list[int]
# error: [non-subscriptable] "Cannot subscript non-generic type: `<types.UnionType special form 'list[str] | list[int]'>` is already specialized"
def _(doubly_specialized: Union[int]):
reveal_type(doubly_specialized) # revealed: Unknown
type MyListAlias[T] = list[T]
MyListOfInts = MyListAlias[int]
# error: [non-subscriptable] "Cannot subscript non-generic type alias: Double specialization is not allowed"
def _(doubly_specialized: MyListOfInts[int]):
reveal_type(doubly_specialized) # revealed: Unknown
```
Specializing a generic implicit type alias with an incorrect number of type arguments also results
@ -695,23 +774,21 @@ def this_does_not_work() -> TypeOf[IntOrStr]:
raise NotImplementedError()
def _(
# TODO: Better error message (of kind `invalid-type-form`)?
# error: [invalid-type-arguments] "Too many type arguments: expected 0, got 1"
# error: [non-subscriptable] "Cannot subscript non-generic type"
specialized: this_does_not_work()[int],
):
reveal_type(specialized) # revealed: int | str
reveal_type(specialized) # revealed: Unknown
```
Similarly, if you try to specialize a union type without a binding context, we emit an error:
```py
# TODO: Better error message (of kind `invalid-type-form`)?
# error: [invalid-type-arguments] "Too many type arguments: expected 0, got 1"
# error: [non-subscriptable] "Cannot subscript non-generic type"
x: (list[T] | set[T])[int]
def _():
# TODO: `list[Unknown] | set[Unknown]` might be better
reveal_type(x) # revealed: list[typing.TypeVar] | set[typing.TypeVar]
reveal_type(x) # revealed: Unknown
```
### Multiple definitions

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@ -989,6 +989,41 @@ impl<'db> Type<'db> {
matches!(self, Type::GenericAlias(_))
}
/// Returns whether the definition of this type is generic
/// (this is different from whether this type *is* a generic type; a type that is already fully specialized is not a generic type).
pub(crate) fn is_definition_generic(self, db: &'db dyn Db) -> bool {
match self {
Type::Union(union) => union
.elements(db)
.iter()
.any(|ty| ty.is_definition_generic(db)),
Type::Intersection(intersection) => {
intersection
.positive(db)
.iter()
.any(|ty| ty.is_definition_generic(db))
|| intersection
.negative(db)
.iter()
.any(|ty| ty.is_definition_generic(db))
}
Type::NominalInstance(instance_type) => instance_type.is_definition_generic(),
Type::ProtocolInstance(protocol) => {
matches!(protocol.inner, Protocol::FromClass(class) if class.is_generic())
}
Type::TypedDict(typed_dict) => typed_dict
.defining_class()
.is_some_and(ClassType::is_generic),
Type::Dynamic(dynamic) => {
matches!(dynamic, DynamicType::UnknownGeneric(_))
}
// Due to inheritance rules, enums cannot be generic.
Type::EnumLiteral(_) => false,
// Once generic NewType is officially specified, handle it.
_ => false,
}
}
const fn is_dynamic(&self) -> bool {
matches!(self, Type::Dynamic(_))
}

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@ -3541,10 +3541,17 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
return Ok(param_type);
}
Type::KnownInstance(known_instance)
Type::KnownInstance(known_instance @ KnownInstanceType::TypeVar(typevar))
if known_instance.class(self.db()) == KnownClass::ParamSpec =>
{
// TODO: Emit diagnostic: "ParamSpec "P" is unbound"
if let Some(diagnostic_builder) =
self.context.report_lint(&INVALID_TYPE_ARGUMENTS, expr)
{
diagnostic_builder.into_diagnostic(format_args!(
"ParamSpec `{}` is unbound",
typevar.name(self.db())
));
}
return Err(());
}
@ -11636,6 +11643,17 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
generic_context: GenericContext<'db>,
specialize: impl FnOnce(&[Option<Type<'db>>]) -> Type<'db>,
) -> Type<'db> {
enum ExplicitSpecializationError {
InvalidParamSpec,
UnsatisfiedBound,
UnsatisfiedConstraints,
/// These two errors override the errors above, causing all specializations to be `Unknown`.
MissingTypeVars,
TooManyArguments,
/// This error overrides the errors above, causing the type itself to be `Unknown`.
NonGeneric,
}
fn add_typevar_definition<'db>(
db: &'db dyn Db,
diagnostic: &mut Diagnostic,
@ -11688,7 +11706,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
}
};
let mut has_error = false;
let mut error: Option<ExplicitSpecializationError> = None;
for (index, item) in typevars.zip_longest(type_arguments.iter()).enumerate() {
match item {
@ -11704,8 +11722,8 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
) {
Ok(paramspec_value) => paramspec_value,
Err(()) => {
has_error = true;
Type::unknown()
error = Some(ExplicitSpecializationError::InvalidParamSpec);
Type::paramspec_value_callable(db, Parameters::unknown())
}
}
} else {
@ -11737,8 +11755,10 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
));
add_typevar_definition(db, &mut diagnostic, typevar);
}
has_error = true;
continue;
error = Some(ExplicitSpecializationError::UnsatisfiedBound);
specialization_types.push(Some(Type::unknown()));
} else {
specialization_types.push(Some(provided_type));
}
}
Some(TypeVarBoundOrConstraints::Constraints(constraints)) => {
@ -11771,14 +11791,16 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
));
add_typevar_definition(db, &mut diagnostic, typevar);
}
has_error = true;
continue;
error = Some(ExplicitSpecializationError::UnsatisfiedConstraints);
specialization_types.push(Some(Type::unknown()));
} else {
specialization_types.push(Some(provided_type));
}
}
None => {}
None => {
specialization_types.push(Some(provided_type));
}
}
specialization_types.push(Some(provided_type));
}
EitherOrBoth::Left(typevar) => {
if typevar.default_type(db).is_none() {
@ -11813,33 +11835,57 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
}
));
}
has_error = true;
error = Some(ExplicitSpecializationError::MissingTypeVars);
}
if let Some(first_excess_type_argument_index) = first_excess_type_argument_index {
let node = get_node(first_excess_type_argument_index);
if let Some(builder) = self.context.report_lint(&INVALID_TYPE_ARGUMENTS, node) {
let description = CallableDescription::new(db, value_ty);
builder.into_diagnostic(format_args!(
"Too many type arguments{}: expected {}, got {}",
if let Some(CallableDescription { kind, name }) = description {
format!(" to {kind} `{name}`")
} else {
String::new()
},
if typevar_with_defaults == 0 {
format!("{typevars_len}")
} else {
format!(
"between {} and {}",
typevars_len - typevar_with_defaults,
typevars_len
)
},
type_arguments.len(),
));
if typevars_len == 0 {
// Type parameter list cannot be empty, so if we reach here, `value_ty` is not a generic type.
if let Some(builder) = self
.context
.report_lint(&NON_SUBSCRIPTABLE, &*subscript.value)
{
let mut diagnostic =
builder.into_diagnostic("Cannot subscript non-generic type");
if match value_ty {
Type::GenericAlias(_) => true,
Type::KnownInstance(KnownInstanceType::UnionType(union)) => union
.value_expression_types(db)
.is_ok_and(|mut tys| tys.any(|ty| ty.is_generic_alias())),
_ => false,
} {
diagnostic.set_primary_message(format_args!(
"`{}` is already specialized",
value_ty.display(db)
));
}
}
error = Some(ExplicitSpecializationError::NonGeneric);
} else {
let node = get_node(first_excess_type_argument_index);
if let Some(builder) = self.context.report_lint(&INVALID_TYPE_ARGUMENTS, node) {
let description = CallableDescription::new(db, value_ty);
builder.into_diagnostic(format_args!(
"Too many type arguments{}: expected {}, got {}",
if let Some(CallableDescription { kind, name }) = description {
format!(" to {kind} `{name}`")
} else {
String::new()
},
if typevar_with_defaults == 0 {
format!("{typevars_len}")
} else {
format!(
"between {} and {}",
typevars_len - typevar_with_defaults,
typevars_len
)
},
type_arguments.len(),
));
}
error = Some(ExplicitSpecializationError::TooManyArguments);
}
has_error = true;
}
if store_inferred_type_arguments {
@ -11849,21 +11895,31 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
);
}
if has_error {
let unknowns = generic_context
.variables(self.db())
.map(|typevar| {
Some(if typevar.is_paramspec(db) {
Type::paramspec_value_callable(db, Parameters::unknown())
} else {
Type::unknown()
match error {
Some(ExplicitSpecializationError::NonGeneric) => Type::unknown(),
Some(
ExplicitSpecializationError::MissingTypeVars
| ExplicitSpecializationError::TooManyArguments,
) => {
let unknowns = generic_context
.variables(self.db())
.map(|typevar| {
Some(if typevar.is_paramspec(db) {
Type::paramspec_value_callable(db, Parameters::unknown())
} else {
Type::unknown()
})
})
})
.collect::<Vec<_>>();
return specialize(&unknowns);
.collect::<Vec<_>>();
specialize(&unknowns)
}
Some(
ExplicitSpecializationError::UnsatisfiedBound
| ExplicitSpecializationError::UnsatisfiedConstraints
| ExplicitSpecializationError::InvalidParamSpec,
)
| None => specialize(&specialization_types),
}
specialize(&specialization_types)
}
fn infer_subscript_expression_types(
@ -12044,9 +12100,17 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
Type::KnownInstance(KnownInstanceType::TypeAliasType(TypeAliasType::PEP695(alias))),
_,
) if alias.generic_context(db).is_none() => {
debug_assert!(alias.specialization(db).is_none());
if let Some(builder) = self.context.report_lint(&NON_SUBSCRIPTABLE, subscript) {
builder
.into_diagnostic(format_args!("Cannot subscript non-generic type alias"));
let value_type = alias.raw_value_type(db);
let mut diagnostic =
builder.into_diagnostic("Cannot subscript non-generic type alias");
if value_type.is_definition_generic(db) {
diagnostic.set_primary_message(format_args!(
"`{}` is already specialized",
value_type.display(db)
));
}
}
Some(Type::unknown())

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@ -919,6 +919,16 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
Type::unknown()
}
KnownInstanceType::TypeAliasType(type_alias @ TypeAliasType::PEP695(_)) => {
if type_alias.specialization(self.db()).is_some() {
if let Some(builder) =
self.context.report_lint(&NON_SUBSCRIPTABLE, subscript)
{
let mut diagnostic =
builder.into_diagnostic("Cannot subscript non-generic type alias");
diagnostic.set_primary_message("Double specialization is not allowed");
}
return Type::unknown();
}
match type_alias.generic_context(self.db()) {
Some(generic_context) => {
let specialized_type_alias = self
@ -943,9 +953,15 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
if let Some(builder) =
self.context.report_lint(&NON_SUBSCRIPTABLE, subscript)
{
builder.into_diagnostic(format_args!(
"Cannot subscript non-generic type alias"
));
let value_type = type_alias.raw_value_type(self.db());
let mut diagnostic = builder
.into_diagnostic("Cannot subscript non-generic type alias");
if value_type.is_definition_generic(self.db()) {
diagnostic.set_primary_message(format_args!(
"`{}` is already specialized",
value_type.display(self.db()),
));
}
}
Type::unknown()

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@ -304,6 +304,14 @@ impl<'db> NominalInstanceType<'db> {
matches!(self.0, NominalInstanceInner::Object)
}
pub(super) fn is_definition_generic(self) -> bool {
match self.0 {
NominalInstanceInner::NonTuple(class) => class.is_generic(),
NominalInstanceInner::ExactTuple(_) => true,
NominalInstanceInner::Object => false,
}
}
/// If this type is an *exact* tuple type (*not* a subclass of `tuple`), returns the
/// tuple spec.
///