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[ty] Add a new assert-type-unspellable-subtype diagnostic
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‎crates/ty/docs/rules.md‎

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‎crates/ty_python_semantic/resources/mdtest/directives/assert_type.md‎

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@@ -53,6 +53,31 @@ def _(a: type[int]):
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assert_type(a, Type[int]) # fine
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```
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## Unspellable types
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<!-- snapshot-diagnostics -->
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If the actual type is an unspellable subtype, we emit `assert-type-unspellable-subtype` instead of
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`type-assertion-failure`, on the grounds that it is often useful to distinguish this from cases
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where the type assertion failure is "fixable".
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```py
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from typing_extensions import assert_type
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class Foo: ...
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class Bar: ...
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class Baz: ...
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def f(x: Foo):
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assert_type(x, Bar) # error: [type-assertion-failure] "Type `Bar` does not match asserted type `Foo`"
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if isinstance(x, Bar):
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assert_type(x, Bar) # error: [assert-type-unspellable-subtype] "Type `Bar` does not match asserted type `Foo & Bar`"
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# The actual type must be a subtype of the asserted type, as well as being unspellable,
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# in order for `assert-type-unspellable-subtype` to be emitted instead of `type-assertion-failure`
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assert_type(x, Baz) # error: [type-assertion-failure]
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```
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## Gradual types
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```py

‎crates/ty_python_semantic/resources/mdtest/snapshots/assert_type.md_-_`assert_type`_-_Unspellable_types_(385d082f9803b184).snap‎

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---
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source: crates/ty_test/src/lib.rs
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expression: snapshot
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---
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---
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mdtest name: assert_type.md - `assert_type` - Unspellable types
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mdtest path: crates/ty_python_semantic/resources/mdtest/directives/assert_type.md
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---
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# Python source files
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## mdtest_snippet.py
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```
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1 | from typing_extensions import assert_type
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2 |
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3 | class Foo: ...
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4 | class Bar: ...
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5 | class Baz: ...
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6 |
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7 | def f(x: Foo):
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8 | assert_type(x, Bar) # error: [type-assertion-failure] "Type `Bar` does not match asserted type `Foo`"
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9 | if isinstance(x, Bar):
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10 | assert_type(x, Bar) # error: [assert-type-unspellable-subtype] "Type `Bar` does not match asserted type `Foo & Bar`"
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11 |
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12 | # The actual type must be a subtype of the asserted type, as well as being unspellable,
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13 | # in order for `assert-type-unspellable-subtype` to be emitted instead of `type-assertion-failure`
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14 | assert_type(x, Baz) # error: [type-assertion-failure]
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```
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# Diagnostics
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```
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error[type-assertion-failure]: Argument does not have asserted type `Bar`
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--> src/mdtest_snippet.py:8:5
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|
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7 | def f(x: Foo):
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8 | assert_type(x, Bar) # error: [type-assertion-failure] "Type `Bar` does not match asserted type `Foo`"
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| ^^^^^^^^^^^^-^^^^^^
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| |
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| Inferred type is `Foo`
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9 | if isinstance(x, Bar):
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10 | assert_type(x, Bar) # error: [assert-type-unspellable-subtype] "Type `Bar` does not match asserted type `Foo & Bar`"
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|
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info: `Bar` and `Foo` are not equivalent types
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info: rule `type-assertion-failure` is enabled by default
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```
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```
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error[assert-type-unspellable-subtype]: Argument does not have asserted type `Bar`
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--> src/mdtest_snippet.py:10:9
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|
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8 | assert_type(x, Bar) # error: [type-assertion-failure] "Type `Bar` does not match asserted type `Foo`"
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9 | if isinstance(x, Bar):
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10 | assert_type(x, Bar) # error: [assert-type-unspellable-subtype] "Type `Bar` does not match asserted type `Foo & Bar`"
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| ^^^^^^^^^^^^-^^^^^^
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| |
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| Inferred type is `Foo & Bar`
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11 |
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12 | # The actual type must be a subtype of the asserted type, as well as being unspellable,
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|
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info: `Foo & Bar` is a subtype of `Bar`, but they are not equivalent
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info: rule `assert-type-unspellable-subtype` is enabled by default
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```
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```
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error[type-assertion-failure]: Argument does not have asserted type `Baz`
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--> src/mdtest_snippet.py:14:9
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|
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12 | # The actual type must be a subtype of the asserted type, as well as being unspellable,
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13 | # in order for `assert-type-unspellable-subtype` to be emitted instead of `type-assertion-failure`
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14 | assert_type(x, Baz) # error: [type-assertion-failure]
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| ^^^^^^^^^^^^-^^^^^^
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| |
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| Inferred type is `Foo & Bar`
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|
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info: `Baz` and `Foo & Bar` are not equivalent types
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info: rule `type-assertion-failure` is enabled by default
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```

‎crates/ty_python_semantic/src/types.rs‎

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@@ -1533,6 +1533,54 @@ impl<'db> Type<'db> {
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if yes { self.negate(db) } else { *self }
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}
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/// Return `true` if it is possible to spell an equivalent type to this one
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/// in user annotations without nonstandard extensions to the type system
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pub(crate) fn is_spellable(&self, db: &'db dyn Db) -> bool {
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match self {
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Type::StringLiteral(_)
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| Type::LiteralString
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| Type::IntLiteral(_)
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| Type::BooleanLiteral(_)
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| Type::BytesLiteral(_)
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| Type::Never
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| Type::NewTypeInstance(_)
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| Type::EnumLiteral(_)
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| Type::NominalInstance(_)
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// `TypedDict` and `Protocol` can be synthesized,
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// but it's always possible to create an equivalent type using a class definition.
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| Type::TypedDict(_)
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| Type::ProtocolInstance(_)
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// Not all `Callable` types are spellable using the `Callable` type form,
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// but they are all spellable using callback protocols.
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| Type::Callable(_)
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// `Unknown` and `@Todo` are nonstandard extensions,
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// but they are both exactly equivalent to `Any`
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| Type::Dynamic(_)
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| Type::TypeVar(_)
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| Type::TypeAlias(_)
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| Type::SubclassOf(_)=> true,
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Type::Intersection(_)
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| Type::SpecialForm(_)
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| Type::BoundSuper(_)
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| Type::BoundMethod(_)
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| Type::KnownBoundMethod(_)
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| Type::AlwaysTruthy
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| Type::AlwaysFalsy
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| Type::TypeIs(_)
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| Type::TypeGuard(_)
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| Type::PropertyInstance(_)
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| Type::FunctionLiteral(_)
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| Type::ModuleLiteral(_)
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| Type::WrapperDescriptor(_)
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| Type::DataclassDecorator(_)
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| Type::DataclassTransformer(_)
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| Type::ClassLiteral(_)
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| Type::GenericAlias(_)
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| Type::KnownInstance(_) => false,
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Type::Union(union) => union.elements(db).iter().all(|ty| ty.is_spellable(db)),
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}
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}
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/// If the type is a union, filters union elements based on the provided predicate.
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///
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/// Otherwise, returns the type unchanged.

‎crates/ty_python_semantic/src/types/diagnostic.rs‎

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@@ -109,6 +109,7 @@ pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
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registry.register_lint(&INEFFECTIVE_FINAL);
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registry.register_lint(&ABSTRACT_METHOD_IN_FINAL_CLASS);
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registry.register_lint(&TYPE_ASSERTION_FAILURE);
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registry.register_lint(&ASSERT_TYPE_UNSPELLABLE_SUBTYPE);
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registry.register_lint(&TOO_MANY_POSITIONAL_ARGUMENTS);
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registry.register_lint(&UNAVAILABLE_IMPLICIT_SUPER_ARGUMENTS);
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registry.register_lint(&UNDEFINED_REVEAL);
@@ -1971,6 +1972,36 @@ declare_lint! {
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}
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}
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declare_lint! {
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/// ## What it does
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/// Checks for `assert_type()` calls where the actual type
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/// is an unspellable subtype of the asserted type.
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///
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/// ## Why is this bad?
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/// `assert_type()` is intended to ensure that the inferred type of a value
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/// is exactly the same as the asserted type. But in some situations, ty
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/// has nonstandard extensions to the type system that allow it to infer
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/// more precise types than can be expressed in user annotations. ty emits a
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/// different error code to `type-assertion-failure` in these situations so
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/// that users can easily differentiate between the two cases.
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///
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/// ## Example
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///
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/// ```python
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/// def _(x: int):
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/// assert_type(x, int) # fine
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/// if x:
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/// assert_type(x, int) # error: [assert-type-unspellable-subtype]
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/// # the actual type is `int & ~AlwaysFalsy`,
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/// # which excludes types like `Literal[0]`
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/// ```
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pub(crate) static ASSERT_TYPE_UNSPELLABLE_SUBTYPE = {
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summary: "detects failed type assertions",
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status: LintStatus::stable("0.0.14"),
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default_level: Level::Error,
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}
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}
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declare_lint! {
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/// ## What it does
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/// Checks for calls that pass more positional arguments than the callable can accept.

‎crates/ty_python_semantic/src/types/function.rs‎

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@@ -68,9 +68,9 @@ use crate::types::call::{Binding, CallArguments};
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use crate::types::constraints::ConstraintSet;
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use crate::types::context::InferContext;
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use crate::types::diagnostic::{
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INVALID_ARGUMENT_TYPE, REDUNDANT_CAST, STATIC_ASSERT_ERROR, TYPE_ASSERTION_FAILURE,
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report_bad_argument_to_get_protocol_members, report_bad_argument_to_protocol_interface,
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report_invalid_total_ordering_call,
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ASSERT_TYPE_UNSPELLABLE_SUBTYPE, INVALID_ARGUMENT_TYPE, REDUNDANT_CAST, STATIC_ASSERT_ERROR,
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TYPE_ASSERTION_FAILURE, report_bad_argument_to_get_protocol_members,
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report_bad_argument_to_protocol_interface, report_invalid_total_ordering_call,
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report_runtime_check_against_non_runtime_checkable_protocol,
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};
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use crate::types::display::DisplaySettings;
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if actual_ty.is_equivalent_to(db, *asserted_ty) {
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return;
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}
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if let Some(builder) = context.report_lint(&TYPE_ASSERTION_FAILURE, call_expression)
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{
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let diagnostic =
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if actual_ty.is_spellable(db) || !actual_ty.is_subtype_of(db, *asserted_ty) {
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&TYPE_ASSERTION_FAILURE
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} else {
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&ASSERT_TYPE_UNSPELLABLE_SUBTYPE
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};
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if let Some(builder) = context.report_lint(diagnostic, call_expression) {
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let mut diagnostic = builder.into_diagnostic(format_args!(
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"Argument does not have asserted type `{}`",
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asserted_ty.display(db),

‎scripts/conformance.py‎

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@@ -346,6 +346,7 @@ def collect_ty_diagnostics(
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"check",
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f"--python-version={python_version}",
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"--output-format=gitlab",
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"--ignore=assert-type-unspellable-subtype",
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"--exit-zero",
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*map(str, test_files),
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],

‎ty.schema.json‎

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