0e2ccaaa3e
Related: #66426 This commit adds handling for opaque types during inference variable fallback. Type variables generated from the instantiatino of opaque types now fallback to the opque type itself. Normally, the type variable for an instantiated opaque type is either unified with the concrete type, or with the opaque type itself (e.g when a function returns an opaque type by calling another function). However, it's possible for the type variable to be left completely unconstrained. This can occur in code like this: ```rust pub type Foo = impl Copy; fn produce() -> Option<Foo> { None } ``` Here, we'll instantatiate the `Foo` in `Option<Foo>` to a fresh type variable, but we will never unify it with anything due to the fact that we return a `None`. This results in the error message: `type annotations needed: cannot resolve `_: std::marker::Copy`` pointing at `pub type Foo = impl Copy`. This message is not only confusing, it's incorrect. When an opaque type inference variable is completely unconstrained, we can always fall back to using the opaque type itself. This effectively turns that particular use of the opaque type into a non-defining use, even if it appears in a defining scope.
224 lines
7.3 KiB
Rust
224 lines
7.3 KiB
Rust
//! A simple test for testing many permutations of allowedness of
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//! impl Trait
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use std::fmt::Debug;
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// Allowed
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fn in_parameters(_: impl Debug) { panic!() }
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// Allowed
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fn in_return() -> impl Debug { panic!() }
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// Allowed
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fn in_adt_in_parameters(_: Vec<impl Debug>) { panic!() }
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// Disallowed
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fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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//~^^ ERROR nested `impl Trait` is not allowed
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// Disallowed
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fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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//~| ERROR nested `impl Trait` is not allowed
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// Disallowed
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fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_Fn_parameter_in_generics<F: Fn(impl Debug)> (_: F) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Allowed
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fn in_impl_Trait_in_parameters(_: impl Iterator<Item = impl Iterator>) { panic!() }
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// Allowed
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fn in_impl_Trait_in_return() -> impl IntoIterator<Item = impl IntoIterator> {
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vec![vec![0; 10], vec![12; 7], vec![8; 3]]
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}
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// Disallowed
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struct InBraceStructField { x: impl Debug }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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struct InAdtInBraceStructField { x: Vec<impl Debug> }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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struct InTupleStructField(impl Debug);
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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// Disallowed
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enum InEnum {
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InBraceVariant { x: impl Debug },
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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InTupleVariant(impl Debug),
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Allowed
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trait InTraitDefnParameters {
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fn in_parameters(_: impl Debug);
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}
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// Disallowed
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trait InTraitDefnReturn {
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fn in_return() -> impl Debug;
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Allowed and disallowed in trait impls
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trait DummyTrait {
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type Out;
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fn in_trait_impl_parameter(_: impl Debug);
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fn in_trait_impl_return() -> Self::Out;
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}
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impl DummyTrait for () {
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type Out = impl Debug;
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//~^ ERROR `impl Trait` in type aliases is unstable
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//~^^ ERROR could not find defining uses
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fn in_trait_impl_parameter(_: impl Debug) { }
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// Allowed
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fn in_trait_impl_return() -> impl Debug { () }
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Allowed
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struct DummyType;
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impl DummyType {
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fn in_inherent_impl_parameters(_: impl Debug) { }
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fn in_inherent_impl_return() -> impl Debug { () }
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}
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// Disallowed
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extern "C" {
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fn in_foreign_parameters(_: impl Debug);
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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fn in_foreign_return() -> impl Debug;
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Allowed
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extern "C" fn in_extern_fn_parameters(_: impl Debug) {
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}
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// Allowed
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extern "C" fn in_extern_fn_return() -> impl Debug {
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22
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}
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type InTypeAlias<R> = impl Debug;
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//~^ ERROR `impl Trait` in type aliases is unstable
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//~^^ ERROR could not find defining uses
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type InReturnInTypeAlias<R> = fn() -> impl Debug;
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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//~| ERROR `impl Trait` in type aliases is unstable
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// Disallowed in impl headers
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impl PartialEq<impl Debug> for () {
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Disallowed in impl headers
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impl PartialEq<()> for impl Debug {
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Disallowed in inherent impls
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impl impl Debug {
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Disallowed in inherent impls
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struct InInherentImplAdt<T> { t: T }
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impl InInherentImplAdt<impl Debug> {
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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// Disallowed in where clauses
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fn in_fn_where_clause()
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where impl Debug: Debug
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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{
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}
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// Disallowed in where clauses
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fn in_adt_in_fn_where_clause()
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where Vec<impl Debug>: Debug
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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{
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}
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// Disallowed
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fn in_trait_parameter_in_fn_where_clause<T>()
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where T: PartialEq<impl Debug>
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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{
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}
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// Disallowed
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fn in_Fn_parameter_in_fn_where_clause<T>()
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where T: Fn(impl Debug)
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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{
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}
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// Disallowed
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fn in_Fn_return_in_fn_where_clause<T>()
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where T: Fn() -> impl Debug
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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{
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}
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fn main() {
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let _in_local_variable: impl Fn() = || {};
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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let _in_return_in_local_variable = || -> impl Fn() { || {} };
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//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
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}
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