mirror of https://github.com/rust-lang/rust
29 lines
750 B
Rust
29 lines
750 B
Rust
#![feature(type_alias_impl_trait)]
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use std::fmt::Debug;
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type Foo = impl Debug;
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fn is_send<T: Send>() {}
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fn not_good() {
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// Error: this function does not constrain `Foo` to any particular
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// hidden type, so it cannot rely on `Send` being true.
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is_send::<Foo>();
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//~^ ERROR: cannot check whether the hidden type of `reveal_local[9507]::Foo::{opaque#0}` satisfies auto traits
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}
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fn not_gooder() -> Foo {
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// Constrain `Foo = u32`
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let x: Foo = 22_u32;
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// while we could know this from the hidden type, it would
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// need extra roundabout logic to support it.
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is_send::<Foo>();
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//~^ ERROR: cannot check whether the hidden type of `reveal_local[9507]::Foo::{opaque#0}` satisfies auto traits
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x
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}
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fn main() {}
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