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Treat str as containing [u8] for auto trait purposes

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This commit is contained in:
Michael Goulet 2023-02-11 23:01:22 +00:00
parent 31448badfd
commit 3560e65c44
4 changed files with 35 additions and 2 deletions
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4
compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs
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@ -20,12 +20,14 @@ pub(super) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
| ty::Float(_)
| ty::FnDef(..)
| ty::FnPtr(_)
| ty::Str
| ty::Error(_)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Never
| ty::Char => Ok(vec![]),
// Treat this like `struct str([u8]);`
ty::Str => Ok(vec![tcx.mk_slice(tcx.types.u8)]),
ty::Dynamic(..)
| ty::Param(..)
| ty::Foreign(..)

4
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -2300,12 +2300,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
| ty::Float(_)
| ty::FnDef(..)
| ty::FnPtr(_)
| ty::Str
| ty::Error(_)
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Never
| ty::Char => ty::Binder::dummy(Vec::new()),
// Treat this like `struct str([u8]);`
ty::Str => ty::Binder::dummy(vec![self.tcx().mk_slice(self.tcx().types.u8)]),
ty::Placeholder(..)
| ty::Dynamic(..)
| ty::Param(..)

13
tests/ui/auto-traits/str-contains-slice-conceptually.rs Normal file
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@ -0,0 +1,13 @@
#![feature(negative_impls)]
#![feature(auto_traits)]
auto trait AutoTrait {}
impl<T> !AutoTrait for [T] {}
fn needs_auto_trait<T: AutoTrait + ?Sized>() {}
fn main() {
needs_auto_trait::<str>();
//~^ ERROR the trait bound `[u8]: AutoTrait` is not satisfied in `str`
}

16
tests/ui/auto-traits/str-contains-slice-conceptually.stderr Normal file
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@ -0,0 +1,16 @@
error[E0277]: the trait bound `[u8]: AutoTrait` is not satisfied in `str`
--> $DIR/str-contains-slice-conceptually.rs:11:22
|
LL | needs_auto_trait::<str>();
| ^^^ within `str`, the trait `AutoTrait` is not implemented for `[u8]`
|
= note: required because it appears within the type `str`
note: required by a bound in `needs_auto_trait`
--> $DIR/str-contains-slice-conceptually.rs:8:24
|
LL | fn needs_auto_trait<T: AutoTrait + ?Sized>() {}
| ^^^^^^^^^ required by this bound in `needs_auto_trait`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.