Rollup of 9 pull requests

compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs

@@ -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(..)

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -3107,6 +3107,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
  self.tcx.def_span(def_id),
  "required because it's used within this closure",
  ),
+ ty::Str => err.note("`str` is considered to contain a `[u8]` slice for auto trait purposes"),
  _ => err.note(&msg),
  };
  }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -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(..)

tests/ui/auto-traits/str-contains-slice-conceptually.rs

@@ -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`
+}

tests/ui/auto-traits/str-contains-slice-conceptually.stderr

@@ -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: `str` is considered to contain a `[u8]` slice for auto trait purposes
+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`.