Check RPIT and AFIT hidden types are well-formed considering regions

Author: compiler-errors

compiler/rustc_hir_analysis/src/check/check.rs

@@ -460,8 +460,6 @@ fn check_opaque_meets_bounds<'tcx>(
         return Err(guar);
     }
     match origin {
-        // Checked when type checking the function containing them.
-        hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) => {}
         // Nested opaque types occur only in associated types:
         // ` type Opaque<T> = impl Trait<&'static T, AssocTy = impl Nested>; `
         // They can only be referenced as `<Opaque<T> as Trait<&'static T>>::AssocTy`.
@@ -470,9 +468,11 @@ fn check_opaque_meets_bounds<'tcx>(
         hir::OpaqueTyOrigin::TyAlias { .. }
             if tcx.def_kind(tcx.parent(def_id.to_def_id())) == DefKind::OpaqueTy => {}
         // Can have different predicates to their defining use
-        hir::OpaqueTyOrigin::TyAlias { .. } => {
-            let wf_tys = ocx.assumed_wf_types_and_report_errors(param_env, def_id)?;
-            let implied_bounds = infcx.implied_bounds_tys(param_env, def_id, wf_tys);
+        hir::OpaqueTyOrigin::TyAlias { .. }
+        | hir::OpaqueTyOrigin::FnReturn(..)
+        | hir::OpaqueTyOrigin::AsyncFn(..) => {
+            let wf_tys = ocx.assumed_wf_types_and_report_errors(param_env, defining_use_anchor)?;
+            let implied_bounds = infcx.implied_bounds_tys(param_env, defining_use_anchor, wf_tys);
             let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
             ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env)?;
         }

compiler/rustc_ty_utils/src/implied_bounds.rs

@@ -118,18 +118,7 @@ fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx [(Ty<'
             }
         },
         DefKind::AssocConst | DefKind::AssocTy => tcx.assumed_wf_types(tcx.local_parent(def_id)),
-        DefKind::OpaqueTy => match tcx.def_kind(tcx.local_parent(def_id)) {
-            DefKind::TyAlias { .. } => ty::List::empty(),
-            DefKind::AssocTy => tcx.assumed_wf_types(tcx.local_parent(def_id)),
-            // Nested opaque types only occur in associated types:
-            // ` type Opaque<T> = impl Trait<&'static T, AssocTy = impl Nested>; `
-            // assumed_wf_types should include those of `Opaque<T>`, `Opaque<T>` itself
-            // and `&'static T`.
-            DefKind::OpaqueTy => bug!("unimplemented implied bounds for nested opaque types"),
-            def_kind => {
-                bug!("unimplemented implied bounds for opaque types with parent {def_kind:?}")
-            }
-        },
+        DefKind::OpaqueTy => bug!("implied bounds are not defined for opaques"),
         DefKind::Mod
         | DefKind::Struct
         | DefKind::Union

tests/ui/impl-trait/check-rpit-is-wf-regions.rs

@@ -0,0 +1,21 @@
+type Static<'a> = &'static &'a ();
+
+trait Extend<'a> {
+    fn extend(self, _: &'a str) -> &'static str;
+}
+
+impl<'a> Extend<'a> for Static<'a> {
+    fn extend(self, s: &'a str) -> &'static str {
+        s
+    }
+}
+
+fn boom<'a>(arg: Static<'_>) -> impl Extend<'a> {
+    //~^ ERROR in type `&'static &'a ()`, reference has a longer lifetime than the data it references
+    arg
+}
+
+fn main() {
+    let y = boom(&&()).extend(&String::from("temporary"));
+    println!("{}", y);
+}

tests/ui/impl-trait/check-rpit-is-wf-regions.stderr

@@ -0,0 +1,16 @@
+error[E0491]: in type `&'static &'a ()`, reference has a longer lifetime than the data it references
+  --> $DIR/check-rpit-is-wf-regions.rs:13:33
+   |
+LL | fn boom<'a>(arg: Static<'_>) -> impl Extend<'a> {
+   |                                 ^^^^^^^^^^^^^^^
+   |
+   = note: the pointer is valid for the static lifetime
+note: but the referenced data is only valid for the lifetime `'a` as defined here
+  --> $DIR/check-rpit-is-wf-regions.rs:13:9
+   |
+LL | fn boom<'a>(arg: Static<'_>) -> impl Extend<'a> {
+   |         ^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0491`.