Error on recursive opaque ty in HIR typeck

compiler/rustc_hir_typeck/src/writeback.rs

@@ -9,17 +9,21 @@
 //! which creates a new `TypeckResults` which doesn't contain any inference variables.
 
 use std::mem;
+use std::ops::ControlFlow;
 
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::unord::ExtendUnord;
-use rustc_errors::ErrorGuaranteed;
+use rustc_errors::{E0720, ErrorGuaranteed};
+use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{self, InferKind, Visitor};
 use rustc_hir::{self as hir, AmbigArg, HirId};
 use rustc_infer::traits::solve::Goal;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCoercion};
 use rustc_middle::ty::{
-    self, DefiningScopeKind, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
-    TypeVisitableExt, fold_regions,
+    self, DefiningScopeKind, OpaqueHiddenType, Ty, TyCtxt, TypeFoldable, TypeFolder,
+    TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
+    fold_regions,
 };
 use rustc_span::{Span, sym};
 use rustc_trait_selection::error_reporting::infer::need_type_info::TypeAnnotationNeeded;
@@ -595,6 +599,35 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
                 entry.span = prev.span.substitute_dummy(hidden_type.span);
             }
         }
+
+        let recursive_opaques: Vec<_> = self
+            .typeck_results
+            .concrete_opaque_types
+            .iter()
+            .filter(|&(&def_id, hidden_ty)| {
+                hidden_ty
+                    .ty
+                    .visit_with(&mut HasRecursiveOpaque {
+                        def_id,
+                        seen: Default::default(),
+                        opaques: &self.typeck_results.concrete_opaque_types,
+                        tcx,
+                    })
+                    .is_break()
+            })
+            .map(|(def_id, hidden_ty)| (*def_id, hidden_ty.span))
+            .collect();
+        for (def_id, span) in recursive_opaques {
+            let guar = self
+                .fcx
+                .dcx()
+                .struct_span_err(span, "cannot resolve opaque type")
+                .with_code(E0720)
+                .emit();
+            self.typeck_results
+                .concrete_opaque_types
+                .insert(def_id, OpaqueHiddenType { span, ty: Ty::new_error(tcx, guar) });
+        }
     }
 
     fn visit_field_id(&mut self, hir_id: HirId) {
@@ -959,3 +992,34 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EagerlyNormalizeConsts<'tcx> {
         self.tcx.try_normalize_erasing_regions(self.typing_env, ct).unwrap_or(ct)
     }
 }
+
+struct HasRecursiveOpaque<'a, 'tcx> {
+    def_id: LocalDefId,
+    seen: FxHashSet<LocalDefId>,
+    opaques: &'a FxIndexMap<LocalDefId, ty::OpaqueHiddenType<'tcx>>,
+    tcx: TyCtxt<'tcx>,
+}
+
+impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasRecursiveOpaque<'_, 'tcx> {
+    type Result = ControlFlow<()>;
+
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
+        if let ty::Alias(ty::Opaque, alias_ty) = *t.kind()
+            && let Some(def_id) = alias_ty.def_id.as_local()
+        {
+            if self.def_id == def_id {
+                return ControlFlow::Break(());
+            }
+
+            if self.seen.insert(def_id)
+                && let Some(hidden_ty) = self.opaques.get(&def_id)
+            {
+                ty::EarlyBinder::bind(hidden_ty.ty)
+                    .instantiate(self.tcx, alias_ty.args)
+                    .visit_with(self)?;
+            }
+        }
+
+        t.super_visit_with(self)
+    }
+}

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -1,6 +1,5 @@
 use std::fmt;
 use std::iter::once;
-use std::ops::ControlFlow;
 
 use rustc_abi::{FIRST_VARIANT, FieldIdx, Integer, VariantIdx};
 use rustc_arena::DroplessArena;
@@ -12,8 +11,7 @@ use rustc_middle::mir::{self, Const};
 use rustc_middle::thir::{self, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{
-    self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
-    TypeVisitableExt, TypeVisitor, VariantDef,
+    self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeVisitableExt, VariantDef,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
@@ -137,22 +135,11 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
     /// Returns the hidden type corresponding to this key if the body under analysis is allowed to
     /// know it.
     fn reveal_opaque_key(&self, key: OpaqueTypeKey<'tcx>) -> Option<Ty<'tcx>> {
-        if let Some(hidden_ty) = self.typeck_results.concrete_opaque_types.get(&key.def_id) {
-            let ty = ty::EarlyBinder::bind(hidden_ty.ty).instantiate(self.tcx, key.args);
-            if ty.visit_with(&mut RecursiveOpaque { def_id: key.def_id.into() }).is_continue() {
-                Some(ty)
-            } else {
-                // HACK: We skip revealing opaque types which recursively expand
-                // to themselves. This is because we may infer hidden types like
-                // `Opaque<T> = Opaque<Opaque<T>>` or `Opaque<T> = Opaque<(T,)>`
-                // in hir typeck.
-                None
-            }
-        } else {
-            None
-        }
+        self.typeck_results
+            .concrete_opaque_types
+            .get(&key.def_id)
+            .map(|x| ty::EarlyBinder::bind(x.ty).instantiate(self.tcx, key.args))
     }
-
     // This can take a non-revealed `Ty` because it reveals opaques itself.
     pub fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool {
         !ty.inhabited_predicate(self.tcx).apply_revealing_opaque(
@@ -1177,20 +1164,3 @@ fn detect_mixed_deref_pat_ctors<'p, 'tcx>(
     }
     Ok(())
 }
-
-struct RecursiveOpaque {
-    def_id: DefId,
-}
-impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for RecursiveOpaque {
-    type Result = ControlFlow<()>;
-
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
-        if let ty::Alias(ty::Opaque, alias_ty) = t.kind() {
-            if alias_ty.def_id == self.def_id {
-                return ControlFlow::Break(());
-            }
-        }
-
-        if t.has_opaque_types() { t.super_visit_with(self) } else { ControlFlow::Continue(()) }
-    }
-}

tests/ui/impl-trait/issues/issue-100075-2.stderr

@@ -1,3 +1,9 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/issue-100075-2.rs:1:23
+   |
+LL | fn opaque<T>(t: T) -> impl Sized {
+   |                       ^^^^^^^^^^
+
 warning: function cannot return without recursing
   --> $DIR/issue-100075-2.rs:1:1
    |
@@ -10,15 +16,6 @@ LL |     opaque(Some(t))
    = help: a `loop` may express intention better if this is on purpose
    = note: `#[warn(unconditional_recursion)]` on by default
 
-error[E0720]: cannot resolve opaque type
-  --> $DIR/issue-100075-2.rs:1:23
-   |
-LL | fn opaque<T>(t: T) -> impl Sized {
-   |                       ^^^^^^^^^^ recursive opaque type
-...
-LL |     opaque(Some(t))
-   |     --------------- returning here with type `impl Sized`
-
 error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0720`.

tests/ui/impl-trait/issues/issue-100075.stderr

@@ -2,10 +2,7 @@ error[E0720]: cannot resolve opaque type
   --> $DIR/issue-100075.rs:13:37
    |
 LL | fn _g<T>(t: &'static T) -> &'static impl Marker {
-   |                                     ^^^^^^^^^^^ recursive opaque type
-...
-LL |         return _g(t);
-   |                ----- returning here with type `&impl Marker`
+   |                                     ^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/issues/issue-103599.rs

@@ -1,9 +1,8 @@
-//@ check-pass
-
 trait T {}
 
 fn wrap(x: impl T) -> impl T {
-    //~^ WARN function cannot return without recursing
+    //~^ ERROR cannot resolve opaque type
+    //~| WARN function cannot return without recursing
     wrap(wrap(x))
 }
 

tests/ui/impl-trait/issues/issue-103599.stderr

@@ -1,14 +1,21 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/issue-103599.rs:3:23
+   |
+LL | fn wrap(x: impl T) -> impl T {
+   |                       ^^^^^^
+
 warning: function cannot return without recursing
-  --> $DIR/issue-103599.rs:5:1
+  --> $DIR/issue-103599.rs:3:1
    |
 LL | fn wrap(x: impl T) -> impl T {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
-LL |
+...
 LL |     wrap(wrap(x))
    |          ------- recursive call site
    |
    = help: a `loop` may express intention better if this is on purpose
    = note: `#[warn(unconditional_recursion)]` on by default
 
-warning: 1 warning emitted
+error: aborting due to 1 previous error; 1 warning emitted
 
+For more information about this error, try `rustc --explain E0720`.

tests/ui/impl-trait/issues/issue-87450.rs

@@ -3,8 +3,8 @@ fn bar() -> impl Fn() {
 }
 
 fn foo() -> impl Fn() {
-    //~^ WARNING 5:1: 5:22: function cannot return without recursing [unconditional_recursion]
-    //~| ERROR 5:13: 5:22: cannot resolve opaque type [E0720]
+    //~^ WARN function cannot return without recursing
+    //~| ERROR cannot resolve opaque type
     wrap(wrap(wrap(wrap(wrap(wrap(wrap(foo())))))))
 }
 

tests/ui/impl-trait/issues/issue-87450.stderr

@@ -1,3 +1,9 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/issue-87450.rs:5:13
+   |
+LL | fn foo() -> impl Fn() {
+   |             ^^^^^^^^^
+
 warning: function cannot return without recursing
   --> $DIR/issue-87450.rs:5:1
    |
@@ -10,18 +16,6 @@ LL |     wrap(wrap(wrap(wrap(wrap(wrap(wrap(foo())))))))
    = help: a `loop` may express intention better if this is on purpose
    = note: `#[warn(unconditional_recursion)]` on by default
 
-error[E0720]: cannot resolve opaque type
-  --> $DIR/issue-87450.rs:5:13
-   |
-LL | fn foo() -> impl Fn() {
-   |             ^^^^^^^^^ recursive opaque type
-...
-LL |     wrap(wrap(wrap(wrap(wrap(wrap(wrap(foo())))))))
-   |     ----------------------------------------------- returning here with type `impl Fn()`
-...
-LL | fn wrap(f: impl Fn()) -> impl Fn() {
-   |                          --------- returning this opaque type `impl Fn()`
-
 error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0720`.

tests/ui/impl-trait/recursive-impl-trait-type-indirect.stderr

@@ -2,112 +2,67 @@ error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:6:22
    |
 LL | fn option(i: i32) -> impl Sized {
-   |                      ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     if i < 0 { None } else { Some((option(i - 1), i)) }
-   |                ----          ------------------------ returning here with type `Option<(impl Sized, i32)>`
-   |                |
-   |                returning here with type `Option<(impl Sized, i32)>`
+   |                      ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:11:15
    |
 LL | fn tuple() -> impl Sized {
-   |               ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     (tuple(),)
-   |     ---------- returning here with type `(impl Sized,)`
+   |               ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:16:15
    |
 LL | fn array() -> impl Sized {
-   |               ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     [array()]
-   |     --------- returning here with type `[impl Sized; 1]`
+   |               ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:21:13
    |
 LL | fn ptr() -> impl Sized {
-   |             ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     &ptr() as *const _
-   |     ------------------ returning here with type `*const impl Sized`
+   |             ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:26:16
    |
 LL | fn fn_ptr() -> impl Sized {
-   |                ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     fn_ptr as fn() -> _
-   |     ------------------- returning here with type `fn() -> impl Sized`
+   |                ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:31:25
    |
-LL |   fn closure_capture() -> impl Sized {
-   |                           ^^^^^^^^^^ recursive opaque type
-...
-LL | /     move || {
-LL | |         x;
-   | |         - closure captures itself here
-LL | |     }
-   | |_____- returning here with type `{closure@$DIR/recursive-impl-trait-type-indirect.rs:34:5: 34:12}`
+LL | fn closure_capture() -> impl Sized {
+   |                         ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:39:29
    |
-LL |   fn closure_ref_capture() -> impl Sized {
-   |                               ^^^^^^^^^^ recursive opaque type
-...
-LL | /     move || {
-LL | |         &x;
-   | |          - closure captures itself here
-LL | |     }
-   | |_____- returning here with type `{closure@$DIR/recursive-impl-trait-type-indirect.rs:42:5: 42:12}`
+LL | fn closure_ref_capture() -> impl Sized {
+   |                             ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:47:21
    |
 LL | fn closure_sig() -> impl Sized {
-   |                     ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     || closure_sig()
-   |     ---------------- returning here with type `{closure@$DIR/recursive-impl-trait-type-indirect.rs:49:5: 49:7}`
+   |                     ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:52:23
    |
 LL | fn coroutine_sig() -> impl Sized {
-   |                       ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     || coroutine_sig()
-   |     ------------------ returning here with type `{closure@$DIR/recursive-impl-trait-type-indirect.rs:54:5: 54:7}`
+   |                       ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:57:27
    |
-LL |   fn coroutine_capture() -> impl Sized {
-   |                             ^^^^^^^^^^ recursive opaque type
-...
-LL | /     move || {
-LL | |         yield;
-LL | |         x;
-   | |         - coroutine captures itself here
-LL | |     }
-   | |_____- returning here with type `{coroutine@$DIR/recursive-impl-trait-type-indirect.rs:62:5: 62:12}`
+LL | fn coroutine_capture() -> impl Sized {
+   |                           ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:68:35
    |
 LL | fn substs_change<T: 'static>() -> impl Sized {
-   |                                   ^^^^^^^^^^ recursive opaque type
-LL |
-LL |     (substs_change::<&T>(),)
-   |     ------------------------ returning here with type `(impl Sized,)`
+   |                                   ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:78:26

tests/ui/impl-trait/recursive-in-exhaustiveness.current.stderr

@@ -1,56 +1,21 @@
-warning: function cannot return without recursing
-  --> $DIR/recursive-in-exhaustiveness.rs:17:1
+error[E0720]: cannot resolve opaque type
+  --> $DIR/recursive-in-exhaustiveness.rs:17:22
    |
 LL | fn build<T>(x: T) -> impl Sized {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
-LL |
-LL |     let (x,) = (build(x),);
-   |                 -------- recursive call site
-   |
-   = help: a `loop` may express intention better if this is on purpose
-   = note: `#[warn(unconditional_recursion)]` on by default
-
-warning: function cannot return without recursing
-  --> $DIR/recursive-in-exhaustiveness.rs:27:1
-   |
-LL | fn build2<T>(x: T) -> impl Sized {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
-...
-LL |     let (x,) = (build2(x),);
-   |                 --------- recursive call site
-   |
-   = help: a `loop` may express intention better if this is on purpose
+   |                      ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-in-exhaustiveness.rs:27:23
    |
 LL | fn build2<T>(x: T) -> impl Sized {
-   |                       ^^^^^^^^^^ recursive opaque type
-...
-LL |     (build2(x),)
-   |     ------------ returning here with type `(impl Sized,)`
+   |                       ^^^^^^^^^^
 
-warning: function cannot return without recursing
-  --> $DIR/recursive-in-exhaustiveness.rs:40:1
-   |
-LL | fn build3<T>(x: T) -> impl Sized {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
-LL |
-LL |     let (x,) = (build3((x,)),);
-   |                 ------------ recursive call site
-   |
-   = help: a `loop` may express intention better if this is on purpose
-
-error[E0792]: expected generic type parameter, found `(T,)`
-  --> $DIR/recursive-in-exhaustiveness.rs:49:5
+error[E0720]: cannot resolve opaque type
+  --> $DIR/recursive-in-exhaustiveness.rs:39:23
    |
 LL | fn build3<T>(x: T) -> impl Sized {
-   |           - this generic parameter must be used with a generic type parameter
-...
-LL |     build3(x)
-   |     ^^^^^^^^^
+   |                       ^^^^^^^^^^
 
-error: aborting due to 2 previous errors; 3 warnings emitted
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0720, E0792.
-For more information about an error, try `rustc --explain E0720`.
+For more information about this error, try `rustc --explain E0720`.

tests/ui/impl-trait/recursive-in-exhaustiveness.next.stderr

@@ -5,19 +5,19 @@ LL |     let (x,) = (build(x),);
    |                 ^^^^^^^^ cannot satisfy `impl Sized == _`
 
 error[E0271]: type mismatch resolving `build2<(_,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:31:6
+  --> $DIR/recursive-in-exhaustiveness.rs:30:6
    |
 LL |     (build2(x),)
    |      ^^^^^^^^^ types differ
 
 error[E0271]: type mismatch resolving `build2<(_,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:31:5
+  --> $DIR/recursive-in-exhaustiveness.rs:30:5
    |
 LL |     (build2(x),)
    |     ^^^^^^^^^^^^ types differ
 
 error[E0277]: the size for values of type `(impl Sized,)` cannot be known at compilation time
-  --> $DIR/recursive-in-exhaustiveness.rs:31:5
+  --> $DIR/recursive-in-exhaustiveness.rs:30:5
    |
 LL |     (build2(x),)
    |     ^^^^^^^^^^^^ doesn't have a size known at compile-time
@@ -26,13 +26,13 @@ LL |     (build2(x),)
    = note: tuples must have a statically known size to be initialized
 
 error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:42:17
+  --> $DIR/recursive-in-exhaustiveness.rs:41:17
    |
 LL |     let (x,) = (build3((x,)),);
    |                 ^^^^^^^^^^^^ types differ
 
 error[E0277]: the size for values of type `(impl Sized,)` cannot be known at compilation time
-  --> $DIR/recursive-in-exhaustiveness.rs:42:16
+  --> $DIR/recursive-in-exhaustiveness.rs:41:16
    |
 LL |     let (x,) = (build3((x,)),);
    |                ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
@@ -41,7 +41,7 @@ LL |     let (x,) = (build3((x,)),);
    = note: tuples must have a statically known size to be initialized
 
 error[E0308]: mismatched types
-  --> $DIR/recursive-in-exhaustiveness.rs:42:16
+  --> $DIR/recursive-in-exhaustiveness.rs:41:16
    |
 LL | fn build3<T>(x: T) -> impl Sized {
    |                       ---------- the found opaque type
@@ -53,21 +53,21 @@ LL |     let (x,) = (build3((x,)),);
              found tuple `(impl Sized,)`
 
 error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:42:17
+  --> $DIR/recursive-in-exhaustiveness.rs:41:17
    |
 LL |     let (x,) = (build3((x,)),);
    |                 ^^^^^^^^^^^^ types differ
    |
    = note: the return type of a function must have a statically known size
 
 error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:42:16
+  --> $DIR/recursive-in-exhaustiveness.rs:41:16
    |
 LL |     let (x,) = (build3((x,)),);
    |                ^^^^^^^^^^^^^^^ types differ
 
 error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:42:17
+  --> $DIR/recursive-in-exhaustiveness.rs:41:17
    |
 LL |     let (x,) = (build3((x,)),);
    |                 ^^^^^^^^^^^^ types differ

tests/ui/impl-trait/recursive-in-exhaustiveness.rs

@@ -15,7 +15,7 @@
 // We unfortunately accept this today, and due to how opaque type relating is implemented
 // in the NLL type relation, this defines `Opaque<T> = T`.
 fn build<T>(x: T) -> impl Sized {
-    //[current]~^ WARN function cannot return without recursing
+    //[current]~^ ERROR cannot resolve opaque type
     let (x,) = (build(x),);
     //[next]~^ ERROR type annotations needed
     build(x)
@@ -26,7 +26,6 @@ fn build<T>(x: T) -> impl Sized {
 // Not allowed today. Detected as recursive.
 fn build2<T>(x: T) -> impl Sized {
     //[current]~^ ERROR cannot resolve opaque type
-    //[current]~| WARN function cannot return without recursing
     let (x,) = (build2(x),);
     (build2(x),)
     //[next]~^ ERROR type mismatch resolving
@@ -38,7 +37,7 @@ fn build2<T>(x: T) -> impl Sized {
 //
 // Not allowed today. Detected as not defining.
 fn build3<T>(x: T) -> impl Sized {
-    //[current]~^ WARN function cannot return without recursing
+    //[current]~^ ERROR cannot resolve opaque type
     let (x,) = (build3((x,)),);
     //[next]~^ ERROR type mismatch resolving
     //[next]~| ERROR type mismatch resolving
@@ -47,7 +46,6 @@ fn build3<T>(x: T) -> impl Sized {
     //[next]~| ERROR the size for values of type
     //[next]~| ERROR mismatched types
     build3(x)
-    //[current]~^ ERROR expected generic type parameter, found `(T,)`
 }
 
 fn main() {}

tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.rs

@@ -1,10 +1,10 @@
 #![feature(type_alias_impl_trait)]
 
 type T = impl Copy;
-//~^ ERROR cannot resolve opaque type
 
 #[define_opaque(T)]
 fn foo() -> T {
+    //~^ ERROR cannot resolve opaque type
     None::<&'static T>
 }
 

tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.stderr

@@ -1,8 +1,8 @@
 error[E0720]: cannot resolve opaque type
-  --> $DIR/infinite-cycle-involving-weak.rs:3:10
+  --> $DIR/infinite-cycle-involving-weak.rs:6:13
    |
-LL | type T = impl Copy;
-   |          ^^^^^^^^^ cannot resolve opaque type
+LL | fn foo() -> T {
+   |             ^
 
 error: aborting due to 1 previous error
 

tests/crashes/139817.rs → tests/ui/type-alias-impl-trait/match-upvar-discriminant-of-opaque.rs

@@ -1,8 +1,12 @@
-//@ known-bug: #139817
+#![feature(type_alias_impl_trait)]
+
 fn enum_upvar() {
     type T = impl Copy;
     let foo: T = Some((42, std::marker::PhantomData::<T>));
     let x = move || match foo {
         None => (),
+        //~^ ERROR cannot resolve opaque type
     };
 }
+
+fn main() {}

tests/ui/type-alias-impl-trait/match-upvar-discriminant-of-opaque.stderr

@@ -0,0 +1,9 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/match-upvar-discriminant-of-opaque.rs:7:9
+   |
+LL |         None => (),
+   |         ^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0720`.

tests/ui/type-alias-impl-trait/recursive-fn-tait.rs

@@ -13,7 +13,7 @@ pub fn add(
     n: Diff,
     m: Diff,
 ) -> Diff {
-    //~^ ERROR concrete type differs
+    //~^ ERROR cannot resolve opaque type
     move |x: usize| m(n(x))
 }
 

tests/ui/type-alias-impl-trait/recursive-fn-tait.stderr

@@ -1,14 +1,9 @@
-error: concrete type differs from previous defining opaque type use
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-fn-tait.rs:15:6
    |
 LL | ) -> Diff {
-   |      ^^^^ expected `{closure@$DIR/recursive-fn-tait.rs:8:5: 8:16}`, got `{closure@$DIR/recursive-fn-tait.rs:17:5: 17:20}`
-   |
-note: previous use here
-  --> $DIR/recursive-fn-tait.rs:7:18
-   |
-LL | pub fn lift() -> Diff {
-   |                  ^^^^
+   |      ^^^^
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0720`.

tests/ui/type-alias-impl-trait/recursive-tait-conflicting-defn-2.rs

@@ -13,7 +13,7 @@ fn transform<S>() -> impl std::fmt::Display {
 }
 #[define_opaque(Op)]
 fn bad() -> Op {
-    //~^ ERROR concrete type differs from previous defining opaque type use
+    //~^ ERROR cannot resolve opaque type
     transform::<Op>()
 }
 

tests/ui/type-alias-impl-trait/recursive-tait-conflicting-defn-2.stderr

@@ -1,14 +1,9 @@
-error: concrete type differs from previous defining opaque type use
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-tait-conflicting-defn-2.rs:15:13
    |
 LL | fn bad() -> Op {
-   |             ^^ expected `&&str`, got `impl std::fmt::Display`
-   |
-note: previous use here
-  --> $DIR/recursive-tait-conflicting-defn-2.rs:7:13
-   |
-LL | fn foo() -> Op {
    |             ^^
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0720`.

tests/ui/type-alias-impl-trait/recursive-tait-conflicting-defn.rs

@@ -23,7 +23,7 @@ pub fn test() -> TestImpl {
 
 #[define_opaque(TestImpl)]
 fn make_option2() -> Option<TestImpl> {
-    //~^ ERROR concrete type differs from previous defining opaque type use
+    //~^ ERROR cannot resolve opaque type
     let inner = make_option().unwrap();
     Some(B { inner })
 }

tests/ui/type-alias-impl-trait/recursive-tait-conflicting-defn.stderr

@@ -1,14 +1,9 @@
-error: concrete type differs from previous defining opaque type use
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-tait-conflicting-defn.rs:25:22
    |
 LL | fn make_option2() -> Option<TestImpl> {
-   |                      ^^^^^^^^^^^^^^^^ expected `A`, got `B<TestImpl>`
-   |
-note: previous use here
-  --> $DIR/recursive-tait-conflicting-defn.rs:20:18
-   |
-LL | pub fn test() -> TestImpl {
-   |                  ^^^^^^^^
+   |                      ^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0720`.