review comments

Author: estebank

src/librustc_typeck/check/mod.rs

@@ -1741,8 +1741,7 @@ fn get_owner_return_paths(
 /// If all the return expressions evaluate to `!`, then we explain that the error will go away
 /// after changing it. This can happen when a user uses `panic!()` or similar as a placeholder.
 fn opaque_type_cycle_error(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
-    let mut err =
-        struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type to a concrete type");
+    let mut err = struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type");
 
     let mut label = false;
     if let Some((hir_id, visitor)) = get_owner_return_paths(tcx, def_id) {
@@ -1751,7 +1750,6 @@ fn opaque_type_cycle_error(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
             .returns
             .iter()
             .filter_map(|expr| tables.node_type_opt(expr.hir_id))
-            .map(|ty| tcx.infer_ctxt().enter(|infcx| infcx.resolve_vars_if_possible(&ty)))
             .all(|ty| matches!(ty.kind, ty::Never))
         {
             let spans = visitor
@@ -1782,9 +1780,6 @@ fn opaque_type_cycle_error(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
                 .iter()
                 .filter_map(|e| tables.node_type_opt(e.hir_id).map(|t| (e.span, t)))
                 .filter(|(_, ty)| !matches!(ty.kind, ty::Never))
-                .map(|(sp, ty)| {
-                    (sp, tcx.infer_ctxt().enter(|infcx| infcx.resolve_vars_if_possible(&ty)))
-                })
             {
                 struct VisitTypes(Vec<DefId>);
                 impl<'tcx> ty::fold::TypeVisitor<'tcx> for VisitTypes {
@@ -1812,7 +1807,7 @@ fn opaque_type_cycle_error(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
         }
     }
     if !label {
-        err.span_label(span, "cannot resolve to a concrete type");
+        err.span_label(span, "cannot resolve opaque type");
     }
     err.emit();
 }
@@ -1824,9 +1819,9 @@ fn binding_opaque_type_cycle_error(
     span: Span,
     partially_expanded_type: Ty<'tcx>,
 ) {
-    let mut err =
-        struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type to a concrete type");
-    err.span_label(span, "cannot resolve to a concrete type");
+    let mut err = struct_span_err!(tcx.sess, span, E0720, "cannot resolve opaque type");
+    err.span_label(span, "cannot resolve opaque type");
+    // Find the the owner that declared this `impl Trait` type.
     let hir_id = tcx.hir().as_local_hir_id(def_id);
     let mut prev_hir_id = hir_id;
     let mut hir_id = tcx.hir().get_parent_node(hir_id);
@@ -1855,15 +1850,12 @@ fn binding_opaque_type_cycle_error(
                 let hir_id = tcx.hir().as_local_hir_id(def_id);
                 let tables =
                     tcx.typeck_tables_of(tcx.hir().local_def_id(tcx.hir().get_parent_item(hir_id)));
-                let ty = tables.node_type_opt(expr.hir_id);
-                if let Some(ty) =
-                    tcx.infer_ctxt().enter(|infcx| infcx.resolve_vars_if_possible(&ty))
-                {
+                if let Some(ty) = tables.node_type_opt(expr.hir_id) {
                     err.span_label(
                         expr.span,
                         &format!(
                             "this is of type `{}`, which doesn't constrain \
-                                `{}` enough to arrive to a concrete type",
+                             `{}` enough to arrive to a concrete type",
                             ty, partially_expanded_type
                         ),
                     );

src/test/ui/impl-trait/binding-without-value.stderr

@@ -1,8 +1,8 @@
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/binding-without-value.rs:5:13
    |
 LL |     let _ : impl Copy;
-   |         -   ^^^^^^^^^ cannot resolve to a concrete type
+   |         -   ^^^^^^^^^ cannot resolve opaque type
    |         |
    |         this binding might not have a concrete type
    |

src/test/ui/impl-trait/issues/infinite-impl-trait-issue-38064.stderr

@@ -1,4 +1,4 @@
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/infinite-impl-trait-issue-38064.rs:8:13
    |
 LL | fn foo() -> impl Quux {
@@ -10,7 +10,7 @@ LL |     Foo(bar())
 LL | fn bar() -> impl Quux {
    |             --------- returning this opaque type `foo::Foo<impl Quux>`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/infinite-impl-trait-issue-38064.rs:14:13
    |
 LL | fn foo() -> impl Quux {

src/test/ui/impl-trait/recursive-impl-trait-type-direct.stderr

@@ -1,4 +1,4 @@
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-direct.rs:5:14
    |
 LL | fn test() -> impl Sized {

src/test/ui/impl-trait/recursive-impl-trait-type-indirect.stderr

@@ -1,4 +1,4 @@
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:7:22
    |
 LL | fn option(i: i32) -> impl Sized {
@@ -9,7 +9,7 @@ LL |     if i < 0 { None } else { Some((option(i - 1), i)) }
    |                |
    |                returning here with type `std::option::Option<(impl Sized, i32)>`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:12:15
    |
 LL | fn tuple() -> impl Sized {
@@ -18,7 +18,7 @@ LL |
 LL |     (tuple(),)
    |     ---------- returning here with type `(impl Sized,)`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:17:15
    |
 LL | fn array() -> impl Sized {
@@ -27,7 +27,7 @@ LL |
 LL |     [array()]
    |     --------- returning here with type `[impl Sized; 1]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:22:13
    |
 LL | fn ptr() -> impl Sized {
@@ -36,7 +36,7 @@ LL |
 LL |     &ptr() as *const _
    |     ------------------ returning here with type `*const impl Sized`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:27:16
    |
 LL | fn fn_ptr() -> impl Sized {
@@ -45,7 +45,7 @@ LL |
 LL |     fn_ptr as fn() -> _
    |     ------------------- returning here with type `fn() -> impl Sized`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:32:25
    |
 LL |   fn closure_capture() -> impl Sized {
@@ -56,7 +56,7 @@ LL | |         x;
 LL | |     }
    | |_____- returning here with type `[closure@$DIR/recursive-impl-trait-type-indirect.rs:35:5: 37:6 x:impl Sized]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:40:29
    |
 LL |   fn closure_ref_capture() -> impl Sized {
@@ -67,7 +67,7 @@ LL | |         &x;
 LL | |     }
    | |_____- returning here with type `[closure@$DIR/recursive-impl-trait-type-indirect.rs:43:5: 45:6 x:impl Sized]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:48:21
    |
 LL | fn closure_sig() -> impl Sized {
@@ -76,7 +76,7 @@ LL |
 LL |     || closure_sig()
    |     ---------------- returning here with type `[closure@$DIR/recursive-impl-trait-type-indirect.rs:50:5: 50:21]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:53:23
    |
 LL | fn generator_sig() -> impl Sized {
@@ -85,7 +85,7 @@ LL |
 LL |     || generator_sig()
    |     ------------------ returning here with type `[closure@$DIR/recursive-impl-trait-type-indirect.rs:55:5: 55:23]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:58:27
    |
 LL |   fn generator_capture() -> impl Sized {
@@ -97,7 +97,7 @@ LL | |         x;
 LL | |     }
    | |_____- returning here with type `[generator@$DIR/recursive-impl-trait-type-indirect.rs:61:5: 64:6 x:impl Sized {()}]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:67:35
    |
 LL | fn substs_change<T: 'static>() -> impl Sized {
@@ -106,7 +106,7 @@ LL |
 LL |     (substs_change::<&T>(),)
    |     ------------------------ returning here with type `(impl Sized,)`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:72:24
    |
 LL |   fn generator_hold() -> impl Sized {
@@ -119,7 +119,7 @@ LL | |         x;
 LL | |     }
    | |_____- returning here with type `[generator@$DIR/recursive-impl-trait-type-indirect.rs:74:5: 78:6 {impl Sized, ()}]`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:86:26
    |
 LL | fn mutual_recursion() -> impl Sync {
@@ -131,7 +131,7 @@ LL |     mutual_recursion_b()
 LL | fn mutual_recursion_b() -> impl Sized {
    |                            ---------- returning this opaque type `impl Sized`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-indirect.rs:91:28
    |
 LL | fn mutual_recursion() -> impl Sync {

src/test/ui/impl-trait/recursive-impl-trait-type-through-non-recursive.stderr

@@ -1,4 +1,4 @@
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-through-non-recursive.rs:7:22
    |
 LL | fn id<T>(t: T) -> impl Sized { t }
@@ -9,7 +9,7 @@ LL | fn recursive_id() -> impl Sized {
 LL |     id(recursive_id2())
    |     ------------------- returning here with type `impl Sized`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-through-non-recursive.rs:11:23
    |
 LL | fn id<T>(t: T) -> impl Sized { t }
@@ -20,7 +20,7 @@ LL | fn recursive_id2() -> impl Sized {
 LL |     id(recursive_id())
    |     ------------------ returning here with type `impl Sized`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-through-non-recursive.rs:17:24
    |
 LL | fn wrap<T>(t: T) -> impl Sized { (t,) }
@@ -31,7 +31,7 @@ LL | fn recursive_wrap() -> impl Sized {
 LL |     wrap(recursive_wrap2())
    |     ----------------------- returning here with type `impl Sized`
 
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/recursive-impl-trait-type-through-non-recursive.rs:21:25
    |
 LL | fn wrap<T>(t: T) -> impl Sized { (t,) }

src/test/ui/impl-trait/where-allowed-2.stderr

@@ -1,10 +1,10 @@
-error[E0720]: cannot resolve opaque type to a concrete type
+error[E0720]: cannot resolve opaque type
   --> $DIR/where-allowed-2.rs:6:30
    |
 LL | fn in_adt_in_return() -> Vec<impl Debug> { panic!() }
    |                              ^^^^^^^^^^    -------- this returned value is of `!` type
    |                              |
-   |                              cannot resolve to a concrete type
+   |                              cannot resolve opaque type
    |
    = help: this error will resolve once the item's body returns a concrete type