Defining use errors yield the error type to reduce irrelevant follow-up diagnostics

Author: oli-obk

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -1109,10 +1109,10 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
             } else {
                 // Don't emit multiple errors for the same set of substs
                 opaque_defn.substs.push(substs);
-                /*opaque_defn.concrete_ty = tcx.ty_error_with_message(
+                opaque_defn.concrete_ty = tcx.ty_error_with_message(
                     self.value_span,
                     "defining use generics differ from previous defining use",
-                );*/
+                );
                 tcx.sess
                     .struct_span_err(
                         self.value_span,

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn.rs

@@ -5,7 +5,6 @@
 #![feature(min_type_alias_impl_trait)]
 
 type X<A, B> = impl Into<&'static A>;
-//~^ ERROR the trait bound `&'static B: From<&A>` is not satisfied
 
 fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
     //~^ ERROR defining use generics `[B, A]` differ from previous defining use

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn.stderr

@@ -1,39 +1,26 @@
 error: defining use generics `[B, A]` differ from previous defining use
-  --> $DIR/multiple-def-uses-in-one-fn.rs:10:45
+  --> $DIR/multiple-def-uses-in-one-fn.rs:9:45
    |
 LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
    |                                             ^^^^^^^^^^^^^^^^^^
    |
 note: previous defining use with different generics `[A, B]` found here
-  --> $DIR/multiple-def-uses-in-one-fn.rs:10:45
+  --> $DIR/multiple-def-uses-in-one-fn.rs:9:45
    |
 LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
    |                                             ^^^^^^^^^^^^^^^^^^
 
-error[E0277]: the trait bound `&'static B: From<&A>` is not satisfied
-  --> $DIR/multiple-def-uses-in-one-fn.rs:7:16
-   |
-LL | type X<A, B> = impl Into<&'static A>;
-   |                ^^^^^^^^^^^^^^^^^^^^^ the trait `From<&A>` is not implemented for `&'static B`
-   |
-   = note: required because of the requirements on the impl of `Into<&'static B>` for `&A`
-help: consider introducing a `where` bound, but there might be an alternative better way to express this requirement
-   |
-LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) where &'static B: From<&A> {
-   |                                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
-
 error: defining use generics `[B, A]` differ from previous defining use
-  --> $DIR/multiple-def-uses-in-one-fn.rs:10:1
+  --> $DIR/multiple-def-uses-in-one-fn.rs:9:1
    |
 LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: previous defining use with different generics `[A, B]` found here
-  --> $DIR/multiple-def-uses-in-one-fn.rs:10:1
+  --> $DIR/multiple-def-uses-in-one-fn.rs:9:1
    |
 LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.rs

@@ -13,6 +13,7 @@ fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>)
 }
 
 fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
+    //~^ ERROR concrete type differs from previous defining opaque type use
     (a, b) //~ ERROR mismatched types
 }
 

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.stderr

@@ -23,12 +23,13 @@ LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
-  --> $DIR/multiple-def-uses-in-one-fn3.rs:16:9
+  --> $DIR/multiple-def-uses-in-one-fn3.rs:17:9
    |
 LL | fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
    |      -                    - found type parameter
    |      |
    |      expected type parameter
+LL |
 LL |     (a, b)
    |         ^ expected type parameter `A`, found type parameter `B`
    |
@@ -37,6 +38,18 @@ LL |     (a, b)
    = note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
    = note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
 
-error: aborting due to 3 previous errors
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/multiple-def-uses-in-one-fn3.rs:15:1
+   |
+LL | fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `[type error]`, got `A`
+   |
+note: previous use here
+  --> $DIR/multiple-def-uses-in-one-fn3.rs:9:1
+   |
+LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0308`.