Emit an error when there are two differently inferred impl traits within a single function

Author: oli-obk

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -1109,22 +1109,26 @@ 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(
+                    self.value_span,
+                    "defining use generics differ from previous defining use",
+                );*/
                 tcx.sess
                     .struct_span_err(
                         self.value_span,
                         &format!(
-                            "defining use generics {:?} differ from previous defining use",
+                            "defining use generics `{:?}` differ from previous defining use",
                             substs
                         ),
                     )
                     .span_note(
                         opaque_defn.definition_span,
                         &format!(
-                            "previous defining use with different generics {:?} found here",
+                            "previous defining use with different generics `{:?}` found here",
                             opaque_defn.substs[0]
                         ),
                     )
-                    .delay_as_bug();
+                    .emit();
             }
         }
         let span = tcx.def_span(def_id);
@@ -1161,7 +1165,7 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
         let definition_span = self.value_span;
 
         // We only keep the first concrete type var, as we will already error
-        // out if there are multiple due to the conflicting obligations 
+        // out if there are multiple due to the conflicting obligations
         if !self.opaque_types.contains_key(&def_id) {
             self.opaque_types.insert(
                 def_id,

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

@@ -0,0 +1,12 @@
+// check-pass
+#![feature(min_type_alias_impl_trait)]
+
+type X<A: ToString + Clone, B: ToString + Clone> = impl ToString;
+
+fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
+    (a.clone(), a)
+}
+
+fn main() {
+    println!("{}", <X<_, _> as ToString>::to_string(&f(42_i32, String::new()).1));
+}

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

@@ -5,9 +5,11 @@
 #![feature(min_type_alias_impl_trait)]
 
 type X<A, B> = impl Into<&'static A>;
-//~^ the trait bound `&'static B: From<&A>` is not satisfied
+//~^ 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
+    //~| ERROR defining use generics `[B, A]` differ from previous defining use
     (a, a)
 }
 

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

@@ -1,3 +1,15 @@
+error: defining use generics `[B, A]` differ from previous defining use
+  --> $DIR/multiple-def-uses-in-one-fn.rs:10:45
+   |
+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
+   |
+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
    |
@@ -10,6 +22,18 @@ help: consider introducing a `where` bound, but there might be an alternative be
 LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) where &'static B: From<&A> {
    |                                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: defining use generics `[B, A]` differ from previous defining use
+  --> $DIR/multiple-def-uses-in-one-fn.rs:10:1
+   |
+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
+   |
+LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn2.rs

@@ -0,0 +1,17 @@
+// https://github.com/rust-lang/rust/issues/73481
+// This test used to cause unsoundness, since one of the two possible
+// resolutions was chosen at random instead of erroring due to conflicts.
+
+#![feature(min_type_alias_impl_trait)]
+
+type X<A: ToString + Clone, B: ToString + Clone> = impl ToString;
+
+fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>) {
+    //~^ ERROR defining use generics `[B, A]` differ from previous defining use
+    //~| ERROR defining use generics `[B, A]` differ from previous defining use
+    (a.clone(), a)
+}
+
+fn main() {
+    println!("{}", <X<_, _> as ToString>::to_string(&f(42_i32, String::new()).1));
+}

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn2.stderr

@@ -0,0 +1,26 @@
+error: defining use generics `[B, A]` differ from previous defining use
+  --> $DIR/multiple-def-uses-in-one-fn2.rs:9:63
+   |
+LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: 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-fn2.rs:9:63
+   |
+LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>) {
+   |                                                               ^^^^^^^^^^^^^^^^^^
+
+error: defining use generics `[B, A]` differ from previous defining use
+  --> $DIR/multiple-def-uses-in-one-fn2.rs:9:1
+   |
+LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: 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-fn2.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 2 previous errors
+

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

@@ -0,0 +1,19 @@
+// https://github.com/rust-lang/rust/issues/73481
+// This test used to cause unsoundness, since one of the two possible
+// resolutions was chosen at random instead of erroring due to conflicts.
+
+#![feature(min_type_alias_impl_trait)]
+
+type X<A: ToString + Clone, B: ToString + Clone> = impl ToString;
+
+fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>) {
+    //~^ ERROR defining use generics `[B, A]` differ from previous defining use
+    //~| ERROR defining use generics `[B, A]` differ from previous defining use
+    (a, b)
+}
+
+fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
+    (a, b) //~ ERROR mismatched types
+}
+
+fn main() {}

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

@@ -0,0 +1,42 @@
+error: defining use generics `[B, A]` differ from previous defining use
+  --> $DIR/multiple-def-uses-in-one-fn3.rs:9:63
+   |
+LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: 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-fn3.rs:9:63
+   |
+LL | fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<B, A>) {
+   |                                                               ^^^^^^^^^^^^^^^^^^
+
+error: defining use generics `[B, A]` differ from previous defining use
+  --> $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>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: previous defining use with different generics `[A, B]` found 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[E0308]: mismatched types
+  --> $DIR/multiple-def-uses-in-one-fn3.rs:16:9
+   |
+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 |     (a, b)
+   |         ^ expected type parameter `A`, found type parameter `B`
+   |
+   = note: expected type parameter `A`
+              found type parameter `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
+
+For more information about this error, try `rustc --explain E0308`.