Make `+` in `impl/dyn Trait` non-associative

2 files changed, 87 insertions, 7 deletions

diff --git a/src/test/parse-fail/impl-trait-plus-priority.rs b/src/test/ui/impl-trait/impl-trait-plus-priority.rs
index 6d12a68cf3d..f451123ca27 100644
--- a/src/test/parse-fail/impl-trait-plus-priority.rs
+++ b/src/test/ui/impl-trait/impl-trait-plus-priority.rs
@@ -10,11 +10,15 @@
 
 // compile-flags: -Z parse-only -Z continue-parse-after-error
 
+fn f() -> impl A + {} // OK
 fn f() -> impl A + B {} // OK
 fn f() -> dyn A + B {} // OK
 fn f() -> A + B {} // OK
 
 impl S {
+    fn f(self) -> impl A + { // OK
+        let _ = |a, b| -> impl A + {}; // OK
+    }
     fn f(self) -> impl A + B { // OK
         let _ = |a, b| -> impl A + B {}; // OK
     }
@@ -26,21 +30,29 @@ impl S {
     }
 }
 
+type A = fn() -> impl A +;
+//~^ ERROR ambiguous `+` in a type
 type A = fn() -> impl A + B;
-//~^ ERROR expected a path on the left-hand side of `+`, not `fn() -> impl A`
+//~^ ERROR ambiguous `+` in a type
 type A = fn() -> dyn A + B;
-//~^ ERROR expected a path on the left-hand side of `+`, not `fn() -> dyn A`
+//~^ ERROR ambiguous `+` in a type
 type A = fn() -> A + B;
 //~^ ERROR expected a path on the left-hand side of `+`, not `fn() -> A`
 
-type A = Fn() -> impl A + B; // OK, interpreted as `(Fn() -> impl A) + B`
-type A = Fn() -> dyn A + B; // OK, interpreted as `(Fn() -> dyn A) + B`
-type A = Fn() -> A + B; // OK, interpreted as `(Fn() -> A) + B`
+type A = Fn() -> impl A +;
+//~^ ERROR ambiguous `+` in a type
+type A = Fn() -> impl A + B;
+//~^ ERROR ambiguous `+` in a type
+type A = Fn() -> dyn A + B;
+//~^ ERROR ambiguous `+` in a type
+type A = Fn() -> A + B; // OK, interpreted as `(Fn() -> A) + B` for compatibility
 
+type A = &impl A +;
+//~^ ERROR ambiguous `+` in a type
 type A = &impl A + B;
-//~^ ERROR expected a path on the left-hand side of `+`, not `&impl A`
+//~^ ERROR ambiguous `+` in a type
 type A = &dyn A + B;
-//~^ ERROR expected a path on the left-hand side of `+`, not `&dyn A`
+//~^ ERROR ambiguous `+` in a type
 type A = &A + B;
 //~^ ERROR expected a path on the left-hand side of `+`, not `&A`
 
diff --git a/src/test/ui/impl-trait/impl-trait-plus-priority.stderr b/src/test/ui/impl-trait/impl-trait-plus-priority.stderr
new file mode 100644
index 00000000000..885c3941971
--- /dev/null
+++ b/src/test/ui/impl-trait/impl-trait-plus-priority.stderr
@@ -0,0 +1,68 @@
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:33:18
+   |
+33 | type A = fn() -> impl A +;
+   |                  ^^^^^^^^ help: use parentheses to disambiguate: `(impl A)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:35:18
+   |
+35 | type A = fn() -> impl A + B;
+   |                  ^^^^^^^^^^ help: use parentheses to disambiguate: `(impl A + B)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:37:18
+   |
+37 | type A = fn() -> dyn A + B;
+   |                  ^^^^^^^^^ help: use parentheses to disambiguate: `(dyn A + B)`
+
+error[E0178]: expected a path on the left-hand side of `+`, not `fn() -> A`
+  --> $DIR/impl-trait-plus-priority.rs:39:10
+   |
+39 | type A = fn() -> A + B;
+   |          ^^^^^^^^^^^^^ perhaps you forgot parentheses?
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:42:18
+   |
+42 | type A = Fn() -> impl A +;
+   |                  ^^^^^^^^ help: use parentheses to disambiguate: `(impl A)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:44:18
+   |
+44 | type A = Fn() -> impl A + B;
+   |                  ^^^^^^^^^^ help: use parentheses to disambiguate: `(impl A + B)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:46:18
+   |
+46 | type A = Fn() -> dyn A + B;
+   |                  ^^^^^^^^^ help: use parentheses to disambiguate: `(dyn A + B)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:50:11
+   |
+50 | type A = &impl A +;
+   |           ^^^^^^^^ help: use parentheses to disambiguate: `(impl A)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:52:11
+   |
+52 | type A = &impl A + B;
+   |           ^^^^^^^^^^ help: use parentheses to disambiguate: `(impl A + B)`
+
+error: ambiguous `+` in a type
+  --> $DIR/impl-trait-plus-priority.rs:54:11
+   |
+54 | type A = &dyn A + B;
+   |           ^^^^^^^^^ help: use parentheses to disambiguate: `(dyn A + B)`
+
+error[E0178]: expected a path on the left-hand side of `+`, not `&A`
+  --> $DIR/impl-trait-plus-priority.rs:56:10
+   |
+56 | type A = &A + B;
+   |          ^^^^^^ help: try adding parentheses: `&(A + B)`
+
+error: aborting due to 11 previous errors
+