Auto merge of #786 - jackh726:inductive_canonical_cycle, r=compiler-errors

Add test for inductive canonical cycle

See https://github.com/rust-lang/rust/blob/885dcb975ba10511ed2296f51b0db3c17ad7399b/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.rs

Author: bors

.gitignore

@@ -12,6 +12,7 @@ chalk-parse/src/parser.rs
 
 ## IDE files
 /.idea/
+/.vscode/
 
 ## Files used in changelog generation
 package.json

tests/test/cycle.rs

@@ -260,3 +260,37 @@ fn cycle_with_ambiguity() {
         }
     }
 }
+
+#[test]
+fn inductive_canonical_cycle() {
+    test! {
+        program {
+            trait Trait<T, U> {}
+
+            impl<T, U> Trait<T, U> for ()
+            where
+                (): Trait<U, T>,
+                T: OtherTrait,
+            {}
+
+            trait OtherTrait {}
+            impl OtherTrait for u32 {}
+        }
+
+        goal {
+            (): Trait<u32, u32>
+        } yields {
+            // FIXME: Should be unique
+            expect![["No possible solution"]]
+        }
+
+        goal {
+            exists<T, U> {
+                (): Trait<T, U>
+            }
+        } yields {
+            // FIXME: Should be unique
+            expect![["No possible solution"]]
+        }
+    }
+}