Merge pull request #58624 from CodaFi/existence-is-suffering

Existential Types Cannot Satisfy Superclass Bounds

Author: CodaFi

lib/Sema/CSSimplify.cpp

@@ -3465,8 +3465,11 @@ ConstraintSystem::matchExistentialTypes(Type type1, Type type2,
               if (!req)
                 return getTypeMatchFailure(locator);
 
-              if (type1->isPlaceholder() ||
-                  req->getRequirementKind() == RequirementKind::Superclass)
+              // Superclass constraints are never satisfied by existentials,
+              // even those that contain the superclass a la `any C & P`.
+              if (!type1->isExistentialType() &&
+                  (type1->isPlaceholder() ||
+                  req->getRequirementKind() == RequirementKind::Superclass))
                 return getTypeMatchSuccess();
 
               auto *fix = fixRequirementFailure(*this, type1, type2, locator);

test/Constraints/members.swift

@@ -753,3 +753,25 @@ func fSR14533(_ s: SR14533) {
     // expected-error@-1{{value of type 'SR14533' has no member 'ys'}}
   }
 }
+
+// rdar://92358570
+class SomeClassBound {}
+protocol ClassBoundProtocol: SomeClassBound {
+}
+
+struct RDAR92358570<Element> {}
+
+extension RDAR92358570 where Element : SomeClassBound {
+// expected-note@-1 2 {{where 'Element' = 'any ClassBoundProtocol', 'SomeClassBound' = 'AnyObject'}}
+// expected-note@-2 2 {{where 'Element' = 'any SomeClassBound & ClassBoundProtocol', 'SomeClassBound' = 'AnyObject'}}
+  func doSomething() {}
+  static func doSomethingStatically() {}
+}
+
+func rdar92358570(_ x: RDAR92358570<ClassBoundProtocol>, _ y: RDAR92358570<SomeClassBound & ClassBoundProtocol>) {
+  x.doSomething() // expected-error {{referencing instance method 'doSomething()' on 'RDAR92358570' requires that 'any ClassBoundProtocol' inherit from 'AnyObject'}}
+  RDAR92358570<ClassBoundProtocol>.doSomethingStatically() // expected-error {{referencing static method 'doSomethingStatically()' on 'RDAR92358570' requires that 'any ClassBoundProtocol' inherit from 'AnyObject'}}
+
+  y.doSomething() // expected-error {{referencing instance method 'doSomething()' on 'RDAR92358570' requires that 'any SomeClassBound & ClassBoundProtocol' inherit from 'AnyObject'}}
+  RDAR92358570<SomeClassBound & ClassBoundProtocol>.doSomethingStatically() // expected-error {{referencing static method 'doSomethingStatically()' on 'RDAR92358570' requires that 'any SomeClassBound & ClassBoundProtocol' inherit from 'AnyObject'}}
+}