[TypeConstraints] Warning cast to unrelated of protocol composition to no existential type

Author: LucianoPAlmeida

lib/Sema/TypeCheckConstraints.cpp

@@ -3554,6 +3554,20 @@ CheckedCastKind TypeChecker::typeCheckCheckedCast(Type fromType,
       if (!couldDynamicallyConformToProtocol(toType, protocolDecl, dc)) {
         return failed();
       }
+    } else if (auto protocolComposition =
+                   fromType->getAs<ProtocolCompositionType>()) {
+      if (!protocolComposition->getMembers().empty() &&
+          llvm::any_of(protocolComposition->getMembers(),
+                       [&](Type protocolType) {
+                         if (auto protocolDecl = dyn_cast_or_null<ProtocolDecl>(
+                                 protocolType->getAnyNominal())) {
+                           return !couldDynamicallyConformToProtocol(
+                               toType, protocolDecl, dc);
+                         }
+                         return false;
+                       })) {
+        return failed();
+      }
     }
 
     // If neither type is class-constrained, anything goes.

test/Constraints/casts.swift

@@ -113,10 +113,10 @@ func protocol_concrete_casts(_ p1: P1, p2: P2, p12: P1 & P2) {
 
   _ = p2 as! S1 // expected-warning {{cast from 'P2' to unrelated type 'S1' always fails}}
 
-  _ = p12 as! S1
-  _ = p12 as! S2
+  _ = p12 as! S1 // expected-warning {{cast from 'P1 & P2' to unrelated type 'S1' always fails}}
+  _ = p12 as! S2 // expected-warning {{cast from 'P1 & P2' to unrelated type 'S2' always fails}}
   _ = p12 as! S12
-  _ = p12 as! S3
+  _ = p12 as! S3 // expected-warning {{cast from 'P1 & P2' to unrelated type 'S3' always fails}}
 
   // Type queries.
   var _:Bool = p1 is S1
@@ -128,10 +128,10 @@ func protocol_concrete_casts(_ p1: P1, p2: P2, p12: P1 & P2) {
 
   var _:Bool = p2 is S1 // expected-warning {{cast from 'P2' to unrelated type 'S1' always fails}}
 
-  var _:Bool = p12 is S1
-  var _:Bool = p12 is S2
+  var _:Bool = p12 is S1 // expected-warning {{cast from 'P1 & P2' to unrelated type 'S1' always fails}}
+  var _:Bool = p12 is S2 // expected-warning {{cast from 'P1 & P2' to unrelated type 'S2' always fails}}
   var _:Bool = p12 is S12
-  var _:Bool = p12 is S3
+  var _:Bool = p12 is S3 // expected-warning {{cast from 'P1 & P2' to unrelated type 'S3' always fails}}
 }
 
 func conditional_cast(_ b: B) -> D? {
@@ -372,6 +372,26 @@ enum ConcreteA: EventA {
   }
 }
 
+protocol ProtocolP1 {}
+protocol ProtocolQ1 {}
+typealias Composition = ProtocolP1 & ProtocolQ1
+
+protocol ProtocolP {}
+protocol ProtocolQ {}
+
+class ConcreteP: ProtocolP {}
+class ConcreteQ: ProtocolQ {}
+class ConcretePQ: ProtocolP, ProtocolQ {}
+class ConcreteCPQ: ConcreteP, ProtocolQ {}
+
+class ConcreteP1: ProtocolP1 {}
+class ConcretePQ1: ProtocolP1, ProtocolQ1 {}
+
+class ConcretePPQ1: ProtocolP, ProtocolP1, ProtocolQ1 {}
+class NotConforms {}
+struct StructNotComforms {}
+final class NotConformsFinal {}
+
 func tests_SR13088_false_positive_always_fail_casts() {
   // SR-13081
   let x: JSON = [4] // [4]
@@ -403,3 +423,20 @@ func tests_SR13088_false_positive_always_fail_casts() {
     }
   }
 }
+
+// Protocol composition
+func protocol_composition(_ c: ProtocolP & ProtocolQ, _ c1: ProtocolP & Composition) {
+  _ = c as? ConcretePQ // Ok
+  _ = c as? ConcreteCPQ // Ok
+  _ = c as? ConcreteP // Ok
+  _ = c as? NotConforms // Ok
+  _ = c as? StructNotComforms // expected-warning {{cast from 'ProtocolP & ProtocolQ' to unrelated type 'StructNotComforms' always fails}}
+  _ = c as? NotConformsFinal // expected-warning {{cast from 'ProtocolP & ProtocolQ' to unrelated type 'NotConformsFinal' always fails}}
+  _ = c1 as? ConcreteP // Ok
+  _ = c1 as? ConcreteP1 // OK
+  _ = c1 as? ConcretePQ1 // OK
+  _ = c1 as? ConcretePPQ1 // Ok
+  _ = c1 as? NotConforms // Ok
+  _ = c1 as? StructNotComforms // expected-warning {{cast from 'ProtocolP & Composition' (aka 'ProtocolP & ProtocolP1 & ProtocolQ1') to unrelated type 'StructNotComforms' always fails}}
+  _ = c1 as? NotConformsFinal // expected-warning {{cast from 'ProtocolP & Composition' (aka 'ProtocolP & ProtocolP1 & ProtocolQ1') to unrelated type 'NotConformsFinal' always fails}}
+}