[Serialization] Write ProtocolComposition as dependencies

A type dependencies are used at deserialization to drop a protocol early
when a dependency is not deserializable. Dependencies on protocols via a
protocol composition were not taken into account. This lead to the
deserialization process failing later. Fix the serialization process to
write protocol dependencies too.

rdar://78631465

Author: xymus

lib/Serialization/Serialization.cpp

@@ -3511,7 +3511,9 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     for (auto element : proto->getInherited()) {
       auto elementType = element.getType();
       assert(!elementType || !elementType->hasArchetype());
-      if (elementType && elementType->is<ProtocolType>())
+      if (elementType &&
+          (elementType->is<ProtocolType>() ||
+           elementType->is<ProtocolCompositionType>()))
         dependencyTypes.insert(elementType);
     }
 

test/Serialization/Recovery/implementation-only-missing.swift

@@ -43,6 +43,8 @@ public protocol HiddenProtocol {
   associatedtype Value
 }
 
+public protocol HiddenProtocol2 {}
+
 public protocol HiddenProtocolWithOverride {
   func hiddenOverride()
 }
@@ -98,6 +100,15 @@ public class SomeClass {
     func funcUsingIoiType(_ a: HiddenClass) {}
 }
 
+// Check that we recover from a reference to an implementation-only
+// imported type in a protocol composition. rdar://78631465
+protocol CompositionMemberInheriting : HiddenProtocol2 {}
+protocol CompositionMemberSimple {}
+protocol InheritingFromComposition : CompositionMemberInheriting & CompositionMemberSimple {}
+struct StructInheritingFromComposition : CompositionMemberInheriting & CompositionMemberSimple {}
+class ClassInheritingFromComposition : CompositionMemberInheriting & CompositionMemberSimple {}
+protocol InheritingFromCompositionDirect : CompositionMemberSimple & HiddenProtocol2 {}
+
 #elseif CLIENT_APP
 
 import public_lib