[Opaque result types] Fix mangling issues with opaque result types.

Fix a trio of issues involving mangling for opaque result types:
* Symbolic references to opaque type descriptors are not substitutions
* Mangle protocol extension contexts correctly
* Mangle generic arguments for opaque result types of generic functions

The (de-)serialization of generic parameter lists for opaque type
declarations is important for the last bullet, to ensure that the
mangling of generic arguments of opaque result types works across
module boundaries.

Fixes the rest of rdar://problem/50038754.

include/swift/Serialization/ModuleFormat.h

@@ -52,7 +52,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 486; // Last change: Opaque result types
+const uint16_t SWIFTMODULE_VERSION_MINOR = 487; // Last change: Opaque result types generic params
 
 using DeclIDField = BCFixed<31>;
 
@@ -1101,6 +1101,7 @@ namespace decls_block {
     TypeIDField, // interface type for opaque type
     GenericEnvironmentIDField, // generic environment
     SubstitutionMapIDField // optional substitution map for underlying type
+    // trailed by generic parameters
   >;
 
   // TODO: remove the unnecessary FuncDecl components here

lib/AST/ASTMangler.cpp

@@ -985,7 +985,7 @@ void ASTMangler::appendType(Type type, const ValueDecl *forDecl) {
       // Use the fully elaborated explicit mangling.
       appendOpaqueDeclName(opaqueDecl);
       bool isFirstArgList = true;
-      appendBoundGenericArgs(opaqueDecl->getInnermostDeclContext(),
+      appendBoundGenericArgs(opaqueDecl,
                              opaqueType->getSubstitutions(),
                              isFirstArgList);
       appendRetroactiveConformances(opaqueType->getSubstitutions(),
@@ -1168,7 +1168,9 @@ unsigned ASTMangler::appendBoundGenericArgs(DeclContext *dc,
   auto decl = dc->getInnermostDeclarationDeclContext();
   if (!decl) return 0;
 
-  // For an extension declaration, use the nominal type declaration instead.
+  // For a non-protocol extension declaration, use the nominal type declaration
+  // instead.
+  //
   // This is important when extending a nested type, because the generic
   // parameters will line up with the (semantic) nesting of the nominal type.
   if (auto ext = dyn_cast<ExtensionDecl>(decl))

lib/Demangling/Demangler.cpp

@@ -690,7 +690,8 @@ NodePointer Demangler::demangleSymbolicReference(unsigned char rawKind,
     return nullptr;
   
   // Types register as substitutions even when symbolically referenced.
-  if (kind == SymbolicReferenceKind::Context)
+  if (kind == SymbolicReferenceKind::Context &&
+      resolved->getKind() != Node::Kind::OpaqueTypeDescriptorSymbolicReference)
     addSubstitution(resolved);
   return resolved;
 }

lib/Serialization/Deserialization.cpp

@@ -3099,6 +3099,9 @@ public:
                                sig, interfaceType);
     declOrOffset = opaqueDecl;
 
+    if (auto genericParams = MF.maybeReadGenericParams(opaqueDecl))
+      opaqueDecl->setGenericParams(genericParams);
+
     auto genericEnv = MF.getGenericEnvironment(genericEnvID);
     opaqueDecl->setGenericEnvironment(genericEnv);
     if (underlyingTypeID)

lib/Serialization/Serialization.cpp

@@ -3437,6 +3437,7 @@ void Serializer::writeDecl(const Decl *D) {
                                  contextID, namingDeclID, interfaceSigID,
                                  interfaceTypeID, genericEnvID,
                                  underlyingTypeID);
+    writeGenericParams(opaqueDecl->getGenericParams());
     break;
   }
 

test/Interpreter/opaque_return_type_protocol_ext.swift

@@ -6,9 +6,16 @@ protocol P {
   func foo() -> AT
 }
 
+struct Adapter<T: P>: P {
+  var inner: T
+  func foo() -> some P {
+    return inner
+  }
+}
+
 extension P {
   func foo() -> some P {
-    return self
+    return Adapter(inner: self)
   }
 }
 
@@ -18,5 +25,5 @@ func getPAT<T: P>(_: T.Type) -> Any.Type {
 
 extension Int: P { }
 
-// CHECK: Int
+// CHECK: Adapter<Int>
 print(getPAT(Int.self))

test/Serialization/Inputs/OpaqueCrossFileB.swift

@@ -19,3 +19,9 @@ public struct Subscript {
     return FooImpl()
   }
 }
+
+extension Foo {
+  public func identity<T>(_: T) -> some Foo {
+    return self
+  }
+}

test/Serialization/opaque_cross_file.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -emit-module-path %t/OpaqueCrossFileB.swiftmodule -module-name OpaqueCrossFileB %S/Inputs/OpaqueCrossFileB.swift
-// RUN: %target-swift-frontend -I %t -emit-ir -verify %s
+// RUN: %target-swift-frontend -I %t -emit-ir -verify %s | %FileCheck %s
 
 import OpaqueCrossFileB
 
@@ -8,3 +8,11 @@ dump(anyFoo())
 dump(anyFooProp)
 dump(Subscript()[])
 
+public struct UsesAdapterMethod: Foo {
+  // Ensure that the mangling of the result type of adaptFoo correctly captures
+  // both the Self type and the parameter type.
+  // CHECK: @"symbolic _____y______SdQo_ 16OpaqueCrossFileB3FooPAAE8identityyQrqd__lFQO 17opaque_cross_file17UsesAdapterMethodV" =
+  public func adaptFoo(_ d: Double) -> some Foo {
+    return identity(d)
+  }
+}