[Serialization] Distinguish between protocol/extension for types too. (#7794)

Replace an existing flag for cross-references to member types (that
wasn't getting much use) with one consistent with how we lookup
values. This fixes the case where someone actually has a useful type
as a member of a protocol extension, and that type gets referenced in
another module; Dispatch does exactly this.

Because you can currently only define typealiases in protocol
extensions, not new types, there's always a workaround for someone
hitting this issue: just use the underlying type.

https://bugs.swift.org/browse/SR-4076

include/swift/Serialization/ModuleFormat.h

@@ -54,7 +54,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// in source control, you should also update the comment to briefly
 /// 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.
-const uint16_t VERSION_MINOR = 320; // Last change: inherited protocols
+const uint16_t VERSION_MINOR = 321; // Last change: restrict to extension
 
 using DeclID = PointerEmbeddedInt<unsigned, 31>;
 using DeclIDField = BCFixed<31>;
@@ -1181,7 +1181,7 @@ namespace decls_block {
   using XRefTypePathPieceLayout = BCRecordLayout<
     XREF_TYPE_PATH_PIECE,
     IdentifierIDField, // name
-    BCFixed<1>         // only in nominal
+    BCFixed<1>         // restrict to protocol extension
   >;
 
   using XRefValuePathPieceLayout = BCRecordLayout<

lib/Serialization/Deserialization.cpp

@@ -1321,11 +1321,10 @@ Decl *ModuleFile::resolveCrossReference(ModuleDecl *baseModule,
     IdentifierID IID;
     TypeID TID = 0;
     bool isType = (recordID == XREF_TYPE_PATH_PIECE);
-    bool onlyInNominal = false;
     bool inProtocolExt = false;
     bool isStatic = false;
     if (isType)
-      XRefTypePathPieceLayout::readRecord(scratch, IID, onlyInNominal);
+      XRefTypePathPieceLayout::readRecord(scratch, IID, inProtocolExt);
     else
       XRefValuePathPieceLayout::readRecord(scratch, TID, IID, inProtocolExt,
                                            isStatic);
@@ -1496,13 +1495,12 @@ Decl *ModuleFile::resolveCrossReference(ModuleDecl *baseModule,
       Identifier memberName;
       Optional<swift::CtorInitializerKind> ctorInit;
       bool isType = false;
-      bool onlyInNominal = false;
       bool inProtocolExt = false;
       bool isStatic = false;
       switch (recordID) {
       case XREF_TYPE_PATH_PIECE: {
         IdentifierID IID;
-        XRefTypePathPieceLayout::readRecord(scratch, IID, onlyInNominal);
+        XRefTypePathPieceLayout::readRecord(scratch, IID, inProtocolExt);
         memberName = getIdentifier(IID);
         isType = true;
         break;
@@ -1548,7 +1546,7 @@ Decl *ModuleFile::resolveCrossReference(ModuleDecl *baseModule,
         return nullptr;
       }
 
-      auto members = nominal->lookupDirect(memberName, onlyInNominal);
+      auto members = nominal->lookupDirect(memberName);
       values.append(members.begin(), members.end());
       filterValues(filterTy, M, genericSig, isType, inProtocolExt, isStatic,
                    ctorInit, values);

lib/Serialization/Serialization.cpp

@@ -1803,18 +1803,17 @@ void Serializer::writeCrossReference(const Decl *D) {
     return;
   }
 
+  bool isProtocolExt = D->getDeclContext()->getAsProtocolExtensionContext();
   if (auto type = dyn_cast<TypeDecl>(D)) {
     abbrCode = DeclTypeAbbrCodes[XRefTypePathPieceLayout::Code];
     XRefTypePathPieceLayout::emitRecord(Out, ScratchRecord, abbrCode,
                                         addIdentifierRef(type->getName()),
-                                        isa<ProtocolDecl>(
+                                        isProtocolExt);
-                                          type->getDeclContext()));
     return;
   }
 
   auto val = cast<ValueDecl>(D);
   auto ty = val->getInterfaceType()->getCanonicalType();
-  bool isProtocolExt = D->getDeclContext()->getAsProtocolExtensionContext();
   abbrCode = DeclTypeAbbrCodes[XRefValuePathPieceLayout::Code];
   XRefValuePathPieceLayout::emitRecord(Out, ScratchRecord, abbrCode,
                                        addTypeRef(ty),

test/Serialization/Inputs/alias.swift

@@ -26,3 +26,8 @@ public struct Base {
   }
 }
 public typealias BaseAlias = Base
+
+public protocol ProtoWrapper {}
+extension ProtoWrapper {
+  public typealias Boolean = Bool
+}

test/Serialization/Inputs/has_xref.swift

@@ -3,6 +3,7 @@ import has_alias
 
 public func numeric(_ x: MyInt64) {}
 public func conditional(_ x: AliasWrapper.Boolean) {}
+public func conditional2(_ x: ProtoWrapper.Boolean) {}
 public func longInt(_ x: Int.EspeciallyMagicalInt) {}
 
 public func numericArray(_ x: IntSlice) {}

test/Serialization/xref.swift

@@ -14,6 +14,7 @@ import has_xref
 
 numeric(42)
 conditional(true)
+conditional2(true)
 longInt(42)
 numericArray([42])