Store the name of the extended module in the SymbolGraph.

lib/SymbolGraphGen/FormatVersion.h

@@ -14,7 +14,7 @@
 #define SWIFT_SYMBOLGRAPHGEN_FORMATVERSION_H
 
 #define SWIFT_SYMBOLGRAPH_FORMAT_MAJOR 0
-#define SWIFT_SYMBOLGRAPH_FORMAT_MINOR 6
+#define SWIFT_SYMBOLGRAPH_FORMAT_MINOR 7
 #define SWIFT_SYMBOLGRAPH_FORMAT_PATCH 0
 
 #endif // SWIFT_SYMBOLGRAPHGEN_FORMATVERSION_H

lib/SymbolGraphGen/SymbolGraph.cpp

@@ -624,16 +624,26 @@ void SymbolGraph::serialize(llvm::json::OStream &OS) {
     }); // end metadata:
 
     OS.attributeObject("module", [&](){
+      std::string ModuleName;
       if (DeclaringModule) {
         // A cross-import overlay can be considered part of its declaring module
-        OS.attribute("name", getFullModuleName(*DeclaringModule));
+        ModuleName = getFullModuleName(*DeclaringModule);
+        OS.attribute("name", ModuleName);
         std::vector<StringRef> B;
         for (auto BModule : BystanderModules) {
           B.push_back(BModule.str());
         }
         OS.attribute("bystanders", B);
       } else {
-        OS.attribute("name", getFullModuleName(&M));
+        ModuleName = getFullModuleName(&M);
+        OS.attribute("name", ModuleName);
+      }
+      if (ExtendedModule) {
+        OS.attribute("extended", getFullModuleName(*ExtendedModule));
+      } else {
+        // When the symbol graph isn't extending another module, signal that to the reader by 
+        // repeating the source module's name.
+        OS.attribute("extended", ModuleName);
       }
       AttributeRAII Platform("platform", OS);
 

test/SymbolGraph/Module/BasicExtension.swift

@@ -35,6 +35,7 @@ extension String {
 // ALL-LABEL: module
 
 // ALL: {{"name": ?"BasicExtension"}}
+// ALL: {{"extended": ?"Swift"}}
 
 
 // Check for Symbols and Documentation Strings:

test/SymbolGraph/Module/Module.swift

@@ -8,6 +8,7 @@ public struct S {
 
 // CHECK: module
 // CHECK-NEXT: "name": "SymbolGraphModule"
+// CHECK-NEXT: "extended": "SymbolGraphModule"
 // CHECK-NEXT: platform
 // CHECK-NEXT:   architecture
 // CHECK:        vendor

test/SymbolGraph/Module/NestedExtensions.swift

@@ -46,5 +46,6 @@ extension AStruct.BStruct.CStruct where Thing: Equatable {
 // NESTED-NOT: BStruct
 // NESTED-NOT: CStruct
 // NESTED-NOT: "swift.extension"
+// NESTEDATA-DAG: "extended": "A"
 // NESTEDATA-DAG: "precise": "s:1A7AStructV1BE7BStructV16NestedExtensionsE7CStructV"
 // NESTEDATA-DAG: "precise": "s:e:s:1A7AStructV1BE7BStructV16NestedExtensionsE7CStructV"