Merge pull request swiftlang#38211 from xymus/incr-info-and-emit-module

[Frontend] Emit incremental compilation info from some emit-module jobs

Author: xymus

lib/AST/Module.cpp

@@ -276,8 +276,11 @@ void SourceLookupCache::populateMemberCache(const ModuleDecl &Mod) {
                              "populate-module-class-member-cache");
 
   for (const FileUnit *file : Mod.getFiles()) {
-    auto &SF = *cast<SourceFile>(file);
-    addToMemberCache(SF.getTopLevelDecls());
+    assert(isa<SourceFile>(file) ||
+           isa<SynthesizedFileUnit>(file));
+    SmallVector<Decl *, 8> decls;
+    file->getTopLevelDecls(decls);
+    addToMemberCache(decls);
   }
 
   MemberCachePopulated = true;

lib/FrontendTool/FrontendTool.cpp

@@ -1494,9 +1494,19 @@ static bool performCompileStepsPostSILGen(CompilerInstance &Instance,
     SerializationOptions serializationOpts =
         Invocation.computeSerializationOptions(outs, Instance.getMainModule());
 
+    // Infer if this is an emit-module job part of an incremental build,
+    // vs a partial emit-module job (with primary files) or other kinds.
+    // We may want to rely on a flag instead to differentiate them.
+    const bool isEmitModuleSeparately =
+        Action == FrontendOptions::ActionType::EmitModuleOnly &&
+        MSF.is<ModuleDecl *>() &&
+        Instance.getInvocation()
+            .getTypeCheckerOptions()
+            .SkipFunctionBodies == FunctionBodySkipping::NonInlinableWithoutTypes;
     const bool canEmitIncrementalInfoIntoModule =
         !serializationOpts.DisableCrossModuleIncrementalInfo &&
-        (Action == FrontendOptions::ActionType::MergeModules);
+        (Action == FrontendOptions::ActionType::MergeModules ||
+         isEmitModuleSeparately);
     if (canEmitIncrementalInfoIntoModule) {
       const auto alsoEmitDotFile =
           Instance.getInvocation()