Revert of Revert "win: Make oilpan plugin work better with delayed template parsing."

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

Index: tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
index 2d221d7667a858c0d1ff8ec4bf1c7ca5b79f919b..2d6eff256817f7b2c897a7a851329e47a54fd382 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
+++ b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
@@ -17,6 +17,7 @@
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendPluginRegistry.h"
+#include "clang/Sema/Sema.h"
 
 using namespace clang;
 using std::string;
@@ -144,6 +145,23 @@ const char kClassMustDeclareGCMixinTraceMethod[] =
     "[blink-gc] Class %0 which inherits from GarbageCollectedMixin must"
     " locally declare and override trace(Visitor*)";
 
+// Use a local RAV implementation to simply collect all FunctionDecls marked for
+// late template parsing. This happens with the flag -fdelayed-template-parsing,
+// which is on by default in MSVC-compatible mode.
+std::set<FunctionDecl*> GetLateParsedFunctionDecls(TranslationUnitDecl* decl) {
+  struct Visitor : public RecursiveASTVisitor<Visitor> {
+    bool VisitFunctionDecl(FunctionDecl* function_decl) {
+      if (function_decl->isLateTemplateParsed())
+        late_parsed_decls.insert(function_decl);
+      return true;
+    }
+
+    std::set<FunctionDecl*> late_parsed_decls;
+  } v;
+  v.TraverseDecl(decl);
+  return v.late_parsed_decls;
+}
+
 struct BlinkGCPluginOptions {
   BlinkGCPluginOptions()
     : enable_oilpan(false)
@@ -1017,6 +1035,8 @@ class BlinkGCPluginConsumer : public ASTConsumer {
     if (diagnostic_.hasErrorOccurred())
       return;
 
+    ParseFunctionTemplates(context.getTranslationUnitDecl());
+
     CollectVisitor visitor;
     visitor.TraverseDecl(context.getTranslationUnitDecl());
 
@@ -1063,6 +1083,31 @@ class BlinkGCPluginConsumer : public ASTConsumer {
     }
   }
 
+  void ParseFunctionTemplates(TranslationUnitDecl* decl) {
+    if (!instance_.getLangOpts().DelayedTemplateParsing)
+      return;  // Nothing to do.
+
+    std::set<FunctionDecl*> late_parsed_decls =
+        GetLateParsedFunctionDecls(decl);
+    clang::Sema& sema = instance_.getSema();
+
+    for (const FunctionDecl* fd : late_parsed_decls) {
+      assert(fd->isLateTemplateParsed());
+
+      if (!Config::IsTraceMethod(fd))
+        continue;
+
+      if (instance_.getSourceManager().isInSystemHeader(
+              instance_.getSourceManager().getSpellingLoc(fd->getLocation())))
+        continue;
+
+      // Force parsing and AST building of the yet-uninstantiated function
+      // template trace method bodies.
+      clang::LateParsedTemplate* lpt = sema.LateParsedTemplateMap[fd];
+      sema.LateTemplateParser(sema.OpaqueParser, *lpt);
+    }
+  }
+
   // Main entry for checking a record declaration.
   void CheckRecord(RecordInfo* info) {
     if (IsIgnored(info))