[BlinkGCPlugin] Allow tracing member in traceImpl.

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This clang plugin checks various invariants of the Blink garbage
 // collection infrastructure.
 //
 // Errors are described at:
 // http://www.chromium.org/developers/blink-gc-plugin-errors
 
@@ skipping 304 matching lines @@
   RecordInfo* receiver_;
   bool dispatched_to_receiver_;
 };
 
 // This visitor checks a tracing method by traversing its body.
 // - A member field is considered traced if it is referenced in the body.
 // - A base is traced if a base-qualified call to a trace method is found.
 class CheckTraceVisitor : public RecursiveASTVisitor<CheckTraceVisitor> {
  public:
   CheckTraceVisitor(CXXMethodDecl* trace, RecordInfo* info)
-      : trace_(trace), info_(info) {}
+      : trace_(trace), info_(info), delegates_to_traceimpl_(false) {}
+
+  bool delegates_to_traceimpl() const { return delegates_to_traceimpl_; }
 
   bool VisitMemberExpr(MemberExpr* member) {
     // In weak callbacks, consider any occurrence as a correct usage.
     // TODO: We really want to require that isAlive is checked on manually
     // processed weak fields.
     if (IsWeakCallback()) {
       if (FieldDecl* field = dyn_cast<FieldDecl>(member->getMemberDecl()))
         FoundField(field);
     }
     return true;
@@ skipping 40 matching lines @@
         return true;
       CXXRecordDecl* decl = base->getPointeeType()->getAsCXXRecordDecl();
       if (decl)
         CheckTraceFieldCall(expr->getMemberName().getAsString(), decl, arg);
       return true;
     }
 
     if (CXXMemberCallExpr* expr = dyn_cast<CXXMemberCallExpr>(call)) {
       if (CheckTraceFieldCall(expr) || CheckRegisterWeakMembers(expr))
         return true;
+
+      if (expr->getMethodDecl()->getNameAsString() == kTraceImplName) {
+        delegates_to_traceimpl_ = true;
+        return true;
+      }
     }
 
     CheckTraceBaseCall(call);
     return true;
   }
 
  private:
 
   CXXRecordDecl* GetDependentTemplatedDecl(CXXDependentScopeMemberExpr* expr) {
     NestedNameSpecifier* qual = expr->getQualifier();
@@ skipping 12 matching lines @@
     TemplateDecl* tmpl_decl = tmpl_type->getTemplateName().getAsTemplateDecl();
     if (!tmpl_decl)
       return 0;
 
     return dyn_cast<CXXRecordDecl>(tmpl_decl->getTemplatedDecl());
   }
 
   void CheckCXXDependentScopeMemberExpr(CallExpr* call,
                                         CXXDependentScopeMemberExpr* expr) {
     string fn_name = expr->getMember().getAsString();
+
+    // Check for VisitorDispatcher::trace(field)
+    if (!expr->isImplicitAccess()) {
+      if (clang::DeclRefExpr* base_decl =
+              clang::dyn_cast<clang::DeclRefExpr>(expr->getBase())) {
+        if (Config::IsVisitorDispatcherType(base_decl->getType()) &&
+            call->getNumArgs() == 1 && fn_name == kTraceName) {
+          FindFieldVisitor finder;
+          finder.TraverseStmt(call->getArg(0));
+          if (finder.field())
+            FoundField(finder.field());
+
+          return;
+        }
+      }
+    }
+
     CXXRecordDecl* tmpl = GetDependentTemplatedDecl(expr);
     if (!tmpl)
       return;
 
     // Check for Super<T>::trace(visitor)
     if (call->getNumArgs() == 1 && fn_name == trace_->getName()) {
       RecordInfo::Bases::iterator it = info_->GetBases().begin();
       for (; it != info_->GetBases().end(); ++it) {
         if (it->first->getName() == tmpl->getName())
           it->second.MarkTraced();
@@ skipping 130 matching lines @@
       }
     } else {
       RecordInfo::Fields::iterator it = info_->GetFields().find(field);
       if (it != info_->GetFields().end())
         MarkTraced(it);
     }
   }
 
   CXXMethodDecl* trace_;
   RecordInfo* info_;
+  bool delegates_to_traceimpl_;
 };
 
 // This visitor checks that the fields of a class and the fields of
 // its part objects don't define GC roots.
 class CheckGCRootsVisitor : public RecursiveEdgeVisitor {
  public:
   typedef std::vector<FieldPoint*> RootPath;
   typedef std::set<RecordInfo*> VisitingSet;
   typedef std::vector<RootPath> Errors;
 
@@ skipping 718 matching lines @@
            ++it) {
         RecordInfo* base = it->second.info();
         if (CXXMethodDecl* other = base->InheritsNonVirtualTrace())
           ReportOverriddenNonVirtualTrace(parent, trace, other);
       }
     }
 
     CheckTraceVisitor visitor(trace, parent);
     visitor.TraverseCXXMethodDecl(trace);
 
+    // Skip reporting if this trace method is a just delegate to
+    // traceImpl method. We will report on CheckTraceMethod on traceImpl method.
+    if (visitor.delegates_to_traceimpl())
+      return;
+
     for (RecordInfo::Bases::iterator it = parent->GetBases().begin();
          it != parent->GetBases().end();
          ++it) {
       if (!it->second.IsProperlyTraced())
         ReportBaseRequiresTracing(parent, trace, it->first);
     }
 
     for (RecordInfo::Fields::iterator it = parent->GetFields().begin();
          it != parent->GetFields().end();
          ++it) {
@@ skipping 571 matching lines @@
 
  private:
   BlinkGCPluginOptions options_;
 };
 
 }  // namespace
 
 static FrontendPluginRegistry::Add<BlinkGCPluginAction> X(
     "blink-gc-plugin",
     "Check Blink GC invariants");