blink_gc_plugin: warn of unused trace methods to stack allocated classes.

tools/clang/blink_gc_plugin/DiagnosticsReporter.cpp

 // Copyright 2016 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.
 
 #include "DiagnosticsReporter.h"
 
 using namespace clang;
 
 namespace {
 
@@ skipping 132 matching lines @@
     "[blink-gc] Left-most base class %0 of derived class %1"
     " must be polymorphic.";
 
 const char kBaseClassMustDeclareVirtualTrace[] =
     "[blink-gc] Left-most base class %0 of derived class %1"
     " must define a virtual trace method.";
 
 const char kIteratorToGCManagedCollectionNote[] =
     "[blink-gc] Iterator field %0 to a GC managed collection declared here:";
 
+const char kTraceMethodOfStackAllocatedParentNote[] =
+    "[blink-gc] The stack allocated class %0 provides an unnecessary "
+    "trace method:";
+
 } // namespace
 
 DiagnosticBuilder DiagnosticsReporter::ReportDiagnostic(
     SourceLocation location,
     unsigned diag_id) {
   SourceManager& manager = instance_.getSourceManager();
   FullSourceLoc full_loc(location, manager);
   return diagnostic_.Report(full_loc, diag_id);
 }
 
@@ skipping 42 matching lines @@
   diag_class_overrides_new_ =
       diagnostic_.getCustomDiagID(getErrorLevel(), kClassOverridesNew);
   diag_class_declares_pure_virtual_trace_ = diagnostic_.getCustomDiagID(
       getErrorLevel(), kClassDeclaresPureVirtualTrace);
   diag_left_most_base_must_be_polymorphic_ = diagnostic_.getCustomDiagID(
       getErrorLevel(), kLeftMostBaseMustBePolymorphic);
   diag_base_class_must_declare_virtual_trace_ = diagnostic_.getCustomDiagID(
       getErrorLevel(), kBaseClassMustDeclareVirtualTrace);
   diag_iterator_to_gc_managed_collection_note_ = diagnostic_.getCustomDiagID(
       getErrorLevel(), kIteratorToGCManagedCollectionNote);
+  diag_trace_method_of_stack_allocated_parent_ = diagnostic_.getCustomDiagID(
+      getErrorLevel(), kTraceMethodOfStackAllocatedParentNote);
 
   // Register note messages.
   diag_base_requires_tracing_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kBaseRequiresTracingNote);
   diag_field_requires_tracing_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kFieldRequiresTracingNote);
   diag_field_should_not_be_traced_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kFieldShouldNotBeTracedNote);
   diag_raw_ptr_to_gc_managed_class_note_ = diagnostic_.getCustomDiagID(
       DiagnosticsEngine::Note, kRawPtrToGCManagedClassNote);
@@ skipping 267 matching lines @@
 }
 
 void DiagnosticsReporter::BaseClassMustDeclareVirtualTrace(
     RecordInfo* derived,
     CXXRecordDecl* base) {
   ReportDiagnostic(base->getLocStart(),
                    diag_base_class_must_declare_virtual_trace_)
       << base << derived->record();
 }
 
+void DiagnosticsReporter::TraceMethodForStackAllocatedClass(
+    RecordInfo* info,
+    CXXMethodDecl* trace) {
+  ReportDiagnostic(trace->getLocStart(),
+                   diag_trace_method_of_stack_allocated_parent_)
+      << info->record();
+}
+
 void DiagnosticsReporter::NoteManualDispatchMethod(CXXMethodDecl* dispatch) {
   ReportDiagnostic(dispatch->getLocStart(),
                    diag_manual_dispatch_method_note_)
       << dispatch;
 }
 
 void DiagnosticsReporter::NoteBaseRequiresTracing(BasePoint* base) {
   ReportDiagnostic(base->spec().getLocStart(),
                    diag_base_requires_tracing_note_)
       << base->info()->record();
@@ skipping 47 matching lines @@
 void DiagnosticsReporter::NoteField(FieldDecl* field, unsigned note) {
   ReportDiagnostic(field->getLocStart(), note) << field;
 }
 
 void DiagnosticsReporter::NoteOverriddenNonVirtualTrace(
     CXXMethodDecl* overridden) {
   ReportDiagnostic(overridden->getLocStart(),
                    diag_overridden_non_virtual_trace_note_)
       << overridden;
 }