blink_gc_plugin: detect singletons with embedded ScriptWrappables.

tools/clang/blink_gc_plugin/CheckSingletonVisitor.h

Index: tools/clang/blink_gc_plugin/CheckSingletonVisitor.h
diff --git a/tools/clang/blink_gc_plugin/CheckSingletonVisitor.h b/tools/clang/blink_gc_plugin/CheckSingletonVisitor.h
new file mode 100644
index 0000000000000000000000000000000000000000..4e6df24f2b78ea0731581a3a0de92ed2644b8c3e
--- /dev/null
+++ b/tools/clang/blink_gc_plugin/CheckSingletonVisitor.h
@@ -0,0 +1,53 @@
+// Copyright 2017 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.
+
+#ifndef TOOLS_BLINK_GC_PLUGIN_CHECK_SINGLETON_VISITOR_H_
+#define TOOLS_BLINK_GC_PLUGIN_CHECK_SINGLETON_VISITOR_H_
+
+#include <set>
+#include <utility>
+#include <vector>
+
+#include "clang/AST/AST.h"
+
+class RecordInfo;
+
+// This visitor checks that a persistent static singleton's type
+// is safe. Safety is currently defined as:
+// - the type doesn't derive from blink::ScriptWrappable.
+// - the type doesn't contain a ScriptWrappable-derived member,
+//   transitively.
+//
+class CheckSingletonVisitor final {
+ public:
+  using Errors = std::vector<std::pair<std::string, const clang::Type*>>;
+
+  CheckSingletonVisitor();
+  ~CheckSingletonVisitor();
+
+  const Errors& illegal_types() const { return illegal_types_; }
+
+  bool CheckIfSafe(RecordInfo*, const clang::Type*);
+
+  bool VisitType(clang::Type*);
+
+ private:
+  void CheckScriptWrappable(const std::string&, const clang::Type*);
+
+  bool IsScriptWrappable(RecordInfo*);
+  bool InheritsScriptWrappable(clang::CXXRecordDecl*);
+
+  void PushType(const clang::Type*);
+  void PushType(const std::string&, const clang::Type*);
+
+  std::string GenerateErrorContext(const std::string&);
+
+  Errors illegal_types_;
+  RecordInfo* info_ = nullptr;
+  std::vector<std::pair<std::string, const clang::Type*>> types_stack_;
+  std::set<const clang::Type*> already_seen_;
+  std::vector<std::string> error_context_;
+};
+
+#endif  // TOOLS_BLINK_GC_PLUGIN_CHECK_SINGLETON_VISITOR_H_