[PATCH] Support in hasDeclaration for types with getDecl()

[Edwin Vane]

Hi klimek,

Re-introducing r175532. The has_getDecl metafunction didn't compile with
Visual Studio. This revision uses approaches has_getDecl from a
different angle that isn't a problem for Visual Studio.

Added dedicated tests for the metafunction.

http://llvm-reviews.chandlerc.com/D452

Files:
  include/clang/ASTMatchers/ASTMatchersInternal.h
  unittests/ASTMatchers/ASTMatchersTest.cpp

Index: include/clang/ASTMatchers/ASTMatchersInternal.h
===================================================================
--- include/clang/ASTMatchers/ASTMatchersInternal.h
+++ include/clang/ASTMatchers/ASTMatchersInternal.h
@@ -353,6 +353,23 @@
   return Matcher<T>(Implementation);
 }
 
+/// \brief Metafunction to determine if type T has a member called getDecl.
+template <typename T> struct has_getDecl {
+  struct Default { int getDecl; };
+  struct Derived : T, Default { };
+
+  template<typename C, C> struct CheckT;
+
+  // If T::getDecl exists, an ambiguity arises and CheckT will
+  // not be instantiable. This makes f(...) the only available
+  // overload.
+  template<typename C>
+  static char (&f(CheckT<int Default::*, &C::getDecl>*))[1];
+  template<typename C> static char (&f(...))[2];
+
+  static bool const value = sizeof(f<Derived>(0)) == 2;
+};
+
 /// \brief Matches declarations for QualType and CallExpr.
 ///
 /// Type argument DeclMatcherT is required by PolymorphicMatcherWithParam1 but
@@ -376,8 +393,9 @@
   /// \brief If getDecl exists as a member of U, returns whether the inner
   /// matcher matches Node.getDecl().
   template <typename U>
-  bool matchesSpecialized(const U &Node, ASTMatchFinder *Finder, 
-                          BoundNodesTreeBuilder *Builder) const {
+  bool matchesSpecialized(
+      const U &Node, ASTMatchFinder *Finder, BoundNodesTreeBuilder *Builder,
+      typename llvm::enable_if<has_getDecl<U>, int>::type = 0) const {
     return matchesDecl(Node.getDecl(), Finder, Builder);
   }
 
Index: unittests/ASTMatchers/ASTMatchersTest.cpp
===================================================================
--- unittests/ASTMatchers/ASTMatchersTest.cpp
+++ unittests/ASTMatchers/ASTMatchersTest.cpp
@@ -818,6 +818,12 @@
                           qualType(hasDeclaration(enumDecl(hasName("X")))))))));
 }
 
+TEST(HasDeclaration, HasGetDeclTraitTest) {
+  EXPECT_TRUE(internal::has_getDecl<TypedefType>::value);
+  EXPECT_TRUE(internal::has_getDecl<RecordType>::value);
+  EXPECT_FALSE(internal::has_getDecl<TemplateSpecializationType>::value);
+}
+
 TEST(HasDeclaration, HasDeclarationOfTypeWithDecl) {
   EXPECT_TRUE(matches("typedef int X; X a;",
                       varDecl(hasName("a"),
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