Add "equalsNode" for types and "isCopyAssignmentOperator" matchers.

[angelgarcia]

Summary

This matchers are going to be used in modernize-use-default, but are generic enough to be placed in ASTMatchers.h.

[klimek]

Please add unit tests :)

[angelgarcia]

Add tests.

[klimek]

lg

include/clang/ASTMatchers/ASTMatchers.h

 /// };
 /// \endcode
 ///
 /// cxxMethodDecl(isConst()) matches A::foo() but not A::bar()
 AST_MATCHER(CXXMethodDecl, isConst) {
   return Node.isConst();
 }
 
+/// \brief Matches if the given method declaration declares a copy assignment
+/// operator.
+///
+/// Given
+/// \code
+/// struct A {
+///   A &operator=(const A &);
+///   A &operator=(A &&);
+/// };
+/// \endcode
+///
+/// cxxMethodDecl(isCopyAssignmentOperator()) matches the first method but not
+/// the second one.
+AST_MATCHER(CXXMethodDecl, isCopyAssignmentOperator) {
+  return Node.isCopyAssignmentOperator();
+}
+
 /// \brief Matches if the given method declaration overrides another method.
 ///
 /// Given
 /// \code
 ///   class A {
 ///    public:
 ///     virtual void x();
 ///   };

 ///
 /// \c Decl has pointer identity in the AST.
 AST_MATCHER_P_OVERLOAD(Decl, equalsNode, const Decl*, Other, 0) {
   return &Node == Other;
 }
 /// \brief Matches if a node equals another node.
 ///
 /// \c Stmt has pointer identity in the AST.
-///
 AST_MATCHER_P_OVERLOAD(Stmt, equalsNode, const Stmt*, Other, 1) {
   return &Node == Other;
 }
+/// \brief Matches if a node equals another node.
+///
+/// \c Type has pointer identity in the AST.
+AST_MATCHER_P_OVERLOAD(Type, equalsNode, const Type*, Other, 2) {
+    return &Node == Other;
+}
 
 /// @}
 
 /// \brief Matches each case or default statement belonging to the given switch
 /// statement. This matcher may produce multiple matches.
 ///
 /// Given
 /// \code