[ASTMatchers] Don't assert-fail in specifiesTypeLoc().

[dlj]

Summary

The specifiesTypeLoc() matcher narrows a nestedNameSpecifier matcher based on a
typeloc within the NNS. However, the matcher does not guard against NNS which
are a namespace, and cause getTypeLoc to assert-fail.

[klimek]

lg, thanks!

include/clang/ASTMatchers/ASTMatchers.h

 ///   struct A { struct B { struct C {}; }; };
 ///   A::B::C c;
 /// \endcode
 /// nestedNameSpecifierLoc(specifiesTypeLoc(loc(type(
 ///   hasDeclaration(cxxRecordDecl(hasName("A")))))))
 ///   matches "A::"
 AST_MATCHER_P(NestedNameSpecifierLoc, specifiesTypeLoc,
               internal::Matcher<TypeLoc>, InnerMatcher) {
-  return Node && InnerMatcher.matches(Node.getTypeLoc(), Finder, Builder);
+  return Node && Node.getNestedNameSpecifier()->getAsType() &&
+         InnerMatcher.matches(Node.getTypeLoc(), Finder, Builder);
 }
 
 /// Matches on the prefix of a \c NestedNameSpecifier.
 ///
 /// Given
 /// \code
 ///   struct A { struct B { struct C {}; }; };
 ///   A::B::C c;

unittests/ASTMatchers/ASTMatchersNodeTest.cpp

 TEST(NNS, MatchesNestedNameSpecifierPrefixes) {
   EXPECT_TRUE(matches(
     "struct A { struct B { struct C {}; }; }; A::B::C c;",
     nestedNameSpecifier(hasPrefix(specifiesType(asString("struct A"))))));
   EXPECT_TRUE(matches(
     "struct A { struct B { struct C {}; }; }; A::B::C c;",
     nestedNameSpecifierLoc(hasPrefix(
       specifiesTypeLoc(loc(qualType(asString("struct A"))))))));
+  EXPECT_TRUE(matches(
+    "namespace N { struct A { struct B { struct C {}; }; }; } N::A::B::C c;",
+    nestedNameSpecifierLoc(hasPrefix(
+      specifiesTypeLoc(loc(qualType(asString("struct N::A"))))))));
 }
 
 
 template <typename T>
 class VerifyAncestorHasChildIsEqual : public BoundNodesCallback {
 public:
   bool run(const BoundNodes *Nodes) override { return false; }