[ASTMatchers] add matcher for decltypeType and its underlyingType

Summary:
This patch introduces a new matcher for `DecltypeType` and its underlying type
in order to fix a bug in clang-tidy, see https://reviews.llvm.org/D48717 for more.

Reviewers: aaron.ballman, alexfh, NoQ, dcoughlin

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D48759

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@337703 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/ASTMatchers/ASTMatchers.h

@@ -5111,6 +5111,18 @@ AST_TYPELOC_TRAVERSE_MATCHER_DECL(hasValueType, getValue,
 ///   matches "auto n" and "auto i"
 extern const AstTypeMatcher<AutoType> autoType;
 
+/// Matches types nodes representing C++11 decltype(<expr>) types.
+///
+/// Given:
+/// \code
+///   short i = 1;
+///   int j = 42;
+///   decltype(i + j) result = i + j;
+/// \endcode
+/// decltypeType() 
+///   matches "decltype(i + j)"
+extern const AstTypeMatcher<DecltypeType> decltypeType;
+
 /// Matches \c AutoType nodes where the deduced type is a specific type.
 ///
 /// Note: There is no \c TypeLoc for the deduced type and thus no
@@ -5128,6 +5140,20 @@ extern const AstTypeMatcher<AutoType> autoType;
 AST_TYPE_TRAVERSE_MATCHER(hasDeducedType, getDeducedType,
                           AST_POLYMORPHIC_SUPPORTED_TYPES(AutoType));
 
+/// Matches \c DecltypeType nodes to find out the underlying type.
+///
+/// Given
+/// \code
+///   decltype(1) a = 1;
+///   decltype(2.0) b = 2.0;
+/// \endcode
+/// decltypeType(hasUnderlyingType(isInteger()))
+///   matches "auto a"
+///
+/// Usable as: Matcher<DecltypeType>
+AST_TYPE_TRAVERSE_MATCHER(hasUnderlyingType, getUnderlyingType,
+                          AST_POLYMORPHIC_SUPPORTED_TYPES(DecltypeType));
+
 /// Matches \c FunctionType nodes.
 ///
 /// Given

lib/ASTMatchers/ASTMatchersInternal.cpp

@@ -800,6 +800,7 @@ const AstTypeMatcher<IncompleteArrayType> incompleteArrayType;
 const AstTypeMatcher<VariableArrayType> variableArrayType;
 const AstTypeMatcher<AtomicType> atomicType;
 const AstTypeMatcher<AutoType> autoType;
+const AstTypeMatcher<DecltypeType> decltypeType;
 const AstTypeMatcher<FunctionType> functionType;
 const AstTypeMatcher<FunctionProtoType> functionProtoType;
 const AstTypeMatcher<ParenType> parenType;

lib/ASTMatchers/Dynamic/Registry.cpp

@@ -188,6 +188,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(decayedType);
   REGISTER_MATCHER(decl);
   REGISTER_MATCHER(declaratorDecl);
+  REGISTER_MATCHER(decltypeType);
   REGISTER_MATCHER(declCountIs);
   REGISTER_MATCHER(declRefExpr);
   REGISTER_MATCHER(declStmt);

unittests/ASTMatchers/ASTMatchersNodeTest.cpp

@@ -1206,6 +1206,12 @@ TEST(TypeMatching, MatchesAutoTypes) {
   //                       autoType(hasDeducedType(isInteger()))));
 }
 
+TEST(TypeMatching, MatchesDeclTypes) {
+  EXPECT_TRUE(matches("decltype(1 + 1) sum = 1 + 1;", decltypeType()));
+  EXPECT_TRUE(matches("decltype(1 + 1) sum = 1 + 1;",
+                      decltypeType(hasUnderlyingType(isInteger()))));
+}
+
 TEST(TypeMatching, MatchesFunctionTypes) {
   EXPECT_TRUE(matches("int (*f)(int);", functionType()));
   EXPECT_TRUE(matches("void f(int i) {}", functionType()));