[clang][AST] Add an AST matcher for deducedTemplateSpeializationType.

[hokein]

Summary

misc-unused-using clang-tidy check needs this matcher to fix a false
positive of C++17 deduced class template types.

[gribozavr2]

clang/include/clang/ASTMatchers/ASTMatchers.h

6043

"in the declaration of the variable \c c"

[hokein]

address review comment.

[merge_guards_bot]

Unit tests: pass. 62408 tests passed, 0 failed and 839 were skipped.

clang-tidy: pass.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[merge_guards_bot]

Unit tests: pass. 62408 tests passed, 0 failed and 839 were skipped.

clang-tidy: pass.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

clang/docs/LibASTMatchersReference.html

Given:
   short i = 1;
   int j = 42;
   decltype(i + j) result = i + j;
 decltypeType()
   matches "decltype(i + j)"
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1Type.html">Type</a>&gt;</td><td class="name" onclick="toggle('deducedTemplateSpecializationType0')"><a name="deducedTemplateSpecializationType0Anchor">deducedTemplateSpecializationType</a></td><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1DeducedTemplateSpecializationType.html">DeducedTemplateSpecializationType</a>&gt;...</td></tr>
+<tr><td colspan="4" class="doc" id="deducedTemplateSpecializationType0"><pre>Matches C++17 deduced template specialization types, e.g. deduced class
+template types.
+
+Given
+  template &lt;typename T&gt;
+  class C { public: C(T); };
+
+  C c(123);
+deducedTemplateSpecializationType() matches the type in the declaration
+of the variable c.
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1Type.html">Type</a>&gt;</td><td class="name" onclick="toggle('dependentSizedArrayType0')"><a name="dependentSizedArrayType0Anchor">dependentSizedArrayType</a></td><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1DependentSizedArrayType.html">DependentSizedArrayType</a>&gt;...</td></tr>
 <tr><td colspan="4" class="doc" id="dependentSizedArrayType0"><pre>Matches C++ arrays whose size is a value-dependent expression.
 
 Given
   template&lt;typename T, int Size&gt;
   class array {
     T data[Size];
   };

 (matcher = functionDecl(hasExternalFormalLinkage()))
 
 namespace {
 void f() {}
 }
 </pre></td></tr>
 
 
-<tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1NamedDecl.html">NamedDecl</a>&gt;</td><td class="name" onclick="toggle('hasName0')"><a name="hasName0Anchor">hasName</a></td><td>const std::string  Name</td></tr>
+<tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1NamedDecl.html">NamedDecl</a>&gt;</td><td class="name" onclick="toggle('hasName0')"><a name="hasName0Anchor">hasName</a></td><td>StringRef Name</td></tr>
 <tr><td colspan="4" class="doc" id="hasName0"><pre>Matches NamedDecl nodes that have the specified name.
 
 Supports specifying enclosing namespaces or classes by prefixing the name
 with '&lt;enclosing&gt;::'.
 Does not match typedefs of an underlying type with the given name.
 
 Example matches X (Name == "X")
   class X;

clang/include/clang/ASTMatchers/ASTMatchers.h

 ///   C<char> var;            // B
 /// \endcode
 ///
 /// \c templateSpecializationType() matches the type of the explicit
 /// instantiation in \c A and the type of the variable declaration in \c B.
 extern const AstTypeMatcher<TemplateSpecializationType>
     templateSpecializationType;
 
+/// Matches C++17 deduced template specialization types, e.g. deduced class
+/// template types.
+///
+/// Given
+/// \code
+///   template <typename T>
+///   class C { public: C(T); };
+///
+///   C c(123);
+/// \endcode
+/// \c deducedTemplateSpecializationType() matches the type in the declaration
+/// of the variable \c c.
+extern const AstTypeMatcher<DeducedTemplateSpecializationType>
+    deducedTemplateSpecializationType;
+
 /// Matches types nodes representing unary type transformations.
 ///
 /// Given:
 /// \code
 ///   typedef __underlying_type(T) type;
 /// \endcode
 /// unaryTransformType()
 ///   matches "__underlying_type(T)"

clang/lib/ASTMatchers/Dynamic/Registry.cpp

RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(cxxUnresolvedConstructExpr);
   REGISTER_MATCHER(decayedType);
   REGISTER_MATCHER(decl);
   REGISTER_MATCHER(declCountIs);
   REGISTER_MATCHER(declRefExpr);
   REGISTER_MATCHER(declStmt);
   REGISTER_MATCHER(declaratorDecl);
   REGISTER_MATCHER(decltypeType);
+  REGISTER_MATCHER(deducedTemplateSpecializationType);
   REGISTER_MATCHER(defaultStmt);
   REGISTER_MATCHER(dependentSizedArrayType);
   REGISTER_MATCHER(designatedInitExpr);
   REGISTER_MATCHER(designatorCountIs);
   REGISTER_MATCHER(doStmt);
   REGISTER_MATCHER(eachOf);
   REGISTER_MATCHER(elaboratedType);
   REGISTER_MATCHER(enumConstantDecl);

clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp

EXPECT_TRUE(matches("typedef int X; X a;", varDecl(hasName("a"),
                                                      hasType(typedefType()))));
 }
 
 TEST(TypeMatching, MatchesTemplateSpecializationType) {
   EXPECT_TRUE(matches("template <typename T> class A{}; A<int> a;",
                       templateSpecializationType()));
 }
 
+TEST(TypeMatching, MatchesDeucedTemplateSpecializationType) {
+  EXPECT_TRUE(matches("template <typename T> class A{ public: A(T) {} }; A a(1);",
+                      deducedTemplateSpecializationType(),
+                      LanguageMode::Cxx17OrLater));
+}
+
 TEST(TypeMatching, MatchesRecordType) {
   EXPECT_TRUE(matches("class C{}; C c;", recordType()));
   EXPECT_TRUE(matches("struct S{}; S s;",
                       recordType(hasDeclaration(recordDecl(hasName("S"))))));
   EXPECT_TRUE(notMatches("int i;",
                          recordType(hasDeclaration(recordDecl(hasName("S"))))));
 }