[clang][Index] Enable indexing of Template Type Parameters behind a flag

Summary:
clangd uses indexing api to provide references and it was not possible
to perform symbol information for template parameters. This patch enables
visiting of TemplateTypeParmTypeLocs.

Reviewers: ilya-biryukov, akyrtzi

Subscribers: javed.absar, kristof.beyls, ioeric, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D58293

llvm-svn: 354560
diff --git a/clang/unittests/Index/IndexTests.cpp b/clang/unittests/Index/IndexTests.cpp
index 61c969f..66cef88 100644
--- a/clang/unittests/Index/IndexTests.cpp
+++ b/clang/unittests/Index/IndexTests.cpp
@@ -216,6 +216,30 @@
                              DeclAt(Position(5, 12)))));
 }
 
+TEST(IndexTest, IndexTypeParmDecls) {
+  std::string Code = R"cpp(
+    template <typename T, int I, template<typename> class C, typename NoRef>
+    struct Foo {
+      T t = I;
+      C<int> x;
+    };
+  )cpp";
+  auto Index = std::make_shared<Indexer>();
+  IndexingOptions Opts;
+  tooling::runToolOnCode(new IndexAction(Index, Opts), Code);
+  EXPECT_THAT(Index->Symbols, AllOf(Not(Contains(QName("Foo::T"))),
+                                    Not(Contains(QName("Foo::I"))),
+                                    Not(Contains(QName("Foo::C"))),
+                                    Not(Contains(QName("Foo::NoRef")))));
+
+  Opts.IndexTemplateParameters = true;
+  Index->Symbols.clear();
+  tooling::runToolOnCode(new IndexAction(Index, Opts), Code);
+  EXPECT_THAT(Index->Symbols,
+              AllOf(Contains(QName("Foo::T")), Contains(QName("Foo::I")),
+                    Contains(QName("Foo::C")), Contains(QName("Foo::NoRef"))));
+}
+
 } // namespace
 } // namespace index
 } // namespace clang