[clangd] Fix DocumentOutline for concepts

Summary: Fixes clangd/clangd#256

Reviewers: kbobyrev

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73056

(cherry picked from commit fb3d915)

Author: kadircet

clang-tools-extra/clangd/FindSymbols.cpp

@@ -193,8 +193,11 @@ class DocumentOutline {
   enum class VisitKind { No, OnlyDecl, DeclAndChildren };
 
   void traverseDecl(Decl *D, std::vector<DocumentSymbol> &Results) {
-    if (auto *Templ = llvm::dyn_cast<TemplateDecl>(D))
-      D = Templ->getTemplatedDecl();
+    if (auto *Templ = llvm::dyn_cast<TemplateDecl>(D)) {
+      // TemplatedDecl might be null, e.g. concepts.
+      if (auto *TD = Templ->getTemplatedDecl())
+        D = TD;
+    }
     auto *ND = llvm::dyn_cast<NamedDecl>(D);
     if (!ND)
       return;

clang-tools-extra/clangd/unittests/FindSymbolsTests.cpp

@@ -449,6 +449,15 @@ TEST_F(DocumentSymbolsTest, DeclarationDefinition) {
                 SymNameRange(Main.range("def")))));
 }
 
+TEST_F(DocumentSymbolsTest, Concepts) {
+  CDB.ExtraClangFlags = {"-std=c++2a"};
+  std::string FilePath = testPath("foo.cpp");
+  addFile(FilePath,
+          "template <typename T> concept C = requires(T t) { t.foo(); };");
+
+  EXPECT_THAT(getSymbols(FilePath), ElementsAre(WithName("C")));
+}
+
 TEST_F(DocumentSymbolsTest, ExternSymbol) {
   std::string FilePath = testPath("foo.cpp");
   addFile(testPath("foo.h"), R"cpp(