[clangd][NFC] Make use of TagDecl inside type for hover on auto

Summary:
We were traversing AST twice to get the Decl in case of sugared
types(auto, decltype). They seem to be same in practice, so this patch gets rid
of the second traversal and makes use of TagDecl inside QualType instead.

Reviewers: ilya-biryukov

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D71597

clang-tools-extra/clangd/Hover.cpp

@@ -342,15 +342,15 @@ HoverInfo getHoverContents(const Decl *D, const SymbolIndex *Index) {
 }
 
 /// Generate a \p Hover object given the type \p T.
-HoverInfo getHoverContents(QualType T, const Decl *D, ASTContext &ASTCtx,
-                                  const SymbolIndex *Index) {
+HoverInfo getHoverContents(QualType T, ASTContext &ASTCtx,
+                           const SymbolIndex *Index) {
   HoverInfo HI;
   llvm::raw_string_ostream OS(HI.Name);
   PrintingPolicy Policy = printingPolicyForDecls(ASTCtx.getPrintingPolicy());
   T.print(OS, Policy);
   OS.flush();
 
-  if (D) {
+  if (const auto *D = T->getAsTagDecl()) {
     HI.Kind = index::getSymbolInfo(D).Kind;
     enhanceFromIndex(HI, D, Index);
   }
@@ -396,12 +396,7 @@ llvm::Optional<HoverInfo> getHover(ParsedAST &AST, Position Pos,
       getBeginningOfIdentifier(Pos, SM, AST.getLangOpts()));
 
   if (auto Deduced = getDeducedType(AST.getASTContext(), SourceLocationBeg)) {
-    // Find the corresponding decl to populate kind and fetch documentation.
-    DeclRelationSet Rel = DeclRelation::TemplatePattern | DeclRelation::Alias;
-    auto Decls =
-        targetDecl(ast_type_traits::DynTypedNode::create(*Deduced), Rel);
-    HI = getHoverContents(*Deduced, Decls.empty() ? nullptr : Decls.front(),
-                          AST.getASTContext(), Index);
+    HI = getHoverContents(*Deduced, AST.getASTContext(), Index);
   } else if (auto M = locateMacroAt(SourceLocationBeg, AST.getPreprocessor())) {
     HI = getHoverContents(*M, AST);
   } else {

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

@@ -1396,6 +1396,32 @@ TEST(Hover, All) {
             HI.Definition = "struct Test &&test = {}";
             HI.Value = "{}";
           }},
+      {
+          R"cpp(// auto on alias
+          typedef int int_type;
+          ^[[auto]] x = int_type();
+          )cpp",
+          [](HoverInfo &HI) { HI.Name = "int"; }},
+      {
+          R"cpp(// auto on alias
+          struct cls {};
+          typedef cls cls_type;
+          ^[[auto]] y = cls_type();
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "struct cls";
+            HI.Kind = index::SymbolKind::Struct;
+          }},
+      {
+          R"cpp(// auto on alias
+          template <class>
+          struct templ {};
+          ^[[auto]] z = templ<int>();
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "struct templ<int>";
+            HI.Kind = index::SymbolKind::Struct;
+          }},
   };
 
   // Create a tiny index, so tests above can verify documentation is fetched.