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

[kadircet]

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.

[merge_guards_bot]

Unit tests: pass. 60932 tests passed, 0 failed and 726 were skipped.

clang-tidy: pass.

clang-format: pass.

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

[ilya-biryukov]

clang-tools-extra/clangd/Hover.cpp

353

This might be a functional change in case of typedefs.

Could you check on these cases (not sure if we already have those in the tests):

typedef int int_type;
^auto x = int_type();

struct cls {};
typedef cls cls_type;
^auto y = cls_type();

template <class>
struct templ {};
^auto z = templ<int>();

Note that I don't necessarily think they will change behavior, but they might.

Also happy to LGTM as is if you remove "NFC" from the description. It seems we're potentially changing behvior, but it's not tested currently and we can land this, discover and fix any regreessions later.

[kadircet]

• Added alias tests, behavior stayed the same.

[ilya-biryukov]

LGTM

[merge_guards_bot]

Unit tests: pass. 60932 tests passed, 0 failed and 726 were skipped.

clang-tidy: pass.

clang-format: pass.

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

clang-tools-extra/clangd/Hover.cpp

HoverInfo getHoverContents(const Decl *D, const SymbolIndex *Index) {
   }
 
   HI.Definition = printDefinition(D);
   enhanceFromIndex(HI, D, Index);
   return HI;
 }
 
 /// 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,
   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);
   }
   return HI;
 }
 
 /// Generate a \p Hover object given the macro \p MacroDecl.
 HoverInfo getHoverContents(const DefinedMacro &Macro, ParsedAST &AST) {
llvm::Optional<HoverInfo> getHover(ParsedAST &AST, Position Pos,
                                    format::FormatStyle Style,
                                    const SymbolIndex *Index) {
   const SourceManager &SM = AST.getSourceManager();
   llvm::Optional<HoverInfo> HI;
   SourceLocation SourceLocationBeg = SM.getMacroArgExpandedLocation(
       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 {
     auto Offset = positionToOffset(SM.getBufferData(SM.getMainFileID()), Pos);
     if (!Offset) {
       llvm::consumeError(Offset.takeError());
       return llvm::None;
     }

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

const std::function<void(HoverInfo &)> ExpectedBuilder;
             HI.Name = "test";
             HI.Kind = index::SymbolKind::Variable;
             HI.NamespaceScope = "";
             HI.LocalScope = "test::";
             HI.Type = "struct Test &&";
             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.
   Symbol IndexSym = func("indexSymbol");
   IndexSym.Documentation = "comment from index";
   SymbolSlab::Builder Symbols;
   Symbols.insert(IndexSym);
   auto Index =