[clangd] Simplify "preferred" vs "definition" logic a bit in XRefs AS…

…T code.

Summary:
Now Preferred is always the canonical (first) decl, Definition is always the def
if available.

In practice the index was already forcing this behaviour anyway, so there's no
change. (Unless you weren't using this index, in which case this patch makes
textDocument/declaration and toggling work as expected).

Reviewers: kadircet

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73369

clang-tools-extra/clangd/XRefs.cpp

@@ -226,23 +226,21 @@ locateASTReferent(SourceLocation CurLoc, const syntax::Token *TouchedIdentifier,
   llvm::DenseMap<SymbolID, size_t> ResultIndex;
 
   auto AddResultDecl = [&](const NamedDecl *D) {
-    const NamedDecl *Def = getDefinition(D);
-    const NamedDecl *Preferred = Def ? Def : D;
-
-    auto Loc = makeLocation(AST.getASTContext(), nameLocation(*Preferred, SM),
-                            MainFilePath);
+    D = llvm::cast<NamedDecl>(D->getCanonicalDecl());
+    auto Loc =
+        makeLocation(AST.getASTContext(), nameLocation(*D, SM), MainFilePath);
     if (!Loc)
       return;
 
     Result.emplace_back();
-    Result.back().Name = printName(AST.getASTContext(), *Preferred);
+    Result.back().Name = printName(AST.getASTContext(), *D);
     Result.back().PreferredDeclaration = *Loc;
-    // Preferred is always a definition if possible, so this check works.
-    if (Def == Preferred)
-      Result.back().Definition = *Loc;
+    if (const NamedDecl *Def = getDefinition(D))
+      Result.back().Definition = makeLocation(
+          AST.getASTContext(), nameLocation(*Def, SM), MainFilePath);
 
     // Record SymbolID for index lookup later.
-    if (auto ID = getSymbolID(Preferred))
+    if (auto ID = getSymbolID(D))
       ResultIndex[*ID] = Result.size() - 1;
   };
 

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

@@ -358,15 +358,15 @@ TEST(LocateSymbol, All) {
       )cpp",
 
       R"cpp(// Forward class declaration
-        class Foo;
-        class [[Foo]] {};
+        class $decl[[Foo]];
+        class $def[[Foo]] {};
         F^oo* foo();
       )cpp",
 
       R"cpp(// Function declaration
-        void foo();
+        void $decl[[foo]]();
         void g() { f^oo(); }
-        void [[foo]]() {}
+        void $def[[foo]]() {}
       )cpp",
 
       R"cpp(