[clangd] Fallback to OrigD when SLoc is invalid

[kadircet]

Summary

Some implicit/built-in decls lack the source location
information. Fallback to OrigD that we've seen in the source code
instead of the canonical one in those cases.

clangd/index/SymbolCollector.cpp

 // Always return true to continue indexing.
 bool SymbolCollector::handleDeclOccurence(
     const Decl *D, index::SymbolRoleSet Roles,
     llvm::ArrayRef<index::SymbolRelation> Relations, SourceLocation Loc,
     index::IndexDataConsumer::ASTNodeInfo ASTNode) {
   assert(ASTCtx && PP.get() && "ASTContext and Preprocessor must be set.");
   assert(CompletionAllocator && CompletionTUInfo);
   assert(ASTNode.OrigD);
+  // Indexing API puts cannonical decl into D, which might not have a valid
+  // source location for implicit/built-in decls. Fallback to original decl in
+  // such cases.
+  if (D->getLocation().isInvalid())
+    D = ASTNode.OrigD;
   // If OrigD is an declaration associated with a friend declaration and it's
   // not a definition, skip it. Note that OrigD is the occurrence that the
   // collector is currently visiting.
   if ((ASTNode.OrigD->getFriendObjectKind() !=
        Decl::FriendObjectKind::FOK_None) &&
       !(Roles & static_cast<unsigned>(index::SymbolRole::Definition)))
     return true;
   // Skip non-semantic references, we should start processing these when we
if (!IsMainFileOnly && isIndexedForCodeCompletion(ND, Ctx))
     S.Flags |= Symbol::IndexedForCodeCompletion;
   if (isImplementationDetail(&ND))
     S.Flags |= Symbol::ImplementationDetail;
   if (!IsMainFileOnly)
     S.Flags |= Symbol::VisibleOutsideFile;
   S.SymInfo = index::getSymbolInfo(&ND);
   std::string FileURI;
   auto Loc = findNameLoc(&ND);
+  assert(Loc.isValid() && "Invalid source location for NamedDecl");
   // FIXME: use the result to filter out symbols.
   shouldIndexFile(SM, SM.getFileID(Loc), Opts, &FilesToIndexCache);
   if (auto DeclLoc =
           getTokenLocation(Loc, SM, Opts, ASTCtx->getLangOpts(), FileURI))
     S.CanonicalDeclaration = *DeclLoc;
 
   S.Origin = Opts.Origin;
   if (ND.getAvailability() == AR_Deprecated)

unittests/clangd/SymbolCollectorTests.cpp

TEST_F(SymbolCollectorTest, CBuiltins) {
   // In C, printf in stdio.h is a redecl of an implicit builtin.
   const char *Header = R"(
     extern int printf(const char*, ...);
   )";
   runSymbolCollector(Header, /**/ "", {"-xc"});
   EXPECT_THAT(Symbols, Contains(QName("printf")));
 }
 
+TEST_F(SymbolCollectorTest, InvalidSourceLoc) {
+  const char *Header = R"(
+      void operator delete(void*)
+        __attribute__((__externally_visible__));)";
+  runSymbolCollector(Header, /**/ "");
+  EXPECT_THAT(Symbols, Contains(QName("operator delete")));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang