[clang][Sema] Add CodeCompletionContext::CCC_ObjCClassForwardDecl

[dgoldman]

Summary

• Use this new context in Sema to limit completions to seen ObjC class names

• Use this new context in clangd to disable include insertions when completing ObjC forward decls

[kadircet]

clang-tools-extra/clangd/CodeComplete.cpp

418

rather than doing this here, can you pass ContextKind into headerToInsertIfAllowed ? we already have some logic there that does something similar (e.g. check if there's a decl in the main file). it'd be nice to group them together, in case we want to extend this in the future. (it'd be great if we can just have a contextAllowsHeaderInsertion helper, which can only return true for ObjCClassForwardDecl for now).

[dgoldman]

Add a contextAllowsHeaderInsertion helper to clangd

[dgoldman]

Rebase

[kadircet]

thanks

clang-tools-extra/clangd/CodeComplete.cpp

struct CompletionCandidate {
   const CodeCompletionResult *SemaResult = nullptr;
   const Symbol *IndexResult = nullptr;
   const RawIdentifier *IdentifierResult = nullptr;
   llvm::SmallVector<SymbolInclude, 1> RankedIncludeHeaders;
 
   // Returns a token identifying the overload set this is part of.
   // 0 indicates it's not part of any overload set.
   size_t overloadSet(const CodeCompleteOptions &Opts, llvm::StringRef FileName,
-                     IncludeInserter *Inserter) const {
+                     IncludeInserter *Inserter,
+                     CodeCompletionContext::Kind CCContextKind) const {
     if (!Opts.BundleOverloads.value_or(false))
       return 0;
 
     // Depending on the index implementation, we can see different header
     // strings (literal or URI) mapping to the same file. We still want to
     // bundle those, so we must resolve the header to be included here.
     std::string HeaderForHash;
     if (Inserter) {
-      if (auto Header = headerToInsertIfAllowed(Opts)) {
+      if (auto Header = headerToInsertIfAllowed(Opts, CCContextKind)) {
         if (auto HeaderFile = toHeaderFile(*Header, FileName)) {
           if (auto Spelled =
                   Inserter->calculateIncludePath(*HeaderFile, FileName))
             HeaderForHash = *Spelled;
         } else {
           vlog("Code completion header path manipulation failed {0}",
                HeaderFile.takeError());
         }
if (SemaResult) {
         D->printQualifiedName(OS);
       }
       return llvm::hash_combine(Scratch, HeaderForHash);
     }
     assert(IdentifierResult);
     return 0;
   }
 
+  bool contextAllowsHeaderInsertion(CodeCompletionContext::Kind Kind) const {
+    // Explicitly disable insertions for forward declarations since they don't
+    // reference the declaration.
+    if (Kind == CodeCompletionContext::CCC_ObjCClassForwardDecl)
+      return false;
+    return true;
+  }
+
   // The best header to include if include insertion is allowed.
   std::optional<llvm::StringRef>
-  headerToInsertIfAllowed(const CodeCompleteOptions &Opts) const {
+  headerToInsertIfAllowed(const CodeCompleteOptions &Opts,
+                          CodeCompletionContext::Kind ContextKind) const {
     if (Opts.InsertIncludes == CodeCompleteOptions::NeverInsert ||
-        RankedIncludeHeaders.empty())
+        RankedIncludeHeaders.empty() ||
+        !contextAllowsHeaderInsertion(ContextKind))
       return std::nullopt;
     if (SemaResult && SemaResult->Declaration) {
       // Avoid inserting new #include if the declaration is found in the current
       // file e.g. the symbol is forward declared.
       auto &SM = SemaResult->Declaration->getASTContext().getSourceManager();
       for (const Decl *RD : SemaResult->Declaration->redecls())
         if (SM.isInMainFile(SM.getExpansionLoc(RD->getBeginLoc())))
           return std::nullopt;
auto Inserted = [&](llvm::StringRef Header)
         return ResolvedInserted.takeError();
       auto Spelled = Includes.calculateIncludePath(*ResolvedInserted, FileName);
       if (!Spelled)
         return error("Header not on include path");
       return std::make_pair(
           std::move(*Spelled),
           Includes.shouldInsertInclude(*ResolvedDeclaring, *ResolvedInserted));
     };
-    bool ShouldInsert = C.headerToInsertIfAllowed(Opts).has_value();
+    bool ShouldInsert =
+        C.headerToInsertIfAllowed(Opts, ContextKind).has_value();
     Symbol::IncludeDirective Directive = insertionDirective(Opts);
     // Calculate include paths and edits for all possible headers.
     for (const auto &Inc : C.RankedIncludeHeaders) {
       if ((Inc.Directive & Directive) == 0)
         continue;
 
       if (auto ToInclude = Inserted(Inc.Header)) {
         CodeCompletion::IncludeCandidate Include;
         Include.Header = ToInclude->first;
         if (ToInclude->second && ShouldInsert)
bool contextAllowsIndex(enum CodeCompletionContext::Kind K) {
   case CodeCompletionContext::CCC_ClassOrStructTag:
   case CodeCompletionContext::CCC_ObjCProtocolName:
   case CodeCompletionContext::CCC_Namespace:
   case CodeCompletionContext::CCC_Type:
   case CodeCompletionContext::CCC_ParenthesizedExpression:
   case CodeCompletionContext::CCC_ObjCInterfaceName:
   case CodeCompletionContext::CCC_Symbol:
   case CodeCompletionContext::CCC_SymbolOrNewName:
+  case CodeCompletionContext::CCC_ObjCClassForwardDecl:
     return true;
   case CodeCompletionContext::CCC_OtherWithMacros:
   case CodeCompletionContext::CCC_DotMemberAccess:
   case CodeCompletionContext::CCC_ArrowMemberAccess:
   case CodeCompletionContext::CCC_ObjCCategoryName:
   case CodeCompletionContext::CCC_ObjCPropertyAccess:
   case CodeCompletionContext::CCC_MacroName:
   case CodeCompletionContext::CCC_MacroNameUse:
bool includeSymbolFromIndex(CodeCompletionContext::Kind Kind,
   // in other places they're confusing, especially when they share the same
   // identifier with a class.
   if (Sym.SymInfo.Kind == index::SymbolKind::Protocol &&
       Sym.SymInfo.Lang == index::SymbolLanguage::ObjC)
     return Kind == CodeCompletionContext::CCC_ObjCProtocolName;
   else if (Kind == CodeCompletionContext::CCC_ObjCProtocolName)
     // Don't show anything else in ObjC protocol completions.
     return false;
+
+  if (Kind == CodeCompletionContext::CCC_ObjCClassForwardDecl)
+    return Sym.SymInfo.Kind == index::SymbolKind::Class &&
+           Sym.SymInfo.Lang == index::SymbolLanguage::ObjC;
   return true;
 }
 
 std::future<std::pair<bool, SymbolSlab>>
 startAsyncFuzzyFind(const SymbolIndex &Index, const FuzzyFindRequest &Req) {
   return runAsync<std::pair<bool, SymbolSlab>>([&Index, Req]() {
     trace::Span Tracer("Async fuzzyFind");
     SymbolSlab::Builder Syms;
auto AddToBundles = [&](const CodeCompletionResult *SemaResult,
         C.Name = IndexResult->Name;
         C.RankedIncludeHeaders = getRankedIncludes(*C.IndexResult);
       } else if (C.SemaResult) {
         C.Name = Recorder->getName(*SemaResult);
       } else {
         assert(IdentifierResult);
         C.Name = IdentifierResult->Name;
       }
-      if (auto OverloadSet =
-              C.overloadSet(Opts, FileName, Inserter ? &*Inserter : nullptr)) {
+      if (auto OverloadSet = C.overloadSet(
+              Opts, FileName, Inserter ? &*Inserter : nullptr, CCContextKind)) {
         auto Ret = BundleLookup.try_emplace(OverloadSet, Bundles.size());
         if (Ret.second)
           Bundles.emplace_back();
         Bundles[Ret.first->second].push_back(std::move(C));
       } else {
         Bundles.emplace_back();
         Bundles.back().push_back(std::move(C));
       }

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

auto Results = completions(R"objc(
       @interface Foo (^)
       @end
     )objc",
                              {FoodCategory},
                              /*Opts=*/{}, "Foo.m");
   EXPECT_THAT(Results.Completions, IsEmpty());
 }
 
+TEST(CompletionTest, ObjectiveCForwardDeclFromIndex) {
+  Symbol FoodClass = objcClass("FoodClass");
+  FoodClass.IncludeHeaders.emplace_back("\"Foo.h\"", 2, Symbol::Import);
+  Symbol SymFood = objcProtocol("Food");
+  auto Results = completions("@class Foo^", {SymFood, FoodClass},
+                             /*Opts=*/{}, "Foo.m");
+
+  // Should only give class names without any include insertion.
+  EXPECT_THAT(Results.Completions,
+              UnorderedElementsAre(AllOf(named("FoodClass"),
+                                         kind(CompletionItemKind::Class),
+                                         Not(insertInclude()))));
+}
+
 TEST(CompletionTest, CursorInSnippets) {
   clangd::CodeCompleteOptions Options;
   Options.EnableSnippets = true;
   auto Results = completions(
       R"cpp(
     void while_foo(int a, int b);
     void test() {
       whil^

clang/include/clang/Sema/CodeCompleteConsumer.h

enum Kind {
     /// Code completion inside the filename part of a #include directive.
     CCC_IncludedFile,
 
     /// Code completion of an attribute name.
     CCC_Attribute,
 
     /// An unknown context, in which we are recovering from a parsing
     /// error and don't know which completions we should give.
-    CCC_Recovery
+    CCC_Recovery,
+
+    /// Code completion in a @class forward declaration.
+    CCC_ObjCClassForwardDecl
   };
 
   using VisitedContextSet = llvm::SmallPtrSet<DeclContext *, 8>;
 
 private:
   Kind CCKind;
 
   /// Indicates whether we are completing a name of a using declaration, e.g.

clang/include/clang/Sema/Sema.h

public:
   void CodeCompleteObjCForCollection(Scope *S,
                                      DeclGroupPtrTy IterationVar);
   void CodeCompleteObjCSelector(Scope *S,
                                 ArrayRef<IdentifierInfo *> SelIdents);
   void CodeCompleteObjCProtocolReferences(
                                          ArrayRef<IdentifierLocPair> Protocols);
   void CodeCompleteObjCProtocolDecl(Scope *S);
   void CodeCompleteObjCInterfaceDecl(Scope *S);
+  void CodeCompleteObjCClassForwardDecl(Scope *S);
   void CodeCompleteObjCSuperclass(Scope *S,
                                   IdentifierInfo *ClassName,
                                   SourceLocation ClassNameLoc);
   void CodeCompleteObjCImplementationDecl(Scope *S);
   void CodeCompleteObjCInterfaceCategory(Scope *S,
                                          IdentifierInfo *ClassName,
                                          SourceLocation ClassNameLoc);
   void CodeCompleteObjCImplementationCategory(Scope *S,

clang/lib/Frontend/ASTUnit.cpp

if (LangOpts.CPlusPlus || isa<ObjCInterfaceDecl>(ND))
       Contexts |= (1LL << CodeCompletionContext::CCC_ObjCMessageReceiver);
 
     // In Objective-C, you can only be a subclass of another Objective-C class
     if (const auto *ID = dyn_cast<ObjCInterfaceDecl>(ND)) {
       // Objective-C interfaces can be used in a class property expression.
       if (ID->getDefinition())
         Contexts |= (1LL << CodeCompletionContext::CCC_Expression);
       Contexts |= (1LL << CodeCompletionContext::CCC_ObjCInterfaceName);
+      Contexts |= (1LL << CodeCompletionContext::CCC_ObjCClassForwardDecl);
     }
 
     // Deal with tag names.
     if (isa<EnumDecl>(ND)) {
       Contexts |= (1LL << CodeCompletionContext::CCC_EnumTag);
 
       // Part of the nested-name-specifier in C++0x.
       if (LangOpts.CPlusPlus11)
static void CalculateHiddenNames(const CodeCompletionContext &Context,
   case CodeCompletionContext::CCC_Other:
   case CodeCompletionContext::CCC_OtherWithMacros:
   case CodeCompletionContext::CCC_ObjCInstanceMessage:
   case CodeCompletionContext::CCC_ObjCClassMessage:
   case CodeCompletionContext::CCC_ObjCCategoryName:
   case CodeCompletionContext::CCC_IncludedFile:
   case CodeCompletionContext::CCC_Attribute:
   case CodeCompletionContext::CCC_NewName:
+  case CodeCompletionContext::CCC_ObjCClassForwardDecl:
     // We're looking for nothing, or we're looking for names that cannot
     // be hidden.
     return;
   }
 
   using Result = CodeCompletionResult;
   for (unsigned I = 0; I != NumResults; ++I) {
     if (Results[I].Kind != Result::RK_Declaration)

clang/lib/Parse/ParseObjc.cpp

 Parser::ParseObjCAtClassDeclaration(SourceLocation atLoc) {
   ConsumeToken(); // the identifier "class"
   SmallVector<IdentifierInfo *, 8> ClassNames;
   SmallVector<SourceLocation, 8> ClassLocs;
   SmallVector<ObjCTypeParamList *, 8> ClassTypeParams;
 
   while (true) {
     MaybeSkipAttributes(tok::objc_class);
+    if (Tok.is(tok::code_completion)) {
+      cutOffParsing();
+      Actions.CodeCompleteObjCClassForwardDecl(getCurScope());
+      return Actions.ConvertDeclToDeclGroup(nullptr);
+    }
     if (expectIdentifier()) {
       SkipUntil(tok::semi);
       return Actions.ConvertDeclToDeclGroup(nullptr);
     }
     ClassNames.push_back(Tok.getIdentifierInfo());
     ClassLocs.push_back(Tok.getLocation());
     ConsumeToken();
 

clang/lib/Sema/CodeCompleteConsumer.cpp

bool CodeCompletionContext::wantConstructorResults() const {
   case CCC_Other:
   case CCC_OtherWithMacros:
   case CCC_ObjCInstanceMessage:
   case CCC_ObjCClassMessage:
   case CCC_ObjCInterfaceName:
   case CCC_ObjCCategoryName:
   case CCC_IncludedFile:
   case CCC_Attribute:
+  case CCC_ObjCClassForwardDecl:
     return false;
   }
 
   llvm_unreachable("Invalid CodeCompletionContext::Kind!");
 }
 
 StringRef clang::getCompletionKindString(CodeCompletionContext::Kind Kind) {
   using CCKind = CodeCompletionContext::Kind;
StringRef clang::getCompletionKindString(CodeCompletionContext::Kind Kind) {
   case CCKind::CCC_ObjCCategoryName:
     return "ObjCCategoryName";
   case CCKind::CCC_IncludedFile:
     return "IncludedFile";
   case CCKind::CCC_Attribute:
     return "Attribute";
   case CCKind::CCC_Recovery:
     return "Recovery";
+  case CCKind::CCC_ObjCClassForwardDecl:
+    return "ObjCClassForwardDecl";
   }
   llvm_unreachable("Invalid CodeCompletionContext::Kind!");
 }
 
 //===----------------------------------------------------------------------===//
 // Code completion string implementation
 //===----------------------------------------------------------------------===//
 

clang/lib/Sema/SemaCodeComplete.cpp

void Sema::CodeCompleteObjCInterfaceDecl(Scope *S) {
   }
 
   Results.ExitScope();
 
   HandleCodeCompleteResults(this, CodeCompleter, Results.getCompletionContext(),
                             Results.data(), Results.size());
 }
 
+void Sema::CodeCompleteObjCClassForwardDecl(Scope *S) {
+  ResultBuilder Results(*this, CodeCompleter->getAllocator(),
+                        CodeCompleter->getCodeCompletionTUInfo(),
+                        CodeCompletionContext::CCC_ObjCClassForwardDecl);
+  Results.EnterNewScope();
+
+  if (CodeCompleter->includeGlobals()) {
+    // Add all classes.
+    AddInterfaceResults(Context.getTranslationUnitDecl(), CurContext, false,
+                        false, Results);
+  }
+
+  Results.ExitScope();
+
+  HandleCodeCompleteResults(this, CodeCompleter, Results.getCompletionContext(),
+                            Results.data(), Results.size());
+}
+
 void Sema::CodeCompleteObjCSuperclass(Scope *S, IdentifierInfo *ClassName,
                                       SourceLocation ClassNameLoc) {
   ResultBuilder Results(*this, CodeCompleter->getAllocator(),
                         CodeCompleter->getCodeCompletionTUInfo(),
                         CodeCompletionContext::CCC_ObjCInterfaceName);
   Results.EnterNewScope();
 
   // Make sure that we ignore the class we're currently defining.

clang/tools/libclang/CIndexCodeCompletion.cpp

switch (kind) {
     }
     case CodeCompletionContext::CCC_ObjCCategoryName: {
       contexts = CXCompletionContext_ObjCCategory;
       break;
     }
     case CodeCompletionContext::CCC_Other:
     case CodeCompletionContext::CCC_ObjCInterface:
     case CodeCompletionContext::CCC_ObjCImplementation:
+    case CodeCompletionContext::CCC_ObjCClassForwardDecl:
     case CodeCompletionContext::CCC_NewName:
     case CodeCompletionContext::CCC_MacroName:
     case CodeCompletionContext::CCC_PreprocessorExpression:
     case CodeCompletionContext::CCC_PreprocessorDirective:
     case CodeCompletionContext::CCC_Attribute:
     case CodeCompletionContext::CCC_TypeQualifiers: {
       //Only Clang results should be accepted, so we'll set all of the other
       //context bits to 0 (i.e. the empty set)