[clang-repl] support code completion at a REPL.

This patch enabled code completion for ClangREPL. The feature was built upon
three existing Clang components: a list completer for LineEditor, a
CompletionConsumer from SemaCodeCompletion, and the ASTUnit::codeComplete method.
The first component serves as the main entry point of handling interactive inputs.

Because a completion point for a compiler instance has to be unchanged once it
is set, an incremental compiler instance is created for each code
completion. Such a compiler instance carries over AST context source from the
main interpreter compiler in order to obtain declarations or bindings from
previous input in the same REPL session.

The most important API codeComplete in Interpreter/CodeCompletion is a thin
wrapper that calls with ASTUnit::codeComplete with necessary arguments, such as
a code completion point and a ReplCompletionConsumer, which communicates
completion results from SemaCodeCompletion back to the list completer for the
REPL.

In addition, PCC_TopLevelOrExpression and CCC_TopLevelOrExpression` top levels
were added so that SemaCodeCompletion can treat top level statements like
expression statements at the REPL. For example,

clang-repl> int foo = 42;
clang-repl> f<tab>

From a parser's persective, the cursor is at a top level. If we used code
completion without any changes, PCC_Namespace would be supplied to
Sema::CodeCompleteOrdinaryName, and thus the completion results would not
include foo.

Currently, the way we use PCC_TopLevelOrExpression and
CCC_TopLevelOrExpression is no different from the way we use PCC_Statement
and CCC_Statement respectively.

Differential revision: https://reviews.llvm.org/D154382

20 files changed, 495 insertions, 28 deletions

diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
index b762be1..c6d0d4d 100644
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -77,6 +77,7 @@ class Preprocessor;
 class PreprocessorOptions;
 class Sema;
 class TargetInfo;
+class SyntaxOnlyAction;
 
 /// \brief Enumerates the available scopes for skipping function bodies.
 enum class SkipFunctionBodiesScope { None, Preamble, PreambleAndMainFile };
@@ -887,6 +888,10 @@ public:
   /// \param IncludeBriefComments Whether to include brief documentation within
   /// the set of code completions returned.
   ///
+  /// \param Act If supplied, this argument is used to parse the input file,
+  /// allowing customized parsing by overriding SyntaxOnlyAction lifecycle
+  /// methods.
+  ///
   /// FIXME: The Diag, LangOpts, SourceMgr, FileMgr, StoredDiagnostics, and
   /// OwnedBuffers parameters are all disgusting hacks. They will go away.
   void CodeComplete(StringRef File, unsigned Line, unsigned Column,
@@ -897,7 +902,8 @@ public:
                     DiagnosticsEngine &Diag, LangOptions &LangOpts,
                     SourceManager &SourceMgr, FileManager &FileMgr,
                     SmallVectorImpl<StoredDiagnostic> &StoredDiagnostics,
-                    SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers);
+                    SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers,
+                    std::unique_ptr<SyntaxOnlyAction> Act = nullptr);
 
   /// Save this translation unit to a file with the given name.
   ///
diff --git a/clang/include/clang/Interpreter/CodeCompletion.h b/clang/include/clang/Interpreter/CodeCompletion.h
new file mode 100644
index 0000000..6631d33
--- /dev/null
+++ b/clang/include/clang/Interpreter/CodeCompletion.h
@@ -0,0 +1,33 @@
+//===----- CodeCompletion.h - Code Completion for ClangRepl ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the classes which performs code completion at the REPL.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_INTERPRETER_CODE_COMPLETION_H
+#define LLVM_CLANG_INTERPRETER_CODE_COMPLETION_H
+#include <string>
+#include <vector>
+
+namespace llvm {
+class StringRef;
+} // namespace llvm
+
+namespace clang {
+class CodeCompletionResult;
+class CompilerInstance;
+
+void codeComplete(CompilerInstance *InterpCI, llvm::StringRef Content,
+                  unsigned Line, unsigned Col, const CompilerInstance *ParentCI,
+                  std::vector<CodeCompletionResult> &CCResults);
+
+std::vector<std::string>
+convertToCodeCompleteStrings(const std::vector<CodeCompletionResult> &Results);
+} // namespace clang
+#endif
diff --git a/clang/include/clang/Sema/CodeCompleteConsumer.h b/clang/include/clang/Sema/CodeCompleteConsumer.h
index bb4b638..c9e8666 100644
--- a/clang/include/clang/Sema/CodeCompleteConsumer.h
+++ b/clang/include/clang/Sema/CodeCompleteConsumer.h
@@ -336,7 +336,10 @@ public:
     CCC_Recovery,
 
     /// Code completion in a @class forward declaration.
-    CCC_ObjCClassForwardDecl
+    CCC_ObjCClassForwardDecl,
+
+    /// Code completion at a top level in a REPL session.
+    CCC_TopLevelOrExpression,
   };
 
   using VisitedContextSet = llvm::SmallPtrSet<DeclContext *, 8>;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index c992e87..eb4cdbb 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -13449,7 +13449,9 @@ public:
     PCC_ParenthesizedExpression,
     /// Code completion occurs within a sequence of declaration
     /// specifiers within a function, method, or block.
-    PCC_LocalDeclarationSpecifiers
+    PCC_LocalDeclarationSpecifiers,
+    /// Code completion occurs at top-level in a REPL session
+    PCC_TopLevelOrExpression,
   };
 
   void CodeCompleteModuleImport(SourceLocation ImportLoc, ModuleIdPath Path);
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index aece722..98d6c08 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -2008,7 +2008,8 @@ static void CalculateHiddenNames(const CodeCompletionContext &Context,
   case CodeCompletionContext::CCC_SymbolOrNewName:
   case CodeCompletionContext::CCC_ParenthesizedExpression:
   case CodeCompletionContext::CCC_ObjCInterfaceName:
-    break;
+  case CodeCompletionContext::CCC_TopLevelOrExpression:
+      break;
 
   case CodeCompletionContext::CCC_EnumTag:
   case CodeCompletionContext::CCC_UnionTag:
@@ -2167,7 +2168,8 @@ void ASTUnit::CodeComplete(
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     DiagnosticsEngine &Diag, LangOptions &LangOpts, SourceManager &SourceMgr,
     FileManager &FileMgr, SmallVectorImpl<StoredDiagnostic> &StoredDiagnostics,
-    SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers) {
+    SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers,
+    std::unique_ptr<SyntaxOnlyAction> Act) {
   if (!Invocation)
     return;
 
@@ -2304,8 +2306,9 @@ void ASTUnit::CodeComplete(
   if (!Clang->getLangOpts().Modules)
     PreprocessorOpts.DetailedRecord = false;
 
-  std::unique_ptr<SyntaxOnlyAction> Act;
-  Act.reset(new SyntaxOnlyAction);
+  if (!Act)
+    Act.reset(new SyntaxOnlyAction);
+
   if (Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0])) {
     if (llvm::Error Err = Act->Execute()) {
       consumeError(std::move(Err)); // FIXME this drops errors on the floor.
diff --git a/clang/lib/Interpreter/CMakeLists.txt b/clang/lib/Interpreter/CMakeLists.txt
index d3781fe..79d2cba 100644
--- a/clang/lib/Interpreter/CMakeLists.txt
+++ b/clang/lib/Interpreter/CMakeLists.txt
@@ -13,6 +13,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_clang_library(clangInterpreter
   DeviceOffload.cpp
+  CodeCompletion.cpp
   IncrementalExecutor.cpp
   IncrementalParser.cpp
   Interpreter.cpp
diff --git a/clang/lib/Interpreter/CodeCompletion.cpp b/clang/lib/Interpreter/CodeCompletion.cpp
new file mode 100644
index 0000000..05a19ae
--- /dev/null
+++ b/clang/lib/Interpreter/CodeCompletion.cpp
@@ -0,0 +1,229 @@
+//===------ CodeCompletion.cpp - Code Completion for ClangRepl -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the classes which performs code completion at the REPL.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Interpreter/CodeCompletion.h"
+#include "clang/AST/ASTImporter.h"
+#include "clang/AST/DeclarationName.h"
+#include "clang/AST/ExternalASTSource.h"
+#include "clang/Basic/IdentifierTable.h"
+#include "clang/Frontend/ASTUnit.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendActions.h"
+#include "clang/Interpreter/Interpreter.h"
+#include "clang/Lex/PreprocessorOptions.h"
+#include "clang/Sema/CodeCompleteConsumer.h"
+#include "clang/Sema/CodeCompleteOptions.h"
+#include "clang/Sema/Sema.h"
+
+namespace clang {
+
+const std::string CodeCompletionFileName = "input_line_[Completion]";
+
+clang::CodeCompleteOptions getClangCompleteOpts() {
+  clang::CodeCompleteOptions Opts;
+  Opts.IncludeCodePatterns = true;
+  Opts.IncludeMacros = true;
+  Opts.IncludeGlobals = true;
+  Opts.IncludeBriefComments = true;
+  return Opts;
+}
+
+class ReplCompletionConsumer : public CodeCompleteConsumer {
+public:
+  ReplCompletionConsumer(std::vector<CodeCompletionResult> &Results)
+      : CodeCompleteConsumer(getClangCompleteOpts()),
+        CCAllocator(std::make_shared<GlobalCodeCompletionAllocator>()),
+        CCTUInfo(CCAllocator), Results(Results){};
+
+  void ProcessCodeCompleteResults(class Sema &S, CodeCompletionContext Context,
+                                  CodeCompletionResult *InResults,
+                                  unsigned NumResults) final;
+
+  CodeCompletionAllocator &getAllocator() override { return *CCAllocator; }
+
+  CodeCompletionTUInfo &getCodeCompletionTUInfo() override { return CCTUInfo; }
+
+private:
+  std::shared_ptr<GlobalCodeCompletionAllocator> CCAllocator;
+  CodeCompletionTUInfo CCTUInfo;
+  std::vector<CodeCompletionResult> &Results;
+};
+
+void ReplCompletionConsumer::ProcessCodeCompleteResults(
+    class Sema &S, CodeCompletionContext Context,
+    CodeCompletionResult *InResults, unsigned NumResults) {
+  for (unsigned I = 0; I < NumResults; ++I) {
+    auto &Result = InResults[I];
+    switch (Result.Kind) {
+    case CodeCompletionResult::RK_Declaration:
+      if (Result.Declaration->getIdentifier()) {
+        Results.push_back(Result);
+      }
+      break;
+    case CodeCompletionResult::RK_Keyword:
+      Results.push_back(Result);
+      break;
+    default:
+      break;
+    }
+  }
+}
+
+std::vector<std::string> convertToCodeCompleteStrings(
+    const std::vector<clang::CodeCompletionResult> &Results) {
+  std::vector<std::string> CompletionStrings;
+  for (auto Res : Results) {
+    switch (Res.Kind) {
+    case clang::CodeCompletionResult::RK_Declaration:
+      if (auto *ID = Res.Declaration->getIdentifier()) {
+        CompletionStrings.push_back(ID->getName().str());
+      }
+      break;
+    case clang::CodeCompletionResult::RK_Keyword:
+      CompletionStrings.push_back(Res.Keyword);
+      break;
+    default:
+      break;
+    }
+  }
+  return CompletionStrings;
+}
+
+class IncrementalSyntaxOnlyAction : public SyntaxOnlyAction {
+  const CompilerInstance *ParentCI;
+
+public:
+  IncrementalSyntaxOnlyAction(const CompilerInstance *ParentCI)
+      : ParentCI(ParentCI) {}
+
+protected:
+  void ExecuteAction() override;
+};
+
+class ExternalSource : public clang::ExternalASTSource {
+  TranslationUnitDecl *ChildTUDeclCtxt;
+  ASTContext &ParentASTCtxt;
+  TranslationUnitDecl *ParentTUDeclCtxt;
+
+  std::unique_ptr<ASTImporter> Importer;
+
+public:
+  ExternalSource(ASTContext &ChildASTCtxt, FileManager &ChildFM,
+                 ASTContext &ParentASTCtxt, FileManager &ParentFM);
+  bool FindExternalVisibleDeclsByName(const DeclContext *DC,
+                                      DeclarationName Name) override;
+  void
+  completeVisibleDeclsMap(const clang::DeclContext *childDeclContext) override;
+};
+
+// This method is intended to set up `ExternalASTSource` to the running
+// compiler instance before the super `ExecuteAction` triggers parsing
+void IncrementalSyntaxOnlyAction::ExecuteAction() {
+  CompilerInstance &CI = getCompilerInstance();
+  ExternalSource *myExternalSource =
+      new ExternalSource(CI.getASTContext(), CI.getFileManager(),
+                         ParentCI->getASTContext(), ParentCI->getFileManager());
+  llvm::IntrusiveRefCntPtr<clang::ExternalASTSource> astContextExternalSource(
+      myExternalSource);
+  CI.getASTContext().setExternalSource(astContextExternalSource);
+  CI.getASTContext().getTranslationUnitDecl()->setHasExternalVisibleStorage(
+      true);
+
+  SyntaxOnlyAction::ExecuteAction();
+}
+
+ExternalSource::ExternalSource(ASTContext &ChildASTCtxt, FileManager &ChildFM,
+                               ASTContext &ParentASTCtxt, FileManager &ParentFM)
+    : ChildTUDeclCtxt(ChildASTCtxt.getTranslationUnitDecl()),
+      ParentASTCtxt(ParentASTCtxt),
+      ParentTUDeclCtxt(ParentASTCtxt.getTranslationUnitDecl()) {
+  ASTImporter *importer =
+      new ASTImporter(ChildASTCtxt, ChildFM, ParentASTCtxt, ParentFM,
+                      /*MinimalImport : ON*/ true);
+  Importer.reset(importer);
+}
+
+bool ExternalSource::FindExternalVisibleDeclsByName(const DeclContext *DC,
+                                                    DeclarationName Name) {
+  IdentifierTable &ParentIdTable = ParentASTCtxt.Idents;
+
+  auto ParentDeclName =
+      DeclarationName(&(ParentIdTable.get(Name.getAsString())));
+
+  DeclContext::lookup_result lookup_result =
+      ParentTUDeclCtxt->lookup(ParentDeclName);
+
+  if (!lookup_result.empty()) {
+    return true;
+  }
+  return false;
+}
+
+void ExternalSource::completeVisibleDeclsMap(
+    const DeclContext *ChildDeclContext) {
+  assert(ChildDeclContext && ChildDeclContext == ChildTUDeclCtxt &&
+         "No child decl context!");
+
+  if (!ChildDeclContext->hasExternalVisibleStorage())
+    return;
+
+  for (auto *DeclCtxt = ParentTUDeclCtxt; DeclCtxt != nullptr;
+       DeclCtxt = DeclCtxt->getPreviousDecl()) {
+    for (auto &IDeclContext : DeclCtxt->decls()) {
+      if (NamedDecl *Decl = llvm::dyn_cast<NamedDecl>(IDeclContext)) {
+        if (auto DeclOrErr = Importer->Import(Decl)) {
+          if (NamedDecl *importedNamedDecl =
+                  llvm::dyn_cast<NamedDecl>(*DeclOrErr)) {
+            SetExternalVisibleDeclsForName(ChildDeclContext,
+                                           importedNamedDecl->getDeclName(),
+                                           importedNamedDecl);
+          }
+
+        } else {
+          llvm::consumeError(DeclOrErr.takeError());
+        }
+      }
+    }
+    ChildDeclContext->setHasExternalLexicalStorage(false);
+  }
+}
+
+void codeComplete(CompilerInstance *InterpCI, llvm::StringRef Content,
+                  unsigned Line, unsigned Col, const CompilerInstance *ParentCI,
+                  std::vector<CodeCompletionResult> &CCResults) {
+  std::unique_ptr<llvm::MemoryBuffer> MB =
+      llvm::MemoryBuffer::getMemBufferCopy(Content, CodeCompletionFileName);
+  llvm::SmallVector<ASTUnit::RemappedFile, 4> RemappedFiles;
+
+  RemappedFiles.push_back(std::make_pair(CodeCompletionFileName, MB.release()));
+
+  auto DiagOpts = DiagnosticOptions();
+  auto consumer = ReplCompletionConsumer(CCResults);
+
+  auto diag = InterpCI->getDiagnosticsPtr();
+  ASTUnit *AU = ASTUnit::LoadFromCompilerInvocationAction(
+      InterpCI->getInvocationPtr(), std::make_shared<PCHContainerOperations>(),
+      diag);
+  llvm::SmallVector<clang::StoredDiagnostic, 8> sd = {};
+  llvm::SmallVector<const llvm::MemoryBuffer *, 1> tb = {};
+  InterpCI->getFrontendOpts().Inputs[0] = FrontendInputFile(
+      CodeCompletionFileName, Language::CXX, InputKind::Source);
+  auto Act = std::unique_ptr<IncrementalSyntaxOnlyAction>(
+      new IncrementalSyntaxOnlyAction(ParentCI));
+  AU->CodeComplete(CodeCompletionFileName, 1, Col, RemappedFiles, false, false,
+                   false, consumer,
+                   std::make_shared<clang::PCHContainerOperations>(), *diag,
+                   InterpCI->getLangOpts(), InterpCI->getSourceManager(),
+                   InterpCI->getFileManager(), sd, tb, std::move(Act));
+}
+
+} // namespace clang
diff --git a/clang/lib/Interpreter/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
index 9e5cf35..370bcbf 100644
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "IncrementalParser.h"
+
 #include "clang/AST/DeclContextInternals.h"
 #include "clang/CodeGen/BackendUtil.h"
 #include "clang/CodeGen/CodeGenAction.h"
@@ -157,16 +158,11 @@ public:
   TranslationUnitKind getTranslationUnitKind() override {
     return TU_Incremental;
   }
+
   void ExecuteAction() override {
     CompilerInstance &CI = getCompilerInstance();
     assert(CI.hasPreprocessor() && "No PP!");
 
-    // FIXME: Move the truncation aspect of this into Sema, we delayed this till
-    // here so the source manager would be initialized.
-    if (hasCodeCompletionSupport() &&
-        !CI.getFrontendOpts().CodeCompletionAt.FileName.empty())
-      CI.createCodeCompletionConsumer();
-
     // Use a code completion consumer?
     CodeCompleteConsumer *CompletionConsumer = nullptr;
     if (CI.hasCodeCompletionConsumer())
@@ -398,5 +394,4 @@ llvm::StringRef IncrementalParser::GetMangledName(GlobalDecl GD) const {
   assert(CG);
   return CG->GetMangledName(GD);
 }
-
 } // end namespace clang
diff --git a/clang/lib/Interpreter/IncrementalParser.h b/clang/lib/Interpreter/IncrementalParser.h
index def5750..e13b74c 100644
--- a/clang/lib/Interpreter/IncrementalParser.h
+++ b/clang/lib/Interpreter/IncrementalParser.h
@@ -13,9 +13,9 @@
 #ifndef LLVM_CLANG_LIB_INTERPRETER_INCREMENTALPARSER_H
 #define LLVM_CLANG_LIB_INTERPRETER_INCREMENTALPARSER_H
 
+#include "clang/AST/GlobalDecl.h"
 #include "clang/Interpreter/PartialTranslationUnit.h"
 
-#include "clang/AST/GlobalDecl.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
@@ -24,7 +24,7 @@
 #include <memory>
 namespace llvm {
 class LLVMContext;
-}
+} // namespace llvm
 
 namespace clang {
 class ASTConsumer;
diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
index 4e10452..7968c62 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -11,13 +11,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/Interpreter/Interpreter.h"
-
 #include "DeviceOffload.h"
 #include "IncrementalExecutor.h"
 #include "IncrementalParser.h"
-
 #include "InterpreterUtils.h"
+
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Mangle.h"
 #include "clang/AST/TypeVisitor.h"
@@ -33,6 +31,7 @@
 #include "clang/Driver/Tool.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/TextDiagnosticBuffer.h"
+#include "clang/Interpreter/Interpreter.h"
 #include "clang/Interpreter/Value.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Sema/Lookup.h"
@@ -127,7 +126,6 @@ CreateCI(const llvm::opt::ArgStringList &Argv) {
 
   Clang->getFrontendOpts().DisableFree = false;
   Clang->getCodeGenOpts().DisableFree = false;
-
   return std::move(Clang);
 }
 
@@ -276,6 +274,7 @@ Interpreter::create(std::unique_ptr<CompilerInstance> CI) {
       std::unique_ptr<Interpreter>(new Interpreter(std::move(CI), Err));
   if (Err)
     return std::move(Err);
+
   auto PTU = Interp->Parse(Runtimes);
   if (!PTU)
     return PTU.takeError();
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index cd7c5dc..d4cc048 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -18,6 +18,7 @@
 #include "clang/Basic/Attributes.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/TargetInfo.h"
+#include "clang/Basic/TokenKinds.h"
 #include "clang/Parse/ParseDiagnostic.h"
 #include "clang/Parse/Parser.h"
 #include "clang/Parse/RAIIObjectsForParser.h"
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index 9a8c9e3..09215b8 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -923,9 +923,16 @@ Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
                                          /*IsInstanceMethod=*/std::nullopt,
                                          /*ReturnType=*/nullptr);
     }
-    Actions.CodeCompleteOrdinaryName(
-        getCurScope(),
-        CurParsedObjCImpl ? Sema::PCC_ObjCImplementation : Sema::PCC_Namespace);
+
+    Sema::ParserCompletionContext PCC;
+    if (CurParsedObjCImpl) {
+      PCC = Sema::PCC_ObjCImplementation;
+    } else if (PP.isIncrementalProcessingEnabled()) {
+      PCC = Sema::PCC_TopLevelOrExpression;
+    } else {
+      PCC = Sema::PCC_Namespace;
+    };
+    Actions.CodeCompleteOrdinaryName(getCurScope(), PCC);
     return nullptr;
   case tok::kw_import: {
     Sema::ModuleImportState IS = Sema::ModuleImportState::NotACXX20Module;
diff --git a/clang/lib/Sema/CodeCompleteConsumer.cpp b/clang/lib/Sema/CodeCompleteConsumer.cpp
index 2024177..9caa1a8 100644
--- a/clang/lib/Sema/CodeCompleteConsumer.cpp
+++ b/clang/lib/Sema/CodeCompleteConsumer.cpp
@@ -51,6 +51,7 @@ bool CodeCompletionContext::wantConstructorResults() const {
   case CCC_ParenthesizedExpression:
   case CCC_Symbol:
   case CCC_SymbolOrNewName:
+  case CCC_TopLevelOrExpression:
     return true;
 
   case CCC_TopLevel:
@@ -169,6 +170,8 @@ StringRef clang::getCompletionKindString(CodeCompletionContext::Kind Kind) {
     return "Recovery";
   case CCKind::CCC_ObjCClassForwardDecl:
     return "ObjCClassForwardDecl";
+  case CCKind::CCC_TopLevelOrExpression:
+    return "ReplTopLevel";
   }
   llvm_unreachable("Invalid CodeCompletionContext::Kind!");
 }
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index 2a3de571..5440e16 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -225,6 +225,7 @@ public:
     case CodeCompletionContext::CCC_ObjCMessageReceiver:
     case CodeCompletionContext::CCC_ParenthesizedExpression:
     case CodeCompletionContext::CCC_Statement:
+    case CodeCompletionContext::CCC_TopLevelOrExpression:
     case CodeCompletionContext::CCC_Recovery:
       if (ObjCMethodDecl *Method = SemaRef.getCurMethodDecl())
         if (Method->isInstanceMethod())
@@ -1850,6 +1851,7 @@ static void AddFunctionSpecifiers(Sema::ParserCompletionContext CCC,
   case Sema::PCC_ObjCInstanceVariableList:
   case Sema::PCC_Expression:
   case Sema::PCC_Statement:
+  case Sema::PCC_TopLevelOrExpression:
   case Sema::PCC_ForInit:
   case Sema::PCC_Condition:
   case Sema::PCC_RecoveryInFunction:
@@ -1907,6 +1909,7 @@ static bool WantTypesInContext(Sema::ParserCompletionContext CCC,
   case Sema::PCC_Type:
   case Sema::PCC_ParenthesizedExpression:
   case Sema::PCC_LocalDeclarationSpecifiers:
+  case Sema::PCC_TopLevelOrExpression:
     return true;
 
   case Sema::PCC_Expression:
@@ -2219,6 +2222,7 @@ static void AddOrdinaryNameResults(Sema::ParserCompletionContext CCC, Scope *S,
     break;
 
   case Sema::PCC_RecoveryInFunction:
+  case Sema::PCC_TopLevelOrExpression:
   case Sema::PCC_Statement: {
     if (SemaRef.getLangOpts().CPlusPlus11)
       AddUsingAliasResult(Builder, Results);
@@ -4208,6 +4212,8 @@ mapCodeCompletionContext(Sema &S, Sema::ParserCompletionContext PCC) {
 
   case Sema::PCC_LocalDeclarationSpecifiers:
     return CodeCompletionContext::CCC_Type;
+  case Sema::PCC_TopLevelOrExpression:
+    return CodeCompletionContext::CCC_TopLevelOrExpression;
   }
 
   llvm_unreachable("Invalid ParserCompletionContext!");
@@ -4348,6 +4354,7 @@ void Sema::CodeCompleteOrdinaryName(Scope *S,
     break;
 
   case PCC_Statement:
+  case PCC_TopLevelOrExpression:
   case PCC_ParenthesizedExpression:
   case PCC_Expression:
   case PCC_ForInit:
@@ -4385,6 +4392,7 @@ void Sema::CodeCompleteOrdinaryName(Scope *S,
   case PCC_ParenthesizedExpression:
   case PCC_Expression:
   case PCC_Statement:
+  case PCC_TopLevelOrExpression:
   case PCC_RecoveryInFunction:
     if (S->getFnParent())
       AddPrettyFunctionResults(getLangOpts(), Results);
diff --git a/clang/test/CodeCompletion/incrememal-mode-completion-no-error.cpp b/clang/test/CodeCompletion/incrememal-mode-completion-no-error.cpp
new file mode 100644
index 0000000..e6846f8
--- /dev/null
+++ b/clang/test/CodeCompletion/incrememal-mode-completion-no-error.cpp
@@ -0,0 +1,3 @@
+void foo(
+// RUN: %clang_cc1 -fincremental-extensions -fsyntax-only -code-completion-at=%s:%(line-1):9 %s | wc -c | FileCheck %s
+// CHECK: 0
diff --git a/clang/test/CodeCompletion/incremental-top-level.cpp b/clang/test/CodeCompletion/incremental-top-level.cpp
new file mode 100644
index 0000000..11f8bd6
--- /dev/null
+++ b/clang/test/CodeCompletion/incremental-top-level.cpp
@@ -0,0 +1,4 @@
+int foo = 10;
+f
+// RUN: %clang_cc1 -fincremental-extensions -fsyntax-only -code-completion-at=%s:%(line-1):1 %s | FileCheck %s
+// CHECK: COMPLETION: foo : [#int#]foo
diff --git a/clang/tools/clang-repl/ClangRepl.cpp b/clang/tools/clang-repl/ClangRepl.cpp
index f46452d..05fc115 100644
--- a/clang/tools/clang-repl/ClangRepl.cpp
+++ b/clang/tools/clang-repl/ClangRepl.cpp
@@ -13,7 +13,9 @@
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendDiagnostic.h"
+#include "clang/Interpreter/CodeCompletion.h"
 #include "clang/Interpreter/Interpreter.h"
+#include "clang/Sema/CodeCompleteConsumer.h"
 
 #include "llvm/ExecutionEngine/Orc/LLJIT.h"
 #include "llvm/LineEditor/LineEditor.h"
@@ -70,6 +72,70 @@ static int checkDiagErrors(const clang::CompilerInstance *CI, bool HasError) {
   return (Errs || HasError) ? EXIT_FAILURE : EXIT_SUCCESS;
 }
 
+struct ReplListCompleter {
+  clang::IncrementalCompilerBuilder &CB;
+  clang::Interpreter &MainInterp;
+  ReplListCompleter(clang::IncrementalCompilerBuilder &CB,
+                    clang::Interpreter &Interp)
+      : CB(CB), MainInterp(Interp){};
+
+  std::vector<llvm::LineEditor::Completion> operator()(llvm::StringRef Buffer,
+                                                       size_t Pos) const;
+  std::vector<llvm::LineEditor::Completion>
+  operator()(llvm::StringRef Buffer, size_t Pos, llvm::Error &ErrRes) const;
+};
+
+std::vector<llvm::LineEditor::Completion>
+ReplListCompleter::operator()(llvm::StringRef Buffer, size_t Pos) const {
+  auto Err = llvm::Error::success();
+  auto res = (*this)(Buffer, Pos, Err);
+  if (Err)
+    llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
+  return res;
+}
+
+std::vector<llvm::LineEditor::Completion>
+ReplListCompleter::operator()(llvm::StringRef Buffer, size_t Pos,
+                              llvm::Error &ErrRes) const {
+  std::vector<llvm::LineEditor::Completion> Comps;
+  std::vector<clang::CodeCompletionResult> Results;
+
+  auto CI = CB.CreateCpp();
+  if (auto Err = CI.takeError()) {
+    ErrRes = std::move(Err);
+    return {};
+  }
+
+  size_t Lines =
+      std::count(Buffer.begin(), std::next(Buffer.begin(), Pos), '\n') + 1;
+  auto Interp = clang::Interpreter::create(std::move(*CI));
+
+  if (auto Err = Interp.takeError()) {
+    // log the error and returns an empty vector;
+    ErrRes = std::move(Err);
+
+    return {};
+  }
+
+  codeComplete(
+      const_cast<clang::CompilerInstance *>((*Interp)->getCompilerInstance()),
+      Buffer, Lines, Pos + 1, MainInterp.getCompilerInstance(), Results);
+
+  size_t space_pos = Buffer.rfind(" ");
+  llvm::StringRef s;
+  if (space_pos == llvm::StringRef::npos) {
+    s = Buffer;
+  } else {
+    s = Buffer.substr(space_pos + 1);
+  }
+
+  for (auto c : convertToCodeCompleteStrings(Results)) {
+    if (c.find(s) == 0)
+      Comps.push_back(llvm::LineEditor::Completion(c.substr(s.size()), c));
+  }
+  return Comps;
+}
+
 llvm::ExitOnError ExitOnErr;
 int main(int argc, const char **argv) {
   ExitOnErr.setBanner("clang-repl: ");
@@ -133,6 +199,7 @@ int main(int argc, const char **argv) {
     DeviceCI->LoadRequestedPlugins();
 
   std::unique_ptr<clang::Interpreter> Interp;
+
   if (CudaEnabled) {
     Interp = ExitOnErr(
         clang::Interpreter::createWithCUDA(std::move(CI), std::move(DeviceCI)));
@@ -155,8 +222,8 @@ int main(int argc, const char **argv) {
 
   if (OptInputs.empty()) {
     llvm::LineEditor LE("clang-repl");
-    // FIXME: Add LE.setListCompleter
     std::string Input;
+    LE.setListCompleter(ReplListCompleter(CB, *Interp));
     while (std::optional<std::string> Line = LE.readLine()) {
       llvm::StringRef L = *Line;
       L = L.trim();
@@ -168,10 +235,10 @@ int main(int argc, const char **argv) {
       }
 
       Input += L;
-
       if (Input == R"(%quit)") {
         break;
-      } else if (Input == R"(%undo)") {
+      }
+      if (Input == R"(%undo)") {
         if (auto Err = Interp->Undo()) {
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
           HasError = true;
diff --git a/clang/tools/libclang/CIndexCodeCompletion.cpp b/clang/tools/libclang/CIndexCodeCompletion.cpp
index 01bad3d..196c64e 100644
--- a/clang/tools/libclang/CIndexCodeCompletion.cpp
+++ b/clang/tools/libclang/CIndexCodeCompletion.cpp
@@ -11,8 +11,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "CIndexer.h"
 #include "CIndexDiagnostic.h"
+#include "CIndexer.h"
 #include "CLog.h"
 #include "CXCursor.h"
 #include "CXSourceLocation.h"
@@ -25,6 +25,7 @@
 #include "clang/Basic/SourceManager.h"
 #include "clang/Frontend/ASTUnit.h"
 #include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendActions.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
 #include "clang/Sema/Sema.h"
 #include "llvm/ADT/SmallString.h"
@@ -41,7 +42,6 @@
 #include <cstdlib>
 #include <string>
 
-
 #ifdef UDP_CODE_COMPLETION_LOGGER
 #include "clang/Basic/Version.h"
 #include <arpa/inet.h>
@@ -543,6 +543,7 @@ static unsigned long long getContextsForContextKind(
     case CodeCompletionContext::CCC_PreprocessorExpression:
     case CodeCompletionContext::CCC_PreprocessorDirective:
     case CodeCompletionContext::CCC_Attribute:
+    case CodeCompletionContext::CCC_TopLevelOrExpression:
     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)
diff --git a/clang/unittests/Interpreter/CMakeLists.txt b/clang/unittests/Interpreter/CMakeLists.txt
index 698494b..712641a 100644
--- a/clang/unittests/Interpreter/CMakeLists.txt
+++ b/clang/unittests/Interpreter/CMakeLists.txt
@@ -9,6 +9,7 @@ set(LLVM_LINK_COMPONENTS
 add_clang_unittest(ClangReplInterpreterTests
   IncrementalProcessingTest.cpp
   InterpreterTest.cpp
+  CodeCompletionTest.cpp
   )
 target_link_libraries(ClangReplInterpreterTests PUBLIC
   clangAST
diff --git a/clang/unittests/Interpreter/CodeCompletionTest.cpp b/clang/unittests/Interpreter/CodeCompletionTest.cpp
new file mode 100644
index 0000000..c7434ae
--- /dev/null
+++ b/clang/unittests/Interpreter/CodeCompletionTest.cpp
@@ -0,0 +1,101 @@
+#include "clang/Interpreter/CodeCompletion.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Interpreter/Interpreter.h"
+#include "clang/Sema/CodeCompleteConsumer.h"
+#include "llvm/LineEditor/LineEditor.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+using namespace clang;
+namespace {
+auto CB = clang::IncrementalCompilerBuilder();
+
+static std::unique_ptr<Interpreter> createInterpreter() {
+  auto CI = cantFail(CB.CreateCpp());
+  return cantFail(clang::Interpreter::create(std::move(CI)));
+}
+
+static std::vector<std::string> runComp(clang::Interpreter &MainInterp,
+                                        llvm::StringRef Prefix,
+                                        llvm::Error &ErrR) {
+  auto CI = CB.CreateCpp();
+  if (auto Err = CI.takeError()) {
+    ErrR = std::move(Err);
+    return {};
+  }
+
+  auto Interp = clang::Interpreter::create(std::move(*CI));
+  if (auto Err = Interp.takeError()) {
+    // log the error and returns an empty vector;
+    ErrR = std::move(Err);
+
+    return {};
+  }
+
+  std::vector<clang::CodeCompletionResult> Results;
+
+  codeComplete(
+      const_cast<clang::CompilerInstance *>((*Interp)->getCompilerInstance()),
+      Prefix, 1, Prefix.size(), MainInterp.getCompilerInstance(), Results);
+
+  std::vector<std::string> Comps;
+  for (auto c : convertToCodeCompleteStrings(Results)) {
+    if (c.find(Prefix) == 0)
+      Comps.push_back(c.substr(Prefix.size()));
+  }
+
+  return Comps;
+}
+
+TEST(CodeCompletionTest, Sanity) {
+  auto Interp = createInterpreter();
+  if (auto R = Interp->ParseAndExecute("int foo = 12;")) {
+    consumeError(std::move(R));
+    return;
+  }
+  auto Err = llvm::Error::success();
+  auto comps = runComp(*Interp, "f", Err);
+  EXPECT_EQ((size_t)2, comps.size()); // foo and float
+  EXPECT_EQ(comps[0], std::string("oo"));
+  EXPECT_EQ((bool)Err, false);
+}
+
+TEST(CodeCompletionTest, SanityNoneValid) {
+  auto Interp = createInterpreter();
+  if (auto R = Interp->ParseAndExecute("int foo = 12;")) {
+    consumeError(std::move(R));
+    return;
+  }
+  auto Err = llvm::Error::success();
+  auto comps = runComp(*Interp, "babanana", Err);
+  EXPECT_EQ((size_t)0, comps.size()); // foo and float
+  EXPECT_EQ((bool)Err, false);
+}
+
+TEST(CodeCompletionTest, TwoDecls) {
+  auto Interp = createInterpreter();
+  if (auto R = Interp->ParseAndExecute("int application = 12;")) {
+    consumeError(std::move(R));
+    return;
+  }
+  if (auto R = Interp->ParseAndExecute("int apple = 12;")) {
+    consumeError(std::move(R));
+    return;
+  }
+  auto Err = llvm::Error::success();
+  auto comps = runComp(*Interp, "app", Err);
+  EXPECT_EQ((size_t)2, comps.size());
+  EXPECT_EQ((bool)Err, false);
+}
+
+TEST(CodeCompletionTest, CompFunDeclsNoError) {
+  auto Interp = createInterpreter();
+  auto Err = llvm::Error::success();
+  auto comps = runComp(*Interp, "void app(", Err);
+  EXPECT_EQ((bool)Err, false);
+}
+
+} // anonymous namespace