diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
--- a/clang-tools-extra/clangd/CodeComplete.cpp
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -821,6 +821,7 @@
   case CodeCompletionContext::CCC_Symbol:
   case CodeCompletionContext::CCC_SymbolOrNewName:
   case CodeCompletionContext::CCC_ObjCClassForwardDecl:
+  case CodeCompletionContext::CCC_TopLevelOrExpression:
     return true;
   case CodeCompletionContext::CCC_OtherWithMacros:
   case CodeCompletionContext::CCC_DotMemberAccess:
diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -77,6 +77,7 @@
 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 @@
   /// \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 @@
                     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/Sema/CodeCompleteConsumer.h b/clang/include/clang/Sema/CodeCompleteConsumer.h
--- a/clang/include/clang/Sema/CodeCompleteConsumer.h
+++ b/clang/include/clang/Sema/CodeCompleteConsumer.h
@@ -336,7 +336,12 @@
     CCC_Recovery,
 
     /// Code completion in a @class forward declaration.
-    CCC_ObjCClassForwardDecl
+    CCC_ObjCClassForwardDecl,
+
+    /// Code completion at a top level, i.e. in a namespace or global scope,
+    /// but also in expression statements. This is because REPL inputs can be
+    /// declarations or expression statements.
+    CCC_TopLevelOrExpression,
   };
 
   using VisitedContextSet = llvm::SmallPtrSet<DeclContext *, 8>;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -13456,7 +13456,9 @@
     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
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -2008,7 +2008,8 @@
   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 @@
     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 @@
   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
--- a/clang/lib/Interpreter/CMakeLists.txt
+++ b/clang/lib/Interpreter/CMakeLists.txt
@@ -13,6 +13,7 @@
 
 add_clang_library(clangInterpreter
   DeviceOffload.cpp
+  CodeCompletion.cpp
   IncrementalExecutor.cpp
   IncrementalParser.cpp
   Interpreter.cpp
diff --git a/clang/lib/Interpreter/IncrementalParser.h b/clang/lib/Interpreter/IncrementalParser.h
--- 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/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
--- 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 @@
   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 @@
   assert(CG);
   return CG->GetMangledName(GD);
 }
-
 } // end namespace clang
diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
--- 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 @@
 
   Clang->getFrontendOpts().DisableFree = false;
   Clang->getCodeGenOpts().DisableFree = false;
-
   return std::move(Clang);
 }
 
@@ -276,6 +274,7 @@
       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
--- 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
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -923,9 +923,16 @@
                                          /*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
--- a/clang/lib/Sema/CodeCompleteConsumer.cpp
+++ b/clang/lib/Sema/CodeCompleteConsumer.cpp
@@ -51,6 +51,7 @@
   case CCC_ParenthesizedExpression:
   case CCC_Symbol:
   case CCC_SymbolOrNewName:
+  case CCC_TopLevelOrExpression:
     return true;
 
   case CCC_TopLevel:
@@ -169,6 +170,8 @@
     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
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -225,6 +225,7 @@
     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 @@
   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 @@
   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 @@
     break;
 
   case Sema::PCC_RecoveryInFunction:
+  case Sema::PCC_TopLevelOrExpression:
   case Sema::PCC_Statement: {
     if (SemaRef.getLangOpts().CPlusPlus11)
       AddUsingAliasResult(Builder, Results);
@@ -4208,6 +4212,8 @@
 
   case Sema::PCC_LocalDeclarationSpecifiers:
     return CodeCompletionContext::CCC_Type;
+  case Sema::PCC_TopLevelOrExpression:
+    return CodeCompletionContext::CCC_TopLevelOrExpression;
   }
 
   llvm_unreachable("Invalid ParserCompletionContext!");
@@ -4348,6 +4354,7 @@
     break;
 
   case PCC_Statement:
+  case PCC_TopLevelOrExpression:
   case PCC_ParenthesizedExpression:
   case PCC_Expression:
   case PCC_ForInit:
@@ -4385,6 +4392,7 @@
   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/tools/clang-repl/ClangRepl.cpp b/clang/tools/clang-repl/ClangRepl.cpp
--- a/clang/tools/clang-repl/ClangRepl.cpp
+++ b/clang/tools/clang-repl/ClangRepl.cpp
@@ -13,6 +13,7 @@
 #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 "llvm/ExecutionEngine/Orc/LLJIT.h"
@@ -70,6 +71,70 @@
   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<std::string> 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 Prefix;
+  if (space_pos == llvm::StringRef::npos) {
+    Prefix = Buffer;
+  } else {
+    Prefix = Buffer.substr(space_pos + 1);
+  }
+
+  for (auto c : Results) {
+    if (c.find(Prefix) == 0)
+      Comps.push_back(llvm::LineEditor::Completion(c.substr(Prefix.size()), c));
+  }
+  return Comps;
+}
+
 llvm::ExitOnError ExitOnErr;
 int main(int argc, const char **argv) {
   ExitOnErr.setBanner("clang-repl: ");
@@ -135,6 +200,7 @@
     DeviceCI->LoadRequestedPlugins();
 
   std::unique_ptr<clang::Interpreter> Interp;
+
   if (CudaEnabled) {
     Interp = ExitOnErr(
         clang::Interpreter::createWithCUDA(std::move(CI), std::move(DeviceCI)));
@@ -157,8 +223,8 @@
 
   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();
@@ -170,10 +236,10 @@
       }
 
       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
--- 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 @@
     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
--- a/clang/unittests/Interpreter/CMakeLists.txt
+++ b/clang/unittests/Interpreter/CMakeLists.txt
@@ -9,6 +9,7 @@
 add_clang_unittest(ClangReplInterpreterTests
   IncrementalProcessingTest.cpp
   InterpreterTest.cpp
+  CodeCompletionTest.cpp
   )
 target_link_libraries(ClangReplInterpreterTests PUBLIC
   clangAST