[ClangRepl] support code completion at the repl

[capfredf]

Summary

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.
with the first component serving 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.

Previous Differential Revision: https://reviews.llvm.org/D154382

clang-tools-extra/clangd/CodeComplete.cpp

bool contextAllowsIndex(enum CodeCompletionContext::Kind K) {
   case CodeCompletionContext::CCC_ObjCClassMessage:
   case CodeCompletionContext::CCC_IncludedFile:
   case CodeCompletionContext::CCC_Attribute:
   // FIXME: Provide identifier based completions for the following contexts:
   case CodeCompletionContext::CCC_Other: // Be conservative.
   case CodeCompletionContext::CCC_NaturalLanguage:
   case CodeCompletionContext::CCC_Recovery:
   case CodeCompletionContext::CCC_NewName:
+  case CodeCompletionContext::CCC_TopLevelOrExpression:
     return false;
   }
   llvm_unreachable("unknown code completion context");
 }
 
 static bool isInjectedClass(const NamedDecl &D) {
   if (auto *R = dyn_cast_or_null<RecordDecl>(&D))
     if (R->isInjectedClassName())

clang/include/clang/Frontend/ASTUnit.h

 class InputKind;
 class InMemoryModuleCache;
 class PCHContainerOperations;
 class PCHContainerReader;
 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 };
 
 /// \brief Enumerates the available kinds for capturing diagnostics.
 enum class CaptureDiagsKind { None, All, AllWithoutNonErrorsFromIncludes };
 
 /// Utility class for loading a ASTContext from an AST file.
public:
   /// results.
   ///
   /// \param IncludeCodePatterns Whether to include code patterns (such as a
   /// for loop) in the code-completion results.
   ///
   /// \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,
                     ArrayRef<RemappedFile> RemappedFiles, bool IncludeMacros,
                     bool IncludeCodePatterns, bool IncludeBriefComments,
                     CodeCompleteConsumer &Consumer,
                     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 = nullptr);
 
   /// Save this translation unit to a file with the given name.
   ///
   /// \returns true if there was a file error or false if the save was
   /// successful.
   bool Save(StringRef File);
 
   /// Serialize this translation unit with the given output stream.
   ///
   /// \returns True if an error occurred, false otherwise.
   bool serialize(raw_ostream &OS);
 };
 
 } // namespace clang
 
 #endif // LLVM_CLANG_FRONTEND_ASTUNIT_H

clang/include/clang/Interpreter/CodeCompletion.h

+//===----- 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

clang/include/clang/Sema/CodeCompleteConsumer.h

enum Kind {
     /// 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,
 
     /// 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>;
 
 private:
   Kind CCKind;
 
   /// Indicates whether we are completing a name of a using declaration, e.g.

clang/include/clang/Sema/Sema.h

enum ParserCompletionContext {
     PCC_RecoveryInFunction,
     /// Code completion occurs where only a type is permitted.
     PCC_Type,
     /// Code completion occurs in a parenthesized expression, which
     /// might also be a type cast.
     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);
   void CodeCompleteOrdinaryName(Scope *S,
                                 ParserCompletionContext CompletionContext);
   void CodeCompleteDeclSpec(Scope *S, DeclSpec &DS,
                             bool AllowNonIdentifiers,
                             bool AllowNestedNameSpecifiers);

clang/lib/Frontend/ASTUnit.cpp

static void CalculateHiddenNames(const CodeCompletionContext &Context,
   case CodeCompletionContext::CCC_ArrowMemberAccess:
   case CodeCompletionContext::CCC_ObjCPropertyAccess:
   case CodeCompletionContext::CCC_Namespace:
   case CodeCompletionContext::CCC_Type:
   case CodeCompletionContext::CCC_Symbol:
   case CodeCompletionContext::CCC_SymbolOrNewName:
   case CodeCompletionContext::CCC_ParenthesizedExpression:
   case CodeCompletionContext::CCC_ObjCInterfaceName:
+  case CodeCompletionContext::CCC_TopLevelOrExpression:
       break;
 
   case CodeCompletionContext::CCC_EnumTag:
   case CodeCompletionContext::CCC_UnionTag:
   case CodeCompletionContext::CCC_ClassOrStructTag:
     OnlyTagNames = true;
     break;
 
   case CodeCompletionContext::CCC_ObjCProtocolName:

 void ASTUnit::CodeComplete(
     StringRef File, unsigned Line, unsigned Column,
     ArrayRef<RemappedFile> RemappedFiles, bool IncludeMacros,
     bool IncludeCodePatterns, bool IncludeBriefComments,
     CodeCompleteConsumer &Consumer,
     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;
 
   SimpleTimer CompletionTimer(WantTiming);
   CompletionTimer.setOutput("Code completion @ " + File + ":" +
                             Twine(Line) + ":" + Twine(Column));
 
   auto CCInvocation = std::make_shared<CompilerInvocation>(*Invocation);
if (OverrideMainBuffer) {
     PreprocessorOpts.PrecompiledPreambleBytes.first = 0;
     PreprocessorOpts.PrecompiledPreambleBytes.second = false;
   }
 
   // Disable the preprocessing record if modules are not enabled.
   if (!Clang->getLangOpts().Modules)
     PreprocessorOpts.DetailedRecord = false;
 
-  std::unique_ptr<SyntaxOnlyAction> Act;
+  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.
     }
     Act->EndSourceFile();
   }
 }
 

clang/lib/Interpreter/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
    core
    native
    MC
    Option
    OrcJit
    OrcShared
    OrcTargetProcess
    Support
    Target
    TargetParser
   )
 
 add_clang_library(clangInterpreter
   DeviceOffload.cpp
+  CodeCompletion.cpp
   IncrementalExecutor.cpp
   IncrementalParser.cpp
   Interpreter.cpp
   InterpreterUtils.cpp
   Value.cpp
 
   DEPENDS
   intrinsics_gen

clang/lib/Interpreter/CodeCompletion.cpp

+//===------ 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 {
+  ASTContext &ChildASTCtxt;
+  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)
+    : ChildASTCtxt(ChildASTCtxt),
+      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

clang/lib/Interpreter/IncrementalParser.h

 //===--- IncrementalParser.h - Incremental Compilation ----------*- C++ -*-===//
 //
 // 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 class which performs incremental code compilation.
 //
 //===----------------------------------------------------------------------===//
 
 #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"
 
 #include <list>
 #include <memory>
 namespace llvm {
 class LLVMContext;
-}
+} // namespace llvm
 
 namespace clang {
 class ASTConsumer;
 class CodeGenerator;
 class CompilerInstance;
 class IncrementalAction;
 class Interpreter;
 class Parser;

clang/lib/Interpreter/IncrementalParser.cpp

 //===--------- IncrementalParser.cpp - Incremental Compilation  -----------===//
 //
 // 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 class which performs incremental code compilation.
 //
 //===----------------------------------------------------------------------===//
 
 #include "IncrementalParser.h"
+
 #include "clang/AST/DeclContextInternals.h"
 #include "clang/CodeGen/BackendUtil.h"
 #include "clang/CodeGen/CodeGenAction.h"
 #include "clang/CodeGen/ModuleBuilder.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendAction.h"
 #include "clang/FrontendTool/Utils.h"
 #include "clang/Interpreter/Interpreter.h"
IncrementalAction(CompilerInstance &CI, llvm::LLVMContext &LLVMCtx,
             break;
           }
           return Act;
         }()) {}
   FrontendAction *getWrapped() const { return WrappedAction.get(); }
   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())
       CompletionConsumer = &CI.getCodeCompletionConsumer();
 
     Preprocessor &PP = CI.getPreprocessor();
     PP.EnterMainSourceFile();
 
void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
   }
 }
 
 llvm::StringRef IncrementalParser::GetMangledName(GlobalDecl GD) const {
   CodeGenerator *CG = getCodeGen();
   assert(CG);
   return CG->GetMangledName(GD);
 }
-
 } // end namespace clang

clang/lib/Interpreter/Interpreter.cpp

 //===------ Interpreter.cpp - Incremental Compilation and Execution -------===//
 //
 // 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 component which performs incremental code
 // compilation and execution.
 //
 //===----------------------------------------------------------------------===//
 
-#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"
 #include "clang/Basic/DiagnosticSema.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/CodeGen/CodeGenAction.h"
 #include "clang/CodeGen/ModuleBuilder.h"
 #include "clang/CodeGen/ObjectFilePCHContainerOperations.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/Job.h"
 #include "clang/Driver/Options.h"
 #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"
 #include "llvm/ExecutionEngine/JITSymbol.h"
 #include "llvm/ExecutionEngine/Orc/LLJIT.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
CreateCI(const llvm::opt::ArgStringList &Argv) {
   Clang->getTarget().adjust(Clang->getDiagnostics(), Clang->getLangOpts());
 
   // Don't clear the AST before backend codegen since we do codegen multiple
   // times, reusing the same AST.
   Clang->getCodeGenOpts().ClearASTBeforeBackend = false;
 
   Clang->getFrontendOpts().DisableFree = false;
   Clang->getCodeGenOpts().DisableFree = false;
-
   return std::move(Clang);
 }
 
 } // anonymous namespace
 
 llvm::Expected<std::unique_ptr<CompilerInstance>>
 IncrementalCompilerBuilder::create(std::vector<const char *> &ClangArgv) {
 

 
 llvm::Expected<std::unique_ptr<Interpreter>>
 Interpreter::create(std::unique_ptr<CompilerInstance> CI) {
   llvm::Error Err = llvm::Error::success();
   auto Interp =
       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();
 
   Interp->ValuePrintingInfo.resize(3);
   // FIXME: This is a ugly hack. Undo command checks its availability by looking
   // at the size of the PTU list. However we have parsed something in the
   // beginning of the REPL so we have to mark them as 'Irrevocable'.

clang/lib/Parse/ParseDecl.cpp

 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/PrettyDeclStackTrace.h"
 #include "clang/Basic/AddressSpaces.h"
 #include "clang/Basic/AttributeCommonInfo.h"
 #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"
 #include "clang/Sema/EnterExpressionEvaluationContext.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/SemaDiagnostic.h"

clang/lib/Parse/Parser.cpp

Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
   case tok::code_completion:
     cutOffParsing();
     if (CurParsedObjCImpl) {
       // Code-complete Objective-C methods even without leading '-'/'+' prefix.
       Actions.CodeCompleteObjCMethodDecl(getCurScope(),
                                          /*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;
     if (getLangOpts().CPlusPlusModules) {
       llvm_unreachable("not expecting a c++20 import here");
       ProhibitAttributes(Attrs);
     }
     SingleDecl = ParseModuleImport(SourceLocation(), IS);

clang/lib/Sema/CodeCompleteConsumer.cpp

bool CodeCompletionContext::wantConstructorResults() const {
   switch (CCKind) {
   case CCC_Recovery:
   case CCC_Statement:
   case CCC_Expression:
   case CCC_ObjCMessageReceiver:
   case CCC_ParenthesizedExpression:
   case CCC_Symbol:
   case CCC_SymbolOrNewName:
+  case CCC_TopLevelOrExpression:
     return true;
 
   case CCC_TopLevel:
   case CCC_ObjCInterface:
   case CCC_ObjCImplementation:
   case CCC_ObjCIvarList:
   case CCC_ClassStructUnion:
   case CCC_DotMemberAccess:
StringRef clang::getCompletionKindString(CodeCompletionContext::Kind Kind) {
   case CCKind::CCC_IncludedFile:
     return "IncludedFile";
   case CCKind::CCC_Attribute:
     return "Attribute";
   case CCKind::CCC_Recovery:
     return "Recovery";
   case CCKind::CCC_ObjCClassForwardDecl:
     return "ObjCClassForwardDecl";
+  case CCKind::CCC_TopLevelOrExpression:
+    return "ReplTopLevel";
   }
   llvm_unreachable("Invalid CodeCompletionContext::Kind!");
 }
 
 //===----------------------------------------------------------------------===//
 // Code completion string implementation
 //===----------------------------------------------------------------------===//
 

clang/lib/Sema/SemaCodeComplete.cpp

explicit ResultBuilder(Sema &SemaRef, CodeCompletionAllocator &Allocator,
         ObjCImplementation(nullptr) {
     // If this is an Objective-C instance method definition, dig out the
     // corresponding implementation.
     switch (CompletionContext.getKind()) {
     case CodeCompletionContext::CCC_Expression:
     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())
           if (ObjCInterfaceDecl *Interface = Method->getClassInterface())
             ObjCImplementation = Interface->getImplementation();
       break;
 
     default:
static void AddFunctionSpecifiers(Sema::ParserCompletionContext CCC,
   case Sema::PCC_Template:
     if (LangOpts.CPlusPlus || LangOpts.C99)
       Results.AddResult(Result("inline"));
     break;
 
   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:
   case Sema::PCC_Type:
   case Sema::PCC_ParenthesizedExpression:
   case Sema::PCC_LocalDeclarationSpecifiers:
     break;
   }
static bool WantTypesInContext(Sema::ParserCompletionContext CCC,
   case Sema::PCC_ObjCInstanceVariableList:
   case Sema::PCC_Template:
   case Sema::PCC_MemberTemplate:
   case Sema::PCC_Statement:
   case Sema::PCC_RecoveryInFunction:
   case Sema::PCC_Type:
   case Sema::PCC_ParenthesizedExpression:
   case Sema::PCC_LocalDeclarationSpecifiers:
+  case Sema::PCC_TopLevelOrExpression:
     return true;
 
   case Sema::PCC_Expression:
   case Sema::PCC_Condition:
     return LangOpts.CPlusPlus;
 
   case Sema::PCC_ObjCInterface:
   case Sema::PCC_ObjCImplementation:
case Sema::PCC_ObjCImplementation:
     AddFunctionSpecifiers(CCC, SemaRef.getLangOpts(), Results);
     break;
 
   case Sema::PCC_ObjCInstanceVariableList:
     AddObjCVisibilityResults(SemaRef.getLangOpts(), Results, true);
     break;
 
   case Sema::PCC_RecoveryInFunction:
+  case Sema::PCC_TopLevelOrExpression:
   case Sema::PCC_Statement: {
     if (SemaRef.getLangOpts().CPlusPlus11)
       AddUsingAliasResult(Builder, Results);
 
     AddTypedefResult(Results);
 
     if (SemaRef.getLangOpts().CPlusPlus && Results.includeCodePatterns() &&
         SemaRef.getLangOpts().CXXExceptions) {
mapCodeCompletionContext(Sema &S, Sema::ParserCompletionContext PCC) {
   case Sema::PCC_Type:
     return CodeCompletionContext::CCC_Type;
 
   case Sema::PCC_ParenthesizedExpression:
     return CodeCompletionContext::CCC_ParenthesizedExpression;
 
   case Sema::PCC_LocalDeclarationSpecifiers:
     return CodeCompletionContext::CCC_Type;
+  case Sema::PCC_TopLevelOrExpression:
+    return CodeCompletionContext::CCC_TopLevelOrExpression;
   }
 
   llvm_unreachable("Invalid ParserCompletionContext!");
 }
 
 /// If we're in a C++ virtual member function, add completion results
 /// that invoke the functions we override, since it's common to invoke the
 /// overridden function as well as adding new functionality.
void Sema::CodeCompleteOrdinaryName(Scope *S,
   case PCC_Template:
   case PCC_MemberTemplate:
   case PCC_Type:
   case PCC_LocalDeclarationSpecifiers:
     Results.setFilter(&ResultBuilder::IsOrdinaryNonValueName);
     break;
 
   case PCC_Statement:
+  case PCC_TopLevelOrExpression:
   case PCC_ParenthesizedExpression:
   case PCC_Expression:
   case PCC_ForInit:
   case PCC_Condition:
     if (WantTypesInContext(CompletionContext, getLangOpts()))
       Results.setFilter(&ResultBuilder::IsOrdinaryName);
     else
       Results.setFilter(&ResultBuilder::IsOrdinaryNonTypeName);
void Sema::CodeCompleteOrdinaryName(Scope *S,
 
   AddOrdinaryNameResults(CompletionContext, S, *this, Results);
   Results.ExitScope();
 
   switch (CompletionContext) {
   case PCC_ParenthesizedExpression:
   case PCC_Expression:
   case PCC_Statement:
+  case PCC_TopLevelOrExpression:
   case PCC_RecoveryInFunction:
     if (S->getFnParent())
       AddPrettyFunctionResults(getLangOpts(), Results);
     break;
 
   case PCC_Namespace:
   case PCC_Class:
   case PCC_ObjCInterface:

clang/test/CodeCompletion/incrememal-mode-completion-no-error.cpp

+void foo(
+// RUN: %clang_cc1 -fincremental-extensions -fsyntax-only -code-completion-at=%s:%(line-1):9 %s | wc -c | FileCheck %s
+// CHECK: 0

clang/test/CodeCompletion/incremental-top-level.cpp

+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

clang/tools/clang-repl/ClangRepl.cpp

 //===--- tools/clang-repl/ClangRepl.cpp - clang-repl - the Clang REPL -----===//
 //
 // 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 a REPL tool on top of clang.
 //
 //===----------------------------------------------------------------------===//
 
 #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"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ManagedStatic.h" // llvm_shutdown
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"
 #include <optional>
if (CI->getDiagnosticOpts().VerifyDiagnostics) {
     Errs = Client->getNumErrors();
 
     // The interpreter expects BeginSourceFile/EndSourceFiles to be balanced.
     Client->BeginSourceFile(CI->getLangOpts(), &CI->getPreprocessor());
   }
   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: ");
   llvm::cl::ParseCommandLineOptions(argc, argv);
 
   llvm::llvm_shutdown_obj Y; // Call llvm_shutdown() on exit.
 
   std::vector<const char *> ClangArgv(ClangArgs.size());
llvm::install_fatal_error_handler(LLVMErrorHandler,
                                     static_cast<void *>(&CI->getDiagnostics()));
 
   // Load any requested plugins.
   CI->LoadRequestedPlugins();
   if (CudaEnabled)
     DeviceCI->LoadRequestedPlugins();
 
   std::unique_ptr<clang::Interpreter> Interp;
+
   if (CudaEnabled) {
     Interp = ExitOnErr(
         clang::Interpreter::createWithCUDA(std::move(CI), std::move(DeviceCI)));
 
     if (CudaPath.empty()) {
       ExitOnErr(Interp->LoadDynamicLibrary("libcudart.so"));
     } else {
       auto CudaRuntimeLibPath = CudaPath + "/lib/libcudart.so";
       ExitOnErr(Interp->LoadDynamicLibrary(CudaRuntimeLibPath.c_str()));
     }
   } else
     Interp = ExitOnErr(clang::Interpreter::create(std::move(CI)));
 
   for (const std::string &input : OptInputs) {
     if (auto Err = Interp->ParseAndExecute(input))
       llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
   }
 
   bool HasError = false;
 
   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();
       if (L.endswith("\\")) {
         // FIXME: Support #ifdef X \ ...
         Input += L.drop_back(1);
         LE.setPrompt("clang-repl...   ");
         continue;
       }
 
       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;
         }
       } else if (Input.rfind("%lib ", 0) == 0) {
         if (auto Err = Interp->LoadDynamicLibrary(Input.data() + 5)) {
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
           HasError = true;

clang/tools/libclang/CIndexCodeCompletion.cpp

 //===- CIndexCodeCompletion.cpp - Code Completion API hooks ---------------===//
 //
 // 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 Clang-C Source Indexing library hooks for
 // code completion.
 //
 //===----------------------------------------------------------------------===//
 
-#include "CIndexer.h"
 #include "CIndexDiagnostic.h"
+#include "CIndexer.h"
 #include "CLog.h"
 #include "CXCursor.h"
 #include "CXSourceLocation.h"
 #include "CXString.h"
 #include "CXTranslationUnit.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/FileManager.h"
 #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"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/raw_ostream.h"
 #include <atomic>
 #include <cstdio>
 #include <cstdlib>
 #include <string>
 
-
 #ifdef UDP_CODE_COMPLETION_LOGGER
 #include "clang/Basic/Version.h"
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <unistd.h>
 #endif
 
switch (kind) {
     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_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)
       contexts = CXCompletionContext_Unexposed;
       break;
     }
     case CodeCompletionContext::CCC_Recovery: {
       //We don't know what the current context is, so we'll return unknown

clang/unittests/Interpreter/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   ${LLVM_TARGETS_TO_BUILD}
   Core
   OrcJIT
   Support
   TargetParser
   )
 
 add_clang_unittest(ClangReplInterpreterTests
   IncrementalProcessingTest.cpp
   InterpreterTest.cpp
+  CodeCompletionTest.cpp
   )
 target_link_libraries(ClangReplInterpreterTests PUBLIC
   clangAST
   clangBasic
   clangInterpreter
   clangFrontend
   clangSema
   )
 
 # Exceptions on Windows are not yet supported.
 if(NOT WIN32)
   add_subdirectory(ExceptionTests)
 endif()
 
 export_executable_symbols(ClangReplInterpreterTests)

clang/unittests/Interpreter/CodeCompletionTest.cpp

+#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