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diff --git a/clang/lib/Interpreter/IncrementalAction.h b/clang/lib/Interpreter/IncrementalAction.h
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+++ b/clang/lib/Interpreter/IncrementalAction.h
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+//===--- IncrementalAction.h - Incremental Frontend Action -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_INTERPRETER_INCREMENTALACTION_H
+#define LLVM_CLANG_INTERPRETER_INCREMENTALACTION_H
+
+#include "clang/Frontend/FrontendActions.h"
+#include "clang/Frontend/MultiplexConsumer.h"
+
+namespace llvm {
+class Module;
+}
+
+namespace clang {
+
+class Interpreter;
+class CodeGenerator;
+
+/// A custom action enabling the incremental processing functionality.
+///
+/// The usual \p FrontendAction expects one call to ExecuteAction and once it
+/// sees a call to \p EndSourceFile it deletes some of the important objects
+/// such as \p Preprocessor and \p Sema assuming no further input will come.
+///
+/// \p IncrementalAction ensures it keep its underlying action's objects alive
+/// as long as the \p IncrementalParser needs them.
+///
+class IncrementalAction : public WrapperFrontendAction {
+private:
+  bool IsTerminating = false;
+  Interpreter &Interp;
+  [[maybe_unused]] CompilerInstance &CI;
+  std::unique_ptr<ASTConsumer> Consumer;
+
+  /// When CodeGen is created the first llvm::Module gets cached in many places
+  /// and we must keep it alive.
+  std::unique_ptr<llvm::Module> CachedInCodeGenModule;
+
+public:
+  IncrementalAction(CompilerInstance &Instance, llvm::LLVMContext &LLVMCtx,
+                    llvm::Error &Err, Interpreter &I,
+                    std::unique_ptr<ASTConsumer> Consumer = nullptr);
+
+  FrontendAction *getWrapped() const { return WrappedAction.get(); }
+
+  TranslationUnitKind getTranslationUnitKind() override {
+    return TU_Incremental;
+  }
+
+  std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
+                                                 StringRef InFile) override;
+
+  void ExecuteAction() override;
+
+  // Do not terminate after processing the input. This allows us to keep various
+  // clang objects alive and to incrementally grow the current TU.
+  void EndSourceFile() override;
+
+  void FinalizeAction();
+
+  /// Cache the current CodeGen module to preserve internal references.
+  void CacheCodeGenModule();
+
+  /// Access the cached CodeGen module.
+  llvm::Module *getCachedCodeGenModule() const;
+
+  /// Access the current code generator.
+  CodeGenerator *getCodeGen() const;
+
+  /// Generate an LLVM module for the most recent parsed input.
+  std::unique_ptr<llvm::Module> GenModule();
+};
+
+class InProcessPrintingASTConsumer final : public MultiplexConsumer {
+  Interpreter &Interp;
+
+public:
+  InProcessPrintingASTConsumer(std::unique_ptr<ASTConsumer> C, Interpreter &I);
+
+  bool HandleTopLevelDecl(DeclGroupRef DGR) override;
+};
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_INTERPRETER_INCREMENTALACTION_H