Index: clangd/refactor/tweaks/CMakeLists.txt
===================================================================
--- clangd/refactor/tweaks/CMakeLists.txt
+++ clangd/refactor/tweaks/CMakeLists.txt
@@ -12,6 +12,7 @@
 # $<TARGET_OBJECTS:obj.clangDaemonTweaks> to a list of sources, see
 # clangd/tool/CMakeLists.txt for an example.
 add_clang_library(clangDaemonTweaks OBJECT
+  RawStringLiteral.cpp
   SwapIfBranches.cpp
 
   LINK_LIBS
Index: clangd/refactor/tweaks/RawStringLiteral.cpp
===================================================================
--- /dev/null
+++ clangd/refactor/tweaks/RawStringLiteral.cpp
@@ -0,0 +1,103 @@
+//===--- RawStringLiteral.cpp ------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+#include "ClangdUnit.h"
+#include "Logger.h"
+#include "SourceCode.h"
+#include "refactor/Tweak.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/AST/Stmt.h"
+#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Tooling/Core/Replacement.h"
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Error.h"
+
+namespace clang {
+namespace clangd {
+namespace {
+/// Converts a string literal to a raw string.
+/// Before:
+///   printf("\"a\"\nb");
+///          ^^^^^^^^^
+/// After:
+///   printf(R"("a"
+/// b)");
+class RawStringLiteral : public Tweak {
+public:
+  const char *id() const override final;
+
+  bool prepare(const Selection &Inputs) override;
+  Expected<tooling::Replacements> apply(const Selection &Inputs) override;
+  std::string title() const override;
+
+private:
+  const clang::StringLiteral *Str = nullptr;
+};
+
+REGISTER_TWEAK(RawStringLiteral)
+
+static bool isNormalString(const StringLiteral &Str, SourceLocation Cursor,
+                          SourceManager &SM) {
+  // All chunks must be normal ASCII strings, not u8"..." etc.
+  if (!Str.isAscii())
+    return false;
+  SourceLocation LastTokenBeforeCursor;
+  for (auto I = Str.tokloc_begin(), E = Str.tokloc_end(); I != E; ++I) {
+    if (I->isMacroID()) // No tokens in the string may be macro expansions.
+      return false;
+    if (SM.isBeforeInTranslationUnit(*I, Cursor) || *I == Cursor)
+      LastTokenBeforeCursor = *I;
+  }
+  // Token we care about must be a normal "string": not raw, u8, etc.
+  const char* Data = SM.getCharacterData(LastTokenBeforeCursor);
+  return Data && *Data == '"';
+}
+
+static bool needsRaw(llvm::StringRef Content) {
+  return Content.find_first_of("\"\n\t") != StringRef::npos;
+}
+
+static bool canBeRaw(llvm::StringRef Content) {
+  for (char C : Content)
+    if (!llvm::isPrint(C) && C != '\n' && C != '\t')
+      return false;
+  return !Content.contains(")\"");
+}
+
+bool RawStringLiteral::prepare(const Selection &Inputs) {
+  const SelectionTree::Node *N = Inputs.ASTSelection.commonAncestor();
+  if (!N)
+    return false;
+  Str = dyn_cast_or_null<StringLiteral>(N->ASTNode.get<Stmt>());
+  return Str &&
+         isNormalString(*Str, Inputs.Cursor,
+                        Inputs.AST.getASTContext().getSourceManager()) &&
+         needsRaw(Str->getBytes()) && canBeRaw(Str->getBytes());
+}
+
+Expected<tooling::Replacements>
+RawStringLiteral::apply(const Selection &Inputs) {
+  return tooling::Replacements(
+      tooling::Replacement(Inputs.AST.getASTContext().getSourceManager(), Str,
+                           ("R\"(" + Str->getBytes() + ")\"").str(),
+                           Inputs.AST.getASTContext().getLangOpts()));
+}
+
+std::string RawStringLiteral::title() const { return "Convert to raw string"; }
+
+} // namespace
+} // namespace clangd
+} // namespace clang
+
Index: clangd/unittests/TweakTests.cpp
===================================================================
--- clangd/unittests/TweakTests.cpp
+++ clangd/unittests/TweakTests.cpp
@@ -105,9 +105,10 @@
 }
 
 void checkTransform(llvm::StringRef ID, llvm::StringRef Input,
-                    llvm::StringRef Output) {
-  EXPECT_THAT_EXPECTED(apply(ID, Input), HasValue(Output))
-      << "action id is" << ID;
+                    std::string Output) {
+  auto Result = apply(ID, Input);
+  ASSERT_TRUE(bool(Result)) << llvm::toString(Result.takeError()) << Input;
+  EXPECT_EQ(Output, std::string(*Result)) << Input;
 }
 
 TEST(TweakTest, SwapIfBranches) {
@@ -185,6 +186,37 @@
   )cpp");
 }
 
+TEST(TweakTest, RawStringLiteral) {
+  llvm::StringLiteral ID = "RawStringLiteral";
+
+  checkAvailable(ID, R"cpp(
+    const char *A = ^"^f^o^o^\^n^";
+    const char *B = R"(multi )" ^"token " "str\ning";
+  )cpp");
+
+  checkNotAvailable(ID, R"cpp(
+    const char *A = ^"f^o^o^o^"; // no chars need escaping
+    const char *B = R"(multi )" ^"token " u8"str\ning"; // not all ascii
+    const char *C = ^R^"^(^multi )" "token " "str\ning"; // chunk is raw
+    const char *D = ^"token\n" __FILE__; // chunk is macro expansion
+    const char *E = ^"a\r\n"; // contains forbidden escape character
+  )cpp");
+
+  const char *Input = R"cpp(
+    const char *X = R"(multi
+token)" "\nst^ring\n" "literal";
+    }
+  )cpp";
+  const char *Output = R"cpp(
+    const char *X = R"(multi
+token
+string
+literal)";
+    }
+  )cpp";
+  checkTransform(ID, Input, Output);
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang