diff --git a/clang-tools-extra/clangd/refactor/tweaks/DefineInline.cpp b/clang-tools-extra/clangd/refactor/tweaks/DefineInline.cpp
--- a/clang-tools-extra/clangd/refactor/tweaks/DefineInline.cpp
+++ b/clang-tools-extra/clangd/refactor/tweaks/DefineInline.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "AST.h"
+#include "FindTarget.h"
 #include "Logger.h"
 #include "Selection.h"
 #include "SourceCode.h"
@@ -59,6 +60,26 @@
 namespace clangd {
 namespace {
 
+// Lexes from end of \p FD until it finds a semicolon.
+llvm::Optional<SourceLocation> getSemiColonForDecl(const FunctionDecl *FD) {
+  const SourceManager &SM = FD->getASTContext().getSourceManager();
+  const LangOptions &LangOpts = FD->getASTContext().getLangOpts();
+
+  SourceLocation SemiColon =
+      Lexer::getLocForEndOfToken(FD->getEndLoc(), 0, SM, LangOpts);
+  llvm::StringRef BufData = SM.getBufferData(SM.getFileID(SemiColon));
+  Lexer RawLexer(SM.getLocForStartOfFile(SM.getFileID(SemiColon)), LangOpts,
+                 BufData.begin(), SM.getCharacterData(SemiColon),
+                 BufData.end());
+  Token CurToken;
+  while (!CurToken.is(tok::semi)) {
+    if (RawLexer.LexFromRawLexer(CurToken))
+      return llvm::None;
+  }
+  SemiColon = CurToken.getLocation();
+  return SemiColon;
+}
+
 // Deduces the FunctionDecl from a selection. Requires either the function body
 // or the function decl to be selected. Returns null if none of the above
 // criteria is met.
@@ -113,6 +134,71 @@
   return true;
 }
 
+// Rewrites body of FD to fully-qualify all of the decls inside.
+llvm::Expected<std::string> qualifyAllDecls(const FunctionDecl *FD) {
+  // There are three types of spellings that needs to be qualified in a function
+  // body:
+  // - Types:       Foo                 -> ns::Foo
+  // - DeclRefExpr: ns2::foo()          -> ns1::ns2::foo();
+  // - UsingDecls:
+  //    using ns2::foo      -> using ns1::ns2::foo
+  //    using namespace ns2 -> using namespace ns1::ns2
+  //    using ns3 = ns2     -> using ns3 = ns1::ns2
+  //
+  // Go over all references inside a function body to generate replacements that
+  // will fully qualify those. So that body can be moved into an arbitrary file.
+  // We perform the qualification by qualyfying the first type/decl in a
+  // (un)qualified name. e.g:
+  //    namespace a { namespace b { class Bar{}; void foo(); } }
+  //    b::Bar x; -> a::b::Bar x;
+  //    foo(); -> a::b::foo();
+  // FIXME: Instead of fully qualyfying we should try deducing visible scopes at
+  // target location and generate minimal edits.
+
+  const SourceManager &SM = FD->getASTContext().getSourceManager();
+  tooling::Replacements Replacements;
+  findExplicitReferences(FD->getBody(), [&](ReferenceLoc Ref) {
+    // Since we want to qualify only the first qualifier, skip names with a
+    // qualifier.
+    if (Ref.Qualifier.hasQualifier())
+      return;
+    // There might be no decl in dependent contexts, there's nothing much we can
+    // do in such cases.
+    if (Ref.Targets.empty())
+      return;
+
+    // All Targets should be in the same nested name scope, so we can safely
+    // chose any one of them.
+    const NamedDecl *ND = Ref.Targets.front();
+    // Skip local symbols.
+    if (index::isFunctionLocalSymbol(ND))
+      return;
+    // Skip members as qualyfying the left side is enough.
+    if (ND->isCXXInstanceMember())
+      return;
+
+    std::string Qualifier = printNamespaceScope(*ND->getDeclContext());
+
+    if (auto Err = Replacements.add(
+            tooling::Replacement(SM, Ref.NameLoc, 0, Qualifier)))
+      elog("Failed to add qualifier: {0}", std::move(Err));
+  });
+
+  auto QualifiedFunc = tooling::applyAllReplacements(
+      SM.getBufferData(SM.getFileID(FD->getLocation())), Replacements);
+  if (!QualifiedFunc)
+    return QualifiedFunc.takeError();
+
+  // Get new begin and end positions for the qualified body.
+  SourceRange OrigFuncRange = FD->getBody()->getSourceRange();
+  unsigned BodyBegin = SM.getFileOffset(OrigFuncRange.getBegin());
+  unsigned BodyEnd = Replacements.getShiftedCodePosition(
+      SM.getFileOffset(OrigFuncRange.getEnd()));
+
+  // Trim the result to function body.
+  return QualifiedFunc->substr(BodyBegin, BodyEnd - BodyBegin + 1);
+}
+
 // Returns the canonical declaration for the given FunctionDecl. This will
 // usually be the first declaration in current translation unit with the
 // exception of template specialization.
@@ -134,6 +220,15 @@
   return PrevDecl;
 }
 
+// Returns the begining location for a FunctionDecl. Returns location of
+// template keyword for templated functions.
+const SourceLocation getBeginLoc(const FunctionDecl *FD) {
+  // Include template parameter list.
+  if (auto *FTD = FD->getDescribedFunctionTemplate())
+    return FTD->getBeginLoc();
+  return FD->getBeginLoc();
+}
+
 /// Moves definition of a function/method to its declaration location.
 /// Before:
 /// a.h:
@@ -157,7 +252,6 @@
   std::string title() const override {
     return "Move function body to declaration";
   }
-  bool hidden() const override { return true; }
 
   // Returns true when selection is on a function definition that does not
   // make use of any internal symbols.
@@ -189,8 +283,51 @@
   }
 
   Expected<Effect> apply(const Selection &Sel) override {
-    return llvm::createStringError(llvm::inconvertibleErrorCode(),
-                                   "Not implemented yet");
+    const ASTContext &AST = Sel.AST.getASTContext();
+    const SourceManager &SM = AST.getSourceManager();
+
+    auto QualifiedBody = qualifyAllDecls(Source);
+    if (!QualifiedBody)
+      return QualifiedBody.takeError();
+
+    auto SemiColon = getSemiColonForDecl(Target);
+    if (!SemiColon) {
+      return llvm::createStringError(
+          llvm::inconvertibleErrorCode(),
+          "Couldn't find semicolon for target declaration");
+    }
+
+    tooling::Replacements Replacements;
+    auto Err = Replacements.add(
+        tooling::Replacement(SM, *SemiColon, 1, *QualifiedBody));
+    if (Err)
+      return std::move(Err);
+    Effect E;
+
+    // We need to generate two edits if the Source and Target are in different
+    // files.
+    if (!SM.isWrittenInSameFile(Source->getBeginLoc(), Target->getBeginLoc())) {
+      auto FE = Effect::fileEdit(SM, SM.getFileID(*SemiColon),
+                                 std::move(Replacements));
+      if (!FE)
+        return FE.takeError();
+      E.ApplyEdits.try_emplace(FE->first, std::move(FE->second));
+      Replacements.clear();
+    }
+
+    SourceLocation BeginLoc = getBeginLoc(Source);
+    unsigned int SourceLen =
+        SM.getFileOffset(Source->getEndLoc()) - SM.getFileOffset(BeginLoc) + 1;
+    Err = Replacements.add(tooling::Replacement(SM, BeginLoc, SourceLen, ""));
+    if (Err)
+      return std::move(Err);
+
+    auto FE =
+        Effect::fileEdit(SM, SM.getFileID(Sel.Cursor), std::move(Replacements));
+    if (!FE)
+      return FE.takeError();
+    E.ApplyEdits.try_emplace(FE->first, std::move(FE->second));
+    return E;
   }
 
 private:
diff --git a/clang-tools-extra/clangd/unittests/TweakTesting.h b/clang-tools-extra/clangd/unittests/TweakTesting.h
--- a/clang-tools-extra/clangd/unittests/TweakTesting.h
+++ b/clang-tools-extra/clangd/unittests/TweakTesting.h
@@ -51,6 +51,7 @@
 
   // Mapping from file name to contents.
   llvm::StringMap<std::string> ExtraFiles;
+  llvm::StringMap<std::string> EditedFiles;
 
 protected:
   TweakTest(const char *TweakID) : TweakID(TweakID) {}
@@ -65,13 +66,15 @@
 
   // Apply the current tweak to the range (or point) in MarkedCode.
   // MarkedCode will be wrapped according to the Context.
-  //  - if the tweak produces edits, returns the edited code (without markings).
+  //  - if the tweak produces edits, returns the edited code (without markings)
+  //    for the main file. Populates \p EditedFiles if there were any other
+  //    changes.
   //    The context added to MarkedCode will be stripped away before returning,
   //    unless the tweak edited it.
   //  - if the tweak produces a message, returns "message:\n<message>"
   //  - if prepare() returns false, returns "unavailable"
   //  - if apply() returns an error, returns "fail: <message>"
-  std::string apply(llvm::StringRef MarkedCode) const;
+  std::string apply(llvm::StringRef MarkedCode);
 
   // Accepts a code snippet with many ranges (or points) marked, and returns a
   // list of snippets with one range marked each.
diff --git a/clang-tools-extra/clangd/unittests/TweakTesting.cpp b/clang-tools-extra/clangd/unittests/TweakTesting.cpp
--- a/clang-tools-extra/clangd/unittests/TweakTesting.cpp
+++ b/clang-tools-extra/clangd/unittests/TweakTesting.cpp
@@ -10,9 +10,11 @@
 
 #include "Annotations.h"
 #include "SourceCode.h"
+#include "TestFS.h"
 #include "refactor/Tweak.h"
 #include "clang/Tooling/Core/Replacement.h"
 #include "llvm/Support/Error.h"
+#include <string>
 
 namespace clang {
 namespace clangd {
@@ -79,12 +81,13 @@
 
 } // namespace
 
-std::string TweakTest::apply(llvm::StringRef MarkedCode) const {
+std::string TweakTest::apply(llvm::StringRef MarkedCode) {
   std::string WrappedCode = wrap(Context, MarkedCode);
   Annotations Input(WrappedCode);
   auto Selection = rangeOrPoint(Input);
   TestTU TU;
   TU.HeaderCode = Header;
+  TU.AdditionalFiles = std::move(ExtraFiles);
   TU.Code = Input.code();
   ParsedAST AST = TU.build();
   Tweak::Selection S(AST, Selection.first, Selection.second);
@@ -101,14 +104,19 @@
     return "message:\n" + *Result->ShowMessage;
   if (Result->ApplyEdits.empty())
     return "no effect";
-  if (Result->ApplyEdits.size() > 1)
-    return "received multi-file edits";
 
-  auto ApplyEdit = Result->ApplyEdits.begin()->second;
-  if (auto NewText = ApplyEdit.apply())
-    return unwrap(Context, *NewText);
-  else
-    return "bad edits: " + llvm::toString(NewText.takeError());
+  std::string EditedMainFile;
+  for (auto &It : Result->ApplyEdits) {
+    auto NewText = It.second.apply();
+    if (!NewText)
+      return "bad edits: " + llvm::toString(NewText.takeError());
+    llvm::StringRef Unwrapped = unwrap(Context, *NewText);
+    if (It.first() == testPath(TU.Filename))
+      EditedMainFile = Unwrapped;
+    else
+      EditedFiles.try_emplace(It.first(), Unwrapped.str());
+  }
+  return EditedMainFile;
 }
 
 ::testing::Matcher<llvm::StringRef> TweakTest::isAvailable() const {
diff --git a/clang-tools-extra/clangd/unittests/TweakTests.cpp b/clang-tools-extra/clangd/unittests/TweakTests.cpp
--- a/clang-tools-extra/clangd/unittests/TweakTests.cpp
+++ b/clang-tools-extra/clangd/unittests/TweakTests.cpp
@@ -25,6 +25,7 @@
 #include "clang/Tooling/Core/Replacement.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -103,7 +104,7 @@
   EXPECT_UNAVAILABLE(R"cpp(R"(multi )" ^"token " u8"str\ning")cpp"); // nonascii
   EXPECT_UNAVAILABLE(R"cpp(^R^"^(^multi )" "token " "str\ning")cpp"); // raw
   EXPECT_UNAVAILABLE(R"cpp(^"token\n" __FILE__)cpp"); // chunk is macro
-  EXPECT_UNAVAILABLE(R"cpp(^"a\r\n";)cpp"); // forbidden escape char
+  EXPECT_UNAVAILABLE(R"cpp(^"a\r\n";)cpp");           // forbidden escape char
 
   const char *Input = R"cpp(R"(multi
 token)" "\nst^ring\n" "literal")cpp";
@@ -772,6 +773,449 @@
     })cpp");
 }
 
+TEST_F(DefineInlineTest, TransformUsings) {
+  EXPECT_EQ(apply(R"cpp(
+  namespace a {
+  void bar();
+  namespace b {
+  void baz();
+  namespace c {
+  void aux();
+  }
+  }
+  }
+
+  void foo();
+  void f^oo() {
+    using namespace a;
+
+    using namespace b;
+    using namespace a::b;
+
+    using namespace c;
+    using namespace b::c;
+    using namespace a::b::c;
+
+    using a::bar;
+
+    using b::baz;
+    using a::b::baz;
+
+    using c::aux;
+    using b::c::aux;
+    using a::b::c::aux;
+
+    namespace d = c;
+    namespace d = b::c;
+  }
+  )cpp"),
+            R"cpp(
+  namespace a {
+  void bar();
+  namespace b {
+  void baz();
+  namespace c {
+  void aux();
+  }
+  }
+  }
+
+  void foo(){
+    using namespace a;
+
+    using namespace a::b;
+    using namespace a::b;
+
+    using namespace a::b::c;
+    using namespace a::b::c;
+    using namespace a::b::c;
+
+    using a::bar;
+
+    using a::b::baz;
+    using a::b::baz;
+
+    using a::b::c::aux;
+    using a::b::c::aux;
+    using a::b::c::aux;
+
+    namespace d = a::b::c;
+    namespace d = a::b::c;
+  }
+  
+  )cpp");
+}
+
+TEST_F(DefineInlineTest, TransformDecls) {
+  EXPECT_EQ(apply(R"cpp(
+  void foo()    /*Comment -_-*/  ;
+
+  void f^oo() {
+    class Foo {
+    public:
+      void foo();
+      int x;
+      static int y;
+    };
+    Foo::y = 0;
+
+    enum En { Zero, One };
+    En x = Zero;
+
+    enum class EnClass { Zero, One };
+    EnClass y = EnClass::Zero;
+
+    template <typename T> class Bar {};
+    Bar<int> z;
+  }
+  )cpp"),
+            R"cpp(
+  void foo()    /*Comment -_-*/  {
+    class Foo {
+    public:
+      void foo();
+      int x;
+      static int y;
+    };
+    Foo::y = 0;
+
+    enum En { Zero, One };
+    En x = Zero;
+
+    enum class EnClass { Zero, One };
+    EnClass y = EnClass::Zero;
+
+    template <typename T> class Bar {};
+    Bar<int> z;
+  }
+
+  
+  )cpp");
+}
+
+TEST_F(DefineInlineTest, TransformTemplDecls) {
+  EXPECT_EQ(apply(R"cpp(
+  namespace a {
+    template <typename T> class Bar {
+    public:
+      void bar();
+    };
+    template <typename T> T bar;
+    template <typename T> void aux() {}
+  }
+
+  void foo()    /*Comment -_-*/  ;
+
+  void f^oo() {
+    using namespace a;
+    bar<Bar<int>>.bar();
+    aux<Bar<int>>();
+  }
+  )cpp"),
+            R"cpp(
+  namespace a {
+    template <typename T> class Bar {
+    public:
+      void bar();
+    };
+    template <typename T> T bar;
+    template <typename T> void aux() {}
+  }
+
+  void foo()    /*Comment -_-*/  {
+    using namespace a;
+    a::bar<a::Bar<int>>.bar();
+    a::aux<a::Bar<int>>();
+  }
+
+  
+  )cpp");
+}
+
+MATCHER_P2(FileWithContents, FileName, Contents, "") {
+  return arg.first() == FileName && arg.second == Contents;
+}
+
+TEST_F(DefineInlineTest, TransformMembers) {
+  EXPECT_EQ(apply(R"cpp(
+  class Foo {
+    void foo()    /*Comment -_-*/  ;
+  };
+
+  void Foo::f^oo() {
+    return;
+  }
+  )cpp"),
+            R"cpp(
+  class Foo {
+    void foo()    /*Comment -_-*/  {
+    return;
+  }
+  };
+
+  
+  )cpp");
+
+  ExtraFiles["a.h"] = R"cpp(
+  class Foo {
+    void foo()    /*Comment -_-*/  ;
+  };)cpp";
+  EXPECT_EQ(apply(R"cpp(
+  #include "a.h"
+  void Foo::f^oo() {
+    return;
+  })cpp"),
+            R"cpp(
+  #include "a.h"
+  )cpp");
+  EXPECT_THAT(EditedFiles,
+              testing::ElementsAre(FileWithContents(testPath("a.h"),
+                                                    R"cpp(
+  class Foo {
+    void foo()    /*Comment -_-*/  {
+    return;
+  }
+  };)cpp")));
+}
+
+TEST_F(DefineInlineTest, TransformDependentTypes) {
+  EXPECT_EQ(apply(R"cpp(
+  namespace a {
+    template <typename T> class Bar {};
+  }
+  using namespace a;
+
+  template <typename T>
+  void foo()    /*Comment -_-*/  ;
+
+  template <typename T>
+  void f^oo() {
+    Bar<T> B;
+    Bar<Bar<T>> q;
+  }
+  )cpp"),
+            R"cpp(
+  namespace a {
+    template <typename T> class Bar {};
+  }
+  using namespace a;
+
+  template <typename T>
+  void foo()    /*Comment -_-*/  {
+    a::Bar<T> B;
+    a::Bar<a::Bar<T>> q;
+  }
+
+  
+  )cpp");
+}
+
+TEST_F(DefineInlineTest, TransformFunctionTempls) {
+  EXPECT_EQ(apply(R"cpp(
+  template <typename T>
+  void foo(T p);
+
+  template <>
+  void foo<int>(int p);
+
+  template <>
+  void foo<char>(char p);
+
+  template <>
+  void fo^o<int>(int p) {
+    return;
+  }
+  )cpp"),
+            R"cpp(
+  template <typename T>
+  void foo(T p);
+
+  template <>
+  void foo<int>(int p){
+    return;
+  }
+
+  template <>
+  void foo<char>(char p);
+
+  
+  )cpp");
+
+  EXPECT_EQ(apply(R"cpp(
+  template <typename T>
+  void foo(T p);
+
+  template <>
+  void foo<int>(int p);
+
+  template <>
+  void foo<char>(char p);
+
+  template <>
+  void fo^o<char>(char p) {
+    return;
+  }
+  )cpp"),
+            R"cpp(
+  template <typename T>
+  void foo(T p);
+
+  template <>
+  void foo<int>(int p);
+
+  template <>
+  void foo<char>(char p){
+    return;
+  }
+
+  
+  )cpp");
+
+  EXPECT_EQ(apply(R"cpp(
+  template <typename T>
+  void foo(T p);
+
+  template <>
+  void foo<int>(int p);
+
+  template <typename T>
+  void fo^o(T p) {
+    return;
+  }
+  )cpp"),
+            R"cpp(
+  template <typename T>
+  void foo(T p){
+    return;
+  }
+
+  template <>
+  void foo<int>(int p);
+
+  
+  )cpp");
+}
+
+TEST_F(DefineInlineTest, TransformTypeLocs) {
+  EXPECT_EQ(apply(R"cpp(
+  namespace a {
+    template <typename T> class Bar {
+    public:
+      template <typename Q> class Baz {};
+    };
+    namespace b{
+    class Foo{};
+    };
+  }
+  using namespace a;
+  using namespace b;
+  using namespace c;
+
+  void foo()    /*Comment -_-*/  ;
+
+  void f^oo() {
+    Bar<int> B;
+    b::Foo foo;
+    a::Bar<Bar<int>>::Baz<Bar<int>> q;
+  }
+  )cpp"),
+            R"cpp(
+  namespace a {
+    template <typename T> class Bar {
+    public:
+      template <typename Q> class Baz {};
+    };
+    namespace b{
+    class Foo{};
+    };
+  }
+  using namespace a;
+  using namespace b;
+  using namespace c;
+
+  void foo()    /*Comment -_-*/  {
+    a::Bar<int> B;
+    a::b::Foo foo;
+    a::Bar<a::Bar<int>>::Baz<a::Bar<int>> q;
+  }
+
+  
+  )cpp");
+}
+
+TEST_F(DefineInlineTest, TransformDeclRefs) {
+  EXPECT_EQ(apply(R"cpp(
+  namespace a {
+    template <typename T> class Bar {
+    public:
+      void foo();
+      static void bar();
+      int x;
+      static int y;
+    };
+    void bar();
+    namespace b {
+    class Foo{};
+    namespace c {
+    void test();
+    }
+    }
+  }
+  using namespace a;
+  using namespace b;
+  using namespace c;
+
+  void foo()    /*Comment -_-*/  ;
+
+  void f^oo() {
+    a::Bar<int> B;
+    B.foo();
+    a::bar();
+    Bar<Bar<int>>::bar();
+    a::Bar<int>::bar();
+    B.x = Bar<int>::y;
+    Bar<int>::y = 3;
+    bar();
+    c::test();
+  }
+  )cpp"),
+            R"cpp(
+  namespace a {
+    template <typename T> class Bar {
+    public:
+      void foo();
+      static void bar();
+      int x;
+      static int y;
+    };
+    void bar();
+    namespace b {
+    class Foo{};
+    namespace c {
+    void test();
+    }
+    }
+  }
+  using namespace a;
+  using namespace b;
+  using namespace c;
+
+  void foo()    /*Comment -_-*/  {
+    a::Bar<int> B;
+    B.foo();
+    a::bar();
+    a::Bar<a::Bar<int>>::bar();
+    a::Bar<int>::bar();
+    B.x = a::Bar<int>::y;
+    a::Bar<int>::y = 3;
+    a::bar();
+    a::b::c::test();
+  }
+
+  
+  )cpp");
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang