From 044eb2f6afba375a914ac9d8024f8f5142bb912e Mon Sep 17 00:00:00 2001
From: Dimitry Andric <dim@FreeBSD.org>
Date: Mon, 18 Dec 2017 20:10:56 +0000
Subject: Vendor import of llvm trunk r321017:
 https://llvm.org/svn/llvm-project/llvm/trunk@321017

---
 include/llvm/Support/Error.h | 721 +++++++++++++++++++++++--------------------
 1 file changed, 387 insertions(+), 334 deletions(-)

(limited to 'include/llvm/Support/Error.h')

diff --git a/include/llvm/Support/Error.h b/include/llvm/Support/Error.h
index 9a7fa0ae6356..8567af392fb0 100644
--- a/include/llvm/Support/Error.h
+++ b/include/llvm/Support/Error.h
@@ -246,18 +246,20 @@ public:
   }
 
 private:
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+  // assertIsChecked() happens very frequently, but under normal circumstances
+  // is supposed to be a no-op.  So we want it to be inlined, but having a bunch
+  // of debug prints can cause the function to be too large for inlining.  So
+  // it's important that we define this function out of line so that it can't be
+  // inlined.
+  LLVM_ATTRIBUTE_NORETURN
+  void fatalUncheckedError() const;
+#endif
+
   void assertIsChecked() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
-    if (!getChecked() || getPtr()) {
-      dbgs() << "Program aborted due to an unhandled Error:\n";
-      if (getPtr())
-        getPtr()->log(dbgs());
-      else
-        dbgs()
-            << "Error value was Success. (Note: Success values must still be "
-               "checked prior to being destroyed).\n";
-      abort();
-    }
+    if (LLVM_UNLIKELY(!getChecked() || getPtr()))
+      fatalUncheckedError();
 #endif
   }
 
@@ -407,235 +409,6 @@ inline Error joinErrors(Error E1, Error E2) {
   return ErrorList::join(std::move(E1), std::move(E2));
 }
 
-/// Helper for testing applicability of, and applying, handlers for
-/// ErrorInfo types.
-template <typename HandlerT>
-class ErrorHandlerTraits
-    : public ErrorHandlerTraits<decltype(
-          &std::remove_reference<HandlerT>::type::operator())> {};
-
-// Specialization functions of the form 'Error (const ErrT&)'.
-template <typename ErrT> class ErrorHandlerTraits<Error (&)(ErrT &)> {
-public:
-  static bool appliesTo(const ErrorInfoBase &E) {
-    return E.template isA<ErrT>();
-  }
-
-  template <typename HandlerT>
-  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
-    assert(appliesTo(*E) && "Applying incorrect handler");
-    return H(static_cast<ErrT &>(*E));
-  }
-};
-
-// Specialization functions of the form 'void (const ErrT&)'.
-template <typename ErrT> class ErrorHandlerTraits<void (&)(ErrT &)> {
-public:
-  static bool appliesTo(const ErrorInfoBase &E) {
-    return E.template isA<ErrT>();
-  }
-
-  template <typename HandlerT>
-  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
-    assert(appliesTo(*E) && "Applying incorrect handler");
-    H(static_cast<ErrT &>(*E));
-    return Error::success();
-  }
-};
-
-/// Specialization for functions of the form 'Error (std::unique_ptr<ErrT>)'.
-template <typename ErrT>
-class ErrorHandlerTraits<Error (&)(std::unique_ptr<ErrT>)> {
-public:
-  static bool appliesTo(const ErrorInfoBase &E) {
-    return E.template isA<ErrT>();
-  }
-
-  template <typename HandlerT>
-  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
-    assert(appliesTo(*E) && "Applying incorrect handler");
-    std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
-    return H(std::move(SubE));
-  }
-};
-
-/// Specialization for functions of the form 'Error (std::unique_ptr<ErrT>)'.
-template <typename ErrT>
-class ErrorHandlerTraits<void (&)(std::unique_ptr<ErrT>)> {
-public:
-  static bool appliesTo(const ErrorInfoBase &E) {
-    return E.template isA<ErrT>();
-  }
-
-  template <typename HandlerT>
-  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
-    assert(appliesTo(*E) && "Applying incorrect handler");
-    std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
-    H(std::move(SubE));
-    return Error::success();
-  }
-};
-
-// Specialization for member functions of the form 'RetT (const ErrT&)'.
-template <typename C, typename RetT, typename ErrT>
-class ErrorHandlerTraits<RetT (C::*)(ErrT &)>
-    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
-
-// Specialization for member functions of the form 'RetT (const ErrT&) const'.
-template <typename C, typename RetT, typename ErrT>
-class ErrorHandlerTraits<RetT (C::*)(ErrT &) const>
-    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
-
-// Specialization for member functions of the form 'RetT (const ErrT&)'.
-template <typename C, typename RetT, typename ErrT>
-class ErrorHandlerTraits<RetT (C::*)(const ErrT &)>
-    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
-
-// Specialization for member functions of the form 'RetT (const ErrT&) const'.
-template <typename C, typename RetT, typename ErrT>
-class ErrorHandlerTraits<RetT (C::*)(const ErrT &) const>
-    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
-
-/// Specialization for member functions of the form
-/// 'RetT (std::unique_ptr<ErrT>) const'.
-template <typename C, typename RetT, typename ErrT>
-class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>)>
-    : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
-
-/// Specialization for member functions of the form
-/// 'RetT (std::unique_ptr<ErrT>) const'.
-template <typename C, typename RetT, typename ErrT>
-class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>) const>
-    : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
-
-inline Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload) {
-  return Error(std::move(Payload));
-}
-
-template <typename HandlerT, typename... HandlerTs>
-Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload,
-                      HandlerT &&Handler, HandlerTs &&... Handlers) {
-  if (ErrorHandlerTraits<HandlerT>::appliesTo(*Payload))
-    return ErrorHandlerTraits<HandlerT>::apply(std::forward<HandlerT>(Handler),
-                                               std::move(Payload));
-  return handleErrorImpl(std::move(Payload),
-                         std::forward<HandlerTs>(Handlers)...);
-}
-
-/// Pass the ErrorInfo(s) contained in E to their respective handlers. Any
-/// unhandled errors (or Errors returned by handlers) are re-concatenated and
-/// returned.
-/// Because this function returns an error, its result must also be checked
-/// or returned. If you intend to handle all errors use handleAllErrors
-/// (which returns void, and will abort() on unhandled errors) instead.
-template <typename... HandlerTs>
-Error handleErrors(Error E, HandlerTs &&... Hs) {
-  if (!E)
-    return Error::success();
-
-  std::unique_ptr<ErrorInfoBase> Payload = E.takePayload();
-
-  if (Payload->isA<ErrorList>()) {
-    ErrorList &List = static_cast<ErrorList &>(*Payload);
-    Error R;
-    for (auto &P : List.Payloads)
-      R = ErrorList::join(
-          std::move(R),
-          handleErrorImpl(std::move(P), std::forward<HandlerTs>(Hs)...));
-    return R;
-  }
-
-  return handleErrorImpl(std::move(Payload), std::forward<HandlerTs>(Hs)...);
-}
-
-/// Behaves the same as handleErrors, except that it requires that all
-/// errors be handled by the given handlers. If any unhandled error remains
-/// after the handlers have run, abort() will be called.
-template <typename... HandlerTs>
-void handleAllErrors(Error E, HandlerTs &&... Handlers) {
-  auto F = handleErrors(std::move(E), std::forward<HandlerTs>(Handlers)...);
-  // Cast 'F' to bool to set the 'Checked' flag if it's a success value:
-  (void)!F;
-}
-
-/// Check that E is a non-error, then drop it.
-inline void handleAllErrors(Error E) {
-  // Cast 'E' to a bool to set the 'Checked' flag if it's a success value:
-  (void)!E;
-}
-
-/// Log all errors (if any) in E to OS. If there are any errors, ErrorBanner
-/// will be printed before the first one is logged. A newline will be printed
-/// after each error.
-///
-/// This is useful in the base level of your program to allow clean termination
-/// (allowing clean deallocation of resources, etc.), while reporting error
-/// information to the user.
-void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner);
-
-/// Write all error messages (if any) in E to a string. The newline character
-/// is used to separate error messages.
-inline std::string toString(Error E) {
-  SmallVector<std::string, 2> Errors;
-  handleAllErrors(std::move(E), [&Errors](const ErrorInfoBase &EI) {
-    Errors.push_back(EI.message());
-  });
-  return join(Errors.begin(), Errors.end(), "\n");
-}
-
-/// Consume a Error without doing anything. This method should be used
-/// only where an error can be considered a reasonable and expected return
-/// value.
-///
-/// Uses of this method are potentially indicative of design problems: If it's
-/// legitimate to do nothing while processing an "error", the error-producer
-/// might be more clearly refactored to return an Optional<T>.
-inline void consumeError(Error Err) {
-  handleAllErrors(std::move(Err), [](const ErrorInfoBase &) {});
-}
-
-/// Helper for Errors used as out-parameters.
-///
-/// This helper is for use with the Error-as-out-parameter idiom, where an error
-/// is passed to a function or method by reference, rather than being returned.
-/// In such cases it is helpful to set the checked bit on entry to the function
-/// so that the error can be written to (unchecked Errors abort on assignment)
-/// and clear the checked bit on exit so that clients cannot accidentally forget
-/// to check the result. This helper performs these actions automatically using
-/// RAII:
-///
-///   @code{.cpp}
-///   Result foo(Error &Err) {
-///     ErrorAsOutParameter ErrAsOutParam(&Err); // 'Checked' flag set
-///     // <body of foo>
-///     // <- 'Checked' flag auto-cleared when ErrAsOutParam is destructed.
-///   }
-///   @endcode
-///
-/// ErrorAsOutParameter takes an Error* rather than Error& so that it can be
-/// used with optional Errors (Error pointers that are allowed to be null). If
-/// ErrorAsOutParameter took an Error reference, an instance would have to be
-/// created inside every condition that verified that Error was non-null. By
-/// taking an Error pointer we can just create one instance at the top of the
-/// function.
-class ErrorAsOutParameter {
-public:
-  ErrorAsOutParameter(Error *Err) : Err(Err) {
-    // Raise the checked bit if Err is success.
-    if (Err)
-      (void)!!*Err;
-  }
-
-  ~ErrorAsOutParameter() {
-    // Clear the checked bit.
-    if (Err && !*Err)
-      *Err = Error::success();
-  }
-
-private:
-  Error *Err;
-};
-
 /// Tagged union holding either a T or a Error.
 ///
 /// This class parallels ErrorOr, but replaces error_code with Error. Since
@@ -861,19 +634,26 @@ private:
 #endif
   }
 
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+  LLVM_ATTRIBUTE_NORETURN
+  LLVM_ATTRIBUTE_NOINLINE
+  void fatalUncheckedExpected() const {
+    dbgs() << "Expected<T> must be checked before access or destruction.\n";
+    if (HasError) {
+      dbgs() << "Unchecked Expected<T> contained error:\n";
+      (*getErrorStorage())->log(dbgs());
+    } else
+      dbgs() << "Expected<T> value was in success state. (Note: Expected<T> "
+                "values in success mode must still be checked prior to being "
+                "destroyed).\n";
+    abort();
+  }
+#endif
+
   void assertIsChecked() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
-    if (Unchecked) {
-      dbgs() << "Expected<T> must be checked before access or destruction.\n";
-      if (HasError) {
-        dbgs() << "Unchecked Expected<T> contained error:\n";
-        (*getErrorStorage())->log(dbgs());
-      } else
-        dbgs() << "Expected<T> value was in success state. (Note: Expected<T> "
-                  "values in success mode must still be checked prior to being "
-                  "destroyed).\n";
-      abort();
-    }
+    if (LLVM_UNLIKELY(Unchecked))
+      fatalUncheckedExpected();
 #endif
   }
 
@@ -887,26 +667,364 @@ private:
 #endif
 };
 
-/// Helper for Expected<T>s used as out-parameters.
-///
-/// See ErrorAsOutParameter.
-template <typename T>
-class ExpectedAsOutParameter {
-public:
-  ExpectedAsOutParameter(Expected<T> *ValOrErr)
-    : ValOrErr(ValOrErr) {
-    if (ValOrErr)
-      (void)!!*ValOrErr;
-  }
-
-  ~ExpectedAsOutParameter() {
-    if (ValOrErr)
-      ValOrErr->setUnchecked();
-  }
+/// Report a serious error, calling any installed error handler. See
+/// ErrorHandling.h.
+LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err,
+                                                bool gen_crash_diag = true);
 
-private:
-  Expected<T> *ValOrErr;
-};
+/// Report a fatal error if Err is a failure value.
+///
+/// This function can be used to wrap calls to fallible functions ONLY when it
+/// is known that the Error will always be a success value. E.g.
+///
+///   @code{.cpp}
+///   // foo only attempts the fallible operation if DoFallibleOperation is
+///   // true. If DoFallibleOperation is false then foo always returns
+///   // Error::success().
+///   Error foo(bool DoFallibleOperation);
+///
+///   cantFail(foo(false));
+///   @endcode
+inline void cantFail(Error Err, const char *Msg = nullptr) {
+  if (Err) {
+    if (!Msg)
+      Msg = "Failure value returned from cantFail wrapped call";
+    llvm_unreachable(Msg);
+  }
+}
+
+/// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
+/// returns the contained value.
+///
+/// This function can be used to wrap calls to fallible functions ONLY when it
+/// is known that the Error will always be a success value. E.g.
+///
+///   @code{.cpp}
+///   // foo only attempts the fallible operation if DoFallibleOperation is
+///   // true. If DoFallibleOperation is false then foo always returns an int.
+///   Expected<int> foo(bool DoFallibleOperation);
+///
+///   int X = cantFail(foo(false));
+///   @endcode
+template <typename T>
+T cantFail(Expected<T> ValOrErr, const char *Msg = nullptr) {
+  if (ValOrErr)
+    return std::move(*ValOrErr);
+  else {
+    if (!Msg)
+      Msg = "Failure value returned from cantFail wrapped call";
+    llvm_unreachable(Msg);
+  }
+}
+
+/// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
+/// returns the contained reference.
+///
+/// This function can be used to wrap calls to fallible functions ONLY when it
+/// is known that the Error will always be a success value. E.g.
+///
+///   @code{.cpp}
+///   // foo only attempts the fallible operation if DoFallibleOperation is
+///   // true. If DoFallibleOperation is false then foo always returns a Bar&.
+///   Expected<Bar&> foo(bool DoFallibleOperation);
+///
+///   Bar &X = cantFail(foo(false));
+///   @endcode
+template <typename T>
+T& cantFail(Expected<T&> ValOrErr, const char *Msg = nullptr) {
+  if (ValOrErr)
+    return *ValOrErr;
+  else {
+    if (!Msg)
+      Msg = "Failure value returned from cantFail wrapped call";
+    llvm_unreachable(Msg);
+  }
+}
+
+/// Helper for testing applicability of, and applying, handlers for
+/// ErrorInfo types.
+template <typename HandlerT>
+class ErrorHandlerTraits
+    : public ErrorHandlerTraits<decltype(
+          &std::remove_reference<HandlerT>::type::operator())> {};
+
+// Specialization functions of the form 'Error (const ErrT&)'.
+template <typename ErrT> class ErrorHandlerTraits<Error (&)(ErrT &)> {
+public:
+  static bool appliesTo(const ErrorInfoBase &E) {
+    return E.template isA<ErrT>();
+  }
+
+  template <typename HandlerT>
+  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
+    assert(appliesTo(*E) && "Applying incorrect handler");
+    return H(static_cast<ErrT &>(*E));
+  }
+};
+
+// Specialization functions of the form 'void (const ErrT&)'.
+template <typename ErrT> class ErrorHandlerTraits<void (&)(ErrT &)> {
+public:
+  static bool appliesTo(const ErrorInfoBase &E) {
+    return E.template isA<ErrT>();
+  }
+
+  template <typename HandlerT>
+  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
+    assert(appliesTo(*E) && "Applying incorrect handler");
+    H(static_cast<ErrT &>(*E));
+    return Error::success();
+  }
+};
+
+/// Specialization for functions of the form 'Error (std::unique_ptr<ErrT>)'.
+template <typename ErrT>
+class ErrorHandlerTraits<Error (&)(std::unique_ptr<ErrT>)> {
+public:
+  static bool appliesTo(const ErrorInfoBase &E) {
+    return E.template isA<ErrT>();
+  }
+
+  template <typename HandlerT>
+  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
+    assert(appliesTo(*E) && "Applying incorrect handler");
+    std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
+    return H(std::move(SubE));
+  }
+};
+
+/// Specialization for functions of the form 'void (std::unique_ptr<ErrT>)'.
+template <typename ErrT>
+class ErrorHandlerTraits<void (&)(std::unique_ptr<ErrT>)> {
+public:
+  static bool appliesTo(const ErrorInfoBase &E) {
+    return E.template isA<ErrT>();
+  }
+
+  template <typename HandlerT>
+  static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
+    assert(appliesTo(*E) && "Applying incorrect handler");
+    std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
+    H(std::move(SubE));
+    return Error::success();
+  }
+};
+
+// Specialization for member functions of the form 'RetT (const ErrT&)'.
+template <typename C, typename RetT, typename ErrT>
+class ErrorHandlerTraits<RetT (C::*)(ErrT &)>
+    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
+
+// Specialization for member functions of the form 'RetT (const ErrT&) const'.
+template <typename C, typename RetT, typename ErrT>
+class ErrorHandlerTraits<RetT (C::*)(ErrT &) const>
+    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
+
+// Specialization for member functions of the form 'RetT (const ErrT&)'.
+template <typename C, typename RetT, typename ErrT>
+class ErrorHandlerTraits<RetT (C::*)(const ErrT &)>
+    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
+
+// Specialization for member functions of the form 'RetT (const ErrT&) const'.
+template <typename C, typename RetT, typename ErrT>
+class ErrorHandlerTraits<RetT (C::*)(const ErrT &) const>
+    : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
+
+/// Specialization for member functions of the form
+/// 'RetT (std::unique_ptr<ErrT>)'.
+template <typename C, typename RetT, typename ErrT>
+class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>)>
+    : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
+
+/// Specialization for member functions of the form
+/// 'RetT (std::unique_ptr<ErrT>) const'.
+template <typename C, typename RetT, typename ErrT>
+class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>) const>
+    : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
+
+inline Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload) {
+  return Error(std::move(Payload));
+}
+
+template <typename HandlerT, typename... HandlerTs>
+Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload,
+                      HandlerT &&Handler, HandlerTs &&... Handlers) {
+  if (ErrorHandlerTraits<HandlerT>::appliesTo(*Payload))
+    return ErrorHandlerTraits<HandlerT>::apply(std::forward<HandlerT>(Handler),
+                                               std::move(Payload));
+  return handleErrorImpl(std::move(Payload),
+                         std::forward<HandlerTs>(Handlers)...);
+}
+
+/// Pass the ErrorInfo(s) contained in E to their respective handlers. Any
+/// unhandled errors (or Errors returned by handlers) are re-concatenated and
+/// returned.
+/// Because this function returns an error, its result must also be checked
+/// or returned. If you intend to handle all errors use handleAllErrors
+/// (which returns void, and will abort() on unhandled errors) instead.
+template <typename... HandlerTs>
+Error handleErrors(Error E, HandlerTs &&... Hs) {
+  if (!E)
+    return Error::success();
+
+  std::unique_ptr<ErrorInfoBase> Payload = E.takePayload();
+
+  if (Payload->isA<ErrorList>()) {
+    ErrorList &List = static_cast<ErrorList &>(*Payload);
+    Error R;
+    for (auto &P : List.Payloads)
+      R = ErrorList::join(
+          std::move(R),
+          handleErrorImpl(std::move(P), std::forward<HandlerTs>(Hs)...));
+    return R;
+  }
+
+  return handleErrorImpl(std::move(Payload), std::forward<HandlerTs>(Hs)...);
+}
+
+/// Behaves the same as handleErrors, except that it requires that all
+/// errors be handled by the given handlers. If any unhandled error remains
+/// after the handlers have run, report_fatal_error() will be called.
+template <typename... HandlerTs>
+void handleAllErrors(Error E, HandlerTs &&... Handlers) {
+  cantFail(handleErrors(std::move(E), std::forward<HandlerTs>(Handlers)...));
+}
+
+/// Check that E is a non-error, then drop it.
+/// If E is an error report_fatal_error will be called.
+inline void handleAllErrors(Error E) {
+  cantFail(std::move(E));
+}
+
+/// Handle any errors (if present) in an Expected<T>, then try a recovery path.
+///
+/// If the incoming value is a success value it is returned unmodified. If it
+/// is a failure value then it the contained error is passed to handleErrors.
+/// If handleErrors is able to handle the error then the RecoveryPath functor
+/// is called to supply the final result. If handleErrors is not able to
+/// handle all errors then the unhandled errors are returned.
+///
+/// This utility enables the follow pattern:
+///
+///   @code{.cpp}
+///   enum FooStrategy { Aggressive, Conservative };
+///   Expected<Foo> foo(FooStrategy S);
+///
+///   auto ResultOrErr =
+///     handleExpected(
+///       foo(Aggressive),
+///       []() { return foo(Conservative); },
+///       [](AggressiveStrategyError&) {
+///         // Implicitly conusme this - we'll recover by using a conservative
+///         // strategy.
+///       });
+///
+///   @endcode
+template <typename T, typename RecoveryFtor, typename... HandlerTs>
+Expected<T> handleExpected(Expected<T> ValOrErr, RecoveryFtor &&RecoveryPath,
+                           HandlerTs &&... Handlers) {
+  if (ValOrErr)
+    return ValOrErr;
+
+  if (auto Err = handleErrors(ValOrErr.takeError(),
+                              std::forward<HandlerTs>(Handlers)...))
+    return std::move(Err);
+
+  return RecoveryPath();
+}
+
+/// Log all errors (if any) in E to OS. If there are any errors, ErrorBanner
+/// will be printed before the first one is logged. A newline will be printed
+/// after each error.
+///
+/// This is useful in the base level of your program to allow clean termination
+/// (allowing clean deallocation of resources, etc.), while reporting error
+/// information to the user.
+void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner);
+
+/// Write all error messages (if any) in E to a string. The newline character
+/// is used to separate error messages.
+inline std::string toString(Error E) {
+  SmallVector<std::string, 2> Errors;
+  handleAllErrors(std::move(E), [&Errors](const ErrorInfoBase &EI) {
+    Errors.push_back(EI.message());
+  });
+  return join(Errors.begin(), Errors.end(), "\n");
+}
+
+/// Consume a Error without doing anything. This method should be used
+/// only where an error can be considered a reasonable and expected return
+/// value.
+///
+/// Uses of this method are potentially indicative of design problems: If it's
+/// legitimate to do nothing while processing an "error", the error-producer
+/// might be more clearly refactored to return an Optional<T>.
+inline void consumeError(Error Err) {
+  handleAllErrors(std::move(Err), [](const ErrorInfoBase &) {});
+}
+
+/// Helper for Errors used as out-parameters.
+///
+/// This helper is for use with the Error-as-out-parameter idiom, where an error
+/// is passed to a function or method by reference, rather than being returned.
+/// In such cases it is helpful to set the checked bit on entry to the function
+/// so that the error can be written to (unchecked Errors abort on assignment)
+/// and clear the checked bit on exit so that clients cannot accidentally forget
+/// to check the result. This helper performs these actions automatically using
+/// RAII:
+///
+///   @code{.cpp}
+///   Result foo(Error &Err) {
+///     ErrorAsOutParameter ErrAsOutParam(&Err); // 'Checked' flag set
+///     // <body of foo>
+///     // <- 'Checked' flag auto-cleared when ErrAsOutParam is destructed.
+///   }
+///   @endcode
+///
+/// ErrorAsOutParameter takes an Error* rather than Error& so that it can be
+/// used with optional Errors (Error pointers that are allowed to be null). If
+/// ErrorAsOutParameter took an Error reference, an instance would have to be
+/// created inside every condition that verified that Error was non-null. By
+/// taking an Error pointer we can just create one instance at the top of the
+/// function.
+class ErrorAsOutParameter {
+public:
+  ErrorAsOutParameter(Error *Err) : Err(Err) {
+    // Raise the checked bit if Err is success.
+    if (Err)
+      (void)!!*Err;
+  }
+
+  ~ErrorAsOutParameter() {
+    // Clear the checked bit.
+    if (Err && !*Err)
+      *Err = Error::success();
+  }
+
+private:
+  Error *Err;
+};
+
+/// Helper for Expected<T>s used as out-parameters.
+///
+/// See ErrorAsOutParameter.
+template <typename T>
+class ExpectedAsOutParameter {
+public:
+  ExpectedAsOutParameter(Expected<T> *ValOrErr)
+    : ValOrErr(ValOrErr) {
+    if (ValOrErr)
+      (void)!!*ValOrErr;
+  }
+
+  ~ExpectedAsOutParameter() {
+    if (ValOrErr)
+      ValOrErr->setUnchecked();
+  }
+
+private:
+  Expected<T> *ValOrErr;
+};
 
 /// This class wraps a std::error_code in a Error.
 ///
@@ -1032,71 +1150,6 @@ private:
   std::function<int(const Error &)> GetExitCode;
 };
 
-/// Report a serious error, calling any installed error handler. See
-/// ErrorHandling.h.
-LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err,
-                                                bool gen_crash_diag = true);
-
-/// Report a fatal error if Err is a failure value.
-///
-/// This function can be used to wrap calls to fallible functions ONLY when it
-/// is known that the Error will always be a success value. E.g.
-///
-///   @code{.cpp}
-///   // foo only attempts the fallible operation if DoFallibleOperation is
-///   // true. If DoFallibleOperation is false then foo always returns
-///   // Error::success().
-///   Error foo(bool DoFallibleOperation);
-///
-///   cantFail(foo(false));
-///   @endcode
-inline void cantFail(Error Err) {
-  if (Err)
-    llvm_unreachable("Failure value returned from cantFail wrapped call");
-}
-
-/// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
-/// returns the contained value.
-///
-/// This function can be used to wrap calls to fallible functions ONLY when it
-/// is known that the Error will always be a success value. E.g.
-///
-///   @code{.cpp}
-///   // foo only attempts the fallible operation if DoFallibleOperation is
-///   // true. If DoFallibleOperation is false then foo always returns an int.
-///   Expected<int> foo(bool DoFallibleOperation);
-///
-///   int X = cantFail(foo(false));
-///   @endcode
-template <typename T>
-T cantFail(Expected<T> ValOrErr) {
-  if (ValOrErr)
-    return std::move(*ValOrErr);
-  else
-    llvm_unreachable("Failure value returned from cantFail wrapped call");
-}
-
-/// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
-/// returns the contained reference.
-///
-/// This function can be used to wrap calls to fallible functions ONLY when it
-/// is known that the Error will always be a success value. E.g.
-///
-///   @code{.cpp}
-///   // foo only attempts the fallible operation if DoFallibleOperation is
-///   // true. If DoFallibleOperation is false then foo always returns a Bar&.
-///   Expected<Bar&> foo(bool DoFallibleOperation);
-///
-///   Bar &X = cantFail(foo(false));
-///   @endcode
-template <typename T>
-T& cantFail(Expected<T&> ValOrErr) {
-  if (ValOrErr)
-    return *ValOrErr;
-  else
-    llvm_unreachable("Failure value returned from cantFail wrapped call");
-}
-
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_ERROR_H
-- 
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