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 //===- llvm/Support/Error.h - Recoverable error handling --------*- 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 defines an API used to report recoverable errors.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_ERROR_H
 #define LLVM_SUPPORT_ERROR_H
 
 #include "llvm-c/Error.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Config/abi-breaking.h"
 #include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <cstdint>
 #include <cstdlib>
 #include <functional>
 #include <memory>
 #include <new>
 #include <optional>
 #include <string>
 #include <system_error>
 #include <type_traits>
 #include <utility>
 #include <vector>
 
 namespace llvm {
 
 class ErrorSuccess;
 
 /// Base class for error info classes. Do not extend this directly: Extend
 /// the ErrorInfo template subclass instead.
 class ErrorInfoBase {
 public:
   virtual ~ErrorInfoBase() = default;
 
   /// Print an error message to an output stream.
   virtual void log(raw_ostream &OS) const = 0;
 
   /// Return the error message as a string.
   virtual std::string message() const {
     std::string Msg;
     raw_string_ostream OS(Msg);
     log(OS);
     return Msg;
   }
 
   /// Convert this error to a std::error_code.
   ///
   /// This is a temporary crutch to enable interaction with code still
   /// using std::error_code. It will be removed in the future.
   virtual std::error_code convertToErrorCode() const = 0;
 
   // Returns the class ID for this type.
   static const void *classID() { return &ID; }
 
   // Returns the class ID for the dynamic type of this ErrorInfoBase instance.
   virtual const void *dynamicClassID() const = 0;
 
   // Check whether this instance is a subclass of the class identified by
   // ClassID.
   virtual bool isA(const void *const ClassID) const {
     return ClassID == classID();
   }
 
   // Check whether this instance is a subclass of ErrorInfoT.
   template <typename ErrorInfoT> bool isA() const {
     return isA(ErrorInfoT::classID());
   }
 
 private:
   virtual void anchor();
 
   static char ID;
 };
 
 /// Lightweight error class with error context and mandatory checking.
 ///
 /// Instances of this class wrap a ErrorInfoBase pointer. Failure states
 /// are represented by setting the pointer to a ErrorInfoBase subclass
 /// instance containing information describing the failure. Success is
 /// represented by a null pointer value.
 ///
 /// Instances of Error also contains a 'Checked' flag, which must be set
 /// before the destructor is called, otherwise the destructor will trigger a
 /// runtime error. This enforces at runtime the requirement that all Error
 /// instances be checked or returned to the caller.
 ///
 /// There are two ways to set the checked flag, depending on what state the
 /// Error instance is in. For Error instances indicating success, it
 /// is sufficient to invoke the boolean conversion operator. E.g.:
 ///
 ///   @code{.cpp}
 ///   Error foo(<...>);
 ///
 ///   if (auto E = foo(<...>))
 ///     return E; // <- Return E if it is in the error state.
 ///   // We have verified that E was in the success state. It can now be safely
 ///   // destroyed.
 ///   @endcode
 ///
 /// A success value *can not* be dropped. For example, just calling 'foo(<...>)'
 /// without testing the return value will raise a runtime error, even if foo
 /// returns success.
 ///
 /// For Error instances representing failure, you must use either the
 /// handleErrors or handleAllErrors function with a typed handler. E.g.:
 ///
 ///   @code{.cpp}
 ///   class MyErrorInfo : public ErrorInfo<MyErrorInfo> {
 ///     // Custom error info.
 ///   };
 ///
 ///   Error foo(<...>) { return make_error<MyErrorInfo>(...); }
 ///
 ///   auto E = foo(<...>); // <- foo returns failure with MyErrorInfo.
 ///   auto NewE =
 ///     handleErrors(std::move(E),
 ///       [](const MyErrorInfo &M) {
 ///         // Deal with the error.
 ///       },
 ///       [](std::unique_ptr<OtherError> M) -> Error {
 ///         if (canHandle(*M)) {
 ///           // handle error.
 ///           return Error::success();
 ///         }
 ///         // Couldn't handle this error instance. Pass it up the stack.
 ///         return Error(std::move(M));
 ///     });
 ///   // Note - The error passed to handleErrors will be marked as checked. If
 ///   // there is no matched handler, a new error with the same payload is
 ///   // created and returned.
 ///   // The handlers take the error checked by handleErrors as an argument,
 ///   // which can be used to retrieve more information. If a new error is
 ///   // created by a handler, it will be passed back to the caller of
 ///   // handleErrors and needs to be checked or return up to the stack.
 ///   // Otherwise, the passed-in error is considered consumed.
 ///   @endcode
 ///
 /// The handleAllErrors function is identical to handleErrors, except
 /// that it has a void return type, and requires all errors to be handled and
 /// no new errors be returned. It prevents errors (assuming they can all be
 /// handled) from having to be bubbled all the way to the top-level.
 ///
 /// *All* Error instances must be checked before destruction, even if
 /// they're moved-assigned or constructed from Success values that have already
 /// been checked. This enforces checking through all levels of the call stack.
 class [[nodiscard]] Error {
   // ErrorList needs to be able to yank ErrorInfoBase pointers out of Errors
   // to add to the error list. It can't rely on handleErrors for this, since
   // handleErrors does not support ErrorList handlers.
   friend class ErrorList;
 
   // handleErrors needs to be able to set the Checked flag.
   template <typename... HandlerTs>
   friend Error handleErrors(Error E, HandlerTs &&... Handlers);
   // visitErrors needs direct access to the payload.
   template <typename HandlerT>
   friend void visitErrors(const Error &E, HandlerT H);
 
   // Expected<T> needs to be able to steal the payload when constructed from an
   // error.
   template <typename T> friend class Expected;
 
   // wrap needs to be able to steal the payload.
   friend LLVMErrorRef wrap(Error);
 
 protected:
   /// Create a success value. Prefer using 'Error::success()' for readability
   Error() {
     setPtr(nullptr);
     setChecked(false);
   }
 
 public:
   /// Create a success value.
   static ErrorSuccess success();
 
   // Errors are not copy-constructable.
   Error(const Error &Other) = delete;
 
   /// Move-construct an error value. The newly constructed error is considered
   /// unchecked, even if the source error had been checked. The original error
   /// becomes a checked Success value, regardless of its original state.
   Error(Error &&Other) {
     setChecked(true);
     *this = std::move(Other);
   }
 
   /// Create an error value. Prefer using the 'make_error' function, but
   /// this constructor can be useful when "re-throwing" errors from handlers.
   Error(std::unique_ptr<ErrorInfoBase> Payload) {
     setPtr(Payload.release());
     setChecked(false);
   }
 
   // Errors are not copy-assignable.
   Error &operator=(const Error &Other) = delete;
 
   /// Move-assign an error value. The current error must represent success, you
   /// you cannot overwrite an unhandled error. The current error is then
   /// considered unchecked. The source error becomes a checked success value,
   /// regardless of its original state.
   Error &operator=(Error &&Other) {
     // Don't allow overwriting of unchecked values.
     assertIsChecked();
     setPtr(Other.getPtr());
 
     // This Error is unchecked, even if the source error was checked.
     setChecked(false);
 
     // Null out Other's payload and set its checked bit.
     Other.setPtr(nullptr);
     Other.setChecked(true);
 
     return *this;
   }
 
   /// Destroy a Error. Fails with a call to abort() if the error is
   /// unchecked.
   ~Error() {
     assertIsChecked();
     delete getPtr();
   }
 
   /// Bool conversion. Returns true if this Error is in a failure state,
   /// and false if it is in an accept state. If the error is in a Success state
   /// it will be considered checked.
   explicit operator bool() {
     setChecked(getPtr() == nullptr);
     return getPtr() != nullptr;
   }
 
   /// Check whether one error is a subclass of another.
   template <typename ErrT> bool isA() const {
     return getPtr() && getPtr()->isA(ErrT::classID());
   }
 
   /// Returns the dynamic class id of this error, or null if this is a success
   /// value.
   const void* dynamicClassID() const {
     if (!getPtr())
       return nullptr;
     return getPtr()->dynamicClassID();
   }
 
 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.
   [[noreturn]] void fatalUncheckedError() const;
 #endif
 
   void assertIsChecked() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     if (LLVM_UNLIKELY(!getChecked() || getPtr()))
       fatalUncheckedError();
 #endif
   }
 
   ErrorInfoBase *getPtr() const {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     return reinterpret_cast<ErrorInfoBase*>(
              reinterpret_cast<uintptr_t>(Payload) &
              ~static_cast<uintptr_t>(0x1));
 #else
     return Payload;
 #endif
   }
 
   void setPtr(ErrorInfoBase *EI) {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     Payload = reinterpret_cast<ErrorInfoBase*>(
                 (reinterpret_cast<uintptr_t>(EI) &
                  ~static_cast<uintptr_t>(0x1)) |
                 (reinterpret_cast<uintptr_t>(Payload) & 0x1));
 #else
     Payload = EI;
 #endif
   }
 
   bool getChecked() const {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     return (reinterpret_cast<uintptr_t>(Payload) & 0x1) == 0;
 #else
     return true;
 #endif
   }
 
   void setChecked(bool V) {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     Payload = reinterpret_cast<ErrorInfoBase*>(
                 (reinterpret_cast<uintptr_t>(Payload) &
                   ~static_cast<uintptr_t>(0x1)) |
                   (V ? 0 : 1));
 #endif
   }
 
   std::unique_ptr<ErrorInfoBase> takePayload() {
     std::unique_ptr<ErrorInfoBase> Tmp(getPtr());
     setPtr(nullptr);
     setChecked(true);
     return Tmp;
   }
 
   friend raw_ostream &operator<<(raw_ostream &OS, const Error &E) {
     if (auto *P = E.getPtr())
       P->log(OS);
     else
       OS << "success";
     return OS;
   }
 
   ErrorInfoBase *Payload = nullptr;
 };
 
 /// Subclass of Error for the sole purpose of identifying the success path in
 /// the type system. This allows to catch invalid conversion to Expected<T> at
 /// compile time.
 class ErrorSuccess final : public Error {};
 
 inline ErrorSuccess Error::success() { return ErrorSuccess(); }
 
 /// Make a Error instance representing failure using the given error info
 /// type.
 template <typename ErrT, typename... ArgTs> Error make_error(ArgTs &&... Args) {
   return Error(std::make_unique<ErrT>(std::forward<ArgTs>(Args)...));
 }
 
 /// Base class for user error types. Users should declare their error types
 /// like:
 ///
 /// class MyError : public ErrorInfo<MyError> {
 ///   ....
 /// };
 ///
 /// This class provides an implementation of the ErrorInfoBase::kind
 /// method, which is used by the Error RTTI system.
 template <typename ThisErrT, typename ParentErrT = ErrorInfoBase>
 class ErrorInfo : public ParentErrT {
 public:
   using ParentErrT::ParentErrT; // inherit constructors
 
   static const void *classID() { return &ThisErrT::ID; }
 
   const void *dynamicClassID() const override { return &ThisErrT::ID; }
 
   bool isA(const void *const ClassID) const override {
     return ClassID == classID() || ParentErrT::isA(ClassID);
   }
 };
 
 /// Special ErrorInfo subclass representing a list of ErrorInfos.
 /// Instances of this class are constructed by joinError.
 class ErrorList final : public ErrorInfo<ErrorList> {
   // handleErrors needs to be able to iterate the payload list of an
   // ErrorList.
   template <typename... HandlerTs>
   friend Error handleErrors(Error E, HandlerTs &&... Handlers);
   // visitErrors needs to be able to iterate the payload list of an
   // ErrorList.
   template <typename HandlerT>
   friend void visitErrors(const Error &E, HandlerT H);
 
   // joinErrors is implemented in terms of join.
   friend Error joinErrors(Error, Error);
 
 public:
   void log(raw_ostream &OS) const override {
     OS << "Multiple errors:\n";
     for (const auto &ErrPayload : Payloads) {
       ErrPayload->log(OS);
       OS << "\n";
     }
   }
 
   std::error_code convertToErrorCode() const override;
 
   // Used by ErrorInfo::classID.
   static char ID;
 
 private:
   ErrorList(std::unique_ptr<ErrorInfoBase> Payload1,
             std::unique_ptr<ErrorInfoBase> Payload2) {
     assert(!Payload1->isA<ErrorList>() && !Payload2->isA<ErrorList>() &&
            "ErrorList constructor payloads should be singleton errors");
     Payloads.push_back(std::move(Payload1));
     Payloads.push_back(std::move(Payload2));
   }
 
   static Error join(Error E1, Error E2) {
     if (!E1)
       return E2;
     if (!E2)
       return E1;
     if (E1.isA<ErrorList>()) {
       auto &E1List = static_cast<ErrorList &>(*E1.getPtr());
       if (E2.isA<ErrorList>()) {
         auto E2Payload = E2.takePayload();
         auto &E2List = static_cast<ErrorList &>(*E2Payload);
         for (auto &Payload : E2List.Payloads)
           E1List.Payloads.push_back(std::move(Payload));
       } else
         E1List.Payloads.push_back(E2.takePayload());
 
       return E1;
     }
     if (E2.isA<ErrorList>()) {
       auto &E2List = static_cast<ErrorList &>(*E2.getPtr());
       E2List.Payloads.insert(E2List.Payloads.begin(), E1.takePayload());
       return E2;
     }
     return Error(std::unique_ptr<ErrorList>(
         new ErrorList(E1.takePayload(), E2.takePayload())));
   }
 
   std::vector<std::unique_ptr<ErrorInfoBase>> Payloads;
 };
 
 /// Concatenate errors. The resulting Error is unchecked, and contains the
 /// ErrorInfo(s), if any, contained in E1, followed by the
 /// ErrorInfo(s), if any, contained in E2.
 inline Error joinErrors(Error E1, Error E2) {
   return ErrorList::join(std::move(E1), std::move(E2));
 }
 
 /// Tagged union holding either a T or a Error.
 ///
 /// This class parallels ErrorOr, but replaces error_code with Error. Since
 /// Error cannot be copied, this class replaces getError() with
 /// takeError(). It also adds an bool errorIsA<ErrT>() method for testing the
 /// error class type.
 ///
 /// Example usage of 'Expected<T>' as a function return type:
 ///
 ///   @code{.cpp}
 ///     Expected<int> myDivide(int A, int B) {
 ///       if (B == 0) {
 ///         // return an Error
 ///         return createStringError(inconvertibleErrorCode(),
 ///                                  "B must not be zero!");
 ///       }
 ///       // return an integer
 ///       return A / B;
 ///     }
 ///   @endcode
 ///
 ///   Checking the results of to a function returning 'Expected<T>':
 ///   @code{.cpp}
 ///     if (auto E = Result.takeError()) {
 ///       // We must consume the error. Typically one of:
 ///       // - return the error to our caller
 ///       // - toString(), when logging
 ///       // - consumeError(), to silently swallow the error
 ///       // - handleErrors(), to distinguish error types
 ///       errs() << "Problem with division " << toString(std::move(E)) << "\n";
 ///       return;
 ///     }
 ///     // use the result
 ///     outs() << "The answer is " << *Result << "\n";
 ///   @endcode
 ///
 ///  For unit-testing a function returning an 'Expected<T>', see the
 ///  'EXPECT_THAT_EXPECTED' macros in llvm/Testing/Support/Error.h
 
 template <class T> class [[nodiscard]] Expected {
   template <class T1> friend class ExpectedAsOutParameter;
   template <class OtherT> friend class Expected;
 
   static constexpr bool isRef = std::is_reference_v<T>;
 
   using wrap = std::reference_wrapper<std::remove_reference_t<T>>;
 
   using error_type = std::unique_ptr<ErrorInfoBase>;
 
 public:
   using storage_type = std::conditional_t<isRef, wrap, T>;
   using value_type = T;
 
 private:
   using reference = std::remove_reference_t<T> &;
   using const_reference = const std::remove_reference_t<T> &;
   using pointer = std::remove_reference_t<T> *;
   using const_pointer = const std::remove_reference_t<T> *;
 
 public:
   /// Create an Expected<T> error value from the given Error.
   Expected(Error &&Err)
       : HasError(true)
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
         // Expected is unchecked upon construction in Debug builds.
         , Unchecked(true)
 #endif
   {
     assert(Err && "Cannot create Expected<T> from Error success value.");
     new (getErrorStorage()) error_type(Err.takePayload());
   }
 
   /// Forbid to convert from Error::success() implicitly, this avoids having
   /// Expected<T> foo() { return Error::success(); } which compiles otherwise
   /// but triggers the assertion above.
   Expected(ErrorSuccess) = delete;
 
   /// Create an Expected<T> success value from the given OtherT value, which
   /// must be convertible to T.
   template <typename OtherT>
   Expected(OtherT &&Val,
            std::enable_if_t<std::is_convertible_v<OtherT, T>> * = nullptr)
       : HasError(false)
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
         // Expected is unchecked upon construction in Debug builds.
         ,
         Unchecked(true)
 #endif
   {
     new (getStorage()) storage_type(std::forward<OtherT>(Val));
   }
 
   /// Move construct an Expected<T> value.
   Expected(Expected &&Other) { moveConstruct(std::move(Other)); }
 
   /// Move construct an Expected<T> value from an Expected<OtherT>, where OtherT
   /// must be convertible to T.
   template <class OtherT>
   Expected(Expected<OtherT> &&Other,
            std::enable_if_t<std::is_convertible_v<OtherT, T>> * = nullptr) {
     moveConstruct(std::move(Other));
   }
 
   /// Move construct an Expected<T> value from an Expected<OtherT>, where OtherT
   /// isn't convertible to T.
   template <class OtherT>
   explicit Expected(
       Expected<OtherT> &&Other,
       std::enable_if_t<!std::is_convertible_v<OtherT, T>> * = nullptr) {
     moveConstruct(std::move(Other));
   }
 
   /// Move-assign from another Expected<T>.
   Expected &operator=(Expected &&Other) {
     moveAssign(std::move(Other));
     return *this;
   }
 
   /// Destroy an Expected<T>.
   ~Expected() {
     assertIsChecked();
     if (!HasError)
       getStorage()->~storage_type();
     else
       getErrorStorage()->~error_type();
   }
 
   /// Return false if there is an error.
   explicit operator bool() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     Unchecked = HasError;
 #endif
     return !HasError;
   }
 
   /// Returns a reference to the stored T value.
   reference get() {
     assertIsChecked();
     return *getStorage();
   }
 
   /// Returns a const reference to the stored T value.
   const_reference get() const {
     assertIsChecked();
     return const_cast<Expected<T> *>(this)->get();
   }
 
   /// Returns \a takeError() after moving the held T (if any) into \p V.
   template <class OtherT>
   Error moveInto(
       OtherT &Value,
       std::enable_if_t<std::is_assignable_v<OtherT &, T &&>> * = nullptr) && {
     if (*this)
       Value = std::move(get());
     return takeError();
   }
 
   /// Check that this Expected<T> is an error of type ErrT.
   template <typename ErrT> bool errorIsA() const {
     return HasError && (*getErrorStorage())->template isA<ErrT>();
   }
 
   /// Take ownership of the stored error.
   /// After calling this the Expected<T> is in an indeterminate state that can
   /// only be safely destructed. No further calls (beside the destructor) should
   /// be made on the Expected<T> value.
   Error takeError() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     Unchecked = false;
 #endif
     return HasError ? Error(std::move(*getErrorStorage())) : Error::success();
   }
 
   /// Returns a pointer to the stored T value.
   pointer operator->() {
     assertIsChecked();
     return toPointer(getStorage());
   }
 
   /// Returns a const pointer to the stored T value.
   const_pointer operator->() const {
     assertIsChecked();
     return toPointer(getStorage());
   }
 
   /// Returns a reference to the stored T value.
   reference operator*() {
     assertIsChecked();
     return *getStorage();
   }
 
   /// Returns a const reference to the stored T value.
   const_reference operator*() const {
     assertIsChecked();
     return *getStorage();
   }
 
 private:
   template <class T1>
   static bool compareThisIfSameType(const T1 &a, const T1 &b) {
     return &a == &b;
   }
 
   template <class T1, class T2>
   static bool compareThisIfSameType(const T1 &, const T2 &) {
     return false;
   }
 
   template <class OtherT> void moveConstruct(Expected<OtherT> &&Other) {
     HasError = Other.HasError;
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     Unchecked = true;
     Other.Unchecked = false;
 #endif
 
     if (!HasError)
       new (getStorage()) storage_type(std::move(*Other.getStorage()));
     else
       new (getErrorStorage()) error_type(std::move(*Other.getErrorStorage()));
   }
 
   template <class OtherT> void moveAssign(Expected<OtherT> &&Other) {
     assertIsChecked();
 
     if (compareThisIfSameType(*this, Other))
       return;
 
     this->~Expected();
     new (this) Expected(std::move(Other));
   }
 
   pointer toPointer(pointer Val) { return Val; }
 
   const_pointer toPointer(const_pointer Val) const { return Val; }
 
   pointer toPointer(wrap *Val) { return &Val->get(); }
 
   const_pointer toPointer(const wrap *Val) const { return &Val->get(); }
 
   storage_type *getStorage() {
     assert(!HasError && "Cannot get value when an error exists!");
     return reinterpret_cast<storage_type *>(&TStorage);
   }
 
   const storage_type *getStorage() const {
     assert(!HasError && "Cannot get value when an error exists!");
     return reinterpret_cast<const storage_type *>(&TStorage);
   }
 
   error_type *getErrorStorage() {
     assert(HasError && "Cannot get error when a value exists!");
     return reinterpret_cast<error_type *>(&ErrorStorage);
   }
 
   const error_type *getErrorStorage() const {
     assert(HasError && "Cannot get error when a value exists!");
     return reinterpret_cast<const error_type *>(&ErrorStorage);
   }
 
   // Used by ExpectedAsOutParameter to reset the checked flag.
   void setUnchecked() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     Unchecked = true;
 #endif
   }
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   [[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() const {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     if (LLVM_UNLIKELY(Unchecked))
       fatalUncheckedExpected();
 #endif
   }
 
   union {
     AlignedCharArrayUnion<storage_type> TStorage;
     AlignedCharArrayUnion<error_type> ErrorStorage;
   };
   bool HasError : 1;
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   bool Unchecked : 1;
 #endif
 };
 
 /// Report a serious error, calling any installed error handler. See
 /// ErrorHandling.h.
 [[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, const char *Msg = nullptr) {
   if (Err) {
     if (!Msg)
       Msg = "Failure value returned from cantFail wrapped call";
 #ifndef NDEBUG
     std::string Str;
     raw_string_ostream OS(Str);
     OS << Msg << "\n" << Err;
     Msg = Str.c_str();
 #endif
     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";
 #ifndef NDEBUG
     std::string Str;
     raw_string_ostream OS(Str);
     auto E = ValOrErr.takeError();
     OS << Msg << "\n" << E;
     Msg = Str.c_str();
 #endif
     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";
 #ifndef NDEBUG
     std::string Str;
     raw_string_ostream OS(Str);
     auto E = ValOrErr.takeError();
     OS << Msg << "\n" << E;
     Msg = Str.c_str();
 #endif
     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_t<HandlerT>::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 by contract all errors
 /// *must* be handled by the given handlers (i.e. there must be no remaining
 /// errors after running the handlers, or llvm_unreachable is 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, llvm_unreachable will be called.
 inline void handleAllErrors(Error E) {
   cantFail(std::move(E));
 }
 
 /// Visit all the ErrorInfo(s) contained in E by passing them to the respective
 /// handler, without consuming the error.
 template <typename HandlerT> void visitErrors(const Error &E, HandlerT H) {
   const ErrorInfoBase *Payload = E.getPtr();
   if (!Payload)
     return;
 
   if (Payload->isA<ErrorList>()) {
     const ErrorList &List = static_cast<const ErrorList &>(*Payload);
     for (const auto &P : List.Payloads)
       H(*P);
     return;
   }
 
   return H(*Payload);
 }
 
 /// 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 function is compatible with the helpers from Support/WithColor.h. You
 /// can pass any of them as the OS. Please consider using them instead of
 /// including 'error: ' in the ErrorBanner.
 ///
 /// 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.
 std::string toString(Error E);
 
 /// Like toString(), but does not consume the error. This can be used to print
 /// a warning while retaining the original error object.
 std::string toStringWithoutConsuming(const Error &E);
 
 /// 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 std::optional<T>.
 inline void consumeError(Error Err) {
   handleAllErrors(std::move(Err), [](const ErrorInfoBase &) {});
 }
 
 /// Convert an Expected to an Optional 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 problems: perhaps the
 /// error should be propagated further, or the error-producer should just
 /// return an Optional in the first place.
 template <typename T> std::optional<T> expectedToOptional(Expected<T> &&E) {
   if (E)
     return std::move(*E);
   consumeError(E.takeError());
   return std::nullopt;
 }
 
 template <typename T> std::optional<T> expectedToStdOptional(Expected<T> &&E) {
   if (E)
     return std::move(*E);
   consumeError(E.takeError());
   return std::nullopt;
 }
 
 /// Helper for converting an Error to a bool.
 ///
 /// This method returns true if Err is in an error state, or false if it is
 /// in a success state.  Puts Err in a checked state in both cases (unlike
 /// Error::operator bool(), which only does this for success states).
 inline bool errorToBool(Error Err) {
   bool IsError = static_cast<bool>(Err);
   if (IsError)
     consumeError(std::move(Err));
   return IsError;
 }
 
 /// 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(Error &Err) : Err(&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.
 ///
 /// This is useful if you're writing an interface that returns a Error
 /// (or Expected) and you want to call code that still returns
 /// std::error_codes.
 class ECError : public ErrorInfo<ECError> {
   friend Error errorCodeToError(std::error_code);
 
   void anchor() override;
 
 public:
   void setErrorCode(std::error_code EC) { this->EC = EC; }
   std::error_code convertToErrorCode() const override { return EC; }
   void log(raw_ostream &OS) const override { OS << EC.message(); }
 
   // Used by ErrorInfo::classID.
   static char ID;
 
 protected:
   ECError() = default;
   ECError(std::error_code EC) : EC(EC) {}
 
   std::error_code EC;
 };
 
 /// The value returned by this function can be returned from convertToErrorCode
 /// for Error values where no sensible translation to std::error_code exists.
 /// It should only be used in this situation, and should never be used where a
 /// sensible conversion to std::error_code is available, as attempts to convert
 /// to/from this error will result in a fatal error. (i.e. it is a programmatic
 /// error to try to convert such a value).
 std::error_code inconvertibleErrorCode();
 
 /// Helper for converting an std::error_code to a Error.
 Error errorCodeToError(std::error_code EC);
 
 /// Helper for converting an ECError to a std::error_code.
 ///
 /// This method requires that Err be Error() or an ECError, otherwise it
 /// will trigger a call to abort().
 std::error_code errorToErrorCode(Error Err);
 
 /// Helper to get errno as an std::error_code.
 ///
 /// errno should always be represented using the generic category as that's what
 /// both libc++ and libstdc++ do. On POSIX systems you can also represent them
 /// using the system category, however this makes them compare differently for
 /// values outside of those used by `std::errc` if one is generic and the other
 /// is system.
 ///
 /// See the libc++ and libstdc++ implementations of `default_error_condition` on
 /// the system category for more details on what the difference is.
 inline std::error_code errnoAsErrorCode() {
   return std::error_code(errno, std::generic_category());
 }
 
 /// Convert an ErrorOr<T> to an Expected<T>.
 template <typename T> Expected<T> errorOrToExpected(ErrorOr<T> &&EO) {
   if (auto EC = EO.getError())
     return errorCodeToError(EC);
   return std::move(*EO);
 }
 
 /// Convert an Expected<T> to an ErrorOr<T>.
 template <typename T> ErrorOr<T> expectedToErrorOr(Expected<T> &&E) {
   if (auto Err = E.takeError())
     return errorToErrorCode(std::move(Err));
   return std::move(*E);
 }
 
 /// This class wraps a string in an Error.
 ///
 /// StringError is useful in cases where the client is not expected to be able
 /// to consume the specific error message programmatically (for example, if the
 /// error message is to be presented to the user).
 ///
 /// StringError can also be used when additional information is to be printed
 /// along with a error_code message. Depending on the constructor called, this
 /// class can either display:
 ///    1. the error_code message (ECError behavior)
 ///    2. a string
 ///    3. the error_code message and a string
 ///
 /// These behaviors are useful when subtyping is required; for example, when a
 /// specific library needs an explicit error type. In the example below,
 /// PDBError is derived from StringError:
 ///
 ///   @code{.cpp}
 ///   Expected<int> foo() {
 ///      return llvm::make_error<PDBError>(pdb_error_code::dia_failed_loading,
 ///                                        "Additional information");
 ///   }
 ///   @endcode
 ///
 class StringError : public ErrorInfo<StringError> {
 public:
   static char ID;
 
   StringError(std::string &&S, std::error_code EC, bool PrintMsgOnly);
   /// Prints EC + S and converts to EC.
   StringError(std::error_code EC, const Twine &S = Twine());
   /// Prints S and converts to EC.
   StringError(const Twine &S, std::error_code EC);
 
   void log(raw_ostream &OS) const override;
   std::error_code convertToErrorCode() const override;
 
   const std::string &getMessage() const { return Msg; }
 
 private:
   std::string Msg;
   std::error_code EC;
   const bool PrintMsgOnly = false;
 };
 
 /// Create formatted StringError object.
 template <typename... Ts>
 inline Error createStringError(std::error_code EC, char const *Fmt,
                                const Ts &... Vals) {
   std::string Buffer;
   raw_string_ostream(Buffer) << format(Fmt, Vals...);
   return make_error<StringError>(Buffer, EC);
 }
 
 Error createStringError(std::string &&Msg, std::error_code EC);
 
 inline Error createStringError(std::error_code EC, const char *S) {
   return createStringError(std::string(S), EC);
 }
 
 inline Error createStringError(std::error_code EC, const Twine &S) {
   return createStringError(S.str(), EC);
 }
 
 /// Create a StringError with an inconvertible error code.
 inline Error createStringError(const Twine &S) {
   return createStringError(llvm::inconvertibleErrorCode(), S);
 }
 
 template <typename... Ts>
 inline Error createStringError(char const *Fmt, const Ts &...Vals) {
   return createStringError(llvm::inconvertibleErrorCode(), Fmt, Vals...);
 }
 
 template <typename... Ts>
 inline Error createStringError(std::errc EC, char const *Fmt,
                                const Ts &... Vals) {
   return createStringError(std::make_error_code(EC), Fmt, Vals...);
 }
 
 /// This class wraps a filename and another Error.
 ///
 /// In some cases, an error needs to live along a 'source' name, in order to
 /// show more detailed information to the user.
 class FileError final : public ErrorInfo<FileError> {
 
   friend Error createFileError(const Twine &, Error);
   friend Error createFileError(const Twine &, size_t, Error);
 
 public:
   void log(raw_ostream &OS) const override {
     assert(Err && "Trying to log after takeError().");
     OS << "'" << FileName << "': ";
     if (Line)
       OS << "line " << *Line << ": ";
     Err->log(OS);
   }
 
   std::string messageWithoutFileInfo() const {
     std::string Msg;
     raw_string_ostream OS(Msg);
     Err->log(OS);
     return Msg;
   }
 
   StringRef getFileName() const { return FileName; }
 
   Error takeError() { return Error(std::move(Err)); }
 
   std::error_code convertToErrorCode() const override;
 
   // Used by ErrorInfo::classID.
   static char ID;
 
 private:
   FileError(const Twine &F, std::optional<size_t> LineNum,
             std::unique_ptr<ErrorInfoBase> E) {
     assert(E && "Cannot create FileError from Error success value.");
     FileName = F.str();
     Err = std::move(E);
     Line = std::move(LineNum);
   }
 
   static Error build(const Twine &F, std::optional<size_t> Line, Error E) {
     std::unique_ptr<ErrorInfoBase> Payload;
     handleAllErrors(std::move(E),
                     [&](std::unique_ptr<ErrorInfoBase> EIB) -> Error {
                       Payload = std::move(EIB);
                       return Error::success();
                     });
     return Error(
         std::unique_ptr<FileError>(new FileError(F, Line, std::move(Payload))));
   }
 
   std::string FileName;
   std::optional<size_t> Line;
   std::unique_ptr<ErrorInfoBase> Err;
 };
 
 /// Concatenate a source file path and/or name with an Error. The resulting
 /// Error is unchecked.
 inline Error createFileError(const Twine &F, Error E) {
   return FileError::build(F, std::optional<size_t>(), std::move(E));
 }
 
 /// Concatenate a source file path and/or name with line number and an Error.
 /// The resulting Error is unchecked.
 inline Error createFileError(const Twine &F, size_t Line, Error E) {
   return FileError::build(F, std::optional<size_t>(Line), std::move(E));
 }
 
 /// Concatenate a source file path and/or name with a std::error_code 
 /// to form an Error object.
 inline Error createFileError(const Twine &F, std::error_code EC) {
   return createFileError(F, errorCodeToError(EC));
 }
 
 /// Concatenate a source file path and/or name with line number and
 /// std::error_code to form an Error object.
 inline Error createFileError(const Twine &F, size_t Line, std::error_code EC) {
   return createFileError(F, Line, errorCodeToError(EC));
 }
 
 /// Create a StringError with the specified error code and prepend the file path
 /// to it.
 inline Error createFileError(const Twine &F, std::error_code EC,
                              const Twine &S) {
   Error E = createStringError(EC, S);
   return createFileError(F, std::move(E));
 }
 
 /// Create a StringError with the specified error code and prepend the file path
 /// to it.
 template <typename... Ts>
 inline Error createFileError(const Twine &F, std::error_code EC,
                              char const *Fmt, const Ts &...Vals) {
   Error E = createStringError(EC, Fmt, Vals...);
   return createFileError(F, std::move(E));
 }
 
 Error createFileError(const Twine &F, ErrorSuccess) = delete;
 
 /// Helper for check-and-exit error handling.
 ///
 /// For tool use only. NOT FOR USE IN LIBRARY CODE.
 ///
 class ExitOnError {
 public:
   /// Create an error on exit helper.
   ExitOnError(std::string Banner = "", int DefaultErrorExitCode = 1)
       : Banner(std::move(Banner)),
         GetExitCode([=](const Error &) { return DefaultErrorExitCode; }) {}
 
   /// Set the banner string for any errors caught by operator().
   void setBanner(std::string Banner) { this->Banner = std::move(Banner); }
 
   /// Set the exit-code mapper function.
   void setExitCodeMapper(std::function<int(const Error &)> GetExitCode) {
     this->GetExitCode = std::move(GetExitCode);
   }
 
   /// Check Err. If it's in a failure state log the error(s) and exit.
   void operator()(Error Err) const { checkError(std::move(Err)); }
 
   /// Check E. If it's in a success state then return the contained value. If
   /// it's in a failure state log the error(s) and exit.
   template <typename T> T operator()(Expected<T> &&E) const {
     checkError(E.takeError());
     return std::move(*E);
   }
 
   /// Check E. If it's in a success state then return the contained reference. If
   /// it's in a failure state log the error(s) and exit.
   template <typename T> T& operator()(Expected<T&> &&E) const {
     checkError(E.takeError());
     return *E;
   }
 
 private:
   void checkError(Error Err) const {
     if (Err) {
       int ExitCode = GetExitCode(Err);
       logAllUnhandledErrors(std::move(Err), errs(), Banner);
       exit(ExitCode);
     }
   }
 
   std::string Banner;
   std::function<int(const Error &)> GetExitCode;
 };
 
 /// Conversion from Error to LLVMErrorRef for C error bindings.
 inline LLVMErrorRef wrap(Error Err) {
   return reinterpret_cast<LLVMErrorRef>(Err.takePayload().release());
 }
 
 /// Conversion from LLVMErrorRef to Error for C error bindings.
 inline Error unwrap(LLVMErrorRef ErrRef) {
   return Error(std::unique_ptr<ErrorInfoBase>(
       reinterpret_cast<ErrorInfoBase *>(ErrRef)));
 }
 
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_ERROR_H

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