1 //===- llvm/Support/Error.h - Recoverable error handling --------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines an API used to report recoverable errors.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_SUPPORT_ERROR_H
15 #define LLVM_SUPPORT_ERROR_H
17 #include "llvm-c/Error.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/ADT/StringExtras.h"
21 #include "llvm/ADT/Twine.h"
22 #include "llvm/Config/abi-breaking.h"
23 #include "llvm/Support/AlignOf.h"
24 #include "llvm/Support/Compiler.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/ErrorOr.h"
28 #include "llvm/Support/Format.h"
29 #include "llvm/Support/raw_ostream.h"
38 #include <system_error>
39 #include <type_traits>
47 /// Base class for error info classes. Do not extend this directly: Extend
48 /// the ErrorInfo template subclass instead.
51 virtual ~ErrorInfoBase() = default;
53 /// Print an error message to an output stream.
54 virtual void log(raw_ostream &OS) const = 0;
56 /// Return the error message as a string.
57 virtual std::string message() const {
59 raw_string_ostream OS(Msg);
64 /// Convert this error to a std::error_code.
66 /// This is a temporary crutch to enable interaction with code still
67 /// using std::error_code. It will be removed in the future.
68 virtual std::error_code convertToErrorCode() const = 0;
70 // Returns the class ID for this type.
71 static const void *classID() { return &ID; }
73 // Returns the class ID for the dynamic type of this ErrorInfoBase instance.
74 virtual const void *dynamicClassID() const = 0;
76 // Check whether this instance is a subclass of the class identified by
78 virtual bool isA(const void *const ClassID) const {
79 return ClassID == classID();
82 // Check whether this instance is a subclass of ErrorInfoT.
83 template <typename ErrorInfoT> bool isA() const {
84 return isA(ErrorInfoT::classID());
88 virtual void anchor();
93 /// Lightweight error class with error context and mandatory checking.
95 /// Instances of this class wrap a ErrorInfoBase pointer. Failure states
96 /// are represented by setting the pointer to a ErrorInfoBase subclass
97 /// instance containing information describing the failure. Success is
98 /// represented by a null pointer value.
100 /// Instances of Error also contains a 'Checked' flag, which must be set
101 /// before the destructor is called, otherwise the destructor will trigger a
102 /// runtime error. This enforces at runtime the requirement that all Error
103 /// instances be checked or returned to the caller.
105 /// There are two ways to set the checked flag, depending on what state the
106 /// Error instance is in. For Error instances indicating success, it
107 /// is sufficient to invoke the boolean conversion operator. E.g.:
110 /// Error foo(<...>);
112 /// if (auto E = foo(<...>))
113 /// return E; // <- Return E if it is in the error state.
114 /// // We have verified that E was in the success state. It can now be safely
118 /// A success value *can not* be dropped. For example, just calling 'foo(<...>)'
119 /// without testing the return value will raise a runtime error, even if foo
122 /// For Error instances representing failure, you must use either the
123 /// handleErrors or handleAllErrors function with a typed handler. E.g.:
126 /// class MyErrorInfo : public ErrorInfo<MyErrorInfo> {
127 /// // Custom error info.
130 /// Error foo(<...>) { return make_error<MyErrorInfo>(...); }
132 /// auto E = foo(<...>); // <- foo returns failure with MyErrorInfo.
135 /// [](const MyErrorInfo &M) {
136 /// // Deal with the error.
138 /// [](std::unique_ptr<OtherError> M) -> Error {
139 /// if (canHandle(*M)) {
141 /// return Error::success();
143 /// // Couldn't handle this error instance. Pass it up the stack.
144 /// return Error(std::move(M));
146 /// // Note - we must check or return NewE in case any of the handlers
147 /// // returned a new error.
150 /// The handleAllErrors function is identical to handleErrors, except
151 /// that it has a void return type, and requires all errors to be handled and
152 /// no new errors be returned. It prevents errors (assuming they can all be
153 /// handled) from having to be bubbled all the way to the top-level.
155 /// *All* Error instances must be checked before destruction, even if
156 /// they're moved-assigned or constructed from Success values that have already
157 /// been checked. This enforces checking through all levels of the call stack.
158 class LLVM_NODISCARD Error {
159 // Both ErrorList and FileError need to be able to yank ErrorInfoBase
160 // pointers out of this class to add to the error list.
161 friend class ErrorList;
162 friend class FileError;
164 // handleErrors needs to be able to set the Checked flag.
165 template <typename... HandlerTs>
166 friend Error handleErrors(Error E, HandlerTs &&... Handlers);
168 // Expected<T> needs to be able to steal the payload when constructed from an
170 template <typename T> friend class Expected;
172 // wrap needs to be able to steal the payload.
173 friend LLVMErrorRef wrap(Error);
176 /// Create a success value. Prefer using 'Error::success()' for readability
183 /// Create a success value.
184 static ErrorSuccess success();
186 // Errors are not copy-constructable.
187 Error(const Error &Other) = delete;
189 /// Move-construct an error value. The newly constructed error is considered
190 /// unchecked, even if the source error had been checked. The original error
191 /// becomes a checked Success value, regardless of its original state.
192 Error(Error &&Other) {
194 *this = std::move(Other);
197 /// Create an error value. Prefer using the 'make_error' function, but
198 /// this constructor can be useful when "re-throwing" errors from handlers.
199 Error(std::unique_ptr<ErrorInfoBase> Payload) {
200 setPtr(Payload.release());
204 // Errors are not copy-assignable.
205 Error &operator=(const Error &Other) = delete;
207 /// Move-assign an error value. The current error must represent success, you
208 /// you cannot overwrite an unhandled error. The current error is then
209 /// considered unchecked. The source error becomes a checked success value,
210 /// regardless of its original state.
211 Error &operator=(Error &&Other) {
212 // Don't allow overwriting of unchecked values.
214 setPtr(Other.getPtr());
216 // This Error is unchecked, even if the source error was checked.
219 // Null out Other's payload and set its checked bit.
220 Other.setPtr(nullptr);
221 Other.setChecked(true);
226 /// Destroy a Error. Fails with a call to abort() if the error is
233 /// Bool conversion. Returns true if this Error is in a failure state,
234 /// and false if it is in an accept state. If the error is in a Success state
235 /// it will be considered checked.
236 explicit operator bool() {
237 setChecked(getPtr() == nullptr);
238 return getPtr() != nullptr;
241 /// Check whether one error is a subclass of another.
242 template <typename ErrT> bool isA() const {
243 return getPtr() && getPtr()->isA(ErrT::classID());
246 /// Returns the dynamic class id of this error, or null if this is a success
248 const void* dynamicClassID() const {
251 return getPtr()->dynamicClassID();
255 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
256 // assertIsChecked() happens very frequently, but under normal circumstances
257 // is supposed to be a no-op. So we want it to be inlined, but having a bunch
258 // of debug prints can cause the function to be too large for inlining. So
259 // it's important that we define this function out of line so that it can't be
261 LLVM_ATTRIBUTE_NORETURN
262 void fatalUncheckedError() const;
265 void assertIsChecked() {
266 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
267 if (LLVM_UNLIKELY(!getChecked() || getPtr()))
268 fatalUncheckedError();
272 ErrorInfoBase *getPtr() const {
273 return reinterpret_cast<ErrorInfoBase*>(
274 reinterpret_cast<uintptr_t>(Payload) &
275 ~static_cast<uintptr_t>(0x1));
278 void setPtr(ErrorInfoBase *EI) {
279 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
280 Payload = reinterpret_cast<ErrorInfoBase*>(
281 (reinterpret_cast<uintptr_t>(EI) &
282 ~static_cast<uintptr_t>(0x1)) |
283 (reinterpret_cast<uintptr_t>(Payload) & 0x1));
289 bool getChecked() const {
290 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
291 return (reinterpret_cast<uintptr_t>(Payload) & 0x1) == 0;
297 void setChecked(bool V) {
298 Payload = reinterpret_cast<ErrorInfoBase*>(
299 (reinterpret_cast<uintptr_t>(Payload) &
300 ~static_cast<uintptr_t>(0x1)) |
304 std::unique_ptr<ErrorInfoBase> takePayload() {
305 std::unique_ptr<ErrorInfoBase> Tmp(getPtr());
311 friend raw_ostream &operator<<(raw_ostream &OS, const Error &E) {
312 if (auto P = E.getPtr())
319 ErrorInfoBase *Payload = nullptr;
322 /// Subclass of Error for the sole purpose of identifying the success path in
323 /// the type system. This allows to catch invalid conversion to Expected<T> at
325 class ErrorSuccess final : public Error {};
327 inline ErrorSuccess Error::success() { return ErrorSuccess(); }
329 /// Make a Error instance representing failure using the given error info
331 template <typename ErrT, typename... ArgTs> Error make_error(ArgTs &&... Args) {
332 return Error(llvm::make_unique<ErrT>(std::forward<ArgTs>(Args)...));
335 /// Base class for user error types. Users should declare their error types
338 /// class MyError : public ErrorInfo<MyError> {
342 /// This class provides an implementation of the ErrorInfoBase::kind
343 /// method, which is used by the Error RTTI system.
344 template <typename ThisErrT, typename ParentErrT = ErrorInfoBase>
345 class ErrorInfo : public ParentErrT {
347 using ParentErrT::ParentErrT; // inherit constructors
349 static const void *classID() { return &ThisErrT::ID; }
351 const void *dynamicClassID() const override { return &ThisErrT::ID; }
353 bool isA(const void *const ClassID) const override {
354 return ClassID == classID() || ParentErrT::isA(ClassID);
358 /// Special ErrorInfo subclass representing a list of ErrorInfos.
359 /// Instances of this class are constructed by joinError.
360 class ErrorList final : public ErrorInfo<ErrorList> {
361 // handleErrors needs to be able to iterate the payload list of an
363 template <typename... HandlerTs>
364 friend Error handleErrors(Error E, HandlerTs &&... Handlers);
366 // joinErrors is implemented in terms of join.
367 friend Error joinErrors(Error, Error);
370 void log(raw_ostream &OS) const override {
371 OS << "Multiple errors:\n";
372 for (auto &ErrPayload : Payloads) {
378 std::error_code convertToErrorCode() const override;
380 // Used by ErrorInfo::classID.
384 ErrorList(std::unique_ptr<ErrorInfoBase> Payload1,
385 std::unique_ptr<ErrorInfoBase> Payload2) {
386 assert(!Payload1->isA<ErrorList>() && !Payload2->isA<ErrorList>() &&
387 "ErrorList constructor payloads should be singleton errors");
388 Payloads.push_back(std::move(Payload1));
389 Payloads.push_back(std::move(Payload2));
392 static Error join(Error E1, Error E2) {
397 if (E1.isA<ErrorList>()) {
398 auto &E1List = static_cast<ErrorList &>(*E1.getPtr());
399 if (E2.isA<ErrorList>()) {
400 auto E2Payload = E2.takePayload();
401 auto &E2List = static_cast<ErrorList &>(*E2Payload);
402 for (auto &Payload : E2List.Payloads)
403 E1List.Payloads.push_back(std::move(Payload));
405 E1List.Payloads.push_back(E2.takePayload());
409 if (E2.isA<ErrorList>()) {
410 auto &E2List = static_cast<ErrorList &>(*E2.getPtr());
411 E2List.Payloads.insert(E2List.Payloads.begin(), E1.takePayload());
414 return Error(std::unique_ptr<ErrorList>(
415 new ErrorList(E1.takePayload(), E2.takePayload())));
418 std::vector<std::unique_ptr<ErrorInfoBase>> Payloads;
421 /// Concatenate errors. The resulting Error is unchecked, and contains the
422 /// ErrorInfo(s), if any, contained in E1, followed by the
423 /// ErrorInfo(s), if any, contained in E2.
424 inline Error joinErrors(Error E1, Error E2) {
425 return ErrorList::join(std::move(E1), std::move(E2));
428 /// Tagged union holding either a T or a Error.
430 /// This class parallels ErrorOr, but replaces error_code with Error. Since
431 /// Error cannot be copied, this class replaces getError() with
432 /// takeError(). It also adds an bool errorIsA<ErrT>() method for testing the
433 /// error class type.
434 template <class T> class LLVM_NODISCARD Expected {
435 template <class T1> friend class ExpectedAsOutParameter;
436 template <class OtherT> friend class Expected;
438 static const bool isRef = std::is_reference<T>::value;
440 using wrap = std::reference_wrapper<typename std::remove_reference<T>::type>;
442 using error_type = std::unique_ptr<ErrorInfoBase>;
445 using storage_type = typename std::conditional<isRef, wrap, T>::type;
446 using value_type = T;
449 using reference = typename std::remove_reference<T>::type &;
450 using const_reference = const typename std::remove_reference<T>::type &;
451 using pointer = typename std::remove_reference<T>::type *;
452 using const_pointer = const typename std::remove_reference<T>::type *;
455 /// Create an Expected<T> error value from the given Error.
458 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
459 // Expected is unchecked upon construction in Debug builds.
463 assert(Err && "Cannot create Expected<T> from Error success value.");
464 new (getErrorStorage()) error_type(Err.takePayload());
467 /// Forbid to convert from Error::success() implicitly, this avoids having
468 /// Expected<T> foo() { return Error::success(); } which compiles otherwise
469 /// but triggers the assertion above.
470 Expected(ErrorSuccess) = delete;
472 /// Create an Expected<T> success value from the given OtherT value, which
473 /// must be convertible to T.
474 template <typename OtherT>
475 Expected(OtherT &&Val,
476 typename std::enable_if<std::is_convertible<OtherT, T>::value>::type
479 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
480 // Expected is unchecked upon construction in Debug builds.
484 new (getStorage()) storage_type(std::forward<OtherT>(Val));
487 /// Move construct an Expected<T> value.
488 Expected(Expected &&Other) { moveConstruct(std::move(Other)); }
490 /// Move construct an Expected<T> value from an Expected<OtherT>, where OtherT
491 /// must be convertible to T.
492 template <class OtherT>
493 Expected(Expected<OtherT> &&Other,
494 typename std::enable_if<std::is_convertible<OtherT, T>::value>::type
496 moveConstruct(std::move(Other));
499 /// Move construct an Expected<T> value from an Expected<OtherT>, where OtherT
500 /// isn't convertible to T.
501 template <class OtherT>
503 Expected<OtherT> &&Other,
504 typename std::enable_if<!std::is_convertible<OtherT, T>::value>::type * =
506 moveConstruct(std::move(Other));
509 /// Move-assign from another Expected<T>.
510 Expected &operator=(Expected &&Other) {
511 moveAssign(std::move(Other));
515 /// Destroy an Expected<T>.
519 getStorage()->~storage_type();
521 getErrorStorage()->~error_type();
524 /// Return false if there is an error.
525 explicit operator bool() {
526 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
527 Unchecked = HasError;
532 /// Returns a reference to the stored T value.
535 return *getStorage();
538 /// Returns a const reference to the stored T value.
539 const_reference get() const {
541 return const_cast<Expected<T> *>(this)->get();
544 /// Check that this Expected<T> is an error of type ErrT.
545 template <typename ErrT> bool errorIsA() const {
546 return HasError && (*getErrorStorage())->template isA<ErrT>();
549 /// Take ownership of the stored error.
550 /// After calling this the Expected<T> is in an indeterminate state that can
551 /// only be safely destructed. No further calls (beside the destructor) should
552 /// be made on the Expected<T> vaule.
554 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
557 return HasError ? Error(std::move(*getErrorStorage())) : Error::success();
560 /// Returns a pointer to the stored T value.
561 pointer operator->() {
563 return toPointer(getStorage());
566 /// Returns a const pointer to the stored T value.
567 const_pointer operator->() const {
569 return toPointer(getStorage());
572 /// Returns a reference to the stored T value.
573 reference operator*() {
575 return *getStorage();
578 /// Returns a const reference to the stored T value.
579 const_reference operator*() const {
581 return *getStorage();
586 static bool compareThisIfSameType(const T1 &a, const T1 &b) {
590 template <class T1, class T2>
591 static bool compareThisIfSameType(const T1 &a, const T2 &b) {
595 template <class OtherT> void moveConstruct(Expected<OtherT> &&Other) {
596 HasError = Other.HasError;
597 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
599 Other.Unchecked = false;
603 new (getStorage()) storage_type(std::move(*Other.getStorage()));
605 new (getErrorStorage()) error_type(std::move(*Other.getErrorStorage()));
608 template <class OtherT> void moveAssign(Expected<OtherT> &&Other) {
611 if (compareThisIfSameType(*this, Other))
615 new (this) Expected(std::move(Other));
618 pointer toPointer(pointer Val) { return Val; }
620 const_pointer toPointer(const_pointer Val) const { return Val; }
622 pointer toPointer(wrap *Val) { return &Val->get(); }
624 const_pointer toPointer(const wrap *Val) const { return &Val->get(); }
626 storage_type *getStorage() {
627 assert(!HasError && "Cannot get value when an error exists!");
628 return reinterpret_cast<storage_type *>(TStorage.buffer);
631 const storage_type *getStorage() const {
632 assert(!HasError && "Cannot get value when an error exists!");
633 return reinterpret_cast<const storage_type *>(TStorage.buffer);
636 error_type *getErrorStorage() {
637 assert(HasError && "Cannot get error when a value exists!");
638 return reinterpret_cast<error_type *>(ErrorStorage.buffer);
641 const error_type *getErrorStorage() const {
642 assert(HasError && "Cannot get error when a value exists!");
643 return reinterpret_cast<const error_type *>(ErrorStorage.buffer);
646 // Used by ExpectedAsOutParameter to reset the checked flag.
647 void setUnchecked() {
648 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
653 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
654 LLVM_ATTRIBUTE_NORETURN
655 LLVM_ATTRIBUTE_NOINLINE
656 void fatalUncheckedExpected() const {
657 dbgs() << "Expected<T> must be checked before access or destruction.\n";
659 dbgs() << "Unchecked Expected<T> contained error:\n";
660 (*getErrorStorage())->log(dbgs());
662 dbgs() << "Expected<T> value was in success state. (Note: Expected<T> "
663 "values in success mode must still be checked prior to being "
669 void assertIsChecked() {
670 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
671 if (LLVM_UNLIKELY(Unchecked))
672 fatalUncheckedExpected();
677 AlignedCharArrayUnion<storage_type> TStorage;
678 AlignedCharArrayUnion<error_type> ErrorStorage;
681 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
686 /// Report a serious error, calling any installed error handler. See
688 LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err,
689 bool gen_crash_diag = true);
691 /// Report a fatal error if Err is a failure value.
693 /// This function can be used to wrap calls to fallible functions ONLY when it
694 /// is known that the Error will always be a success value. E.g.
697 /// // foo only attempts the fallible operation if DoFallibleOperation is
698 /// // true. If DoFallibleOperation is false then foo always returns
699 /// // Error::success().
700 /// Error foo(bool DoFallibleOperation);
702 /// cantFail(foo(false));
704 inline void cantFail(Error Err, const char *Msg = nullptr) {
707 Msg = "Failure value returned from cantFail wrapped call";
708 llvm_unreachable(Msg);
712 /// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
713 /// returns the contained value.
715 /// This function can be used to wrap calls to fallible functions ONLY when it
716 /// is known that the Error will always be a success value. E.g.
719 /// // foo only attempts the fallible operation if DoFallibleOperation is
720 /// // true. If DoFallibleOperation is false then foo always returns an int.
721 /// Expected<int> foo(bool DoFallibleOperation);
723 /// int X = cantFail(foo(false));
725 template <typename T>
726 T cantFail(Expected<T> ValOrErr, const char *Msg = nullptr) {
728 return std::move(*ValOrErr);
731 Msg = "Failure value returned from cantFail wrapped call";
732 llvm_unreachable(Msg);
736 /// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
737 /// returns the contained reference.
739 /// This function can be used to wrap calls to fallible functions ONLY when it
740 /// is known that the Error will always be a success value. E.g.
743 /// // foo only attempts the fallible operation if DoFallibleOperation is
744 /// // true. If DoFallibleOperation is false then foo always returns a Bar&.
745 /// Expected<Bar&> foo(bool DoFallibleOperation);
747 /// Bar &X = cantFail(foo(false));
749 template <typename T>
750 T& cantFail(Expected<T&> ValOrErr, const char *Msg = nullptr) {
755 Msg = "Failure value returned from cantFail wrapped call";
756 llvm_unreachable(Msg);
760 /// Helper for testing applicability of, and applying, handlers for
762 template <typename HandlerT>
763 class ErrorHandlerTraits
764 : public ErrorHandlerTraits<decltype(
765 &std::remove_reference<HandlerT>::type::operator())> {};
767 // Specialization functions of the form 'Error (const ErrT&)'.
768 template <typename ErrT> class ErrorHandlerTraits<Error (&)(ErrT &)> {
770 static bool appliesTo(const ErrorInfoBase &E) {
771 return E.template isA<ErrT>();
774 template <typename HandlerT>
775 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
776 assert(appliesTo(*E) && "Applying incorrect handler");
777 return H(static_cast<ErrT &>(*E));
781 // Specialization functions of the form 'void (const ErrT&)'.
782 template <typename ErrT> class ErrorHandlerTraits<void (&)(ErrT &)> {
784 static bool appliesTo(const ErrorInfoBase &E) {
785 return E.template isA<ErrT>();
788 template <typename HandlerT>
789 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
790 assert(appliesTo(*E) && "Applying incorrect handler");
791 H(static_cast<ErrT &>(*E));
792 return Error::success();
796 /// Specialization for functions of the form 'Error (std::unique_ptr<ErrT>)'.
797 template <typename ErrT>
798 class ErrorHandlerTraits<Error (&)(std::unique_ptr<ErrT>)> {
800 static bool appliesTo(const ErrorInfoBase &E) {
801 return E.template isA<ErrT>();
804 template <typename HandlerT>
805 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
806 assert(appliesTo(*E) && "Applying incorrect handler");
807 std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
808 return H(std::move(SubE));
812 /// Specialization for functions of the form 'void (std::unique_ptr<ErrT>)'.
813 template <typename ErrT>
814 class ErrorHandlerTraits<void (&)(std::unique_ptr<ErrT>)> {
816 static bool appliesTo(const ErrorInfoBase &E) {
817 return E.template isA<ErrT>();
820 template <typename HandlerT>
821 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
822 assert(appliesTo(*E) && "Applying incorrect handler");
823 std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
825 return Error::success();
829 // Specialization for member functions of the form 'RetT (const ErrT&)'.
830 template <typename C, typename RetT, typename ErrT>
831 class ErrorHandlerTraits<RetT (C::*)(ErrT &)>
832 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
834 // Specialization for member functions of the form 'RetT (const ErrT&) const'.
835 template <typename C, typename RetT, typename ErrT>
836 class ErrorHandlerTraits<RetT (C::*)(ErrT &) const>
837 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
839 // Specialization for member functions of the form 'RetT (const ErrT&)'.
840 template <typename C, typename RetT, typename ErrT>
841 class ErrorHandlerTraits<RetT (C::*)(const ErrT &)>
842 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
844 // Specialization for member functions of the form 'RetT (const ErrT&) const'.
845 template <typename C, typename RetT, typename ErrT>
846 class ErrorHandlerTraits<RetT (C::*)(const ErrT &) const>
847 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
849 /// Specialization for member functions of the form
850 /// 'RetT (std::unique_ptr<ErrT>)'.
851 template <typename C, typename RetT, typename ErrT>
852 class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>)>
853 : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
855 /// Specialization for member functions of the form
856 /// 'RetT (std::unique_ptr<ErrT>) const'.
857 template <typename C, typename RetT, typename ErrT>
858 class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>) const>
859 : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
861 inline Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload) {
862 return Error(std::move(Payload));
865 template <typename HandlerT, typename... HandlerTs>
866 Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload,
867 HandlerT &&Handler, HandlerTs &&... Handlers) {
868 if (ErrorHandlerTraits<HandlerT>::appliesTo(*Payload))
869 return ErrorHandlerTraits<HandlerT>::apply(std::forward<HandlerT>(Handler),
871 return handleErrorImpl(std::move(Payload),
872 std::forward<HandlerTs>(Handlers)...);
875 /// Pass the ErrorInfo(s) contained in E to their respective handlers. Any
876 /// unhandled errors (or Errors returned by handlers) are re-concatenated and
878 /// Because this function returns an error, its result must also be checked
879 /// or returned. If you intend to handle all errors use handleAllErrors
880 /// (which returns void, and will abort() on unhandled errors) instead.
881 template <typename... HandlerTs>
882 Error handleErrors(Error E, HandlerTs &&... Hs) {
884 return Error::success();
886 std::unique_ptr<ErrorInfoBase> Payload = E.takePayload();
888 if (Payload->isA<ErrorList>()) {
889 ErrorList &List = static_cast<ErrorList &>(*Payload);
891 for (auto &P : List.Payloads)
894 handleErrorImpl(std::move(P), std::forward<HandlerTs>(Hs)...));
898 return handleErrorImpl(std::move(Payload), std::forward<HandlerTs>(Hs)...);
901 /// Behaves the same as handleErrors, except that by contract all errors
902 /// *must* be handled by the given handlers (i.e. there must be no remaining
903 /// errors after running the handlers, or llvm_unreachable is called).
904 template <typename... HandlerTs>
905 void handleAllErrors(Error E, HandlerTs &&... Handlers) {
906 cantFail(handleErrors(std::move(E), std::forward<HandlerTs>(Handlers)...));
909 /// Check that E is a non-error, then drop it.
910 /// If E is an error, llvm_unreachable will be called.
911 inline void handleAllErrors(Error E) {
912 cantFail(std::move(E));
915 /// Handle any errors (if present) in an Expected<T>, then try a recovery path.
917 /// If the incoming value is a success value it is returned unmodified. If it
918 /// is a failure value then it the contained error is passed to handleErrors.
919 /// If handleErrors is able to handle the error then the RecoveryPath functor
920 /// is called to supply the final result. If handleErrors is not able to
921 /// handle all errors then the unhandled errors are returned.
923 /// This utility enables the follow pattern:
926 /// enum FooStrategy { Aggressive, Conservative };
927 /// Expected<Foo> foo(FooStrategy S);
929 /// auto ResultOrErr =
932 /// []() { return foo(Conservative); },
933 /// [](AggressiveStrategyError&) {
934 /// // Implicitly conusme this - we'll recover by using a conservative
939 template <typename T, typename RecoveryFtor, typename... HandlerTs>
940 Expected<T> handleExpected(Expected<T> ValOrErr, RecoveryFtor &&RecoveryPath,
941 HandlerTs &&... Handlers) {
945 if (auto Err = handleErrors(ValOrErr.takeError(),
946 std::forward<HandlerTs>(Handlers)...))
947 return std::move(Err);
949 return RecoveryPath();
952 /// Log all errors (if any) in E to OS. If there are any errors, ErrorBanner
953 /// will be printed before the first one is logged. A newline will be printed
954 /// after each error.
956 /// This function is compatible with the helpers from Support/WithColor.h. You
957 /// can pass any of them as the OS. Please consider using them instead of
958 /// including 'error: ' in the ErrorBanner.
960 /// This is useful in the base level of your program to allow clean termination
961 /// (allowing clean deallocation of resources, etc.), while reporting error
962 /// information to the user.
963 void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner = {});
965 /// Write all error messages (if any) in E to a string. The newline character
966 /// is used to separate error messages.
967 inline std::string toString(Error E) {
968 SmallVector<std::string, 2> Errors;
969 handleAllErrors(std::move(E), [&Errors](const ErrorInfoBase &EI) {
970 Errors.push_back(EI.message());
972 return join(Errors.begin(), Errors.end(), "\n");
975 /// Consume a Error without doing anything. This method should be used
976 /// only where an error can be considered a reasonable and expected return
979 /// Uses of this method are potentially indicative of design problems: If it's
980 /// legitimate to do nothing while processing an "error", the error-producer
981 /// might be more clearly refactored to return an Optional<T>.
982 inline void consumeError(Error Err) {
983 handleAllErrors(std::move(Err), [](const ErrorInfoBase &) {});
986 /// Helper for converting an Error to a bool.
988 /// This method returns true if Err is in an error state, or false if it is
989 /// in a success state. Puts Err in a checked state in both cases (unlike
990 /// Error::operator bool(), which only does this for success states).
991 inline bool errorToBool(Error Err) {
992 bool IsError = static_cast<bool>(Err);
994 consumeError(std::move(Err));
998 /// Helper for Errors used as out-parameters.
1000 /// This helper is for use with the Error-as-out-parameter idiom, where an error
1001 /// is passed to a function or method by reference, rather than being returned.
1002 /// In such cases it is helpful to set the checked bit on entry to the function
1003 /// so that the error can be written to (unchecked Errors abort on assignment)
1004 /// and clear the checked bit on exit so that clients cannot accidentally forget
1005 /// to check the result. This helper performs these actions automatically using
1009 /// Result foo(Error &Err) {
1010 /// ErrorAsOutParameter ErrAsOutParam(&Err); // 'Checked' flag set
1011 /// // <body of foo>
1012 /// // <- 'Checked' flag auto-cleared when ErrAsOutParam is destructed.
1016 /// ErrorAsOutParameter takes an Error* rather than Error& so that it can be
1017 /// used with optional Errors (Error pointers that are allowed to be null). If
1018 /// ErrorAsOutParameter took an Error reference, an instance would have to be
1019 /// created inside every condition that verified that Error was non-null. By
1020 /// taking an Error pointer we can just create one instance at the top of the
1022 class ErrorAsOutParameter {
1024 ErrorAsOutParameter(Error *Err) : Err(Err) {
1025 // Raise the checked bit if Err is success.
1030 ~ErrorAsOutParameter() {
1031 // Clear the checked bit.
1033 *Err = Error::success();
1040 /// Helper for Expected<T>s used as out-parameters.
1042 /// See ErrorAsOutParameter.
1043 template <typename T>
1044 class ExpectedAsOutParameter {
1046 ExpectedAsOutParameter(Expected<T> *ValOrErr)
1047 : ValOrErr(ValOrErr) {
1052 ~ExpectedAsOutParameter() {
1054 ValOrErr->setUnchecked();
1058 Expected<T> *ValOrErr;
1061 /// This class wraps a std::error_code in a Error.
1063 /// This is useful if you're writing an interface that returns a Error
1064 /// (or Expected) and you want to call code that still returns
1065 /// std::error_codes.
1066 class ECError : public ErrorInfo<ECError> {
1067 friend Error errorCodeToError(std::error_code);
1069 virtual void anchor() override;
1072 void setErrorCode(std::error_code EC) { this->EC = EC; }
1073 std::error_code convertToErrorCode() const override { return EC; }
1074 void log(raw_ostream &OS) const override { OS << EC.message(); }
1076 // Used by ErrorInfo::classID.
1080 ECError() = default;
1081 ECError(std::error_code EC) : EC(EC) {}
1086 /// The value returned by this function can be returned from convertToErrorCode
1087 /// for Error values where no sensible translation to std::error_code exists.
1088 /// It should only be used in this situation, and should never be used where a
1089 /// sensible conversion to std::error_code is available, as attempts to convert
1090 /// to/from this error will result in a fatal error. (i.e. it is a programmatic
1091 ///error to try to convert such a value).
1092 std::error_code inconvertibleErrorCode();
1094 /// Helper for converting an std::error_code to a Error.
1095 Error errorCodeToError(std::error_code EC);
1097 /// Helper for converting an ECError to a std::error_code.
1099 /// This method requires that Err be Error() or an ECError, otherwise it
1100 /// will trigger a call to abort().
1101 std::error_code errorToErrorCode(Error Err);
1103 /// Convert an ErrorOr<T> to an Expected<T>.
1104 template <typename T> Expected<T> errorOrToExpected(ErrorOr<T> &&EO) {
1105 if (auto EC = EO.getError())
1106 return errorCodeToError(EC);
1107 return std::move(*EO);
1110 /// Convert an Expected<T> to an ErrorOr<T>.
1111 template <typename T> ErrorOr<T> expectedToErrorOr(Expected<T> &&E) {
1112 if (auto Err = E.takeError())
1113 return errorToErrorCode(std::move(Err));
1114 return std::move(*E);
1117 /// This class wraps a string in an Error.
1119 /// StringError is useful in cases where the client is not expected to be able
1120 /// to consume the specific error message programmatically (for example, if the
1121 /// error message is to be presented to the user).
1123 /// StringError can also be used when additional information is to be printed
1124 /// along with a error_code message. Depending on the constructor called, this
1125 /// class can either display:
1126 /// 1. the error_code message (ECError behavior)
1128 /// 3. the error_code message and a string
1130 /// These behaviors are useful when subtyping is required; for example, when a
1131 /// specific library needs an explicit error type. In the example below,
1132 /// PDBError is derived from StringError:
1135 /// Expected<int> foo() {
1136 /// return llvm::make_error<PDBError>(pdb_error_code::dia_failed_loading,
1137 /// "Additional information");
1141 class StringError : public ErrorInfo<StringError> {
1145 // Prints EC + S and converts to EC
1146 StringError(std::error_code EC, const Twine &S = Twine());
1148 // Prints S and converts to EC
1149 StringError(const Twine &S, std::error_code EC);
1151 void log(raw_ostream &OS) const override;
1152 std::error_code convertToErrorCode() const override;
1154 const std::string &getMessage() const { return Msg; }
1159 const bool PrintMsgOnly = false;
1162 /// Create formatted StringError object.
1163 template <typename... Ts>
1164 Error createStringError(std::error_code EC, char const *Fmt,
1165 const Ts &... Vals) {
1167 raw_string_ostream Stream(Buffer);
1168 Stream << format(Fmt, Vals...);
1169 return make_error<StringError>(Stream.str(), EC);
1172 Error createStringError(std::error_code EC, char const *Msg);
1174 /// This class wraps a filename and another Error.
1176 /// In some cases, an error needs to live along a 'source' name, in order to
1177 /// show more detailed information to the user.
1178 class FileError final : public ErrorInfo<FileError> {
1180 friend Error createFileError(std::string, Error);
1183 void log(raw_ostream &OS) const override {
1184 assert(Err && !FileName.empty() && "Trying to log after takeError().");
1185 OS << "'" << FileName << "': ";
1189 Error takeError() { return Error(std::move(Err)); }
1191 std::error_code convertToErrorCode() const override;
1193 // Used by ErrorInfo::classID.
1197 FileError(std::string F, std::unique_ptr<ErrorInfoBase> E) {
1198 assert(E && "Cannot create FileError from Error success value.");
1199 assert(!F.empty() &&
1200 "The file name provided to FileError must not be empty.");
1205 static Error build(std::string F, Error E) {
1206 return Error(std::unique_ptr<FileError>(new FileError(F, E.takePayload())));
1209 std::string FileName;
1210 std::unique_ptr<ErrorInfoBase> Err;
1213 /// Concatenate a source file path and/or name with an Error. The resulting
1214 /// Error is unchecked.
1215 inline Error createFileError(std::string F, Error E) {
1216 return FileError::build(F, std::move(E));
1219 Error createFileError(std::string F, ErrorSuccess) = delete;
1221 /// Helper for check-and-exit error handling.
1223 /// For tool use only. NOT FOR USE IN LIBRARY CODE.
1227 /// Create an error on exit helper.
1228 ExitOnError(std::string Banner = "", int DefaultErrorExitCode = 1)
1229 : Banner(std::move(Banner)),
1230 GetExitCode([=](const Error &) { return DefaultErrorExitCode; }) {}
1232 /// Set the banner string for any errors caught by operator().
1233 void setBanner(std::string Banner) { this->Banner = std::move(Banner); }
1235 /// Set the exit-code mapper function.
1236 void setExitCodeMapper(std::function<int(const Error &)> GetExitCode) {
1237 this->GetExitCode = std::move(GetExitCode);
1240 /// Check Err. If it's in a failure state log the error(s) and exit.
1241 void operator()(Error Err) const { checkError(std::move(Err)); }
1243 /// Check E. If it's in a success state then return the contained value. If
1244 /// it's in a failure state log the error(s) and exit.
1245 template <typename T> T operator()(Expected<T> &&E) const {
1246 checkError(E.takeError());
1247 return std::move(*E);
1250 /// Check E. If it's in a success state then return the contained reference. If
1251 /// it's in a failure state log the error(s) and exit.
1252 template <typename T> T& operator()(Expected<T&> &&E) const {
1253 checkError(E.takeError());
1258 void checkError(Error Err) const {
1260 int ExitCode = GetExitCode(Err);
1261 logAllUnhandledErrors(std::move(Err), errs(), Banner);
1267 std::function<int(const Error &)> GetExitCode;
1270 /// Conversion from Error to LLVMErrorRef for C error bindings.
1271 inline LLVMErrorRef wrap(Error Err) {
1272 return reinterpret_cast<LLVMErrorRef>(Err.takePayload().release());
1275 /// Conversion from LLVMErrorRef to Error for C error bindings.
1276 inline Error unwrap(LLVMErrorRef ErrRef) {
1277 return Error(std::unique_ptr<ErrorInfoBase>(
1278 reinterpret_cast<ErrorInfoBase *>(ErrRef)));
1281 } // end namespace llvm
1283 #endif // LLVM_SUPPORT_ERROR_H