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[llvm-complete.git] / include / llvm / Support / Error.h
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1 //===- llvm/Support/Error.h - Recoverable error handling --------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines an API used to report recoverable errors.
11 //===----------------------------------------------------------------------===//
13 #ifndef LLVM_SUPPORT_ERROR_H
14 #define LLVM_SUPPORT_ERROR_H
16 #include "llvm-c/Error.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/StringExtras.h"
20 #include "llvm/ADT/Twine.h"
21 #include "llvm/Config/abi-breaking.h"
22 #include "llvm/Support/AlignOf.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/ErrorHandling.h"
26 #include "llvm/Support/ErrorOr.h"
27 #include "llvm/Support/Format.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include <algorithm>
30 #include <cassert>
31 #include <cstdint>
32 #include <cstdlib>
33 #include <functional>
34 #include <memory>
35 #include <new>
36 #include <string>
37 #include <system_error>
38 #include <type_traits>
39 #include <utility>
40 #include <vector>
42 namespace llvm {
44 class ErrorSuccess;
46 /// Base class for error info classes. Do not extend this directly: Extend
47 /// the ErrorInfo template subclass instead.
48 class ErrorInfoBase {
49 public:
50 virtual ~ErrorInfoBase() = default;
52 /// Print an error message to an output stream.
53 virtual void log(raw_ostream &OS) const = 0;
55 /// Return the error message as a string.
56 virtual std::string message() const {
57 std::string Msg;
58 raw_string_ostream OS(Msg);
59 log(OS);
60 return OS.str();
63 /// Convert this error to a std::error_code.
64 ///
65 /// This is a temporary crutch to enable interaction with code still
66 /// using std::error_code. It will be removed in the future.
67 virtual std::error_code convertToErrorCode() const = 0;
69 // Returns the class ID for this type.
70 static const void *classID() { return &ID; }
72 // Returns the class ID for the dynamic type of this ErrorInfoBase instance.
73 virtual const void *dynamicClassID() const = 0;
75 // Check whether this instance is a subclass of the class identified by
76 // ClassID.
77 virtual bool isA(const void *const ClassID) const {
78 return ClassID == classID();
81 // Check whether this instance is a subclass of ErrorInfoT.
82 template <typename ErrorInfoT> bool isA() const {
83 return isA(ErrorInfoT::classID());
86 private:
87 virtual void anchor();
89 static char ID;
92 /// Lightweight error class with error context and mandatory checking.
93 ///
94 /// Instances of this class wrap a ErrorInfoBase pointer. Failure states
95 /// are represented by setting the pointer to a ErrorInfoBase subclass
96 /// instance containing information describing the failure. Success is
97 /// represented by a null pointer value.
98 ///
99 /// Instances of Error also contains a 'Checked' flag, which must be set
100 /// before the destructor is called, otherwise the destructor will trigger a
101 /// runtime error. This enforces at runtime the requirement that all Error
102 /// instances be checked or returned to the caller.
104 /// There are two ways to set the checked flag, depending on what state the
105 /// Error instance is in. For Error instances indicating success, it
106 /// is sufficient to invoke the boolean conversion operator. E.g.:
108 /// @code{.cpp}
109 /// Error foo(<...>);
111 /// if (auto E = foo(<...>))
112 /// return E; // <- Return E if it is in the error state.
113 /// // We have verified that E was in the success state. It can now be safely
114 /// // destroyed.
115 /// @endcode
117 /// A success value *can not* be dropped. For example, just calling 'foo(<...>)'
118 /// without testing the return value will raise a runtime error, even if foo
119 /// returns success.
121 /// For Error instances representing failure, you must use either the
122 /// handleErrors or handleAllErrors function with a typed handler. E.g.:
124 /// @code{.cpp}
125 /// class MyErrorInfo : public ErrorInfo<MyErrorInfo> {
126 /// // Custom error info.
127 /// };
129 /// Error foo(<...>) { return make_error<MyErrorInfo>(...); }
131 /// auto E = foo(<...>); // <- foo returns failure with MyErrorInfo.
132 /// auto NewE =
133 /// handleErrors(E,
134 /// [](const MyErrorInfo &M) {
135 /// // Deal with the error.
136 /// },
137 /// [](std::unique_ptr<OtherError> M) -> Error {
138 /// if (canHandle(*M)) {
139 /// // handle error.
140 /// return Error::success();
141 /// }
142 /// // Couldn't handle this error instance. Pass it up the stack.
143 /// return Error(std::move(M));
144 /// );
145 /// // Note - we must check or return NewE in case any of the handlers
146 /// // returned a new error.
147 /// @endcode
149 /// The handleAllErrors function is identical to handleErrors, except
150 /// that it has a void return type, and requires all errors to be handled and
151 /// no new errors be returned. It prevents errors (assuming they can all be
152 /// handled) from having to be bubbled all the way to the top-level.
154 /// *All* Error instances must be checked before destruction, even if
155 /// they're moved-assigned or constructed from Success values that have already
156 /// been checked. This enforces checking through all levels of the call stack.
157 class LLVM_NODISCARD Error {
158 // Both ErrorList and FileError need to be able to yank ErrorInfoBase
159 // pointers out of this class to add to the error list.
160 friend class ErrorList;
161 friend class FileError;
163 // handleErrors needs to be able to set the Checked flag.
164 template <typename... HandlerTs>
165 friend Error handleErrors(Error E, HandlerTs &&... Handlers);
167 // Expected<T> needs to be able to steal the payload when constructed from an
168 // error.
169 template <typename T> friend class Expected;
171 // wrap needs to be able to steal the payload.
172 friend LLVMErrorRef wrap(Error);
174 protected:
175 /// Create a success value. Prefer using 'Error::success()' for readability
176 Error() {
177 setPtr(nullptr);
178 setChecked(false);
181 public:
182 /// Create a success value.
183 static ErrorSuccess success();
185 // Errors are not copy-constructable.
186 Error(const Error &Other) = delete;
188 /// Move-construct an error value. The newly constructed error is considered
189 /// unchecked, even if the source error had been checked. The original error
190 /// becomes a checked Success value, regardless of its original state.
191 Error(Error &&Other) {
192 setChecked(true);
193 *this = std::move(Other);
196 /// Create an error value. Prefer using the 'make_error' function, but
197 /// this constructor can be useful when "re-throwing" errors from handlers.
198 Error(std::unique_ptr<ErrorInfoBase> Payload) {
199 setPtr(Payload.release());
200 setChecked(false);
203 // Errors are not copy-assignable.
204 Error &operator=(const Error &Other) = delete;
206 /// Move-assign an error value. The current error must represent success, you
207 /// you cannot overwrite an unhandled error. The current error is then
208 /// considered unchecked. The source error becomes a checked success value,
209 /// regardless of its original state.
210 Error &operator=(Error &&Other) {
211 // Don't allow overwriting of unchecked values.
212 assertIsChecked();
213 setPtr(Other.getPtr());
215 // This Error is unchecked, even if the source error was checked.
216 setChecked(false);
218 // Null out Other's payload and set its checked bit.
219 Other.setPtr(nullptr);
220 Other.setChecked(true);
222 return *this;
225 /// Destroy a Error. Fails with a call to abort() if the error is
226 /// unchecked.
227 ~Error() {
228 assertIsChecked();
229 delete getPtr();
232 /// Bool conversion. Returns true if this Error is in a failure state,
233 /// and false if it is in an accept state. If the error is in a Success state
234 /// it will be considered checked.
235 explicit operator bool() {
236 setChecked(getPtr() == nullptr);
237 return getPtr() != nullptr;
240 /// Check whether one error is a subclass of another.
241 template <typename ErrT> bool isA() const {
242 return getPtr() && getPtr()->isA(ErrT::classID());
245 /// Returns the dynamic class id of this error, or null if this is a success
246 /// value.
247 const void* dynamicClassID() const {
248 if (!getPtr())
249 return nullptr;
250 return getPtr()->dynamicClassID();
253 private:
254 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
255 // assertIsChecked() happens very frequently, but under normal circumstances
256 // is supposed to be a no-op. So we want it to be inlined, but having a bunch
257 // of debug prints can cause the function to be too large for inlining. So
258 // it's important that we define this function out of line so that it can't be
259 // inlined.
260 LLVM_ATTRIBUTE_NORETURN
261 void fatalUncheckedError() const;
262 #endif
264 void assertIsChecked() {
265 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
266 if (LLVM_UNLIKELY(!getChecked() || getPtr()))
267 fatalUncheckedError();
268 #endif
271 ErrorInfoBase *getPtr() const {
272 return reinterpret_cast<ErrorInfoBase*>(
273 reinterpret_cast<uintptr_t>(Payload) &
274 ~static_cast<uintptr_t>(0x1));
277 void setPtr(ErrorInfoBase *EI) {
278 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
279 Payload = reinterpret_cast<ErrorInfoBase*>(
280 (reinterpret_cast<uintptr_t>(EI) &
281 ~static_cast<uintptr_t>(0x1)) |
282 (reinterpret_cast<uintptr_t>(Payload) & 0x1));
283 #else
284 Payload = EI;
285 #endif
288 bool getChecked() const {
289 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
290 return (reinterpret_cast<uintptr_t>(Payload) & 0x1) == 0;
291 #else
292 return true;
293 #endif
296 void setChecked(bool V) {
297 Payload = reinterpret_cast<ErrorInfoBase*>(
298 (reinterpret_cast<uintptr_t>(Payload) &
299 ~static_cast<uintptr_t>(0x1)) |
300 (V ? 0 : 1));
303 std::unique_ptr<ErrorInfoBase> takePayload() {
304 std::unique_ptr<ErrorInfoBase> Tmp(getPtr());
305 setPtr(nullptr);
306 setChecked(true);
307 return Tmp;
310 friend raw_ostream &operator<<(raw_ostream &OS, const Error &E) {
311 if (auto P = E.getPtr())
312 P->log(OS);
313 else
314 OS << "success";
315 return OS;
318 ErrorInfoBase *Payload = nullptr;
321 /// Subclass of Error for the sole purpose of identifying the success path in
322 /// the type system. This allows to catch invalid conversion to Expected<T> at
323 /// compile time.
324 class ErrorSuccess final : public Error {};
326 inline ErrorSuccess Error::success() { return ErrorSuccess(); }
328 /// Make a Error instance representing failure using the given error info
329 /// type.
330 template <typename ErrT, typename... ArgTs> Error make_error(ArgTs &&... Args) {
331 return Error(std::make_unique<ErrT>(std::forward<ArgTs>(Args)...));
334 /// Base class for user error types. Users should declare their error types
335 /// like:
337 /// class MyError : public ErrorInfo<MyError> {
338 /// ....
339 /// };
341 /// This class provides an implementation of the ErrorInfoBase::kind
342 /// method, which is used by the Error RTTI system.
343 template <typename ThisErrT, typename ParentErrT = ErrorInfoBase>
344 class ErrorInfo : public ParentErrT {
345 public:
346 using ParentErrT::ParentErrT; // inherit constructors
348 static const void *classID() { return &ThisErrT::ID; }
350 const void *dynamicClassID() const override { return &ThisErrT::ID; }
352 bool isA(const void *const ClassID) const override {
353 return ClassID == classID() || ParentErrT::isA(ClassID);
357 /// Special ErrorInfo subclass representing a list of ErrorInfos.
358 /// Instances of this class are constructed by joinError.
359 class ErrorList final : public ErrorInfo<ErrorList> {
360 // handleErrors needs to be able to iterate the payload list of an
361 // ErrorList.
362 template <typename... HandlerTs>
363 friend Error handleErrors(Error E, HandlerTs &&... Handlers);
365 // joinErrors is implemented in terms of join.
366 friend Error joinErrors(Error, Error);
368 public:
369 void log(raw_ostream &OS) const override {
370 OS << "Multiple errors:\n";
371 for (auto &ErrPayload : Payloads) {
372 ErrPayload->log(OS);
373 OS << "\n";
377 std::error_code convertToErrorCode() const override;
379 // Used by ErrorInfo::classID.
380 static char ID;
382 private:
383 ErrorList(std::unique_ptr<ErrorInfoBase> Payload1,
384 std::unique_ptr<ErrorInfoBase> Payload2) {
385 assert(!Payload1->isA<ErrorList>() && !Payload2->isA<ErrorList>() &&
386 "ErrorList constructor payloads should be singleton errors");
387 Payloads.push_back(std::move(Payload1));
388 Payloads.push_back(std::move(Payload2));
391 static Error join(Error E1, Error E2) {
392 if (!E1)
393 return E2;
394 if (!E2)
395 return E1;
396 if (E1.isA<ErrorList>()) {
397 auto &E1List = static_cast<ErrorList &>(*E1.getPtr());
398 if (E2.isA<ErrorList>()) {
399 auto E2Payload = E2.takePayload();
400 auto &E2List = static_cast<ErrorList &>(*E2Payload);
401 for (auto &Payload : E2List.Payloads)
402 E1List.Payloads.push_back(std::move(Payload));
403 } else
404 E1List.Payloads.push_back(E2.takePayload());
406 return E1;
408 if (E2.isA<ErrorList>()) {
409 auto &E2List = static_cast<ErrorList &>(*E2.getPtr());
410 E2List.Payloads.insert(E2List.Payloads.begin(), E1.takePayload());
411 return E2;
413 return Error(std::unique_ptr<ErrorList>(
414 new ErrorList(E1.takePayload(), E2.takePayload())));
417 std::vector<std::unique_ptr<ErrorInfoBase>> Payloads;
420 /// Concatenate errors. The resulting Error is unchecked, and contains the
421 /// ErrorInfo(s), if any, contained in E1, followed by the
422 /// ErrorInfo(s), if any, contained in E2.
423 inline Error joinErrors(Error E1, Error E2) {
424 return ErrorList::join(std::move(E1), std::move(E2));
427 /// Tagged union holding either a T or a Error.
429 /// This class parallels ErrorOr, but replaces error_code with Error. Since
430 /// Error cannot be copied, this class replaces getError() with
431 /// takeError(). It also adds an bool errorIsA<ErrT>() method for testing the
432 /// error class type.
433 template <class T> class LLVM_NODISCARD Expected {
434 template <class T1> friend class ExpectedAsOutParameter;
435 template <class OtherT> friend class Expected;
437 static const bool isRef = std::is_reference<T>::value;
439 using wrap = std::reference_wrapper<typename std::remove_reference<T>::type>;
441 using error_type = std::unique_ptr<ErrorInfoBase>;
443 public:
444 using storage_type = typename std::conditional<isRef, wrap, T>::type;
445 using value_type = T;
447 private:
448 using reference = typename std::remove_reference<T>::type &;
449 using const_reference = const typename std::remove_reference<T>::type &;
450 using pointer = typename std::remove_reference<T>::type *;
451 using const_pointer = const typename std::remove_reference<T>::type *;
453 public:
454 /// Create an Expected<T> error value from the given Error.
455 Expected(Error Err)
456 : HasError(true)
457 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
458 // Expected is unchecked upon construction in Debug builds.
459 , Unchecked(true)
460 #endif
462 assert(Err && "Cannot create Expected<T> from Error success value.");
463 new (getErrorStorage()) error_type(Err.takePayload());
466 /// Forbid to convert from Error::success() implicitly, this avoids having
467 /// Expected<T> foo() { return Error::success(); } which compiles otherwise
468 /// but triggers the assertion above.
469 Expected(ErrorSuccess) = delete;
471 /// Create an Expected<T> success value from the given OtherT value, which
472 /// must be convertible to T.
473 template <typename OtherT>
474 Expected(OtherT &&Val,
475 typename std::enable_if<std::is_convertible<OtherT, T>::value>::type
476 * = nullptr)
477 : HasError(false)
478 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
479 // Expected is unchecked upon construction in Debug builds.
480 , Unchecked(true)
481 #endif
483 new (getStorage()) storage_type(std::forward<OtherT>(Val));
486 /// Move construct an Expected<T> value.
487 Expected(Expected &&Other) { moveConstruct(std::move(Other)); }
489 /// Move construct an Expected<T> value from an Expected<OtherT>, where OtherT
490 /// must be convertible to T.
491 template <class OtherT>
492 Expected(Expected<OtherT> &&Other,
493 typename std::enable_if<std::is_convertible<OtherT, T>::value>::type
494 * = nullptr) {
495 moveConstruct(std::move(Other));
498 /// Move construct an Expected<T> value from an Expected<OtherT>, where OtherT
499 /// isn't convertible to T.
500 template <class OtherT>
501 explicit Expected(
502 Expected<OtherT> &&Other,
503 typename std::enable_if<!std::is_convertible<OtherT, T>::value>::type * =
504 nullptr) {
505 moveConstruct(std::move(Other));
508 /// Move-assign from another Expected<T>.
509 Expected &operator=(Expected &&Other) {
510 moveAssign(std::move(Other));
511 return *this;
514 /// Destroy an Expected<T>.
515 ~Expected() {
516 assertIsChecked();
517 if (!HasError)
518 getStorage()->~storage_type();
519 else
520 getErrorStorage()->~error_type();
523 /// Return false if there is an error.
524 explicit operator bool() {
525 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
526 Unchecked = HasError;
527 #endif
528 return !HasError;
531 /// Returns a reference to the stored T value.
532 reference get() {
533 assertIsChecked();
534 return *getStorage();
537 /// Returns a const reference to the stored T value.
538 const_reference get() const {
539 assertIsChecked();
540 return const_cast<Expected<T> *>(this)->get();
543 /// Check that this Expected<T> is an error of type ErrT.
544 template <typename ErrT> bool errorIsA() const {
545 return HasError && (*getErrorStorage())->template isA<ErrT>();
548 /// Take ownership of the stored error.
549 /// After calling this the Expected<T> is in an indeterminate state that can
550 /// only be safely destructed. No further calls (beside the destructor) should
551 /// be made on the Expected<T> value.
552 Error takeError() {
553 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
554 Unchecked = false;
555 #endif
556 return HasError ? Error(std::move(*getErrorStorage())) : Error::success();
559 /// Returns a pointer to the stored T value.
560 pointer operator->() {
561 assertIsChecked();
562 return toPointer(getStorage());
565 /// Returns a const pointer to the stored T value.
566 const_pointer operator->() const {
567 assertIsChecked();
568 return toPointer(getStorage());
571 /// Returns a reference to the stored T value.
572 reference operator*() {
573 assertIsChecked();
574 return *getStorage();
577 /// Returns a const reference to the stored T value.
578 const_reference operator*() const {
579 assertIsChecked();
580 return *getStorage();
583 private:
584 template <class T1>
585 static bool compareThisIfSameType(const T1 &a, const T1 &b) {
586 return &a == &b;
589 template <class T1, class T2>
590 static bool compareThisIfSameType(const T1 &a, const T2 &b) {
591 return false;
594 template <class OtherT> void moveConstruct(Expected<OtherT> &&Other) {
595 HasError = Other.HasError;
596 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
597 Unchecked = true;
598 Other.Unchecked = false;
599 #endif
601 if (!HasError)
602 new (getStorage()) storage_type(std::move(*Other.getStorage()));
603 else
604 new (getErrorStorage()) error_type(std::move(*Other.getErrorStorage()));
607 template <class OtherT> void moveAssign(Expected<OtherT> &&Other) {
608 assertIsChecked();
610 if (compareThisIfSameType(*this, Other))
611 return;
613 this->~Expected();
614 new (this) Expected(std::move(Other));
617 pointer toPointer(pointer Val) { return Val; }
619 const_pointer toPointer(const_pointer Val) const { return Val; }
621 pointer toPointer(wrap *Val) { return &Val->get(); }
623 const_pointer toPointer(const wrap *Val) const { return &Val->get(); }
625 storage_type *getStorage() {
626 assert(!HasError && "Cannot get value when an error exists!");
627 return reinterpret_cast<storage_type *>(TStorage.buffer);
630 const storage_type *getStorage() const {
631 assert(!HasError && "Cannot get value when an error exists!");
632 return reinterpret_cast<const storage_type *>(TStorage.buffer);
635 error_type *getErrorStorage() {
636 assert(HasError && "Cannot get error when a value exists!");
637 return reinterpret_cast<error_type *>(ErrorStorage.buffer);
640 const error_type *getErrorStorage() const {
641 assert(HasError && "Cannot get error when a value exists!");
642 return reinterpret_cast<const error_type *>(ErrorStorage.buffer);
645 // Used by ExpectedAsOutParameter to reset the checked flag.
646 void setUnchecked() {
647 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
648 Unchecked = true;
649 #endif
652 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
653 LLVM_ATTRIBUTE_NORETURN
654 LLVM_ATTRIBUTE_NOINLINE
655 void fatalUncheckedExpected() const {
656 dbgs() << "Expected<T> must be checked before access or destruction.\n";
657 if (HasError) {
658 dbgs() << "Unchecked Expected<T> contained error:\n";
659 (*getErrorStorage())->log(dbgs());
660 } else
661 dbgs() << "Expected<T> value was in success state. (Note: Expected<T> "
662 "values in success mode must still be checked prior to being "
663 "destroyed).\n";
664 abort();
666 #endif
668 void assertIsChecked() {
669 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
670 if (LLVM_UNLIKELY(Unchecked))
671 fatalUncheckedExpected();
672 #endif
675 union {
676 AlignedCharArrayUnion<storage_type> TStorage;
677 AlignedCharArrayUnion<error_type> ErrorStorage;
679 bool HasError : 1;
680 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
681 bool Unchecked : 1;
682 #endif
685 /// Report a serious error, calling any installed error handler. See
686 /// ErrorHandling.h.
687 LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err,
688 bool gen_crash_diag = true);
690 /// Report a fatal error if Err is a failure value.
692 /// This function can be used to wrap calls to fallible functions ONLY when it
693 /// is known that the Error will always be a success value. E.g.
695 /// @code{.cpp}
696 /// // foo only attempts the fallible operation if DoFallibleOperation is
697 /// // true. If DoFallibleOperation is false then foo always returns
698 /// // Error::success().
699 /// Error foo(bool DoFallibleOperation);
701 /// cantFail(foo(false));
702 /// @endcode
703 inline void cantFail(Error Err, const char *Msg = nullptr) {
704 if (Err) {
705 if (!Msg)
706 Msg = "Failure value returned from cantFail wrapped call";
707 #ifndef NDEBUG
708 std::string Str;
709 raw_string_ostream OS(Str);
710 OS << Msg << "\n" << Err;
711 Msg = OS.str().c_str();
712 #endif
713 llvm_unreachable(Msg);
717 /// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
718 /// returns the contained value.
720 /// This function can be used to wrap calls to fallible functions ONLY when it
721 /// is known that the Error will always be a success value. E.g.
723 /// @code{.cpp}
724 /// // foo only attempts the fallible operation if DoFallibleOperation is
725 /// // true. If DoFallibleOperation is false then foo always returns an int.
726 /// Expected<int> foo(bool DoFallibleOperation);
728 /// int X = cantFail(foo(false));
729 /// @endcode
730 template <typename T>
731 T cantFail(Expected<T> ValOrErr, const char *Msg = nullptr) {
732 if (ValOrErr)
733 return std::move(*ValOrErr);
734 else {
735 if (!Msg)
736 Msg = "Failure value returned from cantFail wrapped call";
737 #ifndef NDEBUG
738 std::string Str;
739 raw_string_ostream OS(Str);
740 auto E = ValOrErr.takeError();
741 OS << Msg << "\n" << E;
742 Msg = OS.str().c_str();
743 #endif
744 llvm_unreachable(Msg);
748 /// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
749 /// returns the contained reference.
751 /// This function can be used to wrap calls to fallible functions ONLY when it
752 /// is known that the Error will always be a success value. E.g.
754 /// @code{.cpp}
755 /// // foo only attempts the fallible operation if DoFallibleOperation is
756 /// // true. If DoFallibleOperation is false then foo always returns a Bar&.
757 /// Expected<Bar&> foo(bool DoFallibleOperation);
759 /// Bar &X = cantFail(foo(false));
760 /// @endcode
761 template <typename T>
762 T& cantFail(Expected<T&> ValOrErr, const char *Msg = nullptr) {
763 if (ValOrErr)
764 return *ValOrErr;
765 else {
766 if (!Msg)
767 Msg = "Failure value returned from cantFail wrapped call";
768 #ifndef NDEBUG
769 std::string Str;
770 raw_string_ostream OS(Str);
771 auto E = ValOrErr.takeError();
772 OS << Msg << "\n" << E;
773 Msg = OS.str().c_str();
774 #endif
775 llvm_unreachable(Msg);
779 /// Helper for testing applicability of, and applying, handlers for
780 /// ErrorInfo types.
781 template <typename HandlerT>
782 class ErrorHandlerTraits
783 : public ErrorHandlerTraits<decltype(
784 &std::remove_reference<HandlerT>::type::operator())> {};
786 // Specialization functions of the form 'Error (const ErrT&)'.
787 template <typename ErrT> class ErrorHandlerTraits<Error (&)(ErrT &)> {
788 public:
789 static bool appliesTo(const ErrorInfoBase &E) {
790 return E.template isA<ErrT>();
793 template <typename HandlerT>
794 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
795 assert(appliesTo(*E) && "Applying incorrect handler");
796 return H(static_cast<ErrT &>(*E));
800 // Specialization functions of the form 'void (const ErrT&)'.
801 template <typename ErrT> class ErrorHandlerTraits<void (&)(ErrT &)> {
802 public:
803 static bool appliesTo(const ErrorInfoBase &E) {
804 return E.template isA<ErrT>();
807 template <typename HandlerT>
808 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
809 assert(appliesTo(*E) && "Applying incorrect handler");
810 H(static_cast<ErrT &>(*E));
811 return Error::success();
815 /// Specialization for functions of the form 'Error (std::unique_ptr<ErrT>)'.
816 template <typename ErrT>
817 class ErrorHandlerTraits<Error (&)(std::unique_ptr<ErrT>)> {
818 public:
819 static bool appliesTo(const ErrorInfoBase &E) {
820 return E.template isA<ErrT>();
823 template <typename HandlerT>
824 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
825 assert(appliesTo(*E) && "Applying incorrect handler");
826 std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
827 return H(std::move(SubE));
831 /// Specialization for functions of the form 'void (std::unique_ptr<ErrT>)'.
832 template <typename ErrT>
833 class ErrorHandlerTraits<void (&)(std::unique_ptr<ErrT>)> {
834 public:
835 static bool appliesTo(const ErrorInfoBase &E) {
836 return E.template isA<ErrT>();
839 template <typename HandlerT>
840 static Error apply(HandlerT &&H, std::unique_ptr<ErrorInfoBase> E) {
841 assert(appliesTo(*E) && "Applying incorrect handler");
842 std::unique_ptr<ErrT> SubE(static_cast<ErrT *>(E.release()));
843 H(std::move(SubE));
844 return Error::success();
848 // Specialization for member functions of the form 'RetT (const ErrT&)'.
849 template <typename C, typename RetT, typename ErrT>
850 class ErrorHandlerTraits<RetT (C::*)(ErrT &)>
851 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
853 // Specialization for member functions of the form 'RetT (const ErrT&) const'.
854 template <typename C, typename RetT, typename ErrT>
855 class ErrorHandlerTraits<RetT (C::*)(ErrT &) const>
856 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
858 // Specialization for member functions of the form 'RetT (const ErrT&)'.
859 template <typename C, typename RetT, typename ErrT>
860 class ErrorHandlerTraits<RetT (C::*)(const ErrT &)>
861 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
863 // Specialization for member functions of the form 'RetT (const ErrT&) const'.
864 template <typename C, typename RetT, typename ErrT>
865 class ErrorHandlerTraits<RetT (C::*)(const ErrT &) const>
866 : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
868 /// Specialization for member functions of the form
869 /// 'RetT (std::unique_ptr<ErrT>)'.
870 template <typename C, typename RetT, typename ErrT>
871 class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>)>
872 : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
874 /// Specialization for member functions of the form
875 /// 'RetT (std::unique_ptr<ErrT>) const'.
876 template <typename C, typename RetT, typename ErrT>
877 class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>) const>
878 : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
880 inline Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload) {
881 return Error(std::move(Payload));
884 template <typename HandlerT, typename... HandlerTs>
885 Error handleErrorImpl(std::unique_ptr<ErrorInfoBase> Payload,
886 HandlerT &&Handler, HandlerTs &&... Handlers) {
887 if (ErrorHandlerTraits<HandlerT>::appliesTo(*Payload))
888 return ErrorHandlerTraits<HandlerT>::apply(std::forward<HandlerT>(Handler),
889 std::move(Payload));
890 return handleErrorImpl(std::move(Payload),
891 std::forward<HandlerTs>(Handlers)...);
894 /// Pass the ErrorInfo(s) contained in E to their respective handlers. Any
895 /// unhandled errors (or Errors returned by handlers) are re-concatenated and
896 /// returned.
897 /// Because this function returns an error, its result must also be checked
898 /// or returned. If you intend to handle all errors use handleAllErrors
899 /// (which returns void, and will abort() on unhandled errors) instead.
900 template <typename... HandlerTs>
901 Error handleErrors(Error E, HandlerTs &&... Hs) {
902 if (!E)
903 return Error::success();
905 std::unique_ptr<ErrorInfoBase> Payload = E.takePayload();
907 if (Payload->isA<ErrorList>()) {
908 ErrorList &List = static_cast<ErrorList &>(*Payload);
909 Error R;
910 for (auto &P : List.Payloads)
911 R = ErrorList::join(
912 std::move(R),
913 handleErrorImpl(std::move(P), std::forward<HandlerTs>(Hs)...));
914 return R;
917 return handleErrorImpl(std::move(Payload), std::forward<HandlerTs>(Hs)...);
920 /// Behaves the same as handleErrors, except that by contract all errors
921 /// *must* be handled by the given handlers (i.e. there must be no remaining
922 /// errors after running the handlers, or llvm_unreachable is called).
923 template <typename... HandlerTs>
924 void handleAllErrors(Error E, HandlerTs &&... Handlers) {
925 cantFail(handleErrors(std::move(E), std::forward<HandlerTs>(Handlers)...));
928 /// Check that E is a non-error, then drop it.
929 /// If E is an error, llvm_unreachable will be called.
930 inline void handleAllErrors(Error E) {
931 cantFail(std::move(E));
934 /// Handle any errors (if present) in an Expected<T>, then try a recovery path.
936 /// If the incoming value is a success value it is returned unmodified. If it
937 /// is a failure value then it the contained error is passed to handleErrors.
938 /// If handleErrors is able to handle the error then the RecoveryPath functor
939 /// is called to supply the final result. If handleErrors is not able to
940 /// handle all errors then the unhandled errors are returned.
942 /// This utility enables the follow pattern:
944 /// @code{.cpp}
945 /// enum FooStrategy { Aggressive, Conservative };
946 /// Expected<Foo> foo(FooStrategy S);
948 /// auto ResultOrErr =
949 /// handleExpected(
950 /// foo(Aggressive),
951 /// []() { return foo(Conservative); },
952 /// [](AggressiveStrategyError&) {
953 /// // Implicitly conusme this - we'll recover by using a conservative
954 /// // strategy.
955 /// });
957 /// @endcode
958 template <typename T, typename RecoveryFtor, typename... HandlerTs>
959 Expected<T> handleExpected(Expected<T> ValOrErr, RecoveryFtor &&RecoveryPath,
960 HandlerTs &&... Handlers) {
961 if (ValOrErr)
962 return ValOrErr;
964 if (auto Err = handleErrors(ValOrErr.takeError(),
965 std::forward<HandlerTs>(Handlers)...))
966 return std::move(Err);
968 return RecoveryPath();
971 /// Log all errors (if any) in E to OS. If there are any errors, ErrorBanner
972 /// will be printed before the first one is logged. A newline will be printed
973 /// after each error.
975 /// This function is compatible with the helpers from Support/WithColor.h. You
976 /// can pass any of them as the OS. Please consider using them instead of
977 /// including 'error: ' in the ErrorBanner.
979 /// This is useful in the base level of your program to allow clean termination
980 /// (allowing clean deallocation of resources, etc.), while reporting error
981 /// information to the user.
982 void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner = {});
984 /// Write all error messages (if any) in E to a string. The newline character
985 /// is used to separate error messages.
986 inline std::string toString(Error E) {
987 SmallVector<std::string, 2> Errors;
988 handleAllErrors(std::move(E), [&Errors](const ErrorInfoBase &EI) {
989 Errors.push_back(EI.message());
991 return join(Errors.begin(), Errors.end(), "\n");
994 /// Consume a Error without doing anything. This method should be used
995 /// only where an error can be considered a reasonable and expected return
996 /// value.
998 /// Uses of this method are potentially indicative of design problems: If it's
999 /// legitimate to do nothing while processing an "error", the error-producer
1000 /// might be more clearly refactored to return an Optional<T>.
1001 inline void consumeError(Error Err) {
1002 handleAllErrors(std::move(Err), [](const ErrorInfoBase &) {});
1005 /// Convert an Expected to an Optional without doing anything. This method
1006 /// should be used only where an error can be considered a reasonable and
1007 /// expected return value.
1009 /// Uses of this method are potentially indicative of problems: perhaps the
1010 /// error should be propagated further, or the error-producer should just
1011 /// return an Optional in the first place.
1012 template <typename T> Optional<T> expectedToOptional(Expected<T> &&E) {
1013 if (E)
1014 return std::move(*E);
1015 consumeError(E.takeError());
1016 return None;
1019 /// Helper for converting an Error to a bool.
1021 /// This method returns true if Err is in an error state, or false if it is
1022 /// in a success state. Puts Err in a checked state in both cases (unlike
1023 /// Error::operator bool(), which only does this for success states).
1024 inline bool errorToBool(Error Err) {
1025 bool IsError = static_cast<bool>(Err);
1026 if (IsError)
1027 consumeError(std::move(Err));
1028 return IsError;
1031 /// Helper for Errors used as out-parameters.
1033 /// This helper is for use with the Error-as-out-parameter idiom, where an error
1034 /// is passed to a function or method by reference, rather than being returned.
1035 /// In such cases it is helpful to set the checked bit on entry to the function
1036 /// so that the error can be written to (unchecked Errors abort on assignment)
1037 /// and clear the checked bit on exit so that clients cannot accidentally forget
1038 /// to check the result. This helper performs these actions automatically using
1039 /// RAII:
1041 /// @code{.cpp}
1042 /// Result foo(Error &Err) {
1043 /// ErrorAsOutParameter ErrAsOutParam(&Err); // 'Checked' flag set
1044 /// // <body of foo>
1045 /// // <- 'Checked' flag auto-cleared when ErrAsOutParam is destructed.
1046 /// }
1047 /// @endcode
1049 /// ErrorAsOutParameter takes an Error* rather than Error& so that it can be
1050 /// used with optional Errors (Error pointers that are allowed to be null). If
1051 /// ErrorAsOutParameter took an Error reference, an instance would have to be
1052 /// created inside every condition that verified that Error was non-null. By
1053 /// taking an Error pointer we can just create one instance at the top of the
1054 /// function.
1055 class ErrorAsOutParameter {
1056 public:
1057 ErrorAsOutParameter(Error *Err) : Err(Err) {
1058 // Raise the checked bit if Err is success.
1059 if (Err)
1060 (void)!!*Err;
1063 ~ErrorAsOutParameter() {
1064 // Clear the checked bit.
1065 if (Err && !*Err)
1066 *Err = Error::success();
1069 private:
1070 Error *Err;
1073 /// Helper for Expected<T>s used as out-parameters.
1075 /// See ErrorAsOutParameter.
1076 template <typename T>
1077 class ExpectedAsOutParameter {
1078 public:
1079 ExpectedAsOutParameter(Expected<T> *ValOrErr)
1080 : ValOrErr(ValOrErr) {
1081 if (ValOrErr)
1082 (void)!!*ValOrErr;
1085 ~ExpectedAsOutParameter() {
1086 if (ValOrErr)
1087 ValOrErr->setUnchecked();
1090 private:
1091 Expected<T> *ValOrErr;
1094 /// This class wraps a std::error_code in a Error.
1096 /// This is useful if you're writing an interface that returns a Error
1097 /// (or Expected) and you want to call code that still returns
1098 /// std::error_codes.
1099 class ECError : public ErrorInfo<ECError> {
1100 friend Error errorCodeToError(std::error_code);
1102 virtual void anchor() override;
1104 public:
1105 void setErrorCode(std::error_code EC) { this->EC = EC; }
1106 std::error_code convertToErrorCode() const override { return EC; }
1107 void log(raw_ostream &OS) const override { OS << EC.message(); }
1109 // Used by ErrorInfo::classID.
1110 static char ID;
1112 protected:
1113 ECError() = default;
1114 ECError(std::error_code EC) : EC(EC) {}
1116 std::error_code EC;
1119 /// The value returned by this function can be returned from convertToErrorCode
1120 /// for Error values where no sensible translation to std::error_code exists.
1121 /// It should only be used in this situation, and should never be used where a
1122 /// sensible conversion to std::error_code is available, as attempts to convert
1123 /// to/from this error will result in a fatal error. (i.e. it is a programmatic
1124 ///error to try to convert such a value).
1125 std::error_code inconvertibleErrorCode();
1127 /// Helper for converting an std::error_code to a Error.
1128 Error errorCodeToError(std::error_code EC);
1130 /// Helper for converting an ECError to a std::error_code.
1132 /// This method requires that Err be Error() or an ECError, otherwise it
1133 /// will trigger a call to abort().
1134 std::error_code errorToErrorCode(Error Err);
1136 /// Convert an ErrorOr<T> to an Expected<T>.
1137 template <typename T> Expected<T> errorOrToExpected(ErrorOr<T> &&EO) {
1138 if (auto EC = EO.getError())
1139 return errorCodeToError(EC);
1140 return std::move(*EO);
1143 /// Convert an Expected<T> to an ErrorOr<T>.
1144 template <typename T> ErrorOr<T> expectedToErrorOr(Expected<T> &&E) {
1145 if (auto Err = E.takeError())
1146 return errorToErrorCode(std::move(Err));
1147 return std::move(*E);
1150 /// This class wraps a string in an Error.
1152 /// StringError is useful in cases where the client is not expected to be able
1153 /// to consume the specific error message programmatically (for example, if the
1154 /// error message is to be presented to the user).
1156 /// StringError can also be used when additional information is to be printed
1157 /// along with a error_code message. Depending on the constructor called, this
1158 /// class can either display:
1159 /// 1. the error_code message (ECError behavior)
1160 /// 2. a string
1161 /// 3. the error_code message and a string
1163 /// These behaviors are useful when subtyping is required; for example, when a
1164 /// specific library needs an explicit error type. In the example below,
1165 /// PDBError is derived from StringError:
1167 /// @code{.cpp}
1168 /// Expected<int> foo() {
1169 /// return llvm::make_error<PDBError>(pdb_error_code::dia_failed_loading,
1170 /// "Additional information");
1171 /// }
1172 /// @endcode
1174 class StringError : public ErrorInfo<StringError> {
1175 public:
1176 static char ID;
1178 // Prints EC + S and converts to EC
1179 StringError(std::error_code EC, const Twine &S = Twine());
1181 // Prints S and converts to EC
1182 StringError(const Twine &S, std::error_code EC);
1184 void log(raw_ostream &OS) const override;
1185 std::error_code convertToErrorCode() const override;
1187 const std::string &getMessage() const { return Msg; }
1189 private:
1190 std::string Msg;
1191 std::error_code EC;
1192 const bool PrintMsgOnly = false;
1195 /// Create formatted StringError object.
1196 template <typename... Ts>
1197 inline Error createStringError(std::error_code EC, char const *Fmt,
1198 const Ts &... Vals) {
1199 std::string Buffer;
1200 raw_string_ostream Stream(Buffer);
1201 Stream << format(Fmt, Vals...);
1202 return make_error<StringError>(Stream.str(), EC);
1205 Error createStringError(std::error_code EC, char const *Msg);
1207 inline Error createStringError(std::error_code EC, const Twine &S) {
1208 return createStringError(EC, S.str().c_str());
1211 template <typename... Ts>
1212 inline Error createStringError(std::errc EC, char const *Fmt,
1213 const Ts &... Vals) {
1214 return createStringError(std::make_error_code(EC), Fmt, Vals...);
1217 /// This class wraps a filename and another Error.
1219 /// In some cases, an error needs to live along a 'source' name, in order to
1220 /// show more detailed information to the user.
1221 class FileError final : public ErrorInfo<FileError> {
1223 friend Error createFileError(const Twine &, Error);
1224 friend Error createFileError(const Twine &, size_t, Error);
1226 public:
1227 void log(raw_ostream &OS) const override {
1228 assert(Err && !FileName.empty() && "Trying to log after takeError().");
1229 OS << "'" << FileName << "': ";
1230 if (Line.hasValue())
1231 OS << "line " << Line.getValue() << ": ";
1232 Err->log(OS);
1235 Error takeError() { return Error(std::move(Err)); }
1237 std::error_code convertToErrorCode() const override;
1239 // Used by ErrorInfo::classID.
1240 static char ID;
1242 private:
1243 FileError(const Twine &F, Optional<size_t> LineNum,
1244 std::unique_ptr<ErrorInfoBase> E) {
1245 assert(E && "Cannot create FileError from Error success value.");
1246 assert(!F.isTriviallyEmpty() &&
1247 "The file name provided to FileError must not be empty.");
1248 FileName = F.str();
1249 Err = std::move(E);
1250 Line = std::move(LineNum);
1253 static Error build(const Twine &F, Optional<size_t> Line, Error E) {
1254 return Error(
1255 std::unique_ptr<FileError>(new FileError(F, Line, E.takePayload())));
1258 std::string FileName;
1259 Optional<size_t> Line;
1260 std::unique_ptr<ErrorInfoBase> Err;
1263 /// Concatenate a source file path and/or name with an Error. The resulting
1264 /// Error is unchecked.
1265 inline Error createFileError(const Twine &F, Error E) {
1266 return FileError::build(F, Optional<size_t>(), std::move(E));
1269 /// Concatenate a source file path and/or name with line number and an Error.
1270 /// The resulting Error is unchecked.
1271 inline Error createFileError(const Twine &F, size_t Line, Error E) {
1272 return FileError::build(F, Optional<size_t>(Line), std::move(E));
1275 /// Concatenate a source file path and/or name with a std::error_code
1276 /// to form an Error object.
1277 inline Error createFileError(const Twine &F, std::error_code EC) {
1278 return createFileError(F, errorCodeToError(EC));
1281 /// Concatenate a source file path and/or name with line number and
1282 /// std::error_code to form an Error object.
1283 inline Error createFileError(const Twine &F, size_t Line, std::error_code EC) {
1284 return createFileError(F, Line, errorCodeToError(EC));
1287 Error createFileError(const Twine &F, ErrorSuccess) = delete;
1289 /// Helper for check-and-exit error handling.
1291 /// For tool use only. NOT FOR USE IN LIBRARY CODE.
1293 class ExitOnError {
1294 public:
1295 /// Create an error on exit helper.
1296 ExitOnError(std::string Banner = "", int DefaultErrorExitCode = 1)
1297 : Banner(std::move(Banner)),
1298 GetExitCode([=](const Error &) { return DefaultErrorExitCode; }) {}
1300 /// Set the banner string for any errors caught by operator().
1301 void setBanner(std::string Banner) { this->Banner = std::move(Banner); }
1303 /// Set the exit-code mapper function.
1304 void setExitCodeMapper(std::function<int(const Error &)> GetExitCode) {
1305 this->GetExitCode = std::move(GetExitCode);
1308 /// Check Err. If it's in a failure state log the error(s) and exit.
1309 void operator()(Error Err) const { checkError(std::move(Err)); }
1311 /// Check E. If it's in a success state then return the contained value. If
1312 /// it's in a failure state log the error(s) and exit.
1313 template <typename T> T operator()(Expected<T> &&E) const {
1314 checkError(E.takeError());
1315 return std::move(*E);
1318 /// Check E. If it's in a success state then return the contained reference. If
1319 /// it's in a failure state log the error(s) and exit.
1320 template <typename T> T& operator()(Expected<T&> &&E) const {
1321 checkError(E.takeError());
1322 return *E;
1325 private:
1326 void checkError(Error Err) const {
1327 if (Err) {
1328 int ExitCode = GetExitCode(Err);
1329 logAllUnhandledErrors(std::move(Err), errs(), Banner);
1330 exit(ExitCode);
1334 std::string Banner;
1335 std::function<int(const Error &)> GetExitCode;
1338 /// Conversion from Error to LLVMErrorRef for C error bindings.
1339 inline LLVMErrorRef wrap(Error Err) {
1340 return reinterpret_cast<LLVMErrorRef>(Err.takePayload().release());
1343 /// Conversion from LLVMErrorRef to Error for C error bindings.
1344 inline Error unwrap(LLVMErrorRef ErrRef) {
1345 return Error(std::unique_ptr<ErrorInfoBase>(
1346 reinterpret_cast<ErrorInfoBase *>(ErrRef)));
1349 } // end namespace llvm
1351 #endif // LLVM_SUPPORT_ERROR_H