dom/bindings/ErrorResult.h
author James Teh <jteh@mozilla.com>
Thu, 07 Mar 2019 18:10:13 +0000
changeset 520910 c26d4a8d43c4d0d6f6e13135b8f35924123fe99e
parent 511623 5f4630838d46dd81dadb13220a4af0da9e23a619
permissions -rw-r--r--
Bug 1527922: Ensure the Reload button is disabled when testing against blank tabs in the browser toolbar key nav tests. r=Gijs For a blank tab, the Reload button should be disabled. These tests depend on this. This seems to be true when setting the new tab page to blank in Firefox Options. However, when we open about:blank with BrowserTestUtils.withNewTab, this is unreliable. That is, sometimes the Reload button is enabled, sometimes it isn't. I don't understand why this happens. For the purposes of these tests, just force the Reload button to be disabled for new, blank tabs so we get consistent results. Differential Revision: https://phabricator.services.mozilla.com/D22449

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * A set of structs for tracking exceptions that need to be thrown to JS:
 * ErrorResult and IgnoredErrorResult.
 *
 * Conceptually, these structs represent either success or an exception in the
 * process of being thrown.  This means that a failing ErrorResult _must_ be
 * handled in one of the following ways before coming off the stack:
 *
 * 1) Suppressed via SuppressException().
 * 2) Converted to a pure nsresult return value via StealNSResult().
 * 3) Converted to an actual pending exception on a JSContext via
 *    MaybeSetPendingException.
 * 4) Converted to an exception JS::Value (probably to then reject a Promise
 *    with) via dom::ToJSValue.
 *
 * An IgnoredErrorResult will automatically do the first of those four things.
 */

#ifndef mozilla_ErrorResult_h
#define mozilla_ErrorResult_h

#include <new>
#include <stdarg.h>

#include "js/GCAnnotations.h"
#include "js/Value.h"
#include "nscore.h"
#include "nsString.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/Move.h"
#include "nsTArray.h"
#include "nsISupportsImpl.h"

namespace IPC {
class Message;
template <typename>
struct ParamTraits;
}  // namespace IPC
class PickleIterator;

namespace mozilla {

namespace dom {

enum ErrNum {
#define MSG_DEF(_name, _argc, _exn, _str) _name,
#include "mozilla/dom/Errors.msg"
#undef MSG_DEF
  Err_Limit
};

// Debug-only compile-time table of the number of arguments of each error, for
// use in static_assert.
#if defined(DEBUG) && (defined(__clang__) || defined(__GNUC__))
uint16_t constexpr ErrorFormatNumArgs[] = {
#  define MSG_DEF(_name, _argc, _exn, _str) _argc,
#  include "mozilla/dom/Errors.msg"
#  undef MSG_DEF
};
#endif

uint16_t GetErrorArgCount(const ErrNum aErrorNumber);

namespace binding_detail {
void ThrowErrorMessage(JSContext* aCx, const unsigned aErrorNumber, ...);
}  // namespace binding_detail

template <typename... Ts>
inline bool ThrowErrorMessage(JSContext* aCx, const ErrNum aErrorNumber,
                              Ts&&... aArgs) {
  binding_detail::ThrowErrorMessage(aCx, static_cast<unsigned>(aErrorNumber),
                                    std::forward<Ts>(aArgs)...);
  return false;
}

struct StringArrayAppender {
  static void Append(nsTArray<nsString>& aArgs, uint16_t aCount) {
    MOZ_RELEASE_ASSERT(aCount == 0,
                       "Must give at least as many string arguments as are "
                       "required by the ErrNum.");
  }

  template <typename... Ts>
  static void Append(nsTArray<nsString>& aArgs, uint16_t aCount,
                     const nsAString& aFirst, Ts&&... aOtherArgs) {
    if (aCount == 0) {
      MOZ_ASSERT(false,
                 "There should not be more string arguments provided than are "
                 "required by the ErrNum.");
      return;
    }
    aArgs.AppendElement(aFirst);
    Append(aArgs, aCount - 1, std::forward<Ts>(aOtherArgs)...);
  }
};

}  // namespace dom

class ErrorResult;
class OOMReporter;

namespace binding_danger {

/**
 * Templated implementation class for various ErrorResult-like things.  The
 * instantiations differ only in terms of their cleanup policies (used in the
 * destructor), which they can specify via the template argument.  Note that
 * this means it's safe to reinterpret_cast between the instantiations unless
 * you plan to invoke the destructor through such a cast pointer.
 *
 * A cleanup policy consists of two booleans: whether to assert that we've been
 * reported or suppressed, and whether to then go ahead and suppress the
 * exception.
 */
template <typename CleanupPolicy>
class TErrorResult {
 public:
  TErrorResult()
      : mResult(NS_OK)
#ifdef DEBUG
        ,
        mMightHaveUnreportedJSException(false),
        mUnionState(HasNothing)
#endif
  {
  }

  ~TErrorResult() {
    AssertInOwningThread();

    if (CleanupPolicy::assertHandled) {
      // Consumers should have called one of MaybeSetPendingException
      // (possibly via ToJSValue), StealNSResult, and SuppressException
      AssertReportedOrSuppressed();
    }

    if (CleanupPolicy::suppress) {
      SuppressException();
    }

    // And now assert that we're in a good final state.
    AssertReportedOrSuppressed();
  }

  TErrorResult(TErrorResult&& aRHS)
      // Initialize mResult and whatever else we need to default-initialize, so
      // the ClearUnionData call in our operator= will do the right thing
      // (nothing).
      : TErrorResult() {
    *this = std::move(aRHS);
  }
  TErrorResult& operator=(TErrorResult&& aRHS);

  explicit TErrorResult(nsresult aRv) : TErrorResult() { AssignErrorCode(aRv); }

  operator ErrorResult&();
  operator const ErrorResult&() const;
  operator OOMReporter&();

  void MOZ_MUST_RETURN_FROM_CALLER Throw(nsresult rv) {
    MOZ_ASSERT(NS_FAILED(rv), "Please don't try throwing success");
    AssignErrorCode(rv);
  }

  // This method acts identically to the `Throw` method, however, it does not
  // have the MOZ_MUST_RETURN_FROM_CALLER static analysis annotation. It is
  // intended to be used in situations when additional work needs to be
  // performed in the calling function after the Throw method is called.
  //
  // In general you should prefer using `Throw`, and returning after an error,
  // for example:
  //
  //   if (condition) {
  //     aRv.Throw(NS_ERROR_FAILURE);
  //     return;
  //   }
  //
  // or
  //
  //   if (condition) {
  //     aRv.Throw(NS_ERROR_FAILURE);
  //   }
  //   return;
  //
  // However, if you need to do some other work after throwing, such as:
  //
  //   if (condition) {
  //     aRv.ThrowWithCustomCleanup(NS_ERROR_FAILURE);
  //   }
  //   // Do some important clean-up work which couldn't happen earlier.
  //   // We want to do this clean-up work in both the success and failure
  //   cases. CleanUpImportantState(); return;
  //
  // Then you'll need to use ThrowWithCustomCleanup to get around the static
  // analysis, which would complain that you are doing work after the call to
  // `Throw()`.
  void ThrowWithCustomCleanup(nsresult rv) { Throw(rv); }

  // Duplicate our current state on the given TErrorResult object.  Any
  // existing errors or messages on the target will be suppressed before
  // cloning.  Our own error state remains unchanged.
  void CloneTo(TErrorResult& aRv) const;

  // Use SuppressException when you want to suppress any exception that might be
  // on the TErrorResult.  After this call, the TErrorResult will be back a "no
  // exception thrown" state.
  void SuppressException();

  // Use StealNSResult() when you want to safely convert the TErrorResult to
  // an nsresult that you will then return to a caller.  This will
  // SuppressException(), since there will no longer be a way to report it.
  nsresult StealNSResult() {
    nsresult rv = ErrorCode();
    SuppressException();
    // Don't propagate out our internal error codes that have special meaning.
    if (rv == NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR ||
        rv == NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR ||
        rv == NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION ||
        rv == NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION) {
      // What to pick here?
      return NS_ERROR_DOM_INVALID_STATE_ERR;
    }

    return rv;
  }

  // Use MaybeSetPendingException to convert a TErrorResult to a pending
  // exception on the given JSContext.  This is the normal "throw an exception"
  // codepath.
  //
  // The return value is false if the TErrorResult represents success, true
  // otherwise.  This does mean that in JSAPI method implementations you can't
  // just use this as |return rv.MaybeSetPendingException(cx)| (though you could
  // |return !rv.MaybeSetPendingException(cx)|), but in practice pretty much any
  // consumer would want to do some more work on the success codepath.  So
  // instead the way you use this is:
  //
  //   if (rv.MaybeSetPendingException(cx)) {
  //     bail out here
  //   }
  //   go on to do something useful
  //
  // The success path is inline, since it should be the common case and we don't
  // want to pay the price of a function call in some of the consumers of this
  // method in the common case.
  //
  // Note that a true return value does NOT mean there is now a pending
  // exception on aCx, due to uncatchable exceptions.  It should still be
  // considered equivalent to a JSAPI failure in terms of what callers should do
  // after true is returned.
  //
  // After this call, the TErrorResult will no longer return true from Failed(),
  // since the exception will have moved to the JSContext.
  MOZ_MUST_USE
  bool MaybeSetPendingException(JSContext* cx) {
    WouldReportJSException();
    if (!Failed()) {
      return false;
    }

    SetPendingException(cx);
    return true;
  }

  // Use StealExceptionFromJSContext to convert a pending exception on a
  // JSContext to a TErrorResult.  This function must be called only when a
  // JSAPI operation failed.  It assumes that lack of pending exception on the
  // JSContext means an uncatchable exception was thrown.
  //
  // Codepaths that might call this method must call MightThrowJSException even
  // if the relevant JSAPI calls do not fail.
  //
  // When this function returns, JS_IsExceptionPending(cx) will definitely be
  // false.
  void StealExceptionFromJSContext(JSContext* cx);

  template <dom::ErrNum errorNumber, typename... Ts>
  void ThrowTypeError(Ts&&... messageArgs) {
    ThrowErrorWithMessage<errorNumber>(NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR,
                                       std::forward<Ts>(messageArgs)...);
  }

  template <dom::ErrNum errorNumber, typename... Ts>
  void ThrowRangeError(Ts&&... messageArgs) {
    ThrowErrorWithMessage<errorNumber>(NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR,
                                       std::forward<Ts>(messageArgs)...);
  }

  bool IsErrorWithMessage() const {
    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR ||
           ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR;
  }

  // Facilities for throwing a preexisting JS exception value via this
  // TErrorResult.  The contract is that any code which might end up calling
  // ThrowJSException() or StealExceptionFromJSContext() must call
  // MightThrowJSException() even if no exception is being thrown.  Code that
  // conditionally calls ToJSValue on this TErrorResult only if Failed() must
  // first call WouldReportJSException even if this TErrorResult has not failed.
  //
  // The exn argument to ThrowJSException can be in any compartment.  It does
  // not have to be in the compartment of cx.  If someone later uses it, they
  // will wrap it into whatever compartment they're working in, as needed.
  void ThrowJSException(JSContext* cx, JS::Handle<JS::Value> exn);
  bool IsJSException() const {
    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION;
  }

  // Facilities for throwing a DOMException.  If an empty message string is
  // passed to ThrowDOMException, the default message string for the given
  // nsresult will be used.  The passed-in string must be UTF-8.  The nsresult
  // passed in must be one we create DOMExceptions for; otherwise you may get an
  // XPConnect Exception.
  void ThrowDOMException(nsresult rv,
                         const nsACString& message = EmptyCString());
  bool IsDOMException() const {
    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION;
  }

  // Flag on the TErrorResult that whatever needs throwing has been
  // thrown on the JSContext already and we should not mess with it.
  // If nothing was thrown, this becomes an uncatchable exception.
  void NoteJSContextException(JSContext* aCx);

  // Check whether the TErrorResult says to just throw whatever is on
  // the JSContext already.
  bool IsJSContextException() {
    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_EXCEPTION_ON_JSCONTEXT;
  }

  // Support for uncatchable exceptions.
  void MOZ_MUST_RETURN_FROM_CALLER ThrowUncatchableException() {
    Throw(NS_ERROR_UNCATCHABLE_EXCEPTION);
  }
  bool IsUncatchableException() const {
    return ErrorCode() == NS_ERROR_UNCATCHABLE_EXCEPTION;
  }

  void MOZ_ALWAYS_INLINE MightThrowJSException() {
#ifdef DEBUG
    mMightHaveUnreportedJSException = true;
#endif
  }
  void MOZ_ALWAYS_INLINE WouldReportJSException() {
#ifdef DEBUG
    mMightHaveUnreportedJSException = false;
#endif
  }

  // In the future, we can add overloads of Throw that take more
  // interesting things, like strings or DOM exception types or
  // something if desired.

  // Backwards-compat to make conversion simpler.  We don't call
  // Throw() here because people can easily pass success codes to
  // this.
  void operator=(nsresult rv) { AssignErrorCode(rv); }

  bool Failed() const { return NS_FAILED(mResult); }

  bool ErrorCodeIs(nsresult rv) const { return mResult == rv; }

  // For use in logging ONLY.
  uint32_t ErrorCodeAsInt() const { return static_cast<uint32_t>(ErrorCode()); }

  bool operator==(const ErrorResult& aRight) const;

 protected:
  nsresult ErrorCode() const { return mResult; }

 private:
#ifdef DEBUG
  enum UnionState {
    HasMessage,
    HasDOMExceptionInfo,
    HasJSException,
    HasNothing
  };
#endif  // DEBUG

  friend struct IPC::ParamTraits<TErrorResult>;
  friend struct IPC::ParamTraits<ErrorResult>;
  void SerializeMessage(IPC::Message* aMsg) const;
  bool DeserializeMessage(const IPC::Message* aMsg, PickleIterator* aIter);

  void SerializeDOMExceptionInfo(IPC::Message* aMsg) const;
  bool DeserializeDOMExceptionInfo(const IPC::Message* aMsg,
                                   PickleIterator* aIter);

  // Helper method that creates a new Message for this TErrorResult,
  // and returns the arguments array from that Message.
  nsTArray<nsString>& CreateErrorMessageHelper(const dom::ErrNum errorNumber,
                                               nsresult errorType);

  template <dom::ErrNum errorNumber, typename... Ts>
  void ThrowErrorWithMessage(nsresult errorType, Ts&&... messageArgs) {
#if defined(DEBUG) && (defined(__clang__) || defined(__GNUC__))
    static_assert(
        dom::ErrorFormatNumArgs[errorNumber] == sizeof...(messageArgs),
        "Pass in the right number of arguments");
#endif

    ClearUnionData();

    nsTArray<nsString>& messageArgsArray =
        CreateErrorMessageHelper(errorNumber, errorType);
    uint16_t argCount = dom::GetErrorArgCount(errorNumber);
    dom::StringArrayAppender::Append(messageArgsArray, argCount,
                                     std::forward<Ts>(messageArgs)...);
#ifdef DEBUG
    mUnionState = HasMessage;
#endif  // DEBUG
  }

  MOZ_ALWAYS_INLINE void AssertInOwningThread() const {
#ifdef DEBUG
    if (CleanupPolicy::assertSameThread) {
      NS_ASSERT_OWNINGTHREAD(TErrorResult);
    }
#endif
  }

  void AssignErrorCode(nsresult aRv) {
    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR,
               "Use ThrowTypeError()");
    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR,
               "Use ThrowRangeError()");
    MOZ_ASSERT(!IsErrorWithMessage(), "Don't overwrite errors with message");
    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION,
               "Use ThrowJSException()");
    MOZ_ASSERT(!IsJSException(), "Don't overwrite JS exceptions");
    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION,
               "Use ThrowDOMException()");
    MOZ_ASSERT(!IsDOMException(), "Don't overwrite DOM exceptions");
    MOZ_ASSERT(aRv != NS_ERROR_XPC_NOT_ENOUGH_ARGS,
               "May need to bring back ThrowNotEnoughArgsError");
    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_EXCEPTION_ON_JSCONTEXT,
               "Use NoteJSContextException");
    mResult = aRv;
  }

  void ClearMessage();
  void ClearDOMExceptionInfo();

  // ClearUnionData will try to clear the data in our mExtra union.  After this
  // the union may be in an uninitialized state (e.g. mMessage or
  // mDOMExceptionInfo may point to deleted memory, or mJSException may be a
  // JS::Value containing an invalid gcthing) and the caller must either
  // reinitialize it or change mResult to something that will not involve us
  // touching the union anymore.
  void ClearUnionData();

  // Implementation of MaybeSetPendingException for the case when we're a
  // failure result.
  void SetPendingException(JSContext* cx);

  // Methods for setting various specific kinds of pending exceptions.
  void SetPendingExceptionWithMessage(JSContext* cx);
  void SetPendingJSException(JSContext* cx);
  void SetPendingDOMException(JSContext* cx);
  void SetPendingGenericErrorException(JSContext* cx);

  MOZ_ALWAYS_INLINE void AssertReportedOrSuppressed() {
    MOZ_ASSERT(!Failed());
    MOZ_ASSERT(!mMightHaveUnreportedJSException);
    MOZ_ASSERT(mUnionState == HasNothing);
  }

  // Special values of mResult:
  // NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR -- ThrowTypeError() called on us.
  // NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR -- ThrowRangeError() called on us.
  // NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION -- ThrowJSException() called
  //                                               on us.
  // NS_ERROR_UNCATCHABLE_EXCEPTION -- ThrowUncatchableException called on us.
  // NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION -- ThrowDOMException() called
  //                                               on us.
  nsresult mResult;

  struct Message;
  struct DOMExceptionInfo;
  union Extra {
    // mMessage is set by ThrowErrorWithMessage and reported (and deallocated)
    // by SetPendingExceptionWithMessage.
    MOZ_INIT_OUTSIDE_CTOR
    Message* mMessage;  // valid when IsErrorWithMessage()

    // mJSException is set (and rooted) by ThrowJSException and reported (and
    // unrooted) by SetPendingJSException.
    MOZ_INIT_OUTSIDE_CTOR
    JS::Value mJSException;  // valid when IsJSException()

    // mDOMExceptionInfo is set by ThrowDOMException and reported (and
    // deallocated) by SetPendingDOMException.
    MOZ_INIT_OUTSIDE_CTOR
    DOMExceptionInfo* mDOMExceptionInfo;  // valid when IsDOMException()

    // |mJSException| has a non-trivial constructor and therefore MUST be
    // placement-new'd into existence.
    MOZ_PUSH_DISABLE_NONTRIVIAL_UNION_WARNINGS
    Extra() {}
    MOZ_POP_DISABLE_NONTRIVIAL_UNION_WARNINGS
  } mExtra;

  Message* InitMessage(Message* aMessage) {
    // The |new| here switches the active arm of |mExtra|, from the compiler's
    // point of view.  Mere assignment *won't* necessarily do the right thing!
    new (&mExtra.mMessage) Message*(aMessage);
    return mExtra.mMessage;
  }

  JS::Value& InitJSException() {
    // The |new| here switches the active arm of |mExtra|, from the compiler's
    // point of view.  Mere assignment *won't* necessarily do the right thing!
    new (&mExtra.mJSException) JS::Value();  // sets to undefined
    return mExtra.mJSException;
  }

  DOMExceptionInfo* InitDOMExceptionInfo(DOMExceptionInfo* aDOMExceptionInfo) {
    // The |new| here switches the active arm of |mExtra|, from the compiler's
    // point of view.  Mere assignment *won't* necessarily do the right thing!
    new (&mExtra.mDOMExceptionInfo) DOMExceptionInfo*(aDOMExceptionInfo);
    return mExtra.mDOMExceptionInfo;
  }

#ifdef DEBUG
  // Used to keep track of codepaths that might throw JS exceptions,
  // for assertion purposes.
  bool mMightHaveUnreportedJSException;

  // Used to keep track of what's stored in our union right now.  Note
  // that this may be set to HasNothing even if our mResult suggests
  // we should have something, if we have already cleaned up the
  // something.
  UnionState mUnionState;

  // The thread that created this TErrorResult
  NS_DECL_OWNINGTHREAD;
#endif

  // Not to be implemented, to make sure people always pass this by
  // reference, not by value.
  TErrorResult(const TErrorResult&) = delete;
  void operator=(const TErrorResult&) = delete;
} JS_HAZ_ROOTED;

struct JustAssertCleanupPolicy {
  static const bool assertHandled = true;
  static const bool suppress = false;
  static const bool assertSameThread = true;
};

struct AssertAndSuppressCleanupPolicy {
  static const bool assertHandled = true;
  static const bool suppress = true;
  static const bool assertSameThread = true;
};

struct JustSuppressCleanupPolicy {
  static const bool assertHandled = false;
  static const bool suppress = true;
  static const bool assertSameThread = true;
};

struct ThreadSafeJustSuppressCleanupPolicy {
  static const bool assertHandled = false;
  static const bool suppress = true;
  static const bool assertSameThread = false;
};

}  // namespace binding_danger

// A class people should normally use on the stack when they plan to actually
// do something with the exception.
class ErrorResult : public binding_danger::TErrorResult<
                        binding_danger::AssertAndSuppressCleanupPolicy> {
  typedef binding_danger::TErrorResult<
      binding_danger::AssertAndSuppressCleanupPolicy>
      BaseErrorResult;

 public:
  ErrorResult() : BaseErrorResult() {}

  ErrorResult(ErrorResult&& aRHS) : BaseErrorResult(std::move(aRHS)) {}

  explicit ErrorResult(nsresult aRv) : BaseErrorResult(aRv) {}

  void operator=(nsresult rv) { BaseErrorResult::operator=(rv); }

  ErrorResult& operator=(ErrorResult&& aRHS) {
    BaseErrorResult::operator=(std::move(aRHS));
    return *this;
  }

 private:
  // Not to be implemented, to make sure people always pass this by
  // reference, not by value.
  ErrorResult(const ErrorResult&) = delete;
  void operator=(const ErrorResult&) = delete;
};

template <typename CleanupPolicy>
binding_danger::TErrorResult<CleanupPolicy>::operator ErrorResult&() {
  return *static_cast<ErrorResult*>(
      reinterpret_cast<TErrorResult<AssertAndSuppressCleanupPolicy>*>(this));
}

template <typename CleanupPolicy>
binding_danger::TErrorResult<CleanupPolicy>::operator const ErrorResult&()
    const {
  return *static_cast<const ErrorResult*>(
      reinterpret_cast<const TErrorResult<AssertAndSuppressCleanupPolicy>*>(
          this));
}

// A class for use when an ErrorResult should just automatically be ignored.
// This doesn't inherit from ErrorResult so we don't make two separate calls to
// SuppressException.
class IgnoredErrorResult : public binding_danger::TErrorResult<
                               binding_danger::JustSuppressCleanupPolicy> {};

// A class for use when an ErrorResult needs to be copied to a lambda, into
// an IPDL structure, etc.  Since this will often involve crossing thread
// boundaries this class will assert if you try to copy a JS exception.  Only
// use this if you are propagating internal errors.  In general its best
// to use ErrorResult by default and only convert to a CopyableErrorResult when
// you need it.
class CopyableErrorResult
    : public binding_danger::TErrorResult<
          binding_danger::ThreadSafeJustSuppressCleanupPolicy> {
  typedef binding_danger::TErrorResult<
      binding_danger::ThreadSafeJustSuppressCleanupPolicy>
      BaseErrorResult;

 public:
  CopyableErrorResult() : BaseErrorResult() {}

  explicit CopyableErrorResult(const ErrorResult& aRight) : BaseErrorResult() {
    auto val = reinterpret_cast<const CopyableErrorResult&>(aRight);
    operator=(val);
  }

  CopyableErrorResult(CopyableErrorResult&& aRHS)
      : BaseErrorResult(std::move(aRHS)) {}

  explicit CopyableErrorResult(nsresult aRv) : BaseErrorResult(aRv) {}

  void operator=(nsresult rv) { BaseErrorResult::operator=(rv); }

  CopyableErrorResult& operator=(CopyableErrorResult&& aRHS) {
    BaseErrorResult::operator=(std::move(aRHS));
    return *this;
  }

  CopyableErrorResult(const CopyableErrorResult& aRight) : BaseErrorResult() {
    operator=(aRight);
  }

  CopyableErrorResult& operator=(const CopyableErrorResult& aRight) {
    // We must not copy JS exceptions since it can too easily lead to
    // off-thread use.  Assert this and fall back to a generic error
    // in release builds.
    MOZ_DIAGNOSTIC_ASSERT(
        !IsJSException(),
        "Attempt to copy to ErrorResult with a JS exception value.");
    MOZ_DIAGNOSTIC_ASSERT(
        !aRight.IsJSException(),
        "Attempt to copy from ErrorResult with a JS exception value.");
    if (aRight.IsJSException()) {
      SuppressException();
      Throw(NS_ERROR_FAILURE);
    } else {
      aRight.CloneTo(*this);
    }
    return *this;
  }
};

namespace dom {
namespace binding_detail {
class FastErrorResult : public mozilla::binding_danger::TErrorResult<
                            mozilla::binding_danger::JustAssertCleanupPolicy> {
};
}  // namespace binding_detail
}  // namespace dom

// This part is a bit annoying.  We want an OOMReporter class that has the
// following properties:
//
// 1) Can be cast to from any ErrorResult-like type.
// 2) Has a fast destructor (because we want to use it from bindings).
// 3) Won't be randomly instantiated by non-binding code (because the fast
//    destructor is not so safe.
// 4) Doesn't look ugly on the callee side (e.g. isn't in the binding_detail or
//    binding_danger namespace).
//
// We do this by having two classes: The class callees should use, which has the
// things we want and a private constructor, and a friend subclass in the
// binding_danger namespace that can be used to construct it.
namespace binding_danger {
class OOMReporterInstantiator;
}  // namespace binding_danger

class OOMReporter : private dom::binding_detail::FastErrorResult {
 public:
  void ReportOOM() { Throw(NS_ERROR_OUT_OF_MEMORY); }

 private:
  // OOMReporterInstantiator is a friend so it can call our constructor and
  // MaybeSetPendingException.
  friend class binding_danger::OOMReporterInstantiator;

  // TErrorResult is a friend so its |operator OOMReporter&()| can work.
  template <typename CleanupPolicy>
  friend class binding_danger::TErrorResult;

  OOMReporter() : dom::binding_detail::FastErrorResult() {}
};

namespace binding_danger {
class OOMReporterInstantiator : public OOMReporter {
 public:
  OOMReporterInstantiator() : OOMReporter() {}

  // We want to be able to call MaybeSetPendingException from codegen.  The one
  // on OOMReporter is not callable directly, because it comes from a private
  // superclass.  But we're a friend, so _we_ can call it.
  bool MaybeSetPendingException(JSContext* cx) {
    return OOMReporter::MaybeSetPendingException(cx);
  }
};
}  // namespace binding_danger

template <typename CleanupPolicy>
binding_danger::TErrorResult<CleanupPolicy>::operator OOMReporter&() {
  return *static_cast<OOMReporter*>(
      reinterpret_cast<TErrorResult<JustAssertCleanupPolicy>*>(this));
}

// A class for use when an ErrorResult should just automatically be
// ignored.  This is designed to be passed as a temporary only, like
// so:
//
//    foo->Bar(IgnoreErrors());
class MOZ_TEMPORARY_CLASS IgnoreErrors {
 public:
  operator ErrorResult&() && { return mInner; }
  operator OOMReporter&() && { return mInner; }

 private:
  // We don't use an ErrorResult member here so we don't make two separate calls
  // to SuppressException (one from us, one from the ErrorResult destructor
  // after asserting).
  binding_danger::TErrorResult<binding_danger::JustSuppressCleanupPolicy>
      mInner;
} JS_HAZ_ROOTED;

/******************************************************************************
 ** Macros for checking results
 ******************************************************************************/

#define ENSURE_SUCCESS(res, ret)                \
  do {                                          \
    if (res.Failed()) {                         \
      nsCString msg;                            \
      msg.AppendPrintf(                         \
          "ENSURE_SUCCESS(%s, %s) failed with " \
          "result 0x%X",                        \
          #res, #ret, res.ErrorCodeAsInt());    \
      NS_WARNING(msg.get());                    \
      return ret;                               \
    }                                           \
  } while (0)

#define ENSURE_SUCCESS_VOID(res)                 \
  do {                                           \
    if (res.Failed()) {                          \
      nsCString msg;                             \
      msg.AppendPrintf(                          \
          "ENSURE_SUCCESS_VOID(%s) failed with " \
          "result 0x%X",                         \
          #res, res.ErrorCodeAsInt());           \
      NS_WARNING(msg.get());                     \
      return;                                    \
    }                                            \
  } while (0)

}  // namespace mozilla

#endif /* mozilla_ErrorResult_h */