      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412
    413
    414
    415
    416
    417
    418
    419
    420
    421
    422
    423
    424
    425
    426
    427
    428
    429
    430
    431
    432
    433
    434
    435
    436
    437
    438
    439
    440
    441
    442
    443
    444
    445
    446
    447
    448
    449
    450
    451
    452
    453
    454
    455
    456
    457
    458
    459
    460
    461
    462
    463
    464
    465
    466
    467
    468
    469
    470
    471
    472
    473
    474
    475
    476
    477
    478
    479
    480
    481
    482
    483
    484
    485
    486
    487
    488
    489
    490
    491
    492
    493
    494
    495
    496
    497
    498
    499
    500
    501
    502
    503
    504
    505
    506
    507
    508
    509
    510
    511
    512
    513
    514
    515
    516
    517
    518
    519
    520
    521
    522
    523
    524
    525
    526
    527
    528
    529
    530
    531
    532
    533
    534
    535
    536
    537
    538
    539
    540
    541
    542
    543
    544
    545
    546
    547
    548
    549
    550
    551
    552
    553
    554
    555
    556
    557
    558
    559
    560
    561
    562
    563
    564
    565
    566
    567
    568
    569
    570
    571
    572
    573
    574
    575
    576
    577
    578
    579
    580
    581
    582
    583
    584
    585
    586
    587
    588
    589
    590
    591
    592
    593
    594
    595
    596
    597
    598
    599
    600
    601
    602
    603
    604
    605
    606
    607
    608
    609
    610
    611
    612
    613
    614
    615
    616
    617
    618
    619
    620
    621
    622
    623
    624
    625
    626
    627
    628
    629

    // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    use error;
    use fmt;
    use result;
    use sys;
    use convert::From;

    /// A specialized [`Result`](../result/enum.Result.html) type for I/O
    /// operations.
    ///
    /// This type is broadly used across [`std::io`] for any operation which may
    /// produce an error.
    ///
    /// This typedef is generally used to avoid writing out [`io::Error`] directly and
    /// is otherwise a direct mapping to [`Result`].
    ///
    /// While usual Rust style is to import types directly, aliases of [`Result`]
    /// often are not, to make it easier to distinguish between them. [`Result`] is
    /// generally assumed to be [`std::result::Result`][`Result`], and so users of this alias
    /// will generally use `io::Result` instead of shadowing the prelude's import
    /// of [`std::result::Result`][`Result`].
    ///
    /// [`std::io`]: ../io/index.html
    /// [`io::Error`]: ../io/struct.Error.html
    /// [`Result`]: ../result/enum.Result.html
    ///
    /// # Examples
    ///
    /// A convenience function that bubbles an `io::Result` to its caller:
    ///
    /// ```
    /// use std::io;
    ///
    /// fn get_string() -> io::Result<String> {
    ///     let mut buffer = String::new();
    ///
    ///     io::stdin().read_line(&mut buffer)?;
    ///
    ///     Ok(buffer)
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub type Result<T> = result::Result<T, Error>;

    /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
    /// associated traits.
    ///
    /// Errors mostly originate from the underlying OS, but custom instances of
    /// `Error` can be created with crafted error messages and a particular value of
    /// [`ErrorKind`].
    ///
    /// [`Read`]: ../io/trait.Read.html
    /// [`Write`]: ../io/trait.Write.html
    /// [`Seek`]: ../io/trait.Seek.html
    /// [`ErrorKind`]: enum.ErrorKind.html
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Error {
        repr: Repr,
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Debug for Error {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Debug::fmt(&self.repr, f)
        }
    }

    enum Repr {
        Os(i32),
        Simple(ErrorKind),
        Custom(Box<Custom>),
    }

    #[derive(Debug)]
    struct Custom {
        kind: ErrorKind,
        error: Box<dyn error::Error+Send+Sync>,
    }

    /// A list specifying general categories of I/O error.
    ///
    /// This list is intended to grow over time and it is not recommended to
    /// exhaustively match against it.
    ///
    /// It is used with the [`io::Error`] type.
    ///
    /// [`io::Error`]: struct.Error.html
    #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow(deprecated)]
    pub enum ErrorKind {
        /// An entity was not found, often a file.
        #[stable(feature = "rust1", since = "1.0.0")]
        NotFound,
        /// The operation lacked the necessary privileges to complete.
        #[stable(feature = "rust1", since = "1.0.0")]
        PermissionDenied,
        /// The connection was refused by the remote server.
        #[stable(feature = "rust1", since = "1.0.0")]
        ConnectionRefused,
        /// The connection was reset by the remote server.
        #[stable(feature = "rust1", since = "1.0.0")]
        ConnectionReset,
        /// The connection was aborted (terminated) by the remote server.
        #[stable(feature = "rust1", since = "1.0.0")]
        ConnectionAborted,
        /// The network operation failed because it was not connected yet.
        #[stable(feature = "rust1", since = "1.0.0")]
        NotConnected,
        /// A socket address could not be bound because the address is already in
        /// use elsewhere.
        #[stable(feature = "rust1", since = "1.0.0")]
        AddrInUse,
        /// A nonexistent interface was requested or the requested address was not
        /// local.
        #[stable(feature = "rust1", since = "1.0.0")]
        AddrNotAvailable,
        /// The operation failed because a pipe was closed.
        #[stable(feature = "rust1", since = "1.0.0")]
        BrokenPipe,
        /// An entity already exists, often a file.
        #[stable(feature = "rust1", since = "1.0.0")]
        AlreadyExists,
        /// The operation needs to block to complete, but the blocking operation was
        /// requested to not occur.
        #[stable(feature = "rust1", since = "1.0.0")]
        WouldBlock,
        /// A parameter was incorrect.
        #[stable(feature = "rust1", since = "1.0.0")]
        InvalidInput,
        /// Data not valid for the operation were encountered.
        ///
        /// Unlike [`InvalidInput`], this typically means that the operation
        /// parameters were valid, however the error was caused by malformed
        /// input data.
        ///
        /// For example, a function that reads a file into a string will error with
        /// `InvalidData` if the file's contents are not valid UTF-8.
        ///
        /// [`InvalidInput`]: #variant.InvalidInput
        #[stable(feature = "io_invalid_data", since = "1.2.0")]
        InvalidData,
        /// The I/O operation's timeout expired, causing it to be canceled.
        #[stable(feature = "rust1", since = "1.0.0")]
        TimedOut,
        /// An error returned when an operation could not be completed because a
        /// call to [`write`] returned [`Ok(0)`].
        ///
        /// This typically means that an operation could only succeed if it wrote a
        /// particular number of bytes but only a smaller number of bytes could be
        /// written.
        ///
        /// [`write`]: ../../std/io/trait.Write.html#tymethod.write
        /// [`Ok(0)`]: ../../std/io/type.Result.html
        #[stable(feature = "rust1", since = "1.0.0")]
        WriteZero,
        /// This operation was interrupted.
        ///
        /// Interrupted operations can typically be retried.
        #[stable(feature = "rust1", since = "1.0.0")]
        Interrupted,
        /// Any I/O error not part of this list.
        #[stable(feature = "rust1", since = "1.0.0")]
        Other,

        /// An error returned when an operation could not be completed because an
        /// "end of file" was reached prematurely.
        ///
        /// This typically means that an operation could only succeed if it read a
        /// particular number of bytes but only a smaller number of bytes could be
        /// read.
        #[stable(feature = "read_exact", since = "1.6.0")]
        UnexpectedEof,

        /// A marker variant that tells the compiler that users of this enum cannot
        /// match it exhaustively.
        #[unstable(feature = "io_error_internals",
                   reason = "better expressed through extensible enums that this \
                             enum cannot be exhaustively matched against",
                   issue = "0")]
        #[doc(hidden)]
        __Nonexhaustive,
    }

    impl ErrorKind {
        fn as_str(&self) -> &'static str {
            match *self {
                ErrorKind::NotFound => "entity not found",
                ErrorKind::PermissionDenied => "permission denied",
                ErrorKind::ConnectionRefused => "connection refused",
                ErrorKind::ConnectionReset => "connection reset",
                ErrorKind::ConnectionAborted => "connection aborted",
                ErrorKind::NotConnected => "not connected",
                ErrorKind::AddrInUse => "address in use",
                ErrorKind::AddrNotAvailable => "address not available",
                ErrorKind::BrokenPipe => "broken pipe",
                ErrorKind::AlreadyExists => "entity already exists",
                ErrorKind::WouldBlock => "operation would block",
                ErrorKind::InvalidInput => "invalid input parameter",
                ErrorKind::InvalidData => "invalid data",
                ErrorKind::TimedOut => "timed out",
                ErrorKind::WriteZero => "write zero",
                ErrorKind::Interrupted => "operation interrupted",
                ErrorKind::Other => "other os error",
                ErrorKind::UnexpectedEof => "unexpected end of file",
                ErrorKind::__Nonexhaustive => unreachable!()
            }
        }
    }

    /// Intended for use for errors not exposed to the user, where allocating onto
    /// the heap (for normal construction via Error::new) is too costly.
    #[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
    impl From<ErrorKind> for Error {
        #[inline]
        fn from(kind: ErrorKind) -> Error {
            Error {
                repr: Repr::Simple(kind)
            }
        }
    }

    impl Error {
        /// Creates a new I/O error from a known kind of error as well as an
        /// arbitrary error payload.
        ///
        /// This function is used to generically create I/O errors which do not
        /// originate from the OS itself. The `error` argument is an arbitrary
        /// payload which will be contained in this `Error`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// // errors can be created from strings
        /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
        ///
        /// // errors can also be created from other errors
        /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn new<E>(kind: ErrorKind, error: E) -> Error
            where E: Into<Box<dyn error::Error+Send+Sync>>
        {
            Self::_new(kind, error.into())
        }

        fn _new(kind: ErrorKind, error: Box<dyn error::Error+Send+Sync>) -> Error {
            Error {
                repr: Repr::Custom(Box::new(Custom {
                    kind,
                    error,
                }))
            }
        }

        /// Returns an error representing the last OS error which occurred.
        ///
        /// This function reads the value of `errno` for the target platform (e.g.
        /// `GetLastError` on Windows) and will return a corresponding instance of
        /// `Error` for the error code.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::Error;
        ///
        /// println!("last OS error: {:?}", Error::last_os_error());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn last_os_error() -> Error {
            Error::from_raw_os_error(sys::os::errno() as i32)
        }

        /// Creates a new instance of an `Error` from a particular OS error code.
        ///
        /// # Examples
        ///
        /// On Linux:
        ///
        /// ```
        /// # if cfg!(target_os = "linux") {
        /// use std::io;
        ///
        /// let error = io::Error::from_raw_os_error(22);
        /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
        /// # }
        /// ```
        ///
        /// On Windows:
        ///
        /// ```
        /// # if cfg!(windows) {
        /// use std::io;
        ///
        /// let error = io::Error::from_raw_os_error(10022);
        /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
        /// # }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn from_raw_os_error(code: i32) -> Error {
            Error { repr: Repr::Os(code) }
        }

        /// Returns the OS error that this error represents (if any).
        ///
        /// If this `Error` was constructed via `last_os_error` or
        /// `from_raw_os_error`, then this function will return `Some`, otherwise
        /// it will return `None`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_os_error(err: &Error) {
        ///     if let Some(raw_os_err) = err.raw_os_error() {
        ///         println!("raw OS error: {:?}", raw_os_err);
        ///     } else {
        ///         println!("Not an OS error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "raw OS error: ...".
        ///     print_os_error(&Error::last_os_error());
        ///     // Will print "Not an OS error".
        ///     print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn raw_os_error(&self) -> Option<i32> {
            match self.repr {
                Repr::Os(i) => Some(i),
                Repr::Custom(..) => None,
                Repr::Simple(..) => None,
            }
        }

        /// Returns a reference to the inner error wrapped by this error (if any).
        ///
        /// If this `Error` was constructed via `new` then this function will
        /// return `Some`, otherwise it will return `None`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_error(err: &Error) {
        ///     if let Some(inner_err) = err.get_ref() {
        ///         println!("Inner error: {:?}", inner_err);
        ///     } else {
        ///         println!("No inner error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(&Error::last_os_error());
        ///     // Will print "Inner error: ...".
        ///     print_error(&Error::new(ErrorKind::Other, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "io_error_inner", since = "1.3.0")]
        pub fn get_ref(&self) -> Option<&(dyn error::Error+Send+Sync+'static)> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref c) => Some(&*c.error),
            }
        }

        /// Returns a mutable reference to the inner error wrapped by this error
        /// (if any).
        ///
        /// If this `Error` was constructed via `new` then this function will
        /// return `Some`, otherwise it will return `None`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        /// use std::{error, fmt};
        /// use std::fmt::Display;
        ///
        /// #[derive(Debug)]
        /// struct MyError {
        ///     v: String,
        /// }
        ///
        /// impl MyError {
        ///     fn new() -> MyError {
        ///         MyError {
        ///             v: "oh no!".to_string()
        ///         }
        ///     }
        ///
        ///     fn change_message(&mut self, new_message: &str) {
        ///         self.v = new_message.to_string();
        ///     }
        /// }
        ///
        /// impl error::Error for MyError {
        ///     fn description(&self) -> &str { &self.v }
        /// }
        ///
        /// impl Display for MyError {
        ///     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        ///         write!(f, "MyError: {}", &self.v)
        ///     }
        /// }
        ///
        /// fn change_error(mut err: Error) -> Error {
        ///     if let Some(inner_err) = err.get_mut() {
        ///         inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
        ///     }
        ///     err
        /// }
        ///
        /// fn print_error(err: &Error) {
        ///     if let Some(inner_err) = err.get_ref() {
        ///         println!("Inner error: {}", inner_err);
        ///     } else {
        ///         println!("No inner error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(&change_error(Error::last_os_error()));
        ///     // Will print "Inner error: ...".
        ///     print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
        /// }
        /// ```
        #[stable(feature = "io_error_inner", since = "1.3.0")]
        pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error+Send+Sync+'static)> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref mut c) => Some(&mut *c.error),
            }
        }

        /// Consumes the `Error`, returning its inner error (if any).
        ///
        /// If this `Error` was constructed via `new` then this function will
        /// return `Some`, otherwise it will return `None`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_error(err: Error) {
        ///     if let Some(inner_err) = err.into_inner() {
        ///         println!("Inner error: {}", inner_err);
        ///     } else {
        ///         println!("No inner error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(Error::last_os_error());
        ///     // Will print "Inner error: ...".
        ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "io_error_inner", since = "1.3.0")]
        pub fn into_inner(self) -> Option<Box<dyn error::Error+Send+Sync>> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(c) => Some(c.error)
            }
        }

        /// Returns the corresponding `ErrorKind` for this error.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_error(err: Error) {
        ///     println!("{:?}", err.kind());
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(Error::last_os_error());
        ///     // Will print "Inner error: ...".
        ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn kind(&self) -> ErrorKind {
            match self.repr {
                Repr::Os(code) => sys::decode_error_kind(code),
                Repr::Custom(ref c) => c.kind,
                Repr::Simple(kind) => kind,
            }
        }
    }

    impl fmt::Debug for Repr {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            match *self {
                Repr::Os(code) =>
                    fmt.debug_struct("Os")
                        .field("code", &code)
                        .field("kind", &sys::decode_error_kind(code))
                        .field("message", &sys::os::error_string(code)).finish(),
                Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
                Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Display for Error {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            match self.repr {
                Repr::Os(code) => {
                    let detail = sys::os::error_string(code);
                    write!(fmt, "{} (os error {})", detail, code)
                }
                Repr::Custom(ref c) => c.error.fmt(fmt),
                Repr::Simple(kind) => write!(fmt, "{}", kind.as_str()),
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl error::Error for Error {
        fn description(&self) -> &str {
            match self.repr {
                Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
                Repr::Custom(ref c) => c.error.description(),
            }
        }

        fn cause(&self) -> Option<&dyn error::Error> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref c) => c.error.cause(),
            }
        }
    }

    fn _assert_error_is_sync_send() {
        fn _is_sync_send<T: Sync+Send>() {}
        _is_sync_send::<Error>();
    }

    #[cfg(test)]
    mod test {
        use super::{Error, ErrorKind, Repr, Custom};
        use error;
        use fmt;
        use sys::os::error_string;
        use sys::decode_error_kind;

        #[test]
        fn test_debug_error() {
            let code = 6;
            let msg = error_string(code);
            let kind = decode_error_kind(code);
            let err = Error {
                repr: Repr::Custom(box Custom {
                    kind: ErrorKind::InvalidInput,
                    error: box Error {
                        repr: super::Repr::Os(code)
                    },
                })
            };
            let expected = format!(
                "Custom {{ \
                    kind: InvalidInput, \
                    error: Os {{ \
                        code: {:?}, \
                        kind: {:?}, \
                        message: {:?} \
                    }} \
                }}",
                code, kind, msg
            );
            assert_eq!(format!("{:?}", err), expected);
        }

        #[test]
        fn test_downcasting() {
            #[derive(Debug)]
            struct TestError;

            impl fmt::Display for TestError {
                fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
                    Ok(())
                }
            }

            impl error::Error for TestError {
                fn description(&self) -> &str {
                    "asdf"
                }
            }

            // we have to call all of these UFCS style right now since method
            // resolution won't implicitly drop the Send+Sync bounds
            let mut err = Error::new(ErrorKind::Other, TestError);
            assert!(err.get_ref().unwrap().is::<TestError>());
            assert_eq!("asdf", err.get_ref().unwrap().description());
            assert!(err.get_mut().unwrap().is::<TestError>());
            let extracted = err.into_inner().unwrap();
            extracted.downcast::<TestError>().unwrap();
        }
    }

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g. `str,u8` or `String,struct:Vec,test`)