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
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
|
//! [![github]](https://github.com/dtolnay/anyhow) [![crates-io]](https://crates.io/crates/anyhow) [![docs-rs]](https://docs.rs/anyhow)
//!
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
//!
//! <br>
//!
//! This library provides [`anyhow::Error`][Error], a trait object based error
//! type for easy idiomatic error handling in Rust applications.
//!
//! <br>
//!
//! # Details
//!
//! - Use `Result<T, anyhow::Error>`, or equivalently `anyhow::Result<T>`, as
//! the return type of any fallible function.
//!
//! Within the function, use `?` to easily propagate any error that implements
//! the `std::error::Error` trait.
//!
//! ```
//! # pub trait Deserialize {}
//! #
//! # mod serde_json {
//! # use super::Deserialize;
//! # use std::io;
//! #
//! # pub fn from_str<T: Deserialize>(json: &str) -> io::Result<T> {
//! # unimplemented!()
//! # }
//! # }
//! #
//! # struct ClusterMap;
//! #
//! # impl Deserialize for ClusterMap {}
//! #
//! use anyhow::Result;
//!
//! fn get_cluster_info() -> Result<ClusterMap> {
//! let config = std::fs::read_to_string("cluster.json")?;
//! let map: ClusterMap = serde_json::from_str(&config)?;
//! Ok(map)
//! }
//! #
//! # fn main() {}
//! ```
//!
//! - Attach context to help the person troubleshooting the error understand
//! where things went wrong. A low-level error like "No such file or
//! directory" can be annoying to debug without more context about what higher
//! level step the application was in the middle of.
//!
//! ```
//! # struct It;
//! #
//! # impl It {
//! # fn detach(&self) -> Result<()> {
//! # unimplemented!()
//! # }
//! # }
//! #
//! use anyhow::{Context, Result};
//!
//! fn main() -> Result<()> {
//! # return Ok(());
//! #
//! # const _: &str = stringify! {
//! ...
//! # };
//! #
//! # let it = It;
//! # let path = "./path/to/instrs.json";
//! #
//! it.detach().context("Failed to detach the important thing")?;
//!
//! let content = std::fs::read(path)
//! .with_context(|| format!("Failed to read instrs from {}", path))?;
//! #
//! # const _: &str = stringify! {
//! ...
//! # };
//! #
//! # Ok(())
//! }
//! ```
//!
//! ```console
//! Error: Failed to read instrs from ./path/to/instrs.json
//!
//! Caused by:
//! No such file or directory (os error 2)
//! ```
//!
//! - Downcasting is supported and can be by value, by shared reference, or by
//! mutable reference as needed.
//!
//! ```
//! # use anyhow::anyhow;
//! # use std::fmt::{self, Display};
//! # use std::task::Poll;
//! #
//! # #[derive(Debug)]
//! # enum DataStoreError {
//! # Censored(()),
//! # }
//! #
//! # impl Display for DataStoreError {
//! # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
//! # unimplemented!()
//! # }
//! # }
//! #
//! # impl std::error::Error for DataStoreError {}
//! #
//! # const REDACTED_CONTENT: () = ();
//! #
//! # let error = anyhow!("...");
//! # let root_cause = &error;
//! #
//! # let ret =
//! // If the error was caused by redaction, then return a
//! // tombstone instead of the content.
//! match root_cause.downcast_ref::<DataStoreError>() {
//! Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),
//! None => Err(error),
//! }
//! # ;
//! ```
//!
//! - If using the nightly channel, or stable with `features = ["backtrace"]`, a
//! backtrace is captured and printed with the error if the underlying error
//! type does not already provide its own. In order to see backtraces, they
//! must be enabled through the environment variables described in
//! [`std::backtrace`]:
//!
//! - If you want panics and errors to both have backtraces, set
//! `RUST_BACKTRACE=1`;
//! - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;
//! - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
//! `RUST_LIB_BACKTRACE=0`.
//!
//! The tracking issue for this feature is [rust-lang/rust#53487].
//!
//! [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables
//! [rust-lang/rust#53487]: https://github.com/rust-lang/rust/issues/53487
//!
//! - Anyhow works with any error type that has an impl of `std::error::Error`,
//! including ones defined in your crate. We do not bundle a `derive(Error)`
//! macro but you can write the impls yourself or use a standalone macro like
//! [thiserror].
//!
//! [thiserror]: https://github.com/dtolnay/thiserror
//!
//! ```
//! use thiserror::Error;
//!
//! #[derive(Error, Debug)]
//! pub enum FormatError {
//! #[error("Invalid header (expected {expected:?}, got {found:?})")]
//! InvalidHeader {
//! expected: String,
//! found: String,
//! },
//! #[error("Missing attribute: {0}")]
//! MissingAttribute(String),
//! }
//! ```
//!
//! - One-off error messages can be constructed using the `anyhow!` macro, which
//! supports string interpolation and produces an `anyhow::Error`.
//!
//! ```
//! # use anyhow::{anyhow, Result};
//! #
//! # fn demo() -> Result<()> {
//! # let missing = "...";
//! return Err(anyhow!("Missing attribute: {}", missing));
//! # Ok(())
//! # }
//! ```
//!
//! A `bail!` macro is provided as a shorthand for the same early return.
//!
//! ```
//! # use anyhow::{bail, Result};
//! #
//! # fn demo() -> Result<()> {
//! # let missing = "...";
//! bail!("Missing attribute: {}", missing);
//! # Ok(())
//! # }
//! ```
//!
//! <br>
//!
//! # No-std support
//!
//! In no_std mode, the same API is almost all available and works the same way.
//! To depend on Anyhow in no_std mode, disable our default enabled "std"
//! feature in Cargo.toml. A global allocator is required.
//!
//! ```toml
//! [dependencies]
//! anyhow = { version = "1.0", default-features = false }
//! ```
//!
//! Since the `?`-based error conversions would normally rely on the
//! `std::error::Error` trait which is only available through std, no_std mode
//! will require an explicit `.map_err(Error::msg)` when working with a
//! non-Anyhow error type inside a function that returns Anyhow's error type.
#![doc(html_root_url = "https://docs.rs/anyhow/1.0.71")]
#![cfg_attr(backtrace, feature(error_generic_member_access, provide_any))]
#![cfg_attr(doc_cfg, feature(doc_cfg))]
#![cfg_attr(not(feature = "std"), no_std)]
#![deny(dead_code, unused_imports, unused_mut)]
#![allow(
clippy::doc_markdown,
clippy::enum_glob_use,
clippy::explicit_auto_deref,
clippy::extra_unused_type_parameters,
clippy::let_underscore_untyped,
clippy::missing_errors_doc,
clippy::missing_panics_doc,
clippy::module_name_repetitions,
clippy::must_use_candidate,
clippy::needless_doctest_main,
clippy::new_ret_no_self,
clippy::redundant_else,
clippy::return_self_not_must_use,
clippy::unused_self,
clippy::used_underscore_binding,
clippy::wildcard_imports,
clippy::wrong_self_convention
)]
extern crate alloc;
#[macro_use]
mod backtrace;
mod chain;
mod context;
mod ensure;
mod error;
mod fmt;
mod kind;
mod macros;
mod ptr;
mod wrapper;
use crate::error::ErrorImpl;
use crate::ptr::Own;
use core::fmt::Display;
#[cfg(not(feature = "std"))]
use core::fmt::Debug;
#[cfg(feature = "std")]
use std::error::Error as StdError;
#[cfg(not(feature = "std"))]
trait StdError: Debug + Display {
fn source(&self) -> Option<&(dyn StdError + 'static)> {
None
}
}
#[doc(no_inline)]
pub use anyhow as format_err;
/// The `Error` type, a wrapper around a dynamic error type.
///
/// `Error` works a lot like `Box<dyn std::error::Error>`, but with these
/// differences:
///
/// - `Error` requires that the error is `Send`, `Sync`, and `'static`.
/// - `Error` guarantees that a backtrace is available, even if the underlying
/// error type does not provide one.
/// - `Error` is represented as a narrow pointer — exactly one word in
/// size instead of two.
///
/// <br>
///
/// # Display representations
///
/// When you print an error object using "{}" or to_string(), only the outermost
/// underlying error or context is printed, not any of the lower level causes.
/// This is exactly as if you had called the Display impl of the error from
/// which you constructed your anyhow::Error.
///
/// ```console
/// Failed to read instrs from ./path/to/instrs.json
/// ```
///
/// To print causes as well using anyhow's default formatting of causes, use the
/// alternate selector "{:#}".
///
/// ```console
/// Failed to read instrs from ./path/to/instrs.json: No such file or directory (os error 2)
/// ```
///
/// The Debug format "{:?}" includes your backtrace if one was captured. Note
/// that this is the representation you get by default if you return an error
/// from `fn main` instead of printing it explicitly yourself.
///
/// ```console
/// Error: Failed to read instrs from ./path/to/instrs.json
///
/// Caused by:
/// No such file or directory (os error 2)
/// ```
///
/// and if there is a backtrace available:
///
/// ```console
/// Error: Failed to read instrs from ./path/to/instrs.json
///
/// Caused by:
/// No such file or directory (os error 2)
///
/// Stack backtrace:
/// 0: <E as anyhow::context::ext::StdError>::ext_context
/// at /git/anyhow/src/backtrace.rs:26
/// 1: core::result::Result<T,E>::map_err
/// at /git/rustc/src/libcore/result.rs:596
/// 2: anyhow::context::<impl anyhow::Context<T,E> for core::result::Result<T,E>>::with_context
/// at /git/anyhow/src/context.rs:58
/// 3: testing::main
/// at src/main.rs:5
/// 4: std::rt::lang_start
/// at /git/rustc/src/libstd/rt.rs:61
/// 5: main
/// 6: __libc_start_main
/// 7: _start
/// ```
///
/// To see a conventional struct-style Debug representation, use "{:#?}".
///
/// ```console
/// Error {
/// context: "Failed to read instrs from ./path/to/instrs.json",
/// source: Os {
/// code: 2,
/// kind: NotFound,
/// message: "No such file or directory",
/// },
/// }
/// ```
///
/// If none of the built-in representations are appropriate and you would prefer
/// to render the error and its cause chain yourself, it can be done something
/// like this:
///
/// ```
/// use anyhow::{Context, Result};
///
/// fn main() {
/// if let Err(err) = try_main() {
/// eprintln!("ERROR: {}", err);
/// err.chain().skip(1).for_each(|cause| eprintln!("because: {}", cause));
/// std::process::exit(1);
/// }
/// }
///
/// fn try_main() -> Result<()> {
/// # const IGNORE: &str = stringify! {
/// ...
/// # };
/// # Ok(())
/// }
/// ```
#[cfg_attr(not(doc), repr(transparent))]
pub struct Error {
inner: Own<ErrorImpl>,
}
/// Iterator of a chain of source errors.
///
/// This type is the iterator returned by [`Error::chain`].
///
/// # Example
///
/// ```
/// use anyhow::Error;
/// use std::io;
///
/// pub fn underlying_io_error_kind(error: &Error) -> Option<io::ErrorKind> {
/// for cause in error.chain() {
/// if let Some(io_error) = cause.downcast_ref::<io::Error>() {
/// return Some(io_error.kind());
/// }
/// }
/// None
/// }
/// ```
#[cfg(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
#[derive(Clone)]
pub struct Chain<'a> {
state: crate::chain::ChainState<'a>,
}
/// `Result<T, Error>`
///
/// This is a reasonable return type to use throughout your application but also
/// for `fn main`; if you do, failures will be printed along with any
/// [context][Context] and a backtrace if one was captured.
///
/// `anyhow::Result` may be used with one *or* two type parameters.
///
/// ```rust
/// use anyhow::Result;
///
/// # const IGNORE: &str = stringify! {
/// fn demo1() -> Result<T> {...}
/// // ^ equivalent to std::result::Result<T, anyhow::Error>
///
/// fn demo2() -> Result<T, OtherError> {...}
/// // ^ equivalent to std::result::Result<T, OtherError>
/// # };
/// ```
///
/// # Example
///
/// ```
/// # pub trait Deserialize {}
/// #
/// # mod serde_json {
/// # use super::Deserialize;
/// # use std::io;
/// #
/// # pub fn from_str<T: Deserialize>(json: &str) -> io::Result<T> {
/// # unimplemented!()
/// # }
/// # }
/// #
/// # #[derive(Debug)]
/// # struct ClusterMap;
/// #
/// # impl Deserialize for ClusterMap {}
/// #
/// use anyhow::Result;
///
/// fn main() -> Result<()> {
/// # return Ok(());
/// let config = std::fs::read_to_string("cluster.json")?;
/// let map: ClusterMap = serde_json::from_str(&config)?;
/// println!("cluster info: {:#?}", map);
/// Ok(())
/// }
/// ```
pub type Result<T, E = Error> = core::result::Result<T, E>;
/// Provides the `context` method for `Result`.
///
/// This trait is sealed and cannot be implemented for types outside of
/// `anyhow`.
///
/// <br>
///
/// # Example
///
/// ```
/// use anyhow::{Context, Result};
/// use std::fs;
/// use std::path::PathBuf;
///
/// pub struct ImportantThing {
/// path: PathBuf,
/// }
///
/// impl ImportantThing {
/// # const IGNORE: &'static str = stringify! {
/// pub fn detach(&mut self) -> Result<()> {...}
/// # };
/// # fn detach(&mut self) -> Result<()> {
/// # unimplemented!()
/// # }
/// }
///
/// pub fn do_it(mut it: ImportantThing) -> Result<Vec<u8>> {
/// it.detach().context("Failed to detach the important thing")?;
///
/// let path = &it.path;
/// let content = fs::read(path)
/// .with_context(|| format!("Failed to read instrs from {}", path.display()))?;
///
/// Ok(content)
/// }
/// ```
///
/// When printed, the outermost context would be printed first and the lower
/// level underlying causes would be enumerated below.
///
/// ```console
/// Error: Failed to read instrs from ./path/to/instrs.json
///
/// Caused by:
/// No such file or directory (os error 2)
/// ```
///
/// Refer to the [Display representations] documentation for other forms in
/// which this context chain can be rendered.
///
/// [Display representations]: Error#display-representations
///
/// <br>
///
/// # Effect on downcasting
///
/// After attaching context of type `C` onto an error of type `E`, the resulting
/// `anyhow::Error` may be downcast to `C` **or** to `E`.
///
/// That is, in codebases that rely on downcasting, Anyhow's context supports
/// both of the following use cases:
///
/// - **Attaching context whose type is insignificant onto errors whose type
/// is used in downcasts.**
///
/// In other error libraries whose context is not designed this way, it can
/// be risky to introduce context to existing code because new context might
/// break existing working downcasts. In Anyhow, any downcast that worked
/// before adding context will continue to work after you add a context, so
/// you should freely add human-readable context to errors wherever it would
/// be helpful.
///
/// ```
/// # use anyhow::bail;
/// # use thiserror::Error;
/// #
/// # #[derive(Error, Debug)]
/// # #[error("???")]
/// # struct SuspiciousError;
/// #
/// # fn helper() -> Result<()> {
/// # bail!(SuspiciousError);
/// # }
/// #
/// use anyhow::{Context, Result};
///
/// fn do_it() -> Result<()> {
/// helper().context("Failed to complete the work")?;
/// # const IGNORE: &str = stringify! {
/// ...
/// # };
/// # unreachable!()
/// }
///
/// fn main() {
/// let err = do_it().unwrap_err();
/// if let Some(e) = err.downcast_ref::<SuspiciousError>() {
/// // If helper() returned SuspiciousError, this downcast will
/// // correctly succeed even with the context in between.
/// # return;
/// }
/// # panic!("expected downcast to succeed");
/// }
/// ```
///
/// - **Attaching context whose type is used in downcasts onto errors whose
/// type is insignificant.**
///
/// Some codebases prefer to use machine-readable context to categorize
/// lower level errors in a way that will be actionable to higher levels of
/// the application.
///
/// ```
/// # use anyhow::bail;
/// # use thiserror::Error;
/// #
/// # #[derive(Error, Debug)]
/// # #[error("???")]
/// # struct HelperFailed;
/// #
/// # fn helper() -> Result<()> {
/// # bail!("no such file or directory");
/// # }
/// #
/// use anyhow::{Context, Result};
///
/// fn do_it() -> Result<()> {
/// helper().context(HelperFailed)?;
/// # const IGNORE: &str = stringify! {
/// ...
/// # };
/// # unreachable!()
/// }
///
/// fn main() {
/// let err = do_it().unwrap_err();
/// if let Some(e) = err.downcast_ref::<HelperFailed>() {
/// // If helper failed, this downcast will succeed because
/// // HelperFailed is the context that has been attached to
/// // that error.
/// # return;
/// }
/// # panic!("expected downcast to succeed");
/// }
/// ```
pub trait Context<T, E>: context::private::Sealed {
/// Wrap the error value with additional context.
fn context<C>(self, context: C) -> Result<T, Error>
where
C: Display + Send + Sync + 'static;
/// Wrap the error value with additional context that is evaluated lazily
/// only once an error does occur.
fn with_context<C, F>(self, f: F) -> Result<T, Error>
where
C: Display + Send + Sync + 'static,
F: FnOnce() -> C;
}
/// Equivalent to Ok::<_, anyhow::Error>(value).
///
/// This simplifies creation of an anyhow::Result in places where type inference
/// cannot deduce the `E` type of the result — without needing to write
/// `Ok::<_, anyhow::Error>(value)`.
///
/// One might think that `anyhow::Result::Ok(value)` would work in such cases
/// but it does not.
///
/// ```console
/// error[E0282]: type annotations needed for `std::result::Result<i32, E>`
/// --> src/main.rs:11:13
/// |
/// 11 | let _ = anyhow::Result::Ok(1);
/// | - ^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `E` declared on the enum `Result`
/// | |
/// | consider giving this pattern the explicit type `std::result::Result<i32, E>`, where the type parameter `E` is specified
/// ```
#[allow(non_snake_case)]
pub fn Ok<T>(t: T) -> Result<T> {
Result::Ok(t)
}
// Not public API. Referenced by macro-generated code.
#[doc(hidden)]
pub mod __private {
use crate::Error;
use alloc::fmt;
use core::fmt::Arguments;
pub use crate::ensure::{BothDebug, NotBothDebug};
pub use alloc::format;
pub use core::result::Result::Err;
pub use core::{concat, format_args, stringify};
#[doc(hidden)]
pub mod kind {
pub use crate::kind::{AdhocKind, TraitKind};
#[cfg(feature = "std")]
pub use crate::kind::BoxedKind;
}
#[doc(hidden)]
#[inline]
#[cold]
pub fn format_err(args: Arguments) -> Error {
#[cfg(anyhow_no_fmt_arguments_as_str)]
let fmt_arguments_as_str = None::<&str>;
#[cfg(not(anyhow_no_fmt_arguments_as_str))]
let fmt_arguments_as_str = args.as_str();
if let Some(message) = fmt_arguments_as_str {
// anyhow!("literal"), can downcast to &'static str
Error::msg(message)
} else {
// anyhow!("interpolate {var}"), can downcast to String
Error::msg(fmt::format(args))
}
}
#[doc(hidden)]
#[inline]
#[cold]
#[must_use]
pub fn must_use(error: Error) -> Error {
error
}
}
|