Implement error interoperation (RFC 70) #17753

aturon · 2014-10-03T21:36:22Z

This PR:

Adds the error interoperation traits (Error and FromError) to a new module, std::error, as per RFC 70. Note that this module must live in std in order to refer to String.

Note that, until multidispatch lands, the FromError trait cannot be
usefully implemented outside of the blanket impl given here.
Incorporates std::error::FromError into the try! macro.
Implements Error for most existing error enumerations.

Closes #17747

rust-highfive · 2014-10-03T21:36:27Z

Warning

These commits modify unsafe code. Please review it carefully!

japaric · 2014-10-03T22:13:08Z

src/libstd/error.rs

+//! pub trait Error: Send + Any {
+//!     fn description(&self) -> &str;
+//!
+//!     fn detail(&self) -> Option<&str> { None }


Here, the return type is Option<&str>, but in the actual definition of the trait, the return type is Option<String>

aturon · 2014-10-03T22:14:37Z

@japaric Thanks, fixed.

alexcrichton · 2014-10-03T22:15:10Z

src/libstd/error.rs

+// }
+
+// Note: the definitions below are copied from core::any, and should be unified
+// as soon as possible.


Do we have a path forward for unifying these other than allowing &Error to be casted to &Any?

That's the ideal path; I'm not sure how soon that's likely to happen.

Alternatively, we could probably define macros for this, but given visibility rules that seemed more pain than gain right now.

aturon · 2014-10-03T22:17:24Z

@alexcrichton fixed, thanks.

alexcrichton · 2014-10-03T22:18:50Z

src/libstd/prelude.rs

@@ -66,6 +64,7 @@
 #[doc(no_inline)] pub use cmp::{Ordering, Less, Equal, Greater, Equiv};
 #[doc(no_inline)] pub use collections::{Collection, Mutable, Map, MutableMap, MutableSeq};
 #[doc(no_inline)] pub use collections::{Set, MutableSet};
+#[doc(no_inline)] pub use error::Error;


I would actually expect inspection of errors to not fall under "an overwhelming majority of rust code does this", but rather just the tip of the stack is the one to inspect the error. Along those lines, I'm not sure I'd put this in the prelude to get access to the methods.

On the other hand, implementing the trait is always convenient if you don't have to import it (and it avoids the std::error::Error stutter).

The RFC doesn't look like it mentions any modifications to the prelude, so I'm curious, what was your rationale for placing this here?

I was just writing a comment to get your opinion about this. You're right, it wasn't mentioned in the RFC and for that reason alone probably shouldn't happen here.

I also worry about having the name Error show up in the prelude. So maybe an explicit import makes more sense.

(My rationale was just that you'd generally expect methods like description to be available on error types without needing to import a trait, but that's pretty weak sauce.)

alexcrichton · 2014-10-03T22:22:23Z

Do you think it may be best to wait for multidispatch to land before landing this? This is a pretty minimal change, so I don't think it's too susceptible to bitrot (ok on that front). I'd be more curious in going ahead and leveraging this trait throughout some examples in the stdlib/compiler/etc to give it a bit of usage and make sure the try! macro works as expected.

aturon · 2014-10-03T22:25:06Z

@alexcrichton Addressed comments, removed from prelude.

aturon · 2014-10-03T22:26:00Z

@alexcrichton Sure, we can wait to land this until multidispatch, and I can add tests/examples to docs.

aturon · 2014-10-13T18:48:53Z

Just an update: I've tried rolling this out with multidispatch now being snapshotted. However, there are some problems with type inference. @nikomatsakis is looking into it. We can't land this change to try! until that's resolved.

In general, also, the two blanket impls in the RFC conflict (the one that passes through a value unchanged, and the one that boxes it). If we had negative bounds, we could work around that. Instead, if you want to be able to get automatic boxing for a particular concrete error you'll have to write an impl for it.

nikomatsakis · 2014-10-14T09:49:10Z

cc #18019

ghost · 2014-10-23T17:45:54Z

@aturon Is this good to go after the next snapshot?

alexcrichton · 2014-10-24T16:47:38Z

cc #18259 for new snapshots

aturon · 2014-10-31T02:56:55Z

@alexcrichton I've updated with documentation and use of multidispatch. Building fine here. re-r?

This PR: * Adds the error interoperation traits (`Error` and `FromError`) to a new module, `std::error`, as per [RFC 70](https://github.com/rust-lang/rfcs/blob/master/active/0070-error-chaining.md). Note that this module must live in `std` in order to refer to `String`. Note that, until multidispatch lands, the `FromError` trait cannot be usefully implemented outside of the blanket impl given here. * Incorporates `std::error::FromError` into the `try!` macro. * Implements `Error` for most existing error enumerations. Closes #17747

As per [RFC 70](https://github.com/rust-lang/rfcs/blob/master/active/0070-error-chaining.md) Closes rust-lang#17747 Note that the `error` module must live in `std` in order to refer to `String`. Note that, until multidispatch lands, the `FromError` trait cannot be usefully implemented outside of the blanket impl given here.

This PR: * Adds the error interoperation traits (`Error` and `FromError`) to a new module, `std::error`, as per [RFC 70](https://github.com/rust-lang/rfcs/blob/master/active/0070-error-chaining.md). Note that this module must live in `std` in order to refer to `String`. Note that, until multidispatch lands, the `FromError` trait cannot be usefully implemented outside of the blanket impl given here. * Incorporates `std::error::FromError` into the `try!` macro. * Implements `Error` for most existing error enumerations. Closes #17747

aturon force-pushed the error-interop branch 2 times, most recently from 9b13971 to 4f22561 Compare October 3, 2014 21:47

japaric reviewed Oct 3, 2014
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aturon force-pushed the error-interop branch from 4f22561 to 7090bb1 Compare October 3, 2014 22:14

alexcrichton reviewed Oct 3, 2014
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aturon force-pushed the error-interop branch from 7090bb1 to e276032 Compare October 3, 2014 22:17

alexcrichton reviewed Oct 3, 2014
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aturon force-pushed the error-interop branch from e276032 to 4fd0b24 Compare October 3, 2014 22:24

aturon force-pushed the error-interop branch 2 times, most recently from 4110531 to 5a7810e Compare October 3, 2014 22:28

aturon force-pushed the error-interop branch from 5a7810e to 30f86e3 Compare October 31, 2014 02:56

aturon force-pushed the error-interop branch from 30f86e3 to bc1bc9d Compare October 31, 2014 17:32

aturon force-pushed the error-interop branch from bc1bc9d to 276919c Compare October 31, 2014 19:54

aturon force-pushed the error-interop branch from 276919c to 896da2e Compare November 1, 2014 05:51

aturon force-pushed the error-interop branch from 896da2e to ec228c1 Compare November 2, 2014 23:26

aturon added 2 commits November 2, 2014 15:31

Add Error impls to a few key error types

7c152f8

Add type annotation to deal with fallout

38e0745

aturon force-pushed the error-interop branch from ec228c1 to 38e0745 Compare November 2, 2014 23:32

bors closed this Nov 3, 2014

bors merged commit 38e0745 into rust-lang:master Nov 3, 2014

michaelsproul mentioned this pull request Dec 26, 2014

Implement error interoperation #17747

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Implement error interoperation (RFC 70) #17753

Implement error interoperation (RFC 70) #17753

aturon commented Oct 3, 2014

rust-highfive commented Oct 3, 2014

japaric Oct 3, 2014

aturon commented Oct 3, 2014

alexcrichton Oct 3, 2014

aturon Oct 3, 2014

aturon commented Oct 3, 2014

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aturon Oct 3, 2014

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aturon commented Oct 13, 2014

nikomatsakis commented Oct 14, 2014

ghost commented Oct 23, 2014

alexcrichton commented Oct 24, 2014

aturon commented Oct 31, 2014

Implement error interoperation (RFC 70) #17753

Implement error interoperation (RFC 70) #17753

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