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Export std error type so no_std data formats don't need a "std" feature #1620

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merged 1 commit into from Sep 8, 2019
Merged

Export std error type so no_std data formats don't need a "std" feature #1620

merged 1 commit into from Sep 8, 2019

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dtolnay
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@dtolnay dtolnay commented Sep 5, 2019

This PR adds serde::ser::StdError and serde::de::StdError which are either a re-export of std::error::Error (if "std" is enabled) or a new identical trait (otherwise).

#[cfg(feature = "std")]
pub use std::error::Error as StdError;

#[cfg(not(feature = "std"))]
pub trait StdError: Debug + Display {
    fn source(&self) -> Option<&(Error + 'static)> { None }
}

Serde's error traits serde::ser::Error and serde::de::Error require std::error::Error as a supertrait, but only when Serde is built with "std" enabled. Data formats that don't care about no_std support should generally provide their error types with a std::error::Error impl directly:

#[derive(Debug)]
struct MySerError {...}

impl serde::ser::Error for MySerError {...}

impl std::fmt::Display for MySerError {...}

// We don't support no_std!
impl std::error::Error for MySerError {}

Data formats that do support no_std may either have a "std" feature of their own:

[features]
std = ["serde/std"]
#[cfg(feature = "std")]
impl std::error::Error for MySerError {}

... or else provide the std Error impl unconditionally via Serde's re-export:

impl serde::ser::StdError for MySerError {}

FYI @oli-obk, @cbeck88

@dtolnay
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@dtolnay dtolnay commented Sep 5, 2019

It looks like a re-export like this used to exist but was lost to time. This is from 0.7.15:

serde/serde/src/error.rs

Lines 28 to 44 in 78e7488

pub trait Error: Debug + Display {
/// A short description of the error.
///
/// The description should not contain newlines or sentence-ending
/// punctuation, to facilitate embedding in larger user-facing
/// strings.
fn description(&self) -> &str;
/// The lower-level cause of this error, if any.
fn cause(&self) -> Option<&Error> { None }
/// Stubbed! Returns type_id of `()`
#[doc(hidden)]
fn type_id(&self) -> TypeId where Self: 'static {
TypeId::of::<()>()
}
}

#[cfg(feature = "std")]
use std::error;
#[cfg(not(feature = "std"))]
use error;

pub trait Error: Sized + error::Error {

@dtolnay dtolnay merged commit 3343885 into serde-rs:master Sep 8, 2019
1 check passed
@dtolnay dtolnay deleted the error branch Sep 8, 2019
Xanewok added a commit to Xanewok/json that referenced this issue Feb 7, 2020
Relevant Serde PR: serde-rs/serde#1620

To support both no-/std builds without using somewhat noisy
conditional compilation directives, we implement the re-exported
`serde:🇩🇪:StdError` trait in serde-rs#606.

However, this was only introduced in >= 1.0.100, so we need to bump
the version requirement of serde.

On the off chance of someone pulling in incompatible 1.0.4{5,6} versions
of serde_json, I believe it'd be good to yank those and cut a new
release with this patch.

Sorry for the omission in the original PR.

Fixes serde-rs#621.
Xanewok added a commit to Xanewok/json that referenced this issue Feb 7, 2020
Relevant Serde PR: serde-rs/serde#1620

To support both no-/std builds without using somewhat noisy
conditional compilation directives, we implement the re-exported
`serde:🇩🇪:StdError` trait in serde-rs#606.

However, this was only introduced in >= 1.0.100, so we need to bump
the version requirement of serde.

On the off chance of someone pulling in incompatible 1.0.4{5,6} versions
of serde_json, I believe it'd be good to yank those and cut a new
release with this patch.

Sorry for the omission in the original PR.

Fixes serde-rs#621.
Xanewok added a commit to Xanewok/json that referenced this issue Feb 7, 2020
Relevant Serde PR: serde-rs/serde#1620

To support both no-/std builds without using somewhat noisy
conditional compilation directives, we implement the re-exported
`serde:🇩🇪:StdError` trait in serde-rs#606.

However, this was only introduced in >= 1.0.100, so we need to bump
the version requirement of serde.

On the off chance of someone pulling in incompatible 1.0.4{5,6} versions
of serde_json, I believe it'd be good to yank those and cut a new
release with this patch.

Sorry for the omission in the original PR.

Fixes serde-rs#612.
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