Derive Error for more error types

[killercup]

Objective

Align all error-like types to implement Error.

Fixes #10176

Solution

• Derive Error on more types
• Refactor instances of manual implementations that could be derived

This adds thiserror as a dependency to bevy_transform, which might increase compilation time -- but I don't know of any situation where you might only use that but not any other crate that pulls in bevy_utils.

The contributors example has a LoadContributorsError type, but as it's an example I have not updated it. Doing that would mean either having a use bevy_internal::utils::thiserror::Error; in an example file, or adding thiserror as a dev-dependency to the main bevy crate.

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Changelog

• All …Error types now implement the Error trait

[killercup]

This covers all types found by (struct|enum).*Error. If you know of more types or a better pattern, let me know.

[james7132]

This adds thiserror as a dependency to bevy_transform, which might increase compilation time -- but I don't know of any situation where you might only use that but not any other crate that pulls in bevy_utils.

I think it already is a transitive dependency via bevy_ecs, so this might not be a significant change.

The contributors example has a LoadContributorsError type, but as it's an example I have not updated it. Doing that would mean either having a use bevy_internal::utils::thiserror::Error; in an example file, or adding thiserror as a dev-dependency to the main bevy crate.

Note that the bevy_utils crate should still be accessible via bevy::utils, so bevy::utils::thiserror

[killercup]

I don't think updating the example blocks this PR.

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Note that the bevy_utils crate should still be accessible via bevy::utils, so bevy::utils::thiserror

Are we committed enough to this dependency to promote it in our examples?

But also with use bevy::utils::thiserror::Error;, I get this:

error[E0433]: failed to resolve: use of undeclared crate or module `thiserror`
   --> examples/games/contributors.rs:315:17
    |
315 | #[derive(Debug, Error)]
    |                 ^^^^^ use of undeclared crate or module `thiserror`
    |
    = note: this error originates in the derive macro `Error` (in Nightly builds, run with -Z macro-backtrace for more info)

However (and unintuitively), this works:

use bevy::utils::thiserror;

#[derive(Debug, thiserror::Error)]
enum LoadContributorsError {
    #[error("An IO error occurred while reading the git log.")]
    Io(#[from] io::Error),
    #[error("The CARGO_MANIFEST_DIR environment variable was not set.")]
    Var(#[from] VarError),
    #[error("The git process did not return a stdout handle.")]
    Stdout,
}

If you think this is a good example, I can push a commit with this change.

[alice-i-cecile]

Are we committed enough to this dependency to promote it in our examples?

IMO yes: it's an ecosystem standard and really helpful to teach Rust newcomers (even if it's not particularly Bevy-related).

[killercup]

IMO yes: it's an ecosystem standard and really helpful to teach Rust newcomers (even if it's not particularly Bevy-related).

Alright! Updated the example, too.