[ShryukGrandhi]

Fixes #414

Checklist

• My branch is up-to-date with main branch.
• Everything works and tested on latest stable Rust.
• Coverage and Linting have been applied

Current behaviour

src/error/mod.rs imports std::error::Error and std::fmt for the Failed and FailedError types. This ties the error module to std and blocks the no-std work in #413.

New expected behaviour

The module imports core::error::Error and core::fmt. core::error::Error is stable since Rust 1.81, so it is in the MSRV (1.85). The behaviour does not change, because std::error::Error and std::fmt are re-exports of the core items. The use std::error::Error in the test module stays as it is, as the issue says.

A new unit test, failed_implements_core_error, uses Failed as a &dyn core::error::Error and checks the Display output and source().

Tested with:

• cargo fmt --all -- --check
• cargo clippy --all-features -- -Drust-2018-idioms -Drust-2024-compatibility -Dwarnings
• cargo test --all-features (all pass)
• cargo +1.85.0 build --all-features (MSRV)

Change logs

Changed

• src/error/mod.rs: use core::error::Error and core::fmt instead of the std:: paths.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.58%. Comparing base (9eaae9e) to head (35cabff).
⚠️ Report is 203 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #498       +/-   ##
===========================================
+ Coverage   43.97%   85.58%   +41.60%     
===========================================
  Files          85       96       +11     
  Lines        7281     9373     +2092     
===========================================
+ Hits         3202     8022     +4820     
+ Misses       4079     1351     -2728     

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[Mec-iS]

Thanks for the PR, @ShryukGrandhi. This is a good, minimal first step for #414/#413.

What I checked

• core::error::Error is stable since Rust 1.81, so it is fine with the 1.85 MSRV.
• std::error::Error and std::fmt re-export the core items, so there is no behaviour change. impl Error for Failed {} and both fmt::Display impls compile unchanged.
• The diff touches only src/error/mod.rs. Codecov reports all modified lines covered.

Suggestions (non-blocking)

1. failed_implements_core_error largely duplicates failed_implements_error_with_no_source, which already checks source().is_none() and the trait-object cast. The new part is the Display assertion on Failed::predict. You could fold that assertion into the existing test, or keep the new test but reword the comment. Its name suggests it proves the module is std-free, which it doesn't, because the test module still uses std.
2. This change doesn't make the module no-std yet. Failed still uses String and msg.to_string(), which come from the std prelude. Under #![no_std] they will need extern crate alloc; and use alloc::string::{String, ToString};. It would help to note in the PR description that this is step 1 and that the alloc imports are left for the follow-up in feat: no-std feature flag for embedded/edge targets #413, so the issue isn't closed prematurely. Fixes #414 is fine only if no-std Step 1: swap std::error::Error and std::fmt to core:: in error/mod.rs #414 is scoped to this swap.
3. The serde derives on Failed and FailedError need serde built with default-features = false plus alloc for no-std. That is worth tracking in the feat: no-std feature flag for embedded/edge targets #413 checklist.
4. Consider adding a CI job that builds with --no-default-features, or later a thumbv7em-none-eabihf target, so regressions are caught once the no-std work lands.

Codecov's base commit is 203 commits behind head, so please rebase on main to refresh CI before merge. Otherwise LGTM for this step. @Mec-iS, over to you.