444

[RAprogramm]

Closes #444

Adds the app_error! expression macro — ad-hoc AppError construction in one line, closing the ergonomic gap with anyhow!.

Forms

• app_error!(AppErrorKind::Timeout) → AppError::bare(kind), zero allocation
• app_error!(AppErrorKind::Validation, "bad {value}") → AppError::with(kind, ...), full format! grammar with implicit capture, single allocation

Design notes

• Named app_error! (not error!) to avoid colliding with tracing::error! in user imports
• Composes with the existing statement macros: fail!(app_error!(...)); fail! grammar intentionally untouched (it accepts arbitrary error expressions, incl. custom error types)
• Works under no_std (default-features = false) via a hidden alloc::format re-export
• Documented next to ensure!/fail! in README (regenerated) and macro docs with doctests for every form

Tests

10 new integration tests (bare form, trailing comma, implicit/positional formatting, kind+code correctness, expression position via ok_or_else/map_err, composition with ensure!/fail!); full workspace suite, doctests (175), clippy zero warnings, nightly fmt, readme_sync 36/36 — all green.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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