Version History: Error Handling in Rust

Standard-library error features by Rust version, the thiserror 1 to 2 migration, and anyhow notes, so advice matches the project's MSRV and dependency versions.

#Contents

• Standard library
• thiserror 1 -> 2
• anyhow
• Still unstable
• MSRV guidance

#Standard library

Notes:

• Backtrace::capture() respects RUST_BACKTRACE and RUST_LIB_BACKTRACE; Backtrace::force_capture() always captures. Capturing is expensive: do it at error creation in rare paths only.
• fn main() -> Result<(), E> prints Error: {e:?} (the Debug form) and exits with code 1.
• Error::description is deprecated (since 1.42); implement Display instead.

#thiserror 1 -> 2

thiserror 2.0 (November 2024) is a small migration for most code:

Migration steps: bump to thiserror = "2", cargo check, fix any raw-identifier placeholders, run tests that pin Display text. Both majors can coexist in one dependency graph (different crates).

#anyhow

• anyhow 1.x is stable and backwards compatible; anyhow::Error requires Send + Sync + 'static sources.
• Backtraces: on Rust 1.65+ anyhow uses std::backtrace and captures when RUST_BACKTRACE=1 or RUST_LIB_BACKTRACE=1 is set; printed by the {:?} report.
• Result<T, anyhow::Error> alias: anyhow::Result<T>; anyhow::Ok(v) helps type inference in closures.
• Formats: {} outermost message, {:#} whole chain on one line joined by : , {:?} multi-line report with Caused by: and the backtrace, {:#?} struct-style debug.
• Alternatives with similar APIs: eyre/color-eyre (customisable reports), miette (diagnostics with source spans), error-stack (typed contexts with attachments).

#Still unstable

#MSRV guidance

• Below 1.81: no core::error::Error; no_std libraries need their own error trait or a feature-gated std impl.
• Below 1.65: no std::backtrace; use the backtrace crate or skip backtraces.
• Below 1.61: no ExitCode; exit codes need process::exit (accept ERR013 there, or upgrade).
• Check thiserror 2's own rust-version before upgrading a crate with an old MSRV; staying on thiserror 1 is fine if the MSRV cannot move.