dtolnay/thiserror

This system is the thiserror crate, a Rust library that provides a derive macro to automatically implement the std::error::Error trait for custom types. It enables developers to define error types with custom display messages, source error chaining, and backtrace support through declarative attributes. The implementation includes comprehensive validation, no-std compatibility, and robust test coverage to ensure correct code generation and clear compiler diagnostics.

This change introduces the core implementation for the \thiserror\ crate's \\#\[derive(Error)\]\ macro. It adds the internal \impl/src\ module containing the AST definitions, attribute parsing, format string expansion, code generation, and validation logic required to automatically implement \std::error::Error\, \Display\, and \From\ for user-defined types. This enables users to derive error types with custom display messages, source error chaining, and backtrace support.

impl/src · high confidence

The project now offers users a choice of license, providing both the MIT and Apache License 2.0 texts. This allows downstream consumers to select the license that best fits their project's requirements, rather than being restricted to a single licensing option.

(repo-wide) · high confidence

The library's internal source files have been restructured to improve trait safety and formatting consistency. The private \AsDynError\ and \AsDisplay\ traits are now sealed to prevent external implementation, and the \AsDisplay\ trait specifically wraps interpolated variables to correctly forward the \Pointer\ trait for path formatting. Additionally, the \Var\ wrapper ensures that pointer-style formatting is handled consistently, and the \ThiserrorProvide\ trait is introduced to support the standard library's \Error::provide\ API for backtrace forwarding.

src · high confidence

The build script's detection logic for the \error\_generic\_member\_access\ feature has been moved from an inline string literal into a dedicated \build/probe.rs\ file. This change improves maintainability and ensures that the \RUSTC\_BOOTSTRAP\ environment variable is correctly tracked in the dependency info, which aids in accurate caching (e.g., via sccache) when the Rust compiler bootstrap flag is used.

build · high confidence

Added no-std compatibility tests; Comprehensive test suite for thiserror macro; Expanded UI test coverage for thiserror derive macro validation.

This release updates the thiserror crate to version 2.0.21, raising the minimum required Rust compiler version to 1.77. The implementation dependency has been upgraded from syn 2 to syn 3, and the crate now supports no-std environments via a new \std\ feature flag (enabled by default). The project structure has been reorganized into a workspace containing the main crate, the \thiserror-impl\ proc-macro crate, and a dedicated \tests/no-std\ test package.

(dependencies) · high confidence

The impl subcrate now includes symlinks to the project's Apache-2.0 and MIT license files, ensuring that license information is accessible within this specific component.

impl · high confidence

Written by watchdog.canine.dev from the codebase's own history, inside the signed delivery this page is composed from.

• CAI 68 → 69 (+0.6)
• Rubric changed (rubric-2026.09.10 → rubric-2026.09.18) — scores are not directly comparable.

• Code Health 85 → 84 (-0.7)
• Architecture 100 → 100 (+0.0)
• Maturity 57 → 57 (+0.0)
• Readiness 60 → 66 (+5.7)
• Security 100 → 100 (+0.0)

• Documentation: no installation or build instructions (README.md)

• Dependency hygiene PARTLY measured — Cargo dependencies read, no committed lock to grade for currency
• Inverted test pyramid
• thiserror_impl::attr::parse_token_expr (cyclomatic 19) (impl/src/attr.rs)

• 8 commits — 8 feature/other, 0 fixes

• (root) — 3 commits
• tests/ui — 2 commits
• (repo) — 1 commit
• impl/src — 1 commit
• tests/test_source.rs — 1 commit

• change: Keep track of nested turbofish depth
• change: Merge pull request #459 from dtolnay/turbofish
• change: Raise required compiler to Rust 1.74
• change: Raise required compiler to Rust 1.77
• change: Release 2.0.21
• change: Resolve io_other_error clippy lint in tests
• change: Update ui test suite to nightly-2026-09-22
• change: Update ui tests for version 2.0.21

Written by watchdog.canine.dev from the codebase's own history, inside the signed delivery this page is composed from.

dtolnay/thiserror was measured the same way every project in this corpus was: the same rubric, at a pinned commit, with the result published in full. Point a surveyor at a repository you know and see whether you agree with it.