v0.39.0

In this release

• 20 new lints, for a total of 127!
• Spotlight: Merging into cargo

This release requires Rust 1.81+ both to install (MSRV) and at runtime. Future releases will require Rust 1.83+.

Spotlight: Merging into cargo

While cargo-semver-checks is currently a standalone tool, Rust's cargo team plans to eventually make it a built-in part of cargo itself. Here's how that would work.

When users run cargo publish today, cargo first runs a series of checks to make sure everything is in order. For example, it ensures that the code repository doesn't include any uncommitted changes, so as not to accidentally publish uncommitted code to crates.io:

$ cargo publish
    Updating crates.io index
error: 1 files in the working directory contain changes that were not yet committed into git:

src/lib.rs

to proceed despite this and include the uncommitted changes, pass the `--allow-dirty` flag

cargo-semver-checks is planned to become another such pre-publish check, equivalent to running cargo semver-checks && cargo publish today. Of course, there are situations where maintainers may prefer to intentionally publish breaking changes in a non-major version, such as for a sufficiently critical security fix. The automatic semver-check will be overridable by passing a flag analogous to the --allow-dirty flag for uncommitted changes.

While we're excited to merge cargo-semver-checks into cargo, we are proceeding with caution before enabling it by default. We want to ensure "merge day" is a day of celebration for the entire Rust community, instead of causing frustration and further breakage! Good news: you can help us do that! Consider:

• Reporting any issues you find, including any suspected false-positives with our lints.
• Contributing lints to make cargo-semver-checks smarter
• Funding the project via GitHub Sponsors

New lints

Preventing breakage caused by changes in generic parameters (lifetimes, const generics, and generic types), changes in package features, union field changes, and more:

• feature_not_enabled_by_default
• function_abi_now_unwind
• function_requires_different_const_generic_params
• function_requires_different_generic_type_params
• method_requires_different_const_generic_params
• method_requires_different_generic_type_params
• proc_macro_now_doc_hidden
• trait_allows_fewer_const_generic_params
• trait_allows_fewer_generic_type_params
• trait_method_parameter_count_changed
• trait_method_requires_different_const_generic_params
• trait_method_requires_different_generic_type_params
• trait_requires_more_const_generic_params
• trait_requires_more_generic_type_params
• type_allows_fewer_const_generic_params
• type_allows_fewer_generic_type_params
• type_requires_more_const_generic_params
• type_requires_more_generic_type_params
• union_field_added_with_all_pub_fields
• union_field_added_with_non_pub_fields

Additionally, we've renamed one lint to align with the shift in preferred Rust terminology:

• trait_no_longer_object_safe -> trait_no_longer_dyn_compatible

Thanks to @Frank-III for contributing lints to this release!

All merged PRs

• Bump mozilla-actions/sccache-action from 0.0.6 to 0.0.7 by @dependabot in #1044
• Fix false-positive "macro no longer exported" report. by @obi1kenobi in #1043
• Weekly cargo update of dependencies by @obi1kenobi in #1045
• Use the new importable_path edge to clean up declarative macro lints. by @obi1kenobi in #1046
• Use importable_path data in proc macro lints. by @obi1kenobi in #1047
• Add two lints looking for new fields in repr(C) unions. by @obi1kenobi in #1049
• Add proc_macro_now_doc_hidden lint. by @obi1kenobi in #1050
• Add feature_not_enabled_by_default lint. by @obi1kenobi in #1051
• Add the type_requires_more_const_generic_params lint. by @obi1kenobi in #1052
• Add the type_allows_fewer_const_generic_params lint. by @obi1kenobi in #1054
• Rename test crate to match lint name. by @obi1kenobi in #1053
• Add function_requires_different_const_generic_params lint. by @obi1kenobi in #1056
• Remove unnecessary snapshot file. by @obi1kenobi in #1057
• Add method_requires_different_const_generic_params lint. by @obi1kenobi in #1058
• Add matching lints for const-generics breakage in traits. by @obi1kenobi in #1055
• Add trait_method_requires_different_const_generic_params lint. by @obi1kenobi in #1060
• Add trait_method_parameter_count_changed lint. by @obi1kenobi in #1059
• Add function_abi_now_unwind lint and fix function_abi_no_longer_unwind. by @obi1kenobi in #1061
• Weekly cargo update of dependencies by @obi1kenobi in #1062
• Weekly cargo update of dependencies by @obi1kenobi in #1064
• Update to the latest trustfall_rustdoc version. by @obi1kenobi in #1065
• Update funding info for 2025. by @obi1kenobi in #1066
• Small tweaks to funding manifest to make it valid. by @obi1kenobi in #1067
• Add next Rust minor to test matrix by @obi1kenobi in #1072
• Weekly cargo update of dependencies by @obi1kenobi in #1069
• Weekly cargo update of dependencies by @obi1kenobi in #1074
• Update trustfall to avoid missed optimization perf regression. by @obi1kenobi in #1075
• Weekly cargo update of dependencies by @obi1kenobi in #1077
• Bump to latest (including major) versions of all dependencies. by @obi1kenobi in #1078
• Add two lints over types' use of generic type arguments. by @obi1kenobi in #1079
• Add lints over changes in generic types in traits. by @obi1kenobi in #1080
• Add lints for type generics in functions, methods, and trait methods. by @obi1kenobi in #1081
• Weekly cargo update of dependencies by @obi1kenobi in #1082
• Add support for rustdoc JSON format v39. by @obi1kenobi in #1084
• replace object_safe with dyn_compatible by @Frank-III in #1083
• Release v0.39.0 with 20 new lints. by @obi1kenobi in #1085

New Contributors

• @Frank-III made their first contribution in #1083

Full Changelog: v0.38.0...v0.39.0