Build breakage with 0.18 in `SolverConstraintsSet`

[kvark]

Building with Rust-1.73:

error[E0446]: crate-private type `SolverConstraintsSet<contact_constraints_set::ContactConstraintTypes>` in public interface
  --> /home/kvark/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rapier3d-0.18.0/src/dynamics/solver/contact_constraint/contact_constraints_set.rs:87:1
   |
87 | pub type ContactConstraintsSet = SolverConstraintsSet<ContactConstraintTypes>;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't leak crate-private type
   |
  ::: /home/kvark/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rapier3d-0.18.0/src/dynamics/solver/solver_constraints_set.rs:39:1
   |
39 | pub(crate) struct SolverConstraintsSet<Constraints: ConstraintTypes> {
   | -------------------------------------------------------------------- `SolverConstraintsSet<contact_constraints_set::ContactConstraintTypes>` declared as crate-private

My Cargo lock entry:

[[package]]
name = "rapier3d"
version = "0.18.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "92d07a833e0aa3bc57010caaa50bf75fa78afc03a74207607db740da4e4579a1"
...

[yutannihilation]

I see similar errors (e.g. #586) are reported recently not only in this repo.

I found this error was relaxed only since Rust 1.74.0. This change:

Replace private_in_public lint with private_interfaces and private_bounds per RFC 2145. Read more in RFC 2145.

Since rapier doesn't have a policy about MSRV (right?), technically, this might not be what is considered as a semver breakage. But, I personally feel Rust 1.74 is a bit too strict requirement for a non-experimental library.

[sebcrozet]

@kvark I’m not sure I understand what semver breakage means here. Rapier got bumped from 0.17 to 0.18 here, isn’t hat what semvers dictates in case of breaking change (apparently including, in this case, a MSRV change)?

[kvark]

Sorry about the confusion! I was reporting other similar issues to other repos, and they were actually semver-related.
For Rapier3d, it's not about semver at all. Let me edit the title accordingly.

[kvark]

I strongly recommend exposing MSRV and having your CI build/run with it specifically instead of the latest stable version.