LTS for Rust dependencies

Trying to use an old compiler, and all the dependencies are broken? Here's a workaround.

This is a proof of concept of an alternative crates registry that contains crates compatible with old Rust versions.

You can set crates-io registry state per project to contain only crates that are compatible with a selected Rust version.

Requirements

• Rust 1.13 or later (this is so old, that even Debian has it),
• git command in PATH.

Tested on macOS and Linux.

Current vs future implementation

The current implementation just rewinds the crates-io registry to a previous commit from a date of release of a specific Rust version, and configures Cargo to use the truncated registry. This means that the registry won't contain any newer crates, even if they'd be compatible.

A future implementation will use a specially-filtered custom registry, allowing use of all crate versions as long as they're compatible.

Installation

cargo install -f lts

Usage

cd to your project's directory (where Cargo.toml is), and run:

cargo lts

It will configure the current project to use registry compatible with the current compiler. On the first run, it may take a few minutes to download the full registry.

You can specify an old Rust version as a compatibility target cargo lts 1.26.0 or a specific date cargo lts 2018-01-01.

And then run:

cargo update

to update Cargo.lock from the stale registry. To go back to the future, delete [source.crates-io] replace-with = … from ./.cargo/config.

You can set CARGO_MANIFEST_DIR environmental variable to modify other than the current directory. cargo lts assumes the index is in $CARGO_HOME/registry/index/github.com-1ecc6299db9ec823/.git. You can set CARGO_REGISTRY_GIT_DIR to reference another checkout of the index.

cargo lts prefetch fetches the registry without altering the local project. Useful to cache registry state in Docker images.