Cargo standard library dependencies (original) (raw)

This issue is for tracking the writing of an RFC for extending Cargo.toml to specify dependencies on standard library crates.

There are a few needs and requirements:

• Opt-in to building the standard library instead of using pre-built artifacts.
• Specifying alternate standard library implementations.
• Create a way for Cargo to pass --extern=foo to rustc to specify explicit dependencies to add to the extern prelude, even for pre-built artifacts. This can help obviate the need for extern crate for crates like proc-macro.
  • We may also consider this to be implicit in some cases. For example, proc-macro could be automatically added with proc-macro = true.

There have been a few different proposals for syntax, please see the following:

• RFC 1133 proposal
• RFC 2663 proposal
• #5002 — Explicit standard library dependencies
• #5003 — Implicit standard library dependencies
• #57288 — Tracking issue for no more extern crate for sysroot crates

Some issues to consider:

• How does cargo treat multiple crates in a graph declaring dependencies on the standard library?
• How to balance implicit vs explicit dependencies?
• How to express a dependency on a pre-built artifact vs building one from source.