The rustc-std-workspace-core crate
This crate is a shim and empty crate which simply depends on libcore and
reexports all of its contents. The crate is the crux of empowering the standard
library to depend on crates from crates.io
Crates on crates.io that the standard library depend on need to depend on the
rustc-std-workspace-core crate from crates.io, which is empty. We use
[patch] to override it to this crate in this repository. As a result, crates
on crates.io will draw a dependency edge to libcore, the version defined in
this repository. That should draw all the dependency edges to ensure Cargo
builds crates successfully!
rustc-std-workspace-core also ensures compiler-builtins is in the crate
graph. This crate is used by other crates in library/, other than std and
alloc, so the compiler-builtins setup only needs to be configured in a
single place. (Otherwise these crates would just need to depend on core and
compiler-builtins separately.)
Note that crates on crates.io need to depend on this crate with the name core
for everything to work correctly. To do that they can use:
core = { version = "1.0.0", optional = true, package = 'rustc-std-workspace-core' }
Through the use of the package key the crate is renamed to core, meaning
it'll look like
--extern core=.../librustc_std_workspace_core-XXXXXXX.rlib
when Cargo invokes the compiler, satisfying the implicit extern crate core
directive injected by the compiler.
The sources for the crates.io version can be found in
src/rustc-std-workspace.