library/rustc-std-workspace-core/README.md

# 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:

```toml
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`](../../src/rustc-std-workspace).