Weihang Lo

> The compiler has [an example of a hasher](https://github.com/rust-lang/rust/blob/96df4943409564a187894018f15f795426dc2e1f/compiler/rustc_data_structures/src/stable_hasher.rs#L55) the gives the same result on different kinds of platforms. Good reference! Thank you! I guess cargo might want to adopt...

> Registries in general are not platform specific, so there is no reason why an identifier for a registry should be platform specific. Totally agree on this. We might want...

> How strong do we expect these expectations to be I am pretty sure that we don't want to change the layout too often, as it may hurt caches. It...

> * One way to possibly mitigate this is to provide something like a `$CARGO_HOME/source_links` directory that has a stable, well-defined layout with symlinks to the various directories: This is...

I had a hard time understanding the question. If you want to use your own custom toolchain, you might want to [link to it via rustup](https://rust-lang.github.io/rustup/concepts/toolchains.html?highlight=link#custom-toolchains). If not, could you...

Instead of proposing a solution, could you elaborate more on the workflow issue you encountered? Why [optional dependencies](https://doc.rust-lang.org/cargo/reference/features.html#optional-dependencies) don't work well for your case?

This might also be a good candidate for the build scipt API: .

Could you try getting a minimal set of steps to reproduce? It would help investigate the issue. Some possibly relevant issues: * https://github.com/rust-lang/cargo/issues/12896 * https://github.com/rust-lang/cargo/issues/11780 * https://github.com/rust-lang/cargo/issues/11984

There is that should cover this scenario with a bit more extensibility. For now, I would recommend some patterns like [`cargo-xtask`](https://github.com/matklad/cargo-xtask). Cargo the project itself also [adopts it](https://github.com/rust-lang/cargo/blob/1d8980511ef3d315926ba79f5129f1a34f878aff/.cargo/config.toml#L1-L4).

@rfcbot reviewed BTW, do we have a plan for `SourceId`?