Add an alias from cargo x to cargo run -- in .cargo/config.toml.

[jyn514]

This helps with #94829 by making it more visually similar to the existing src/tools/x command.

Originally posted by @bjorn3 in #95854 (comment)

@rustbot label +S-tracking-design-concerns

[jyn514]

@rustbot label +E-easy +E-help-wanted

[hi-rustin]

@rustbot claim

[jyn514]

@Mark-Simulacrum: #95980 (comment)

I am not sure this is really worth it -- do we think that the long-term expectation for user interface is cargo x build?

Hmm, that's fair - I would like to eventually have the entrypoint be x and deprecate other entrypoints, which allows us to do things like cargo +beta-20YY-MM-DD without requiring rust-toolchain in the top-level directory. But that said, I think it's unusual to have a custom entrypoint like that? Maybe we should be using existing standard tools, like cargo xtask build? cc @Lokathor @thomcc

I am also happy to run a mini user survey in Zulip / the community discord; I think it will be good to learn what entrypoints people expect, even if the decision is not actually a democratic process. (update: done and done)

I think it might be worth holding off on a change like this PR until we have a clearer story around cargo run -- working and an expectation that users should migrate to it. I'm not sure we're there yet, though there's definitely a relatively happy path to getting there I expect.

👍

Maybe there's a general integration point -- similar to https://github.com/matklad/cargo-xtask/, but without .cargo/config.toml modifications which feel to me like somewhat of an anti-pattern (it's sort of a user, not upstream file, it seems to me).

That makes sense to me, but if we're avoiding changes to .cargo/config in rustbuild, we should also avoid them in bootstrap.py - it's very strange to me that bootstrap.py tries to guess whether you'd like vendoring or not and set that it up itself, IMO the user should have to configure that, which is closer to a normal cargo workflow. If we really want to support autoconfiguring vendoring, we should have that as part of x.py setup, rather than redoing it on each run.

It might be that we push for ability to declare aliased commands from Cargo.toml, pointing to subcrates in the workspace explicitly, as an unstable feature. That could mean a natural path for xbuild/xdoc/xcheck and so on to work out of the box, for example, if you already have a local rustc sysroot. Features like that have stalled out historically, but I think given a strong use case and interested hands, it's not impossible we could add something quite limited and unstable, though likely hard.

I don't really want to pursue that, especially since the cargo team is short on review time lately. I'd rather get cargo xtask or aliases to work.

[thomcc]

cc ... @thomcc

I actually think the current situation is largely fine, FWIW. But I may be too used to the status quo -- I did have to explain how to do the build to someone in a PR recently, I assume they were trying cargo build to no avail.

[jyn514]

Some good points brought up by various people:

• @5225225 would expect the entrypoint to work from anywhere in tree, not just at top-level like x.py does currently
• @digama0 thinks x anywhere is confusing and we should have more explicit names
• cargo run run expand-yaml-anchors is ... strange. cargo run in general is confusing, since it's not clear that "run" is referring to bootstrap itself.
• there is surprisingly (at least to me) strong support for "x.py is fine as is"

[jyn514]

I am also happy to run a mini user survey in Zulip / the community discord; I think it will be good to learn what entrypoints people expect, even if the decision is not actually a democratic process. (update: done and done)

The conclusion from that survey is we're going to use x.sh and x.ps1 scripts rather than cargo aliases. https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/bootstrap.20user.20survey/near/283897117