rust: add rust-src

[kidonng]

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This PR adds rust-src to rust formula, which is required by some third-party programs (such as rust-analyzer).

Default installation with rustup comes rust-src (shown with rustup component list --installed):

cargo
clippy
rust-docs
rust-src
rust-std
rustc
rustfmt

While Homebrew's installation is approximately equivalent to:

cargo
rust-docs
rustc

Since rust-src is just 37MB (as of Rust 1.48.0), and go ships with src too (though that's a little different from Rust), I think it's worth adding it to Homebrew's installation as well.

Not sure if there are any environment variables or build flags for installing it with official build scripts, but I guess this won't hurt since it's just moving files around.

[kidonng]

Not sure why the tests hanged, I tested with brew install rust -s on GitHub Actions and it took about 1h40m. The files are installed into the correct place.

[fxcoudert]

We have some CI trouble at the moment. One question is: why isn't it installed by default by make install? We generally prefer to rely on upstream deciding what to ship, through install targets or build scripts.

[kidonng]

I think my initial comments are a little misleading. make install just installs the rustc (along with its docs), and cargo gets added in as a resource. It's pretty clear why rust-src is not included.

The problem is, unlike other things such as rustfmt, rust-src can't be installed easily if not using Rustup. Thus it is inconvenient if one wants to install rust via Homebrew and some tools doesn't work.

Or let's see how others do this. Arch's rust bundles rust-src, Debian has rust-src as a package and rustc suggests rust-src.

If adding rust-src into rust formula is not favorable, can we add a new rust-src formula instead?

[carlocab]

unlike other things such as rustfmt, rust-src can't be installed easily if not using Rustup

This sounds like an excellent reason to me.

why isn't it installed by default by make install

My best guess, having looked at their docs:

1. Their primary target for building from source appear to be compiler developers [1]. They probably expect compiler developers to have a release build of the complete Rust toolchain separate from their development compiler, so they don't bother including the rest of the toolchain when you build from source.
2. They seem to have (softly) deprecated using make to build from source. Their preferred method now is to use a Python script called x.py. Perhaps their Makefiles are no longer up-to-date with the Rust toolchain.

We generally prefer to rely on upstream deciding what to ship

I think what upstream decides to ship with their own package (i.e. through rustup) is our most reliable indicator of what upstream ought to be shipped. (Cf. point above re Makefiles)

[1] E.g. the detailed guide to building from source is contained in their "Guide to Rustc Development". Their abridged instructions in the repo README suggest cloning the master branch of the Rust repo. Moreover, as mentioned already, cargo isn't even installed by make install; it needs to be built as a resource.

Apologies for writing a novel. Wasn't my intention.

[BrewTestBot]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[carlocab]

@kidonng, if you're still interested in this PR, please rebase it against master, and give rust a revision bump. If not, just close it again. Thanks.

[BrewTestBot]

@carlocab has triggered a merge.

[kidonng]

Thank you @carlocab!