Do not build tools if user do not want them

[mati865]

Fixes #71307

[rust-highfive]

r? @Mark-Simulacrum

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[Mark-Simulacrum]

@bors r+

Thanks!

[bors]

📌 Commit 9296d3b has been approved by Mark-Simulacrum

[tshepang]

I see cargo is getting built, even though I asked only for rustfmt

[build]
extended = true
tools = ["rustfmt"]

[tshepang]

Ok, I suppose that was because cargo-fmt also needed to get built

[mati865]

@tshepang I'm on my mobile right now but I think there was piece of code somewhere that always enables Cargo when extended = true.

[tshepang]

Is it this https://github.com/rust-lang/rust/blob/master/src/bootstrap/tool.rs#L560-L563

[mati865]

@tshepang exactly. I don't know whether it's fine to skip Cargo when bulidng other tools though.

[tshepang]

I would rather have a warning, or at least the behavior documented (in config.toml.example), than be surprised. Perhaps I should prepare a PR?

[mati865]

@tshepang sure but maybe this condition should be changed from

rust/src/bootstrap/tool.rs

Line 562 in 4bfd62a

run.path("src/tools/cargo").default_condition(builder.config.extended)

to

run.path("src/tools/cargo").default_condition(
    builder.config.extended
    && builder.config.tools.as_ref().map_or(true, |t| t.contains("cargo")))

since Cargo won't be installed if it's not present in tools list?

[tshepang]

That makes me wonder why cargo is not made part of that tools_extended macro... code looks similar?

[mati865]

I have no idea, probably because of this line:

rust/src/bootstrap/tool.rs

Line 584 in 9296d3b

.expect("expected to build -- essential tool")

[tshepang]

@Mark-Simulacrum why is cargo marked as a essential tool?

[Mark-Simulacrum]

We can't not ship a cargo, since essentially that just means a broken nightly (or whatever toolchain). It might be that there's a better way of doing it in the code though, I'm happy to review PRs and such changing the terminology or specific implementation details so long as we keep the property that our dist builders all build cargo and error if they're not able to.