Restore Servo’s style crate in cargotest?

[SimonSapin]

src/tools/cargotest in this repository runs cargo test for a few crates as part of CI, including some of https://github.com/servo/servo/. This used to select the selectors and stylo_tests crates, whose dependency graph include most Servo crates that don’t rely on unstable language or std features.

In #54451 (comment) stylo_tests was removed. This in turn greatly reduced the coverage of what ends up being compiled during this test, since stylo_tests depended on the style crate which is one of the big components. With only the selectors crate and its dependency graph, much less of Servo is compiled which makes including Servo in cargotest less useful. On the other hand, compiling more stuff might increase the time taken by CI.

Some options here are:

• Add style_tests (note e v.s. o), which depends on the style crate, to the crates being tested in order to restore test coverage to roughly what it was before rustc: Allow #[no_mangle] anywhere in a crate #54451
• Remove Servo entirely from cargotest in order to reduce CI time spent cloning a large repository only to compile a small part
• No functional change, but remove this comment which is outdated since rustc: Allow #[no_mangle] anywhere in a crate #54451:

rust/src/tools/cargotest/main.rs

Lines 48 to 49 in b387f62

	// Only test Stylo a.k.a. Quantum CSS, the parts of Servo going into Firefox.
	// This takes much less time to build than all of Servo and supports stable Rust.

[SimonSapin]

CC @rust-lang/infra who might have thoughts about CI time

[shepmaster]

Discussed in our meeting. We'd accept a PR re-adding it.