Suggest installing rustc-dev when rustc_* crate can't be found on nightly

[bjorn3]

The current error message can't find crate ... is not very helpful. Suggesting installation of rustc-dev would avoid things like rust-lang/miri#1241 (comment).

[pierwill]

@rustbot claim

[bjorn3]

Looks like this is already implemented:

rust/compiler/rustc_metadata/src/locator.rs

Lines 1109 to 1114 in 5728bd6

	} else if crate_name.as_str().starts_with("rustc_") {
	err.help(
	"maybe you need to install the missing components with: \
	`rustup component add rust-src rustc-dev llvm-tools-preview`",
	);
	}

[bjorn3]

This was done in #88830.

[pierwill]

Is this restricted to nightly builds?

rust/compiler/rustc_metadata/src/locator.rs

Line 1109 in 5728bd6

} else if crate_name.as_str().starts_with("rustc_") {

[pierwill]

Does the existing code need else if crate_name.as_str().starts_with("rustc_") && sess.is_nightly_build()?

[bjorn3]

Looks like it isn't restricted to nightly builds.