"rust.all_targets": false still builds cfg(test) targets.

[eddyb]

See #1714 for context, but I suspect this can be repeated on even simple crates, they just build much faster so it's harder to tell.
(Just checked on another project I had handy, glOOF, and it also builds gloof cfg(test) on every change, can barely see it for a second in the status bar, but it's there - there might be a better way to confirm but I don't know how to get a proper log)

I'm not sure how this is happening, based on this (and the relevant Cargo code) I would expect it to "just" work:

rls/rls/src/build/cargo.rs

Lines 214 to 227 in 581415c

	filter: CompileFilter::from_raw_arguments(
	opts.lib,
	opts.bin,
	opts.bins,
	// TODO: support more crate target types.
	Vec::new(),
	// Check all integration tests under `tests/`.
	cfg_test,
	Vec::new(),
	false,
	Vec::new(),
	false,
	opts.all_targets,
	),

EDIT: "rust.build_lib": true also doesn't seem to restrict the set of targets, but I'm not sure it does nothing

[eddyb]

This is confusing, I thought I could use [lib] test = false in Cargo.toml to remove cfg(test) targets, but that doesn't remove it?
Even weirder, it seems to build cfg(test) before the library itself, at least sometimes?

Is it possible "cfg(test)" doesn't come from Cargo as a string, and RLS is misinterpreting what Cargo is actually building?