Try to get the target triple from rustc itself

[cuviper]

The prior method was trying to pick the triple out of the sysroot path.
A FIXME comment already notes that this doesn't work with custom
toolchains in rustup. It also fails with distro-installed toolchains,
where the sysroot may simply be /usr.

The output of rustc -Vv is a more reliable source, as it contains a
line like host: x86_64-unknown-linux-gnu. This should be enough to
identify the triple for any rustc, but just in case, the path-based
code is kept as a fallback.

[cuviper]

Note, it's already a bit of a problem to assume that the host/toolchain triple matches the target. That appears to be part of the cross-compilation issue rust-lang/rls#309. Eventually, I expect the real target triple should be communicated directly, but for now this PR should still be an improvement.

[Xanewok]

That's definitely an improvement, thanks. I assume the logic at

rls-analysis/src/loader.rs

Lines 90 to 96 in 7c39452

	let sys_root_path = sys_root_path();
	let target_triple = extract_target_triple(sys_root_path.as_path());
	let libs_path = sys_root_path
	.join("lib")
	.join("rustlib")
	.join(&target_triple)
	.join("analysis");

will continue to work for /usr or similarly globally installed toolchains?

[cuviper]

I assume the logic at [...] will continue to work for /usr or similarly globally installed toolchains?

Yes, /usr is my primary motivation as a Fedora & RHEL packager. :)

However, there's still some assumption in {sysroot}/lib/rustlib/... in that /lib/, which may be something else if the toolchain was built with ./configure --libdir PATH or [install] libdir = "PATH" in config.toml. Early on I did use this in Fedora, where 64-bit wants /usr/lib64, but I stopped because it was often fragile in the old makefiles and in rustbuild. I don't know if other distros currently change libdir, but I also don't know anyway to discover the configured path.

I'll add a FIXME comment noting this, at least.

[cuviper]

Anything else for me to do here?

[nrc]

Anything else for me to do here?

Doesn't look like it, sorry for the delay and thanks for the reminder!