Trim executable name when getting function color

[mkeeter]

On illumos, the DTrace script prints the library or executable before the function in the stack trace, e.g.

libc.so.1`__fdsync+0xa
cru-ds-fdsync-v1`std::fs::File::sync_all::hcd4d0768a77cbc2e+0x14
cru-ds-fdsync-v1`<crucible_downstairs::extent_inner_raw::RawInner as crucible_downstairs::extent::ExtentInner>::flush::h68fcf1774758d74e+0x9c
cru-ds-fdsync-v1`crucible_downstairs::extent::Extent::flush::h0eac5b95dfa4f5f0+0x472
cru-ds-fdsync-v1`std::panicking::try::h7ba6611983f64757+0x4c
cru-ds-fdsync-v1`_$LT$rayon_core..job..HeapJob$LT$BODY$GT$$u20$as$u20$rayon_core..job..Job$GT$::execute::h60b9d586fc4f8a0f (.llvm.8052073739315931670)+0x46
cru-ds-fdsync-v1`rayon_core::registry::WorkerThread::wait_until_cold::haa78671c0e7aa9b1+0x50f
cru-ds-fdsync-v1`rayon_core::registry::ThreadBuilder::run::hf28d413d115bded0+0x398
cru-ds-fdsync-v1`std::sys_common::backtrace::__rust_begin_short_backtrace::hfcd6324a3e87fc1e+0x48
cru-ds-fdsync-v1`core::ops::function::FnOnce::call_once{{vtable.shim}}::hbfa4fc2e086997af+0xb2
cru-ds-fdsync-v1`std::sys::unix::thread::Thread::new::thread_start::h1783cbcbbf061711+0x29
libc.so.1`_thrp_setup+0x77
libc.so.1`_lwp_start

This means that tests like name.starts_with("core::") don't work.

This PR updates the Rust color selector to drop anything before the backtick, so that calls to starts_with(..) correctly classify functions in core / std / etc.

I only did it for Rust because that's what I'm using; if you want, I can make the equivalent change for Java and Python resolvers (which also use starts_with).

Thanks!

[jonhoo]

Just a small nit! I'm okay landing it for just Rust if we're not sure whether you end up with the same kinds of trace lines for other languages. If on the other hand you have evidence that the exact same thing applies to other languages, I think it's worthwhile changing for all of them!

[jonhoo]

I think you can use split_once to great effect here:

Suggested change

	let name = if let Some(i) = name.find('`') {
	&name[i + 1..]
	} else {
	name
	};
	let name = name.split_once('`').map(|(_, after)| after).unwrap_or(name);

[mkeeter]

Nice, done in c41a5ba

[mkeeter]

I'm okay landing it for just Rust if we're not sure whether you end up with the same kinds of trace lines for other languages. If on the other hand you have evidence that the exact same thing applies to other languages, I think it's worthwhile changing for all of them!

It looks like Java and Python are profiled differently (using AsyncProfiler and austin respectively?), so I'm going to leave this as Rust-exclusive for now.