Remove the rationale field from BashBinaryRequest.

[benjyw]

It exists only to provide slightly more context for an error
message. But this context isn't actionable (the rationale doesn't
affect how you fix the error). And the downside is that the
rationale affects the cache key, so we have to re-find bash
for every rationale, which is superfluous extra work.

Right now there are only two rationales, so the work is only
done twice instead of once (and the underlying process is still cached
so the extra work is just in-process). But this field models "bad behavior":
If in the future someone, naively, makes the rationale a dynamic
message, here or in some similar case that they cargo-culted from here,
then the rule will thrash. Better to remove this landmine preemptively.

[ci skip-rust]

[ci skip-build-wheels]

[jsirois]

Since the rationale provided little value in this case, the change probably makes sense. That said, if we expected more fluent use of dataclasses / more thought about the types used in rule signatures / Gets, this could just have been, IIUC:

@dataclass(frozen=True)
class BashBinaryRequest:
    rationale: str = dataclasses.field(compare=False)

[stuhood]

The Process.description field is ignored in equality for the underlying intrinsics: see

pants/src/rust/engine/process_execution/src/tests.rs

Lines 30 to 37 in 7817286

	let a = process_generator("One thing".to_string(), Some(Duration::new(0, 0)));
	let b = process_generator("Another".to_string(), Some(Duration::new(0, 0)));
	let c = process_generator("One thing".to_string(), Some(Duration::new(5, 0)));
	let d = process_generator("One thing".to_string(), None);
	// Process should derive a PartialEq and Hash that ignores the description
	assert_eq!(a, b);
	assert_eq!(hash(&a), hash(&b));

How did you confirm that the process was running multiple times?

[benjyw]

I didn't confirm it. In fact I mentioned the opposite - that it wouldn't run multiple times. But that's mainly because we were only using the rationale for the error message, not for the process description.

This is more about not superfluously re-running and re-caching rules that differ only on this rationale.