mir_build: Rename TestCase to TestableCase

[Zalathar]

In the spirit of #149946, this is another renaming of something I've always found confusing.

When lowering match conditions, there is a subtle distinction between the kind of test being performed (on a scrutinee place), the possible outcomes of that test, and the different “cases” (corresponding to pattern nodes) that the test is distinguishing. Cases imply a particular preferred test, but once a test is chosen it can also interact with other cases as well.

I have often mixed up TestKind and TestCase, since the names are so similar, and they share several variant names. Therefore, this PR renames TestCase to TestableCase, to emphasise that these are the things selected by whatever test is being performed.

There should be no change to compiler behaviour.

[rustbot]

Some changes occurred in match lowering

cc @Nadrieril

[rustbot]

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[Nadrieril]

For me TestableCase is more confusing than TestCase. I would prefer TestOutcome for example

[Zalathar]

Hmm, my main motivation is to get rid of the Test prefix, because that's the part that keeps confusing me.

I think I would find TestOutcome even more confusing, because of TestBranch.

[Nadrieril]

oh, fair point x)

[Nadrieril]

r? me

[Zalathar]

I would like to give this thing a better name, but I think it's only worth changing if we can agree on a new name that's clearly better.

So I would be fine with closing this for now, since it would conflict with some other simplifications/improvements that I'm investigating.

[Nadrieril]

I can live with TestableCase. The Or and Deref variants prevent other names I thought of, this is just a confusing enum in general honestly. If this helps you, let's do this.

@bors r+ rollup

[bors]

📌 Commit 7f6f522 has been approved by Nadrieril

It is now in the queue for this repository.