Rename trait DepNodeParams to DepNodeKey

[Zalathar]

In query system plumbing, we usually refer to a query's explicit argument value as a “key”.

The first few commits do some preliminary cleanup that would conflict with the rename; the rename itself is in the final commit.

r? nnethercote (or compiler)

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[nnethercote]

Good renaming. I especially like how Key is singular, which matches reality.

One question about the to_fingerprint default.

View changes since this review

[nnethercote]

Heh, DepNodeConstructor no longer exists

[nnethercote]

How does this default method interact with the default to_finger_print method in the blanket impl below? Seems like we have two defaults, and I honestly don't know how this is treated.

[Zalathar]

I'm not sure either.

The blanket impl also has a HashStable bound, so maybe the trait-default is used for explicit impls on types that aren't HashStable?

I also noticed that removing the default body from the trait doesn't seem to cause any compile errors, so maybe it's not being used?

[nnethercote]

The output of this program is default 2.

![allow(incomplete_features)]
#![feature(specialization)]

trait Blah {
    fn f() {
        eprintln!("default 1");
    }
}

impl<T> Blah for T {
    default fn f() {
        eprintln!("default 2");
    }
}

fn main() {
    u32::f();
}

I think you can remove the panicking default in the trait definition.

[Zalathar]

Normally I try to refrain from “functional” changes in renaming PRs (to make review and archaology easier), but this seems innocent enough, and if we're right then it doesn't change any actual behaviour.

[nnethercote]

I think commit boundaries are more important than PR boundaries for this kind of thing. So we are good here.

[nnethercote]

@bors r+

[rust-bors]

📌 Commit b902f89 has been approved by nnethercote

It is now in the queue for this repository.