Stop using ty::GenericPredicates for non-predicates_of queries

[compiler-errors]

GenericPredicates is a struct of several parts: A list of of an item's own predicates, and a parent def id (and some effects related stuff, but ignore that since it's kinda irrelevant). When instantiating these generic predicates, it calls predicates_of on the parent and instantiates its predicates, and appends the item's own instantiated predicates too:

rust/compiler/rustc_middle/src/ty/generics.rs

Lines 407 to 413 in acb4e8b

	if let Some(def_id) = self.parent {
	tcx.predicates_of(def_id).instantiate_into(tcx, instantiated, args);
	}
	instantiated.predicates.extend(
	self.predicates.iter().map(|(p, _)| EarlyBinder::bind(*p).instantiate(tcx, args)),
	);
	instantiated.spans.extend(self.predicates.iter().map(|(_, sp)| *sp));

Notice how this should result in a recursive set of calls to predicates_of... However, GenericPredicates is also misused by a bunch of other queries as a convenient way of passing around a list of predicates. For these queries, we don't ever set the parent def id of the GenericPredicates, but if we did, then this would be very easy to mistakenly call predicates_of instead of some other intended parent query.

Given that footgun, and the fact that we don't ever even use the parent def id in the GenericPredicates returned from queries like explicit_super_predicates_of, It really has no benefit over just returning &'tcx [(Clause<'tcx>, Span)].

This PR additionally opts to wrap the results of EarlyBinder, as we've tended to use that in the return type of these kinds of queries to properly convey that the user has params to deal with, and it also gives a convenient way of iterating over a slice of things after instantiating.

[rustbot]

r? @nnethercote

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[rustbot]

HIR ty lowering was modified

cc @fmease

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[compiler-errors]

r? @fmease or reassign :)

[fmease]

r=me with comment addressed in one way or another

[compiler-errors]

I'm not certain that I understand your idea of encoding EarlyBinder<&'tcx [(Clause<'tcx>, Span)]> as LazyArray<EarlyBinder<(Clause<'tcx>, Span)>> -- I wouldn't want to change the query result to be &'tcx [EarlyBinder<(Clause<'tcx>, Span)>] since that's more awkward to work with, and it seems like it would require an annoying amount of shunting between EarlyBinders on the elements and on the whole slice. It would also be an objectively worse encoding if we ever tracked the real bound vars on the EarlyBinder.

@rustbot ready

[fmease]

Thanks for checking and sorry for the confusion.

@bors r+ rollup (no behavioral change)

[bors]

📌 Commit 9200452 has been approved by fmease

It is now in the queue for this repository.