"explicit predicates of" and "predicates of" have the same dep-node

[nikomatsakis]

Both the explicit_predicates_of and predicates_of queries have the same dep-node:

rust/src/librustc/ty/maps/mod.rs

Lines 104 to 105 in c131bdc

	[] fn predicates_of: PredicatesOfItem(DefId) -> ty::GenericPredicates<'tcx>,
	[] fn explicit_predicates_of: PredicatesOfItem(DefId) -> ty::GenericPredicates<'tcx>,

This causes failures when the infer_outlives_requirements feature is used with incremental compilation. What needs to be done to fix this is the following:

1. First, create a test.
2. Second, create a new dep-node ExplicitPredicatesOfItem for this query.

Test

If we add a test in src/test/incremental sort of like this, it ought to fail:

// revisions: one 

// Regression test that `infer_outlives_predicates` can be used with
// incremental without an ICE.

#![feature(infer_outlives_requirements)]

struct Foo<'a, T> {
  x: &'a T 
}

fn main() { }

New dep-node

To make a new dep-node, you want to copy and paste this variant here:

rust/src/librustc/dep_graph/dep_node.rs

Line 502 in c131bdc

[] PredicatesOfItem(DefId),

The compiler should then lead you on a little tour of what else needs to be modified.

cc @toidiu

[Smibu]

This can be closed; the fix message format of #51467 was slightly wrong so GitHub left this open.