Handle ReErased in responses in new solver

[compiler-errors]

There are legitimate cases in the compiler where we return ReErased for lifetimes that are uncaptured in the hidden type of an opaque. For example, in the test committed below, we ignore ignore the bivariant lifetimes of an opaque when it's inferred as the hidden type of another opaque. This may result in a type_of(Opaque) call returning a type that references ReErased. Let's handle this gracefully in the new solver.

Also added a rustc_hidden_type_of_opaques attr to print hidden types. This seems useful for opaques.

r? lcnr

[rustbot]

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

[lcnr]

r=me after nit

[compiler-errors]

@bors r=lcnr

[bors]

📌 Commit a387a3c has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit a387a3c with merge 271dcc1...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing 271dcc1 to master...

[rust-timer]

Finished benchmarking commit (271dcc1): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.5%	[-1.5%, -1.5%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.3%	[1.5%, 4.2%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-3.1%, -1.3%]	7
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	6.2%	[6.2%, 6.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.5%, -1.5%]	2
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: missing data
Artifact size: 304.35 MiB -> 304.37 MiB (0.01%)