support revealing uses of opaques

[lcnr]

the following now works, needs a bit of cleanup to actually land :3

fn foo(x: &u32) -> impl Sized + '_ {
    let _ = || {
        let temp = 1;
        // normalization of the return type results
        // in `opaque<'local1> = &'local2 u32`.
        foo(&temp);
    };
    x
}

final breakage?

fn proj<F: FnOnce() -> P, P: Iterator<Item = Q>, Q>(_: F) {}
struct Lts<'a, 'b>(&'a (), &'b ());
fn expectations<'a>() -> impl Iterator<Item = Lts<'a, 'static>> + use<'a> {
    // opaque<'a> = Map<std::iter::Empty<Lts<'0, '1>>, {closure@src/main.rs:5:28: 5:31}>``
    proj::<_, _, Lts<'a, 'static>>(|| expectations());
    std::iter::empty().map(|x| x)
}

struct Foo<F, T>(T, F);
trait Trait {
    type Assoc;
}
impl<F: FnOnce(T) -> R, T, R> Trait for Foo<F, T> {
    type Assoc = R;
}

fn new_defining_use<F: FnOnce() -> R, R>(f: F) {}
fn rpit<'a>() -> impl Trait<Assoc = &'static ()> + use<'a> {
    new_defining_use(rpit::<'a>);
    Foo(&(), |x: &'static ()| x)
}

use std::convert::identity;
struct Foo<F, T>(T, F);
trait Trait {
    type Assoc;
}
impl<F: FnOnce(T) -> R, T, R> Trait for Foo<F, T> {
    type Assoc = R;
}

fn new_defining_use<F: FnOnce() -> R, R>(_: F) {}
fn rpit<'a>() -> impl Trait<Assoc = &'static ()> + use<'a> {
    new_defining_use(rpit::<'a>);
    Foo(&(), identity as fn(_) -> _)
}

struct Inv<'a, 'b>(*mut (&'a (), &'b ()));
fn new_defining_use<F: FnOnce() -> R, R>(_: F) {}
fn rpit<'a>() -> impl Sized + use<'a> {
    new_defining_use(rpit::<'a>);
    Inv::<'a, 'static>(std::ptr::null_mut())
}

fn new_defining_use<F: FnOnce(T) -> R, T, R>(_: F) {}
fn rpit<'a,  'b: 'b>(x: &'b ()) -> impl Sized + use<'a, 'b> {
    new_defining_use(rpit::<'a, 'b>);
    x
}

r? @compiler-errors

[lcnr]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 22d34c4 with merge 14ea441...

[bors]

☀️ Try build successful - checks-actions
Build commit: 14ea441 (14ea4416942169f85851de68119f43a59ef8801f)

[rust-timer]

Finished benchmarking commit (14ea441): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.2%, 1.1%]	62
Regressions ❌ (secondary)	0.5%	[0.3%, 0.8%]	16
Improvements ✅ (primary)	-0.3%	[-0.3%, -0.2%]	2
Improvements ✅ (secondary)	-0.5%	[-1.1%, -0.2%]	27
All ❌✅ (primary)	0.5%	[-0.3%, 1.1%]	64

Max RSS (memory usage)

Results (primary 2.0%, secondary -1.3%)

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)	2.0%	[1.2%, 2.8%]	5
Regressions ❌ (secondary)	3.1%	[2.5%, 3.6%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-7.2%, -1.2%]	5
All ❌✅ (primary)	2.0%	[1.2%, 2.8%]	5

Cycles

Results (primary 1.1%, secondary 1.5%)

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)	1.1%	[0.8%, 1.3%]	12
Regressions ❌ (secondary)	1.5%	[1.2%, 1.9%]	10
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[0.8%, 1.3%]	12

Binary size

Results (secondary -0.1%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	6
All ❌✅ (primary)	-	-	0

Bootstrap: 780.245s -> 782.612s (0.30%)
Artifact size: 366.19 MiB -> 366.30 MiB (0.03%)