Expand free alias types during variance computation

[fmease]

Instead of computing variances for them since they can never be rigid anyway.

Fixes #140230.

[fmease]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 1c11869 with merge 1b77fcd...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1b77fcd (1b77fcd0847b6d6dcac3b0857fc0acc504e9f357)

[rust-timer]

Finished benchmarking commit (1b77fcd): comparison URL.

Overall result: ❌ regressions - 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)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	0.7%	[0.7%, 0.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[1.1%, 1.1%]	1

Max RSS (memory usage)

Results (primary 3.2%, secondary 5.0%)

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)	3.2%	[0.5%, 9.0%]	4
Regressions ❌ (secondary)	5.0%	[4.6%, 5.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.2%	[0.5%, 9.0%]	4

Cycles

Results (primary -0.8%, secondary -10.5%)

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.8%	[-0.8%, -0.8%]	1
Improvements ✅ (secondary)	-10.5%	[-14.0%, -2.6%]	7
All ❌✅ (primary)	-0.8%	[-0.8%, -0.8%]	1

Binary size

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

Bootstrap: 773.561s -> 773.719s (0.02%)
Artifact size: 365.44 MiB -> 365.31 MiB (-0.04%)

[fmease]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 9429c14 with merge f04a108…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: f04a108 (f04a1083ef0335f753c2d52583e8cc33a34e95fb, parent: 119574f83576dc1f3ae067f9a97986d4e2b0826c)

[rust-timer]

Finished benchmarking commit (f04a108): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

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

Instruction count

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

Max RSS (memory usage)

Results (primary -1.5%, secondary 1.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.6%	[3.1%, 6.1%]	2
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	1
Improvements ✅ (secondary)	-5.0%	[-5.0%, -5.0%]	1
All ❌✅ (primary)	-1.5%	[-1.5%, -1.5%]	1

Cycles

Results (secondary 2.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary -0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-	-	0

Bootstrap: 463.013s -> 463.287s (0.06%)
Artifact size: 374.51 MiB -> 374.53 MiB (0.01%)

[fmease]

Ready :)

A lot of the diff is test additions to increase coverage.

[rust-bors]

☔ The latest upstream changes (presumably #155083) made this pull request unmergeable. Please resolve the merge conflicts.

[BoxyUwU]

v

View changes since this review

[BoxyUwU]

i kind of prefer keeping this "exhaustive" and matching on the rest of the kind here

[BoxyUwU]

can you add a test that we expand multiple layers of type alias, e.g.

type Foo<'a> = &'a u8;
type Bar<'a> = Foo<'a>;
type Qux<'a> = Bar<'a>;
type Co<'a> = Qux<'a>;
struct Co2<'a>(Co<'a>);

[BoxyUwU]

can you also add a test for unused params of an adt due to unused params of an LTA:

type Unused<T> = ();
struct Foo<T>(Unused<T>);

[BoxyUwU]

I expect this probably errors? because T winds up unconstrained. Unsure whether that is desirable or not. We should note this as a thing to figure out pre-stabilization (though it's forwards compatible with making T invariant)