TypeRelating emit WellFormed, not generalize

[lcnr]

fixes rust-lang/trait-system-refactor-initiative#250

r? BoxyUwU

[rustbot]

changes to the core type system

cc @compiler-errors, @lcnr

[rustbot]

BoxyUwU is currently at their maximum review capacity.
They may take a while to respond.

[lcnr]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 20a081a (20a081aa36c390f34fa701ef245698110b60e282, parent: 9312cd6d38396a13a08be73bb589fb1cf3dd32e6)

[rust-timer]

Finished benchmarking commit (20a081a): comparison URL.

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

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.0%, 2.8%]	6
Regressions ❌ (secondary)	5.7%	[0.1%, 15.2%]	6
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.8%	[-1.3%, 2.8%]	7

Max RSS (memory usage)

Results (secondary 1.2%)

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)	3.9%	[3.9%, 3.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.3%, secondary 10.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.2%, 2.5%]	3
Regressions ❌ (secondary)	10.1%	[2.6%, 14.9%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.3%	[2.2%, 2.5%]	3

Binary size

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

Bootstrap: 477.625s -> 479.621s (0.42%)
Artifact size: 391.41 MiB -> 391.37 MiB (-0.01%)

[lcnr]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 3d1dd7d (3d1dd7d76f85165ff58987a09d383f7d3e8fbb59, parent: 95aeb4696545eb4c9cbb68516f2912770e3846ea)

[rust-timer]

Finished benchmarking commit (3d1dd7d): comparison URL.

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

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	4.0%	[3.4%, 4.8%]	6
Regressions ❌ (secondary)	10.3%	[1.4%, 26.9%]	6
Improvements ✅ (primary)	-0.7%	[-1.4%, -0.0%]	2
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	6
All ❌✅ (primary)	2.8%	[-1.4%, 4.8%]	8

Max RSS (memory usage)

Results (primary 1.5%, secondary 0.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	1.8%	[1.5%, 2.0%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	1.5%	[1.5%, 1.5%]	1

Cycles

Results (primary 2.8%, secondary 3.6%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.6%, 3.1%]	3
Regressions ❌ (secondary)	9.6%	[3.3%, 23.4%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-3.1%, -1.8%]	6
All ❌✅ (primary)	2.8%	[2.6%, 3.1%]	3

Binary size

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

Bootstrap: 474.976s -> 475.327s (0.07%)
Artifact size: 391.06 MiB -> 391.12 MiB (0.02%)

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[lcnr]

@bors try @rust-timer queue

let's try to get the addition of combine_ty_args to be perf neutral. I didn't really expect this to have a large perf impact for any reasonable code

[rust-bors]

☀️ Try build successful (CI)
Build commit: c68c666 (c68c666b8da09235a6e7c2bb7df932e791eb9b19, parent: 5dbf4069dc98bbbca98dd600a65f50c258fbfd56)

[rust-timer]

Finished benchmarking commit (c68c666): comparison URL.

Overall result: ✅ improvements - 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

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-2.9%, -0.1%]	8
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	6
All ❌✅ (primary)	-0.6%	[-2.9%, -0.1%]	8

Max RSS (memory usage)

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

Cycles

Results (primary -2.9%)

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)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-2.9%, -2.9%]	1

Binary size

Results (primary -1.1%)

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)	-	-	0
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Bootstrap: 474.258s -> 474.449s (0.04%)
Artifact size: 388.39 MiB -> 388.41 MiB (0.01%)

[lcnr]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 898f13c (898f13cd81a0ddff99ba0cc248c43c60d4738716, parent: d682af88a57b0045f8348507682c16c6160b522d)

[rust-timer]

Finished benchmarking commit (898f13c): comparison URL.

Overall result: ✅ improvements - 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

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-0.5%	[-1.3%, -0.1%]	3
Improvements ✅ (secondary)	-0.8%	[-1.4%, -0.2%]	12
All ❌✅ (primary)	-0.5%	[-1.3%, -0.1%]	3

Max RSS (memory usage)

Results (primary 1.9%)

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

	mean	range	count
Regressions ❌ (primary)	4.6%	[4.6%, 4.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.8%	[-0.8%, -0.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.9%	[-0.8%, 4.6%]	2

Cycles

Results (secondary 3.7%)

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)	3.7%	[2.1%, 4.8%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 472.838s -> 476.429s (0.76%)
Artifact size: 388.40 MiB -> 388.47 MiB (0.02%)

[BoxyUwU]

is the perf win we get from making this diagnostic worse, necessary to land this PR? I don't like this diagnostic change and think it was signfiicantly better before. Variance is subtle and it seems quite valuable to me to be explicitly telling people that they have lifetime issues due to variance

[lcnr]

This diagnostics change is 1e593fd and imo the current diagnostic relies on a bug. If we're already in an invariant context, the fact that S is invariant over T doesn't matter.

I do still need to add tests for the fixed next-solver behavior before merging this PR regardless.