Implement new effects desugaring

[fee1-dead]

cc @rust-lang/project-const-traits.

Notes for the new desugaring: https://hackmd.io/@beef/HJyX7wF70

• See if we want T: Tr to desugar into T: Tr, T::Effects: Compat<true>
• Fix ICEs on type Assoc: ~const Tr and type Assoc<T: ~const Tr>
• add types and traits to minicore test
• update rustc-dev-guide

Fixes #119717
Fixes #123664
Fixes #124857
Fixes #126148

[rustbot]

r? @oli-obk

(rustbot has picked a reviewer for you, use r? to override)

[oli-obk]

Could feed this query.

Also: don't we need a where Self: Sized bound to avoid breaking all dyn Trait for now?

[fee1-dead]

assoc types don't break object safety (we'd just need to make it default to Runtime)

what breaks object safety would probably be the const host: bool that we now insert onto each method.

[bors]

☔ The latest upstream changes (presumably #120392) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #120991) made this pull request unmergeable. Please resolve the merge conflicts.

[fee1-dead]

This PR changes T: Tr where Tr is #[const_trait] to also lower into an additional bound of <T as Tr>::{opaque}: Compat<true>. That means potentially more work for the trait solver. Let's see what the perf impact is like, as right now we have Add as a #[const_trait]

@bors try @rust-timer queue

[fee1-dead]

@bors try

[bors]

⌛ Trying commit f1cd746 with merge c5d6267...

[bors]

💔 Test failed - checks-actions

[fee1-dead]

@bors try @rust-timer queue

[rust-timer]

Finished benchmarking commit (ba1d7f4): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.3%	[0.2%, 0.6%]	72
Regressions ❌ (secondary)	0.4%	[0.1%, 0.9%]	24
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.2%, 0.6%]	72

Max RSS (memory usage)

Results (primary -0.1%, secondary 3.4%)

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)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	3.4%	[3.0%, 3.8%]	3
Improvements ✅ (primary)	-1.0%	[-1.0%, -1.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-1.0%, 0.8%]	2

Cycles

Results (secondary -8.2%)

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)	-8.2%	[-8.5%, -8.0%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, secondary 0.4%)

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)	0.1%	[0.0%, 0.4%]	93
Regressions ❌ (secondary)	0.4%	[0.0%, 0.5%]	33
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.4%]	93

Bootstrap: 697.982s -> 695.844s (-0.31%)
Artifact size: 324.48 MiB -> 324.63 MiB (0.05%)

[fee1-dead]

Opened #127144 as an attempt to fix the performance regression

[pnkfelix]

Visiting for weekly rustc perf triage.

• Biggest (>=0.4%) primary regressions: regex, bitmaps, typenum, stm32f4, exa. (19 variants of those five benchmarks.)
• the PR author (fee1-dead) has made a couple follow-up attempts to address the regressions, but nothing has hit yet.
• not marking as triaged, in order to encourage addressing the regressions. (note however: the cycles:u metric didn't regress, at least not past our noise-filtering significance threshold. Nor did task-clock:u. It is not totally clear how much effort is warranted here, apart from a desire to keep the instruction count low just because that is our most stable proxy for "computational effort")