Add `Forget` trait feature gate - #165376

jdonszelmann · 2026-11-02T22:48:23Z

r? jonathanbrouwer

Add an unstable feature gate for the Forget trait. Creating the feature gate allows experimentation with its implementation. Note that this does not commit to anything w.r.t. stabilization of the forget trait. A feature gate can be removed at any time.

Part of #165370

JonathanBrouwer

@bors r+ rollup

View changes since this review

rust-bors · 2026-11-03T08:50:28Z

📌 Commit e6ae420 has been tentatively approved by JonathanBrouwer

It will be put into the queue for this repository once PR CI succeeds.

rust-bors · 2026-11-03T09:33:16Z

❌ Commit e6ae420 has been unapproved due to PR CI failure. Reapprove it with @bors r+ force if you want to ignore the failure.

jdonszelmann · 2026-11-03T09:33:23Z

sigh, that makes sense, should've checked that. I'll fix it in a bit

JonathanBrouwer · 2026-11-03T09:35:00Z

@bors try @rust-timer queue

Add `Forget` trait feature gate

jdonszelmann · 2026-11-03T13:44:44Z

This should fix it for the time being. Enabling forget will cost the extra 10% though so it's not ideal when actually landing forget trait but at least without the feature enabled this handles it gracefully

jdonszelmann · 2026-11-03T13:48:40Z

Local benchmarks show that this indeed solves the issue fyi

fmease · 2026-11-03T13:49:12Z

The "auto trait finder" that uses the old solver sucks; under the next solver we use a much faster but more limited one. In the future, when everything is more settled, adding new auto traits should hopefully not regress doc build times as much (inevitably tho, it'll regress HTML artifact size)

jdonszelmann · 2026-11-03T13:57:27Z

@fmease yea I figured. However, this is fine as a temporary solution right?

fmease · 2026-11-03T14:07:41Z

Yea, absolutely fine!

rust-bors · 2026-11-03T14:42:39Z

☀️ Try build successful (CI)
Build commit: 1167d71 (1167d715d42f42542c2dc76efa80a34e061bba9d)
Base parent: 6a98084 (6a98084e4a21b04504c034dfc640e35e32ab9854)

rust-timer · 2026-11-03T17:18:25Z

Finished benchmarking commit (1167d71): comparison URL.

Overall result: ❌ regressions - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@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)	0.4%	[0.2%, 0.7%]	10
Regressions ❌ (secondary)	0.5%	[0.2%, 1.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.2%, 0.7%]	10

Max RSS (memory usage)

Results (secondary -3.4%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.4%	[-6.3%, -1.6%]	3
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -2.8%)

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)	-2.8%	[-2.8%, -2.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.8%	[-2.8%, -2.8%]	1

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 482.475s -> 482.923s (0.09%)
Artifact size: 406.38 MiB -> 406.39 MiB (0.00%)

jdonszelmann · 2026-11-03T20:24:11Z

ok, @fmease or @rust-lang/rustdoc do you agree that 1% regressions on rustdoc are acceptable for this kind of change? I've looked and it's all just in html emitting basically, which is to be expected. We're likely going to do another change like it soon with Move.

GuillaumeGomez · 2026-11-04T10:06:30Z

Sounds acceptable. 👍

jdonszelmann · 2026-11-04T10:07:27Z

@JonathanBrouwer

JonathanBrouwer

@bors r+ rollup

View changes since this review

rust-bors · 2026-11-04T10:08:28Z

📌 Commit b70d2a2 has been approved by JonathanBrouwer

It is now in the queue for this repository.

JonathanBrouwer · 2026-11-04T10:09:31Z

@bors rollup=iffy
perf

…gate, r=JonathanBrouwer Add `Forget` trait feature gate r? jonathanbrouwer Add an unstable feature gate for the `Forget` trait. Creating the feature gate allows experimentation with its implementation. Note that this does not commit to anything w.r.t. stabilization of the forget trait. A feature gate can be removed at any time. Part of rust-lang#165370

…uwer Rollup of 7 pull requests Successful merges: - #164752 (Apply the Cortex-A53 843419 CC mitigation to aarch64 targets ) - #165376 (Add `Forget` trait feature gate) - #165257 (Revert FCW on lint attributes on macro calls) - #165364 (Update books) - #165424 (Update amdgpu datalayout for LLVM 24) - #165443 (Add `Discriminant::ord`) - #165445 (Add an unstable option to increase the chain depth of the next solver overflow FCW)

…gate, r=JonathanBrouwer Add `Forget` trait feature gate r? jonathanbrouwer Add an unstable feature gate for the `Forget` trait. Creating the feature gate allows experimentation with its implementation. Note that this does not commit to anything w.r.t. stabilization of the forget trait. A feature gate can be removed at any time. Part of rust-lang#165370

…uwer Rollup of 17 pull requests Successful merges: - #164752 (Apply the Cortex-A53 843419 CC mitigation to aarch64 targets ) - #165011 (std: Clean up and improve errors for `is_*_feature_detected` macros) - #165376 (Add `Forget` trait feature gate) - #164482 (Remove the label starting with 0 in the test binary_asm_labels_allowed.rs) - #165201 (Move a bunch of methods out of `AttributeExt`) - #165268 (Fix constant-pattern equality suggestion spans in macros) - #165318 (Fix explicit destructor-call suggestion spans in macros) - #164440 ([Outreachy] alloc: Add test coverage for try_clone_from_ref_in (Box, Arc, Rc)) - #165001 (Document allocator swap in BinaryHeap::append) - #165257 (Revert FCW on lint attributes on macro calls) - #165330 (Impl read_le/read_be for f16 and f128) - #165364 (Update books) - #165414 (Remove unusued query key impl) - #165424 (Update amdgpu datalayout for LLVM 24) - #165440 (docker: bump node to v24.22.2 in shared script) - #165443 (Add `Discriminant::ord`) - #165445 (Add an unstable option to increase the chain depth of the next solver overflow FCW)

rustbot assigned JonathanBrouwer Nov 2, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Nov 2, 2026

jdonszelmann mentioned this pull request Nov 2, 2026

Tracking Issue for the Forget trait #165370

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