[DO NOT MERGE] `-Znext-solver=globally` experiments by lcnr · Pull Request #133502 · rust-lang/rust

lcnr · 2024-11-26T15:26:47Z

A revival of #124812. See

Current status:

~~./x.py b --stage 2 passes 🎉~~

try builds succeed 🎉 🎉 🎉

first perf run 👻 second perf run 👻 third perf run 👻

crater

This does not detect hangs or memory issues. We are triaging the regressions in https://rust-lang.zulipchat.com/#narrow/channel/364551-t-types.2Ftrait-system-refactor/topic/crater.20triage.20.3A3/with/572783267 and welcome your help there.

date	#crates	#regressions
2025.04.11	100	2
2025.04.11	1000	27
2025.04.17	10000	456
2025.04.18	10000	437
2025.04.24	10000	164
2025.04.26	10000	108
2025.04.28	10000	91
2025.05.01	10000	145 woops
2025.05.03	624228¹	1585²
2025.05.05	8964³	931²
2025.05.06	4401³	726²
2025.05.07	2704³	668²
2025.05.09	2345³	664²
2025.09.20	701952¹	4739 + 7039 spurious
2025.10.02	11712³	2568 + 2014 spurious
2025.10.04	4582³	1173 + 1147 spurious²
2025.12.30	761102¹	1424 + 8938 spurious ²
2026.01.01	5745³	1371 + 3227 spurious ²
2026.01.06	4171³	1361 + 2623 spurious ²

in-flight changes

7ebf298 double recursion limit
stepping into NormalizesTo where-clauses may be productive #155388
when bailing on ambiguity, don't force other results to ambig #155914

r? @ghost

a complete crater run ↩ ↩² ↩³
with doubled recursion_limit when evaluating goals ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹
only testing crates which may have regressed from the above run ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

compiler-errors · 2024-11-27T04:03:51Z

@bors try

[DO NOT MERGE] bootstrap with `-Znext-solver=globally` A revival of rust-lang#124812. Current status, we're failing in: - failing in `rustc_next_trait_solver` with 126 instances of the following error ``` error[E0311]: the parameter type `I` may not live long enough | help: consider adding an explicit lifetime bound --> compiler/rustc_next_trait_solver/src/solve/trait_goals.rs:624:53 | 624 ~ fn consider_structural_builtin_unsize_candidates<'a>( 625 ~ ecx: &mut EvalCtxt<'a, D>, 626 | goal: Goal<I, Self>, 627 ~ ) -> Vec<Candidate<I>> where I: 'a { ``` - `itertools` hangs, we're already encountered this hang in our previous attempt due to large type sizes. I believe that it's simply caused by a missing cache somewhere, potentially in `wf.rs`, but other visitors may also be responsible. See rust-itertools/itertools#945 for more details ### commits - rust-lang#133501 - rust-lang#133493 - 9456bfe and b21b116 reimplement candidate preference based on rust-lang#132325, not yet a separate PR - c3ef9cd is a rebased version of rust-lang#125334, unsure whether I actually want to land this PR for now r? `@ghost`

bors · 2024-11-27T04:05:03Z

⌛ Trying commit f631ca8 with merge ca04381...

compiler-errors · 2024-11-27T04:05:17Z

I also pushed:

I think this is sufficient to make the compiler build, or at least ./x.py build --stage=2 completes successfully on my local branch.

bors · 2024-11-27T06:15:40Z

💔 Test failed - checks-actions

bors · 2024-11-27T10:43:04Z

☔ The latest upstream changes (presumably #133527) made this pull request unmergeable. Please resolve the merge conflicts.

lqd · 2024-11-27T11:42:49Z

Next failure is on color-print-proc-macro-0.3.6 while building cargo.

pub fn repro() -> impl FnMut() {
    if true {
        || ()
    } else {
        || ()
    }
}

godbolt

compiler-errors · 2024-11-27T17:49:50Z

@bors try

[DO NOT MERGE] bootstrap with `-Znext-solver=globally` A revival of rust-lang#124812. Current status: `./x.py b --stage 2` passes 🎉 ### commits - rust-lang#133501 - rust-lang#133493 - 9456bfe and b21b116 reimplement candidate preference based on rust-lang#132325, not yet a separate PR - c3ef9cd is a rebased version of rust-lang#125334, unsure whether I actually want to land this PR for now - rust-lang#133517 * rust-lang#133518 * rust-lang#133519 * rust-lang#133520 * rust-lang#133521 * rust-lang#133524 r? `@ghost`

bors · 2024-11-27T17:51:02Z

⌛ Trying commit 6210ed3 with merge ac5ccad...

bors · 2024-11-27T20:03:42Z

💔 Test failed - checks-actions

compiler-errors · 2024-11-27T20:15:22Z

@bors try

[DO NOT MERGE] bootstrap with `-Znext-solver=globally` A revival of rust-lang#124812. Current status: `./x.py b --stage 2` passes 🎉 ### commits - rust-lang#133501 - rust-lang#133493 - 9456bfe and b21b116 reimplement candidate preference based on rust-lang#132325, not yet a separate PR - c3ef9cd is a rebased version of rust-lang#125334, unsure whether I actually want to land this PR for now - rust-lang#133517 * rust-lang#133518 * rust-lang#133519 * rust-lang#133520 * rust-lang#133521 * rust-lang#133524 r? `@ghost`

bors · 2024-11-27T20:16:33Z

⌛ Trying commit 8fa8f40 with merge 550ae0d...

lqd · 2024-11-27T20:26:10Z

I was reducing the new failure but you've already fixed it ^^

adwinwhite · 2026-07-08T02:27:01Z

@bors try @rust-timer queue

adwinwhite · 2026-07-08T06:37:37Z

@bors try @rust-timer queue

rust-bors · 2026-07-08T08:43:36Z

💔 Test for 286dc6d failed: CI. Failed job:

try - dist-x86_64-linux-quick (web logs, enhanced plaintext logs)

lqd · 2026-07-08T09:19:58Z

Ah, it seems building cargo is making the new solver ICE.

adwinwhite · 2026-07-08T13:59:03Z

@bors try @rust-timer queue

rust-log-analyzer · 2026-07-08T14:36:54Z

The job aarch64-gnu-llvm-21-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

failures:

---- tests::test_unstable_options_tracking_hash stdout ----

thread 'tests::test_unstable_options_tracking_hash' (47825) panicked at compiler/rustc_interface/src/tests.rs:856:5:
assertion `left != right` failed
  left: NextSolverConfig { coherence: true, globally: true }
 right: NextSolverConfig { coherence: true, globally: true }
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_failed::<rustc_session::config::NextSolverConfig, rustc_session::config::NextSolverConfig>

rust-bors · 2026-07-08T16:08:38Z

☀️ Try build successful (CI)
Build commit: b668081 (b66808126f24f2f30898306a881e1676824ea80c)
Base parent: c290daa (c290daa1e5274a52e54a0f49e31bd70192abc606)

adwinwhite · 2026-07-08T16:22:50Z

@craterbot check

craterbot · 2026-07-08T16:23:19Z

👌 Experiment pr-133502-23 created and queued.
🤖 Automatically detected try build b668081
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rust-timer · 2026-07-08T16:51:12Z

Finished benchmarking commit (b668081): comparison URL.

Overall result: ❌✅ regressions and improvements - 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
@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)	19.6%	[0.3%, 491.0%]	240
Regressions ❌ (secondary)	17.8%	[0.1%, 135.2%]	225
Improvements ✅ (primary)	-5.5%	[-16.4%, -0.5%]	12
Improvements ✅ (secondary)	-10.4%	[-81.3%, -0.0%]	59
All ❌✅ (primary)	18.4%	[-16.4%, 491.0%]	252

Max RSS (memory usage)

Results (primary 5.9%, 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)	6.2%	[1.1%, 24.4%]	117
Regressions ❌ (secondary)	4.1%	[0.8%, 9.0%]	25
Improvements ✅ (primary)	-1.0%	[-1.5%, -0.7%]	5
Improvements ✅ (secondary)	-3.1%	[-6.6%, -0.8%]	41
All ❌✅ (primary)	5.9%	[-1.5%, 24.4%]	122

Cycles

Results (primary 20.6%, secondary 19.8%)

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

	mean	range	count
Regressions ❌ (primary)	21.7%	[1.5%, 372.0%]	160
Regressions ❌ (secondary)	27.4%	[2.1%, 128.6%]	115
Improvements ✅ (primary)	-5.6%	[-9.5%, -2.4%]	7
Improvements ✅ (secondary)	-28.9%	[-80.0%, -0.9%]	18
All ❌✅ (primary)	20.6%	[-9.5%, 372.0%]	167

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.4%]	67
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	23
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.4%]	67

Bootstrap: 488.694s -> 504.328s (3.20%)
Artifact size: 389.00 MiB -> 385.17 MiB (-0.99%)

lcnr · 2026-07-13T08:38:11Z

@bors p=1 :>

next solver is important

lcnr · 2026-07-13T08:38:16Z

@craterbot p=1

craterbot · 2026-07-13T08:38:19Z

📝 Configuration of the pr-133502-23 experiment changed.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

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. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Nov 26, 2024

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compiler-errors force-pushed the rust4 branch from c3ef9cd to f631ca8 Compare November 27, 2024 04:03

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bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 27, 2024

compiler-errors force-pushed the rust4 branch from f631ca8 to 6210ed3 Compare November 27, 2024 17:49

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compiler-errors force-pushed the rust4 branch from 6210ed3 to 8fa8f40 Compare November 27, 2024 20:15

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lcnr and others added 6 commits July 8, 2026 21:28

enable -Znext-solver by default

1276577

emit a fatal error for generic_const_exprs

31402f6

double recursion limit for next-solver

ce9dd23

when bailing on ambiguity, don't force other results to ambig

6f96cb6

stepping into NormalizesTo where-clauses may be productive

19b4b0c

rerun if we meet any opaques in post analysis

4c1b070

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crater

in-flight changes

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rust-timer commented Jul 8, 2026

Overall result: ❌✅ regressions and improvements - please read:

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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lcnr commented Nov 26, 2024 •

edited by rustbot

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