[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 👻 fourth perf run 👻 fifth 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
2026.07.17	1014957¹	6502 + 11187 spurious ²
2026.07.20	17458³	991 + 3331 spurious ²
2026.07.23	4322³	959 + 1680 spurious ²
2026.07.31	1049848¹	1254 + 13493 spurious
2026.08.03	14035³	679 + 2245 spurious
2026.08.05	2915³	457 + 997 spurious
2026.10.11	63749⁴	419 + 2846 spurious
2026.10.11	3265³	114 + 310 spurious

in-flight changes

r? @ghost

a complete crater run ↩ ↩² ↩³ ↩⁴ ↩⁵
with doubled recursion_limit when evaluating goals ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²
only testing crates which may have regressed from the above run ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³
testing all crates that failed when compiling with -Znext-solver modulo crates which already failed in the baseline run of the last complete crater run ↩

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 ^^

lcnr · 2026-10-07T09:47:55Z

we've got time, gonna fix the issues from #163589 first

@craterbot cancel :>

craterbot · 2026-10-07T09:47:58Z

🚨 Error: failed to parse the command

🆘 If you have any trouble with Crater please ask in t-infra on Zulip
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

lcnr · 2026-10-07T10:47:20Z

@bors try

theemathas · 2026-10-08T05:54:50Z

@craterbot cancel

craterbot · 2026-10-08T05:54:54Z

🗑️ Experiment pr-133502-30 deleted!

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

lcnr · 2026-10-08T07:17:23Z

@craterbot run mode=check-only start=df71ca4bba430db14e784e45bb5259340e88b3ad+rustflags=-Znext-solver=coherence end=df71ca4bba430db14e784e45bb5259340e88b3ad crates=https://gist.githubusercontent.com/lcnr/0e2a09bb6b565ee9392c664a3c8cb47d/raw/a7aee74336eeb45df44563106cc3c9fc5930eece/failed-crates.txt p=6

craterbot · 2026-10-08T07:17:31Z

👌 Experiment pr-133502-30 created and queued.
🔍 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

lcnr · 2026-10-09T21:01:40Z

@bors try

lcnr · 2026-10-09T21:03:24Z

@craterbot cancel

craterbot · 2026-10-09T21:03:27Z

🗑️ Experiment pr-133502-30 deleted!

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

rust-log-analyzer · 2026-10-09T21:04:47Z

A job failed! Check out the build log: (web) (plain enhanced) (plain)

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

rust-bors · 2026-10-09T22:28:20Z

☀️ Try build successful (CI)
Build commit: 3154cc1 (3154cc1a3e6424e44f438a95007d043ed5ceaaf6)
Base parent: 69bccf0 (69bccf03c4733f57482f9691456efcd80f86a5f6)

lcnr · 2026-10-10T10:12:20Z

@craterbot run mode=check-only start=3154cc1a3e6424e44f438a95007d043ed5ceaaf6+rustflags=-Znext-solver=coherence end=3154cc1a3e6424e44f438a95007d043ed5ceaaf6 crates=https://gist.githubusercontent.com/lcnr/0e2a09bb6b565ee9392c664a3c8cb47d/raw/a7aee74336eeb45df44563106cc3c9fc5930eece/failed-crates.txt p=6

craterbot · 2026-10-10T10:12:29Z

👌 Experiment pr-133502-30 created and queued.
🔍 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

craterbot · 2026-10-10T16:08:27Z

🚧 Experiment pr-133502-30 is now running

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

craterbot · 2026-10-11T10:03:13Z

🎉 Experiment pr-133502-30 is completed!
📊 419 regressed and 1 fixed (63749 total)
📊 2846 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-133502-30/retry-regressed-list.txt ↩

lcnr · 2026-10-11T11:10:34Z

@craterbot run mode=check-only start=3154cc1a3e6424e44f438a95007d043ed5ceaaf6+rustflags=-Znext-solver=coherence end=3154cc1a3e6424e44f438a95007d043ed5ceaaf6 crates=https://crater-reports.s3.amazonaws.com/pr-133502-30/retry-regressed-list.txt p=4

craterbot · 2026-10-11T11:10:42Z

👌 Experiment pr-133502-31 created and queued.
🔍 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

craterbot · 2026-10-11T13:24:56Z

🚧 Experiment pr-133502-31 is now running

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

craterbot · 2026-10-11T14:17:21Z

🎉 Experiment pr-133502-31 is completed!
📊 114 regressed and 0 fixed (3265 total)
📊 310 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-133502-31/retry-regressed-list.txt ↩

lcnr · 2026-10-11T14:58:57Z

@craterbot run mode=check-only start=3154cc1a3e6424e44f438a95007d043ed5ceaaf6+rustflags=-Znext-solver=coherence end=3154cc1a3e6424e44f438a95007d043ed5ceaaf6 crates=https://crater-reports.s3.amazonaws.com/pr-133502-31/retry-regressed-list.txt p=4

craterbot · 2026-10-11T14:59:00Z

👌 Experiment pr-133502-32 created and queued.
🔍 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-bors · 2026-10-12T19:48:38Z

☔ The latest upstream changes (presumably #164216) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

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 mentioned this pull request Oct 7, 2026

do not prefer trivially true candidates with -Znext-solver #163928

Draft

lcnr added 4 commits October 9, 2026 23:00

enable -Znext-solver by default

4ff6337

do not prefer trivially true candidates

e851c8c

don't just ignore ambig goals in MIR borrowck

b4a4af6

add regression test for old solver unsoundness

b3ac43b

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