[experiment][1] mew by WaffleLapkin · Pull Request #155500 · rust-lang/rust

WaffleLapkin · 2026-04-18T22:15:56Z

No description provided.

WaffleLapkin · 2026-04-18T22:23:42Z

[experiment][1] mew

rust-bors · 2026-04-19T00:36:56Z

☀️ Try build successful (CI)
Build commit: 1bdcb63 (1bdcb63291ccffc030f8223f6f978568dd240e3e, parent: b2f1ccf524a3a4cf9c34545167cc23b659cf1cbd)

WaffleLapkin · 2026-04-19T01:08:50Z

@craterbot check p=1 crates=https://crater-reports.s3.amazonaws.com/pr-154887/retry-regressed-list.txt

craterbot · 2026-04-19T01:08:55Z

👌 Experiment pr-155500 created and queued.
🤖 Automatically detected try build 1bdcb63
⚠️ Try build based on commit e51d87b, but latest commit is 58bbf50. Did you forget to make a new try build?
🔍 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 · 2026-04-20T08:35:19Z

🚧 Experiment pr-155500 is now running

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

craterbot · 2026-04-20T13:41:28Z

🎉 Experiment pr-155500 is completed!
📊 3315 regressed and 0 fixed (9024 total)
📊 1169 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-155500/retry-regressed-list.txt ↩

WaffleLapkin · 2026-04-21T11:31:08Z

@craterbot check p=1 name=155501-infallible-never-with-reservation start=try#5ec4d3b0c83717313176eefa7d71e9d36dc83355 end=try#1bdcb63291ccffc030f8223f6f978568dd240e3e crates=https://crater-reports.s3.amazonaws.com/pr-154887/retry-regressed-list.txt

Failures of this PR, on top of #155501 (i.e. what is broken by the reservation impl if infallible is never)

craterbot · 2026-04-21T11:31:12Z

👌 Experiment 155501-infallible-never-with-reservation 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 · 2026-04-27T07:00:40Z

🚧 Experiment 155501-infallible-never-with-reservation is now running

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

craterbot · 2026-04-27T12:07:37Z

🎉 Experiment 155501-infallible-never-with-reservation is completed!
📊 14 regressed and 0 fixed (9025 total)
📊 916 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/155501-infallible-never-with-reservation/retry-regressed-list.txt ↩

The reason `rustc_ast_ir` and `rustc_pattern_analysis` have nested `cfg_attr`s is so that they don't mention `cfg(bootstrap)` when nightly or rustc cargo feature turned on. If you don't do it like that, they stop compiling on stable (or rather, they emit unexpected cfg warnings...).

??? why wasn't this detected by compiletest ???

rust-log-analyzer · 2026-06-17T10:25:16Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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

   Compiling rustc_next_trait_solver v0.0.0 (/checkout/compiler/rustc_next_trait_solver)
warning: unreachable statement
   --> compiler/rustc_next_trait_solver/src/solve/normalizes_to.rs:370:25
    |
369 |                         ecx.opaque_accesses.rerun_always(RerunReason::FetchEligibleAssocItem)?;
    |                         ---------------------------------------------------------------------- any code following this expression is unreachable
370 |                         return Err(NoSolution.into());
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unreachable statement
    |
    = note: `#[warn(unreachable_code)]` (part of `#[warn(unused)]`) on by default

[RUSTC-TIMING] rustc_proc_macro test:false 7.304
   Compiling rand v0.8.5
warning: unreachable statement
   --> compiler/rustc_next_trait_solver/src/solve/trait_goals.rs:243:17
    |
242 |                 ecx.opaque_accesses.rerun_always(RerunReason::AutoTraitLeakage)?;
    |                 ---------------------------------------------------------------- any code following this expression is unreachable
243 |                 return Err(NoSolution.into());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unreachable statement

[RUSTC-TIMING] rand test:false 1.914

rust-bors · 2026-06-17T21:38:53Z

☔ The latest upstream changes (presumably #158043) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

… r=JonathanBrouwer stabilize never type ### This PR - stabilizes the [never type](https://doc.rust-lang.org/stable/std/primitive.never.html) (aka `!`) (!!!) - sets the [never type fallback](https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html) to `!` on all editions (breaking change, see [crater report analysis](rust-lang#155499 (comment)) and [refresher on never type fallback](rust-lang#155499 (comment))) - makes `Infallible` an alias to `!` - removes `dependency_on_unit_never_type_fallback` lint (there is no more never type fallback to `()` so this lint can't be triggered) ### Cat <img width="1024" height="683" alt="52270233795_5979a3174d_b" src="https://github.com/user-attachments/assets/f6b4737e-32ef-4c33-86b2-76b81673cf20" /> ### Tracking - rust-lang#35121 - rust-lang#148922 ### FCPs - rust-lang#123508 (comment) (stabilization plan, T-lang) - rust-lang#155499 (comment) (never type stabilization modulo bugs, T-lang) - rust-lang#155924 (comment) (make `Infallible = !`, T-libs) ### Related changes - Lint bump: rust-lang#141937 - Rust 2024 edition change: - rust-lang#123748 - rust-lang#123508 - Various changes to lessen the effect of the breaking changes: - rust-lang#157820 - rust-lang#156047 - rust-lang#160705 - Never type documentation changes: rust-lang#158370 (blocked on this pr) ### Experiments - Fallback change and never type stabilization: - Run: rust-lang#155499 (comment) - Analysis: rust-lang#155499 (comment) - Status of backports: rust-lang#155499 (comment) - Fallback change, never type stabilization and making `Infallible = !`: rust-lang#155500 - Fallback change, never type stabilization, making `Infallible = !`, and removing reservation impl: rust-lang#155501 - Never type stabilization and `Infallible = !` change, _without_ fallback change: rust-lang#155657 --- Closes rust-lang#35121 Closes rust-lang#148922

…Brouwer stabilize never type ### This PR - stabilizes the [never type](https://doc.rust-lang.org/stable/std/primitive.never.html) (aka `!`) (!!!) - sets the [never type fallback](https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html) to `!` on all editions (breaking change, see [crater report analysis](#155499 (comment)) and [refresher on never type fallback](#155499 (comment))) - makes `Infallible` an alias to `!` - removes `dependency_on_unit_never_type_fallback` lint (there is no more never type fallback to `()` so this lint can't be triggered) ### Cat <img width="1024" height="683" alt="52270233795_5979a3174d_b" src="https://github.com/user-attachments/assets/f6b4737e-32ef-4c33-86b2-76b81673cf20" /> ### Tracking - #35121 - #148922 ### FCPs - #123508 (comment) (stabilization plan, T-lang) - #155499 (comment) (never type stabilization modulo bugs, T-lang) - #155924 (comment) (make `Infallible = !`, T-libs) ### Related changes - Lint bump: #141937 - Rust 2024 edition change: - #123748 - #123508 - Various changes to lessen the effect of the breaking changes: - #157820 - #156047 - #160705 - Never type documentation changes: #158370 (blocked on this pr) ### Experiments - Fallback change and never type stabilization: - Run: #155499 (comment) - Analysis: #155499 (comment) - Status of backports: #155499 (comment) - Fallback change, never type stabilization and making `Infallible = !`: #155500 - Fallback change, never type stabilization, making `Infallible = !`, and removing reservation impl: #155501 - Never type stabilization and `Infallible = !` change, _without_ fallback change: #155657 --- Closes #35121 Closes #148922

… r=JonathanBrouwer stabilize never type ### This PR - stabilizes the [never type](https://doc.rust-lang.org/stable/std/primitive.never.html) (aka `!`) (!!!) - sets the [never type fallback](https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html) to `!` on all editions (breaking change, see [crater report analysis](rust-lang#155499 (comment)) and [refresher on never type fallback](rust-lang#155499 (comment))) - makes `Infallible` an alias to `!` - removes `dependency_on_unit_never_type_fallback` lint (there is no more never type fallback to `()` so this lint can't be triggered) ### Cat <img width="1024" height="683" alt="52270233795_5979a3174d_b" src="https://github.com/user-attachments/assets/f6b4737e-32ef-4c33-86b2-76b81673cf20" /> ### Tracking - rust-lang#35121 - rust-lang#148922 ### FCPs - rust-lang#123508 (comment) (stabilization plan, T-lang) - rust-lang#155499 (comment) (never type stabilization modulo bugs, T-lang) - rust-lang#155924 (comment) (make `Infallible = !`, T-libs) ### Related changes - Lint bump: rust-lang#141937 - Rust 2024 edition change: - rust-lang#123748 - rust-lang#123508 - Various changes to lessen the effect of the breaking changes: - rust-lang#157820 - rust-lang#156047 - rust-lang#160705 - Never type documentation changes: rust-lang#158370 (blocked on this pr) ### Experiments - Fallback change and never type stabilization: - Run: rust-lang#155499 (comment) - Analysis: rust-lang#155499 (comment) - Status of backports: rust-lang#155499 (comment) - Fallback change, never type stabilization and making `Infallible = !`: rust-lang#155500 - Fallback change, never type stabilization, making `Infallible = !`, and removing reservation impl: rust-lang#155501 - Never type stabilization and `Infallible = !` change, _without_ fallback change: rust-lang#155657 --- Closes rust-lang#35121 Closes rust-lang#148922

…Brouwer stabilize never type ### This PR - stabilizes the [never type](https://doc.rust-lang.org/stable/std/primitive.never.html) (aka `!`) (!!!) - sets the [never type fallback](https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html) to `!` on all editions (breaking change, see [crater report analysis](#155499 (comment)) and [refresher on never type fallback](#155499 (comment))) - makes `Infallible` an alias to `!` - removes `dependency_on_unit_never_type_fallback` lint (there is no more never type fallback to `()` so this lint can't be triggered) ### Cat <img width="1024" height="683" alt="52270233795_5979a3174d_b" src="https://github.com/user-attachments/assets/f6b4737e-32ef-4c33-86b2-76b81673cf20" /> ### Tracking - #35121 - #148922 ### FCPs - #123508 (comment) (stabilization plan, T-lang) - #155499 (comment) (never type stabilization modulo bugs, T-lang) - #155924 (comment) (make `Infallible = !`, T-libs) ### Related changes - Lint bump: #141937 - Rust 2024 edition change: - #123748 - #123508 - Various changes to lessen the effect of the breaking changes: - #157820 - #156047 - #160705 - Never type documentation changes: #158370 (blocked on this pr) ### Experiments - Fallback change and never type stabilization: - Run: #155499 (comment) - Analysis: #155499 (comment) - Status of backports: #155499 (comment) - Fallback change, never type stabilization and making `Infallible = !`: #155500 - Fallback change, never type stabilization, making `Infallible = !`, and removing reservation impl: #155501 - Never type stabilization and `Infallible = !` change, _without_ fallback change: #155657 --- Closes #35121 Closes #148922

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rust-bors Bot pushed a commit that referenced this pull request Apr 18, 2026

Auto merge of #155500 - WaffleLapkin:make-infallible-never, r=<try>

1bdcb63

[experiment][1] mew

WaffleLapkin force-pushed the make-infallible-never branch from e51d87b to 58bbf50 Compare April 19, 2026 01:05

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 19, 2026

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Apr 20, 2026

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 21, 2026

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WaffleLapkin added 3 commits June 16, 2026 22:18

Set never type fallback to always be !

2db9efe

stabilize the never type (!)

d4256a7

fixup clippy::empty_enums

9535220

WaffleLapkin force-pushed the make-infallible-never branch from 33fee27 to 1a28c6f Compare June 16, 2026 20:20

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WaffleLapkin added 13 commits June 17, 2026 12:05

remove #![feature(never_type)] from tests

19d5689

remove #![feature(never_type)] from library

7500db5

remove #![feature(never_type)] from tools

ed511a1

bless tests

7b598a6

bless mir-opt tests

5d9c72f

update tests which depended on never fallback to ()

4d8c0f6

remove dependency_on_unit_never_type_fallback lint

e0fc1d2

remove stray stderr files

77c0b63

??? why wasn't this detected by compiletest ???

update edition-guide submodule to unfuck tests there

4967024

Make Infallible = !

be0d17c

fixup tests to account for Infallible = !

34b3918

bless mir-opt tests

1147509

WaffleLapkin force-pushed the make-infallible-never branch from 1a28c6f to 1147509 Compare June 17, 2026 10:07

WaffleLapkin closed this Jun 22, 2026

WaffleLapkin mentioned this pull request Aug 14, 2026

stabilize never type #155499

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