Fast path nitpicks #143307

compiler-errors · 2025-07-02T00:38:38Z

Miscellaneous commits that I didn't really want to fold into anything else.

Fixes one theoretical bug with the fast path not considering polarity for T: !Sized bounds.

rustbot · 2025-07-02T00:38:43Z

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compiler-errors · 2025-07-02T00:39:00Z

compiler/rustc_traits/src/codegen.rs

@@ -34,13 +34,6 @@ pub(crate) fn codegen_select_candidate<'tcx>(
    let (infcx, param_env) = tcx.infer_ctxt().ignoring_regions().build_with_typing_env(typing_env);
    let mut selcx = SelectionContext::new(&infcx);

-    if sizedness_fast_path(tcx, trait_ref.upcast(tcx)) {


This function shouldn't ever be reached -- we never do Instance::resolve on Sized.

compiler-errors · 2025-07-02T00:39:59Z

@bors2 try @rust-timer queue

r? lcnr perhaps

rust-bors · 2025-07-02T00:40:03Z

⌛ Trying commit 91c53c9 with merge 227ec3b…

To cancel the try build, run the command @bors2 try cancel.

Fast path nitpicks Miscellaneous commits that I didn't really want to fold into anything else. Fixes one theoretical bug with the fast path not considering polarity for `T: !Sized` bounds.

rust-bors · 2025-07-02T02:57:12Z

☀️ Try build successful (CI)
Build commit: 227ec3b (227ec3b415808af85fe11410d8e1b4d8349c32bc, parent: 71e4c005caa812a16fcb08d0bf1e6f1eda7c8381)

lcnr · 2025-07-03T13:06:28Z

compiler/rustc_trait_selection/src/traits/util.rs

        predicate.kind().skip_binder()
+        && trait_pred.polarity == ty::PredicatePolarity::Positive


this has happened multiple times by now 🤔 forgetting the polarity is too damn easy right now 🤔

I can't really think of a good alternative apart from actually splitting ClauseKind::Trait and ClauseKind::NegTrait 🤔

removing the def_id etc functions on TraitPredicate to require trait_pred.trait_ref.def_id() instead feels really cumbersome and not that helpful 🤔 changing ClauseKind::Trait to have TraitRef and Polarity as separate fields so that we always have to use (_, _) could work but feels really ugly

anyways, not part of this PR

lcnr · 2025-07-03T13:07:00Z

@rust-timer build 227ec3b

lcnr · 2025-07-03T13:07:48Z

r=me after getting perf to work ☠️

rust-timer · 2025-07-03T13:19:27Z

Finished benchmarking commit (227ec3b): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.2%, -0.2%]	2

Max RSS (memory usage)

Results (primary -2.1%, secondary -2.0%)

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)	-2.1%	[-2.6%, -1.7%]	2
Improvements ✅ (secondary)	-2.0%	[-2.6%, -1.3%]	2
All ❌✅ (primary)	-2.1%	[-2.6%, -1.7%]	2

Cycles

Results (primary 0.3%, secondary 0.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.7%	[1.5%, 1.9%]	2
Regressions ❌ (secondary)	1.6%	[0.6%, 2.5%]	2
Improvements ✅ (primary)	-1.0%	[-1.1%, -1.0%]	2
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	0.3%	[-1.1%, 1.9%]	4

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 463.343s -> 462.134s (-0.26%)
Artifact size: 372.24 MiB -> 372.24 MiB (-0.00%)

lcnr · 2025-07-03T14:26:49Z

@bors r+

bors · 2025-07-03T14:26:52Z

📌 Commit 91c53c9 has been approved by lcnr

It is now in the queue for this repository.

compiler-errors · 2025-07-03T19:46:31Z

@bors rollup

Rollup of 11 pull requests Successful merges: - #142749 (Add methods for converting bool to `Result<(), E>`) - #143288 (Fix `x clean` with a fifo) - #143307 (Fast path nitpicks) - #143346 (update coherence example) - #143356 (use unsigned_abs instead of `abs` on signed int to silence clippy) - #143370 (remove redundant #[must_use]) - #143378 (simplify receivers for some array method calls) - #143380 (Replace kw_span by full span for generic const parameters.) - #143381 (rustdoc: don't treat methods under const impls or traits as const) - #143394 (compiler: Document and reduce `fn provide`s in hir crates) - #143395 (Always use the pure Rust fallback instead of `llvm.{maximum,minimum}`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143307 - compiler-errors:fast-path-nitpicks, r=lcnr Fast path nitpicks Miscellaneous commits that I didn't really want to fold into anything else. Fixes one theoretical bug with the fast path not considering polarity for `T: !Sized` bounds.

Rollup of 11 pull requests Successful merges: - rust-lang/rust#142749 (Add methods for converting bool to `Result<(), E>`) - rust-lang/rust#143288 (Fix `x clean` with a fifo) - rust-lang/rust#143307 (Fast path nitpicks) - rust-lang/rust#143346 (update coherence example) - rust-lang/rust#143356 (use unsigned_abs instead of `abs` on signed int to silence clippy) - rust-lang/rust#143370 (remove redundant #[must_use]) - rust-lang/rust#143378 (simplify receivers for some array method calls) - rust-lang/rust#143380 (Replace kw_span by full span for generic const parameters.) - rust-lang/rust#143381 (rustdoc: don't treat methods under const impls or traits as const) - rust-lang/rust#143394 (compiler: Document and reduce `fn provide`s in hir crates) - rust-lang/rust#143395 (Always use the pure Rust fallback instead of `llvm.{maximum,minimum}`) r? `@ghost` `@rustbot` modify labels: rollup

…ix, r=davidtwco Do not consider a `T: !Sized` candidate to satisfy a `T: !MetaSized` obligation. This example should fail to compile (and does under this PR, with the old and new solvers), but currently compiles successfully ([playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=6e0e5d0ae0cdf0571dea97938fb4a86d)), because (IIUC) the old solver's `lazily_elaborate_sizedness_candidate`/callers and the new solver's `TraitPredicate::fast_reject_assumption`/`match_assumption` consider a `T: _ Sized` candidate to satisfy a `T: _ MetaSized` obligation, for either polarity `_`, when that should only hold for positive polarity. ```rs #![feature(negative_bounds)] #![feature(sized_hierarchy)] use std::marker::MetaSized; fn foo<T: !MetaSized>() {} fn bar<T: !Sized + MetaSized>() { foo::<T>(); //~^ ERROR the trait bound `T: !MetaSized` is not satisfied // error under this PR } ``` Only observable with the internal-only `feature(negative_bounds)`, so might just be "wontfix". This example is added as a test in this PR (as well as testing that `foo<()>` and `foo<str>` are disallowed for `fn foo<T: !MetaSized`). cc `@davidtwco` for `feature(sized_hierarchy)` Maybe similar to 91c53c9 from <rust-lang#143307>

…ix, r=davidtwco Do not consider a `T: !Sized` candidate to satisfy a `T: !MetaSized` obligation. This example should fail to compile (and does under this PR, with the old and new solvers), but currently compiles successfully ([playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=6e0e5d0ae0cdf0571dea97938fb4a86d)), because (IIUC) the old solver's `lazily_elaborate_sizedness_candidate`/callers and the new solver's `TraitPredicate::fast_reject_assumption`/`match_assumption` consider a `T: _ Sized` candidate to satisfy a `T: _ MetaSized` obligation, for either polarity `_`, when that should only hold for positive polarity. ```rs #![feature(negative_bounds)] #![feature(sized_hierarchy)] use std::marker::MetaSized; fn foo<T: !MetaSized>() {} fn bar<T: !Sized + MetaSized>() { foo::<T>(); //~^ ERROR the trait bound `T: !MetaSized` is not satisfied // error under this PR } ``` Only observable with the internal-only `feature(negative_bounds)`, so might just be "wontfix". This example is added as a test in this PR (as well as testing that `foo<()>` and `foo<str>` are disallowed for `fn foo<T: !MetaSized`). cc ``@davidtwco`` for `feature(sized_hierarchy)` Maybe similar to 91c53c9 from <rust-lang#143307>

…ix, r=davidtwco Do not consider a `T: !Sized` candidate to satisfy a `T: !MetaSized` obligation. This example should fail to compile (and does under this PR, with the old and new solvers), but currently compiles successfully ([playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=6e0e5d0ae0cdf0571dea97938fb4a86d)), because (IIUC) the old solver's `lazily_elaborate_sizedness_candidate`/callers and the new solver's `TraitPredicate::fast_reject_assumption`/`match_assumption` consider a `T: _ Sized` candidate to satisfy a `T: _ MetaSized` obligation, for either polarity `_`, when that should only hold for positive polarity. ```rs #![feature(negative_bounds)] #![feature(sized_hierarchy)] use std::marker::MetaSized; fn foo<T: !MetaSized>() {} fn bar<T: !Sized + MetaSized>() { foo::<T>(); //~^ ERROR the trait bound `T: !MetaSized` is not satisfied // error under this PR } ``` Only observable with the internal-only `feature(negative_bounds)`, so might just be "wontfix". This example is added as a test in this PR (as well as testing that `foo<()>` and `foo<str>` are disallowed for `fn foo<T: !MetaSized`). cc `@davidtwco` for `feature(sized_hierarchy)` Maybe similar to 91c53c9 from <rust-lang#143307>

Rollup merge of #145537 - zachs18:metasized-negative-bound-fix, r=davidtwco Do not consider a `T: !Sized` candidate to satisfy a `T: !MetaSized` obligation. This example should fail to compile (and does under this PR, with the old and new solvers), but currently compiles successfully ([playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=6e0e5d0ae0cdf0571dea97938fb4a86d)), because (IIUC) the old solver's `lazily_elaborate_sizedness_candidate`/callers and the new solver's `TraitPredicate::fast_reject_assumption`/`match_assumption` consider a `T: _ Sized` candidate to satisfy a `T: _ MetaSized` obligation, for either polarity `_`, when that should only hold for positive polarity. ```rs #![feature(negative_bounds)] #![feature(sized_hierarchy)] use std::marker::MetaSized; fn foo<T: !MetaSized>() {} fn bar<T: !Sized + MetaSized>() { foo::<T>(); //~^ ERROR the trait bound `T: !MetaSized` is not satisfied // error under this PR } ``` Only observable with the internal-only `feature(negative_bounds)`, so might just be "wontfix". This example is added as a test in this PR (as well as testing that `foo<()>` and `foo<str>` are disallowed for `fn foo<T: !MetaSized`). cc `@davidtwco` for `feature(sized_hierarchy)` Maybe similar to 91c53c9 from <#143307>

…idtwco Do not consider a `T: !Sized` candidate to satisfy a `T: !MetaSized` obligation. This example should fail to compile (and does under this PR, with the old and new solvers), but currently compiles successfully ([playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=6e0e5d0ae0cdf0571dea97938fb4a86d)), because (IIUC) the old solver's `lazily_elaborate_sizedness_candidate`/callers and the new solver's `TraitPredicate::fast_reject_assumption`/`match_assumption` consider a `T: _ Sized` candidate to satisfy a `T: _ MetaSized` obligation, for either polarity `_`, when that should only hold for positive polarity. ```rs #![feature(negative_bounds)] #![feature(sized_hierarchy)] use std::marker::MetaSized; fn foo<T: !MetaSized>() {} fn bar<T: !Sized + MetaSized>() { foo::<T>(); //~^ ERROR the trait bound `T: !MetaSized` is not satisfied // error under this PR } ``` Only observable with the internal-only `feature(negative_bounds)`, so might just be "wontfix". This example is added as a test in this PR (as well as testing that `foo<()>` and `foo<str>` are disallowed for `fn foo<T: !MetaSized`). cc `@davidtwco` for `feature(sized_hierarchy)` Maybe similar to 91c53c9 from <rust-lang/rust#143307>

compiler-errors added 3 commits July 2, 2025 00:33

Remove fast path from codegen_select, since Sized has no methods

ae0bef7

Use is_trivially_wf for ProvePredicate fast path

d3c0ef0

Consider polarity in sizedness fast path

91c53c9

rustbot assigned SparrowLii Jul 2, 2025

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lcnr reviewed Jul 3, 2025

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jhpratt mentioned this pull request Jul 4, 2025

Rollup of 11 pull requests #143407

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bors merged commit 9de211b into rust-lang:master Jul 4, 2025
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rustbot added this to the 1.90.0 milestone Jul 4, 2025

zachs18 mentioned this pull request Aug 17, 2025

Do not consider a T: !Sized candidate to satisfy a T: !MetaSized obligation. #145537

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		predicate.kind().skip_binder()
		&& trait_pred.polarity == ty::PredicatePolarity::Positive

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Overall result: ✅ improvements - no action needed

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