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Limited nonzero coercion #143629

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@oli-obk oli-obk commented Jul 8, 2025

coercing NonZero<T> to T if all the types are available at the cast site.

This is fairly limited, as (as the tests show), this does not allow "reborrowing" &NonZero<T> as &T. It also fails quickly if the types aren't fully clear at the coercion site, but only resolved later.

Also cannot aid in trait selection or similar, even if there is clearly only one option.

Related:

cc @traviscross

@rustbot rustbot added 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 Jul 8, 2025
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@bors2 try @rust-timer queue

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rust-bors bot commented Jul 8, 2025

⌛ Trying commit e341923 with merge 4a4dd8e…

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

rust-bors bot added a commit that referenced this pull request Jul 8, 2025
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Auto merge of #143629 - oli-obk:limited-nonzero-coercion, r=<try>
4a4dd8e 
Limited nonzero coercion

coercing `NonZero<T>` to `T` if all the types are available at the cast site.

This is fairly limited, as (as the tests show), this does not allow "reborrowing" `&NonZero<T>` as `&T`. It also fails quickly if the types aren't fully clear at the coercion site, but only resolved later.

Also cannot aid in trait selection or similar, even if there is clearly only one option.

Related:

* #143594
* rust-lang/rfcs#3786

cc `@traviscross`
@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 8, 2025
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☀️ Try build successful (CI)
Build commit: 4a4dd8e (4a4dd8eb0e65f6bfdacfb10fa73970e2a130d69a, parent: 040e2f8b9ff2d76fbe2146d6003e297ed4532088)

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@traviscross traviscross added the T-lang Relevant to the language team label Jul 8, 2025
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Finished benchmarking commit (4a4dd8e): comparison URL.

Overall result: ❌✅ regressions and 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)		 1.6% [1.6%, 1.6%] 1
Regressions ❌
(secondary)		 1.6% [1.6%, 1.6%] 1
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -0.1% [-0.1%, -0.1%] 2
All ❌✅ (primary) 1.6% [1.6%, 1.6%] 1

Max RSS (memory usage)

Results (primary -4.6%)

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)		 -4.6% [-4.6%, -4.6%] 1
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) -4.6% [-4.6%, -4.6%] 1

Cycles

Results (primary -3.1%, secondary -4.0%)

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)		 -3.1% [-3.1%, -3.1%] 1
Improvements ✅
(secondary)		 -4.0% [-4.0%, -4.0%] 1
All ❌✅ (primary) -3.1% [-3.1%, -3.1%] 1

Binary size

Results (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
Regressions ❌
(secondary)		 0.0% [0.0%, 0.0%] 1
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) - - 0

Bootstrap: 467.351s -> 465.395s (-0.42%)
Artifact size: 372.36 MiB -> 372.37 MiB (0.00%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 8, 2025
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