Constify conversion traits (part 1) #145279

clarfonthey · 2025-08-11T23:49:04Z

This is the first part of #144289 being split into smaller pieces. It adds/moves constness of several traits under the const_convert feature:

From
Into
TryFrom
TryInto
FromStr
AsRef
AsMut
Borrow
BorrowMut
Deref
DerefMut

There are a few methods that are intrinsically tied to these traits which I've included in the feature. Particularly, those which are wrappers over AsRef:

ByteStr::new (unstable under bstr feature)
OsStr::new
Path::new

Those which directly use Into:

Result::into_ok
Result::into_err

And those which use Deref and DerefMut:

Pin::as_ref
Pin::as_mut
Pin::as_deref_mut
Option::as_deref
Option::as_deref_mut
Result::as_deref
Result::as_deref_mut

(note: the Option and Result methods were suggested by @npmccallum initially as #146101)

The parts which are missing from this PR are:

Anything that involves heap-allocated types
Making any method const than the ones listed above
Anything that could rely on the above, or could rely on system-specific code for OsStr or Path (note: this mostly makes these methods useless since str doesn't implement AsRef<OsStr> yet, but it's better to track the method for now and add impls later, IMHO)

r? @tgross35 (who mostly already reviewed this)

clarfonthey · 2025-08-11T23:49:41Z

library/alloc/src/lib.rs

 #![feature(const_default)]
 #![feature(const_eval_select)]
 #![feature(const_heap)]
-#![feature(const_trait_impl)]


Was listed under library features, and is actually a language feature. Since the diff doesn't make that clear.

clarfonthey · 2025-08-11T23:50:59Z

library/core/src/char/convert.rs

+        // FIXME(const-hack): this should use map_err instead
+        match u8::try_from(u32::from(c)) {
+            Ok(b) => Ok(b),
+            Err(_) => Err(TryFromCharError(())),
+        }


You mentioned not wanting to add any more const-hacks, but I figured this one (+ for u16 below) was okay because we're already going to have to fix a lot of const code once things are stable, and I think that simple char <-> integer conversions are useful enough to get on nightly sooner. Especially since const closures seem pretty far off at the moment.

bors · 2025-08-13T11:57:46Z

☔ The latest upstream changes (presumably #145334) made this pull request unmergeable. Please resolve the merge conflicts.

clarfonthey · 2025-08-17T18:56:41Z

Rebasing over #144847 since that one conflicts with this one, which is why I was going to do this one before I got to that one, but, it's in the queue now, so, 🤷🏻.

Only changes with the rebase are eliminating more additions of const_from which is renamed to const_convert.

rustbot · 2025-08-17T18:58:13Z

This PR was rebased onto a different master commit! Check out the changes with our range-diff.

bors · 2025-08-20T09:39:35Z

☔ The latest upstream changes (presumably #145644) made this pull request unmergeable. Please resolve the merge conflicts.

clarfonthey · 2025-08-20T19:23:35Z

Will rebase once that PR gets merged. I can mark it as blocked, but it still can be reviewed before to verify you're comfortable with the changes.

clarfonthey · 2025-08-21T00:48:05Z

(Un-rebased over that PR since it's no longer in the queue.)

…oshtriplett `const`ify (the unstable) `str::as_str` Tracking issue: rust-lang#130366 The method was not initially marked `const` presumably because it is only useful with `Deref`. But now that const traits seem to be a thing that can actually become real, why not make it `const`? PR `const`ifying `Deref`: rust-lang#145279

Rollup merge of #145930 - GrigorenkoPV:const_str_as_str, r=joshtriplett `const`ify (the unstable) `str::as_str` Tracking issue: #130366 The method was not initially marked `const` presumably because it is only useful with `Deref`. But now that const traits seem to be a thing that can actually become real, why not make it `const`? PR `const`ifying `Deref`: #145279

rustbot · 2025-08-29T12:52:06Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

clarfonthey · 2025-09-02T01:40:52Z

Incorporated the methods from #146101 and listed them in the issue description.

tgross35 · 2025-09-02T18:54:45Z

Argh I'm sorry for the delay here, bit behind on reviews. But thank you for the updates; everything here seems reasonably useful so LGTM.

@bors r+

bors · 2025-09-02T18:54:48Z

📌 Commit 1c64d3e has been approved by tgross35

It is now in the queue for this repository.

clarfonthey · 2025-09-02T19:45:21Z

All good! I didn't want to bug you since I figured you were busy. Thanks for getting to this.

bors · 2025-09-03T01:34:15Z

⌛ Testing commit 1c64d3e with merge 72bf547...

Constify conversion traits (part 1) This is the first part of #144289 being split into smaller pieces. It adds/moves constness of several traits under the `const_convert` feature: * `From` * `Into` * `TryFrom` * `TryInto` * `FromStr` * `AsRef` * `AsMut` * `Borrow` * `BorrowMut` * `Deref` * `DerefMut` There are a few methods that are intrinsically tied to these traits which I've included in the feature. Particularly, those which are wrappers over `AsRef`: * `ByteStr::new` (unstable under `bstr` feature) * `OsStr::new` * `Path::new` Those which directly use `Into`: * `Result::into_ok` * `Result::into_err` And those which use `Deref` and `DerefMut`: * `Pin::as_ref` * `Pin::as_mut` * `Pin::as_deref_mut` * `Option::as_deref` * `Option::as_deref_mut` * `Result::as_deref` * `Result::as_deref_mut` (note: the `Option` and `Result` methods were suggested by `@npmccallum` initially as #146101) The parts which are missing from this PR are: * Anything that involves heap-allocated types * Making any method const than the ones listed above * Anything that could rely on the above, *or* could rely on system-specific code for `OsStr` or `Path` (note: this mostly makes these methods useless since `str` doesn't implement `AsRef<OsStr>` yet, but it's better to track the method for now and add impls later, IMHO) r? `@tgross35` (who mostly already reviewed this)

… r=tgross35 Constify conversion traits (part 1) This is the first part of rust-lang#144289 being split into smaller pieces. It adds/moves constness of several traits under the `const_convert` feature: * `From` * `Into` * `TryFrom` * `TryInto` * `FromStr` * `AsRef` * `AsMut` * `Borrow` * `BorrowMut` * `Deref` * `DerefMut` There are a few methods that are intrinsically tied to these traits which I've included in the feature. Particularly, those which are wrappers over `AsRef`: * `ByteStr::new` (unstable under `bstr` feature) * `OsStr::new` * `Path::new` Those which directly use `Into`: * `Result::into_ok` * `Result::into_err` And those which use `Deref` and `DerefMut`: * `Pin::as_ref` * `Pin::as_mut` * `Pin::as_deref_mut` * `Option::as_deref` * `Option::as_deref_mut` * `Result::as_deref` * `Result::as_deref_mut` (note: the `Option` and `Result` methods were suggested by `@npmccallum` initially as rust-lang#146101) The parts which are missing from this PR are: * Anything that involves heap-allocated types * Making any method const than the ones listed above * Anything that could rely on the above, *or* could rely on system-specific code for `OsStr` or `Path` (note: this mostly makes these methods useless since `str` doesn't implement `AsRef<OsStr>` yet, but it's better to track the method for now and add impls later, IMHO) r? `@tgross35` (who mostly already reviewed this)

tgross35 · 2025-09-03T01:56:45Z

@bors retry
Put in a rollup

Rollup of 8 pull requests Successful merges: - #139113 (unstable book: in a sanitizer example, check the code) - #145279 (Constify conversion traits (part 1)) - #145414 (unicode-table-generator refactors) - #145823 (editorconfig: don't use nonexistent syntax) - #145944 (std: Start supporting WASIp2 natively ) - #145961 (resolve: Avoid a regression from splitting prelude into two scopes) - #146032 (Explicity disable LSX feature for `loongarch64-unknown-none` target) - #146106 (fix(lexer): Only allow horizontal whitespace in frontmatter ) r? `@ghost` `@rustbot` modify labels: rollup

… r=tgross35 Constify conversion traits (part 1) This is the first part of rust-lang#144289 being split into smaller pieces. It adds/moves constness of several traits under the `const_convert` feature: * `From` * `Into` * `TryFrom` * `TryInto` * `FromStr` * `AsRef` * `AsMut` * `Borrow` * `BorrowMut` * `Deref` * `DerefMut` There are a few methods that are intrinsically tied to these traits which I've included in the feature. Particularly, those which are wrappers over `AsRef`: * `ByteStr::new` (unstable under `bstr` feature) * `OsStr::new` * `Path::new` Those which directly use `Into`: * `Result::into_ok` * `Result::into_err` And those which use `Deref` and `DerefMut`: * `Pin::as_ref` * `Pin::as_mut` * `Pin::as_deref_mut` * `Option::as_deref` * `Option::as_deref_mut` * `Result::as_deref` * `Result::as_deref_mut` (note: the `Option` and `Result` methods were suggested by `@npmccallum` initially as rust-lang#146101) The parts which are missing from this PR are: * Anything that involves heap-allocated types * Making any method const than the ones listed above * Anything that could rely on the above, *or* could rely on system-specific code for `OsStr` or `Path` (note: this mostly makes these methods useless since `str` doesn't implement `AsRef<OsStr>` yet, but it's better to track the method for now and add impls later, IMHO) r? `@tgross35` (who mostly already reviewed this)

Rollup of 9 pull requests Successful merges: - #145279 (Constify conversion traits (part 1)) - #145414 (unicode-table-generator refactors) - #145823 (editorconfig: don't use nonexistent syntax) - #145944 (std: Start supporting WASIp2 natively ) - #145961 (resolve: Avoid a regression from splitting prelude into two scopes) - #146032 (Explicity disable LSX feature for `loongarch64-unknown-none` target) - #146106 (fix(lexer): Only allow horizontal whitespace in frontmatter ) - #146112 (don't uppercase error messages) - #146154 (CI: rfl: move job forward to Linux v6.17-rc3 plus 2 commits) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 8 pull requests Successful merges: - #145279 (Constify conversion traits (part 1)) - #145414 (unicode-table-generator refactors) - #145823 (editorconfig: don't use nonexistent syntax) - #145944 (std: Start supporting WASIp2 natively ) - #145961 (resolve: Avoid a regression from splitting prelude into two scopes) - #146032 (Explicity disable LSX feature for `loongarch64-unknown-none` target) - #146106 (fix(lexer): Only allow horizontal whitespace in frontmatter ) - #146154 (CI: rfl: move job forward to Linux v6.17-rc3 plus 2 commits) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #145279 - clarfonthey:const-convert-initial, r=tgross35 Constify conversion traits (part 1) This is the first part of #144289 being split into smaller pieces. It adds/moves constness of several traits under the `const_convert` feature: * `From` * `Into` * `TryFrom` * `TryInto` * `FromStr` * `AsRef` * `AsMut` * `Borrow` * `BorrowMut` * `Deref` * `DerefMut` There are a few methods that are intrinsically tied to these traits which I've included in the feature. Particularly, those which are wrappers over `AsRef`: * `ByteStr::new` (unstable under `bstr` feature) * `OsStr::new` * `Path::new` Those which directly use `Into`: * `Result::into_ok` * `Result::into_err` And those which use `Deref` and `DerefMut`: * `Pin::as_ref` * `Pin::as_mut` * `Pin::as_deref_mut` * `Option::as_deref` * `Option::as_deref_mut` * `Result::as_deref` * `Result::as_deref_mut` (note: the `Option` and `Result` methods were suggested by ``@npmccallum`` initially as #146101) The parts which are missing from this PR are: * Anything that involves heap-allocated types * Making any method const than the ones listed above * Anything that could rely on the above, *or* could rely on system-specific code for `OsStr` or `Path` (note: this mostly makes these methods useless since `str` doesn't implement `AsRef<OsStr>` yet, but it's better to track the method for now and add impls later, IMHO) r? ``@tgross35`` (who mostly already reviewed this)

rustbot assigned tgross35 Aug 11, 2025

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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 11, 2025

clarfonthey commented Aug 11, 2025

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clarfonthey force-pushed the const-convert-initial branch from 365fcde to 97c330f Compare August 13, 2025 16:40

clarfonthey force-pushed the const-convert-initial branch from 97c330f to 4ebb4b7 Compare August 17, 2025 18:58

clarfonthey force-pushed the const-convert-initial branch from 4ebb4b7 to 4bcf7bd Compare August 21, 2025 00:47

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GrigorenkoPV mentioned this pull request Aug 27, 2025

constify (the unstable) str::as_str #145930

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clarfonthey force-pushed the const-convert-initial branch from 4bcf7bd to 66dcd76 Compare August 29, 2025 12:52

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clarfonthey mentioned this pull request Sep 2, 2025

Tracking Issue for const Derefs #88955

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clarfonthey force-pushed the const-convert-initial branch from 66dcd76 to 636cfe4 Compare September 2, 2025 01:34

Constify conversion traits

1c64d3e

clarfonthey force-pushed the const-convert-initial branch from 636cfe4 to 1c64d3e Compare September 2, 2025 01:38

clarfonthey mentioned this pull request Sep 2, 2025

constify as_deref() / as_deref_mut() on Option / Result #146101

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clarfonthey mentioned this pull request Sep 2, 2025

alloc: make Cow From impls const #146067

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tgross35 approved these changes Sep 2, 2025

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 2, 2025

tgross35 mentioned this pull request Sep 3, 2025

Rollup of 8 pull requests #146141

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Zalathar mentioned this pull request Sep 3, 2025

Rollup of 9 pull requests #146157

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Zalathar mentioned this pull request Sep 3, 2025

Rollup of 8 pull requests #146160

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bors merged commit f4b946a into rust-lang:master Sep 3, 2025
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clarfonthey mentioned this pull request Sep 3, 2025

Tracking Issue for const_from #143773

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Constify conversion traits (part 1) #145279

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