Stabilize some Option methods as const #76135

CDirkx · 2020-08-31T00:26:30Z

Stabilize the following methods of Option as const:

is_some
is_none
as_ref

These methods are currently const under the unstable feature const_option (tracking issue: #67441).
I believe these methods to be eligible for stabilization because of the stabilization of #49146 (Allow if and match in constants) and the trivial implementations, see also: PR#75463.

Related: #76225

rust-highfive · 2020-08-31T00:26:33Z

r? @KodrAus

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CDirkx · 2020-08-31T00:57:21Z

r? @ecstatic-morse

ecstatic-morse · 2020-08-31T16:16:27Z

r? @KodrAus (Needs FCP)

CDirkx · 2020-09-01T23:42:50Z

Created an issue for similar stabilizations: #76225

KodrAus · 2020-09-04T05:38:24Z

For reference, there's also an equivalent push to constify some Result methods at #76136

@rfcbot fcp merge

KodrAus · 2020-09-04T07:01:56Z

@rfcbot fcp merge

rfcbot · 2020-09-04T07:01:57Z

Team member @KodrAus has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

rfcbot · 2020-09-07T03:34:56Z

🔔 This is now entering its final comment period, as per the review above. 🔔

josephlr · 2020-09-12T10:47:24Z

It seems like Option::iter() Option::flatten() and Option::transpose() could also be stabilized without needing to Drop anything.

ecstatic-morse · 2020-09-12T18:49:04Z

Option::iter has been previously discussed. It's not very useful, since you can't do anything with it in a const context without const trait methods, which are unstable.

I believe (someone should verify this) that the other two would depend on the unstable const_precise_live_drops feature gate. They can (and should) be made unstably const, but cannot be stabilized at the moment.

CDirkx · 2020-09-13T00:39:30Z

I checked, even though nothing actually gets dropped inside flatten and transpose, const_precise_live_drops is required for the compiler to see this. You get error[E0493]: destructors cannot be evaluated at compile-time otherwise.

josephlr · 2020-09-13T10:19:00Z

I believe (someone should verify this) that the other two would depend on the unstable const_precise_live_drops feature gate. They can (and should) be made unstably const, but cannot be stabilized at the moment.

This makes sense (example playground), and also resolves my comment here: #76136 (comment).

Stabilize some Option methods as const Stabilize the following methods of `Option` as const: - `is_some` - `is_none` - `as_ref` These methods are currently const under the unstable feature `const_option` (tracking issue: rust-lang#67441). I believe these methods to be eligible for stabilization because of the stabilization of rust-lang#49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](rust-lang#75463). Related: rust-lang#76225

RalfJung · 2020-09-19T07:50:04Z

@bors rollup

RalfJung · 2020-09-19T09:45:52Z

I think this caused the clippy test failure in #76907 (comment). The affected test, redundant_pattern_matching_const_result, mentions const option methods.

@bors r-

CDirkx · 2020-09-19T21:39:31Z

~~Yeah I'm looking into it, Clippy has a special case to not suggest is_some, is_none, is_ok and is_err inside a const context (clippy#5724).~~

Now that this stabilization for Option and the related one for Result (#76136) were accepted, would it be okay if I opened a new PR that merges them and also fixes Clippy for the both of them by removing the special casing machinery?

Edit: see #76136 (comment), after #76136 gets merged the Clippy check can_suggest will be removed entirely in this PR.

Stabilize some Result methods as const Stabilize the following methods of Result as const: - `is_ok` - `is_err` - `as_ref` A test is also included, analogous to the test for `const_option`. These methods are currently const under the unstable feature `const_result` (tracking issue: rust-lang#67520). I believe these methods to be eligible for stabilization because of the stabilization of rust-lang#49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](rust-lang#75463) and [PR#76135](rust-lang#76135). Note: these methods are the only methods currently under the `const_result` feature, thus this PR results in the removal of the feature. Related: rust-lang#76225

Stabilize the following methods of `Option` as const: - `is_some` - `is_none` - `as_ref` Possible because of stabilization of rust-lang#49146 (Allow if and match in constants).

Part of rust-lang#76268

Update the test `redundant_pattern_matching`: check if `is_some` and `is_none` are suggested within const contexts.

Removes `can_suggest` from as it is no longer used. Reverts rust-clippy#5724.

CDirkx · 2020-09-20T22:04:07Z

With #76136 merged I updated the testcases and now completely removed can_suggest from Clippy, essentially just reverting the changes made in rust-clippy#5724.

RalfJung · 2020-09-21T07:18:26Z

LGTM. @rust-lang/clippy could someone take a look at the clippy changes here?

oli-obk · 2020-09-21T07:26:26Z

@bors r=dtolnay,oli-obk

bors · 2020-09-21T07:26:27Z

📌 Commit 43cba34 has been approved by dtolnay,oli-obk

Rollup of 13 pull requests Successful merges: - rust-lang#76135 (Stabilize some Option methods as const) - rust-lang#76628 (Add sample defaults for config.toml ) - rust-lang#76846 (Avoiding unnecesary allocations at rustc_errors) - rust-lang#76867 (Use intra-doc links in core/src/iter when possible) - rust-lang#76868 (Finish moving to intra doc links for std::sync) - rust-lang#76872 (Remove DeclareMethods) - rust-lang#76936 (Add non-`unsafe` `.get_mut()` for `Unsafecell`) - rust-lang#76958 (Replace manual as_nanos and as_secs_f64 reimplementations) - rust-lang#76959 (Replace write_fmt with write!) - rust-lang#76961 (Add test for issue rust-lang#34634) - rust-lang#76962 (Use const_cstr macro in consts.rs) - rust-lang#76963 (Remove unused static_assert macro) - rust-lang#77000 (update Miri) Failed merges: r? `@ghost`

Stabilize some Result methods as const Stabilize the following methods of Result as const: - `is_ok` - `is_err` - `as_ref` A test is also included, analogous to the test for `const_option`. These methods are currently const under the unstable feature `const_result` (tracking issue: #67520). I believe these methods to be eligible for stabilization because of the stabilization of #49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](rust-lang/rust#75463) and [PR#76135](rust-lang/rust#76135). Note: these methods are the only methods currently under the `const_result` feature, thus this PR results in the removal of the feature. Related: #76225

rust-highfive assigned KodrAus Aug 31, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 31, 2020

CDirkx mentioned this pull request Aug 31, 2020

Stabilize some Result methods as const #76136

Merged

rust-highfive assigned ecstatic-morse and BurntSushi and unassigned KodrAus and ecstatic-morse Aug 31, 2020

rust-highfive assigned KodrAus and unassigned BurntSushi Aug 31, 2020

CDirkx mentioned this pull request Sep 1, 2020

Stabilize enum is_variant methods as const #76225

Closed

6 tasks

scottmcm added the needs-fcp This change is insta-stable, so needs a completed FCP to proceed. label Sep 2, 2020

jyn514 added the A-const-fn label Sep 3, 2020

KodrAus added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Sep 4, 2020

jonas-schievink added the relnotes Marks issues that should be documented in the release notes of the next release. label Sep 13, 2020

RalfJung mentioned this pull request Sep 19, 2020

Rollup of 13 pull requests #76907

Closed

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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 19, 2020

CDirkx mentioned this pull request Sep 19, 2020

redundant_pattern_matching: Option and Result methods stabilized as const rust-lang/rust-clippy#6067

Closed

CDirkx and others added 2 commits September 20, 2020 22:42

Stabilize some Option methods as const

9486f72

Stabilize the following methods of `Option` as const: - `is_some` - `is_none` - `as_ref` Possible because of stabilization of rust-lang#49146 (Allow if and match in constants).

Move const tests for Option to library\core

4f859fb

Part of rust-lang#76268

CDirkx force-pushed the const-option branch from 04e4a39 to 4f859fb Compare September 20, 2020 21:47

CDirkx added 2 commits September 20, 2020 23:59

Update Clippy testcases

e58d062

Update the test `redundant_pattern_matching`: check if `is_some` and `is_none` are suggested within const contexts.

Remove can_suggest from Clippy.

43cba34

Removes `can_suggest` from as it is no longer used. Reverts rust-clippy#5724.

CDirkx force-pushed the const-option branch from fa5a5d7 to 43cba34 Compare September 20, 2020 22:00

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 21, 2020

RalfJung mentioned this pull request Sep 21, 2020

Rollup of 13 pull requests #77004

Merged

bors merged commit c3abb82 into rust-lang:master Sep 21, 2020

rustbot added this to the 1.48.0 milestone Sep 21, 2020

CDirkx deleted the const-option branch September 23, 2020 19:23

dtolnay self-assigned this Mar 24, 2024

RalfJung added the A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) label Dec 1, 2024

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Stabilize some Option methods as const #76135

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CDirkx commented Aug 31, 2020 •

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Stabilize some Option methods as const #76135

Stabilize some Option methods as const #76135

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