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Tracking issue for RFC 2086: Allow Irrefutable Patterns in if-let and while-let statements #44495
Description
This is a tracking issue for the RFC "Allow Irrefutable Patterns in if-let and while-let statements" (rust-lang/rfcs#2086).
Steps:
- Implement the RFC (mentoring instructions here)
- Adjust documentation (Document
irrefutable_let_patternsreference#507) - Stabilization PR (Stabilise irrefutable if-let and while-let patterns #57535)
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Blocker: Approved by a merged RFC but not yet implemented.Category: An issue tracking the progress of sth. like the implementation of an RFCCall for participation: This issue has a mentor. Use #t-compiler/help on Zulip for discussion.Relevant to the compiler team, which will review and decide on the PR/issue.Relevant to the language teamThis issue / PR is in PFCP or FCP with a disposition to merge it.The final comment period is finished for this PR / Issue.
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arielb1 commentedon Sep 19, 2017
Mentoring Instructions
This is actually an easy one:
The code that emits the error message is the
check_armsfunction here:rust/src/librustc_const_eval/check_match.rs
Line 317 in 325ba23
It nicely contains branches for
if letandwhile let, so we just need to adapt them to emit lints instead of errors. We emit lints using thelint_nodefunction - you can see an example calls of it below in the function. Remember to add a feature gate.You'll also want to declare the new lints you are using, which is done in:
rust/src/librustc/lint/builtin.rs
Line 19 in 325ba23
Just add another
declare_lint!for each new lint.Feature Gates
I should add some version of this to the README.md, but until then:
Also, you'll want to feature gate the new feature, so that it can't be used accidentally until its stabilized. For that, add a feature gate to the list of feature gates here:
rust/src/libsyntax/feature_gate.rs
Line 388 in 325ba23
And link this tracking issue (#44495). You can test the feature in
tcx.sess(e.g.tcx.sess.features.borrow().specialization). If it's not present, you should maintain the old behavior.Don't forget to add tests, both for the new behavior and the old one (the test that the old behavior remains without a feature gate should be in
src/test/compile-fail/feature-gate-YOUR-FEATURE.rs).Nokel81 commentedon Sep 19, 2017
I will now start on the implementation of this
nikomatsakis commentedon Sep 25, 2017
@Nokel81 just checking in -- how's it going? Any questions?
Nokel81 commentedon Sep 25, 2017
No, school work came up but I should have a PR ready by Wednesday
35 remaining items
rfcbot commentedon Oct 7, 2018
The final comment period, with a disposition to merge, as per the review above, is now complete.
Centril commentedon Oct 7, 2018
@Nokel81 would you be willing to write up a stabilization PR?
Nokel81 commentedon Oct 7, 2018
Sure, however, there was a little discussion on the level. Shall I go with what was proposed in the merge by you (that is
Warninstead ofDeny)Centril commentedon Oct 7, 2018
@Nokel81 Thank you.
What was proposed in the FCP merge proposal; that is:
Warn.Nokel81 commentedon Oct 12, 2018
I will see if I can do this tonight
Centril commentedon Oct 27, 2018
@Nokel81 any progress? :)
Nokel81 commentedon Oct 27, 2018
@Centril I have made the code change but I wanted to make sure that I could build it before making the PR. My build fails (even without the code change so I think it is something to do with my environment) with the following error
Nokel81 commentedon Nov 3, 2018
#55639
Would any of you be able to review the stabilization PR?
Stabilise irrefutable if-let and while-let patterns
Rollup merge of rust-lang#57535 - varkor:stabilise-if-while-let-patte…
Centril commentedon Jan 12, 2019
Stabilized in #57535.
Reference issue: rust-lang/reference#507.
Nothing left to do, so closing out.