stop marking `deref_patterns` as an incomplete feature by cyrgani · Pull Request #153053 · rust-lang/rust

cyrgani · 2026-02-24T16:12:11Z

This PR removes the incomplete_feature warning for deref_patterns. The reason given for this in the tracking issue (#87121) was

Per policy, the incomplete_feature is supposed to stay on until the feature has an accepted RFC. We're slowly working on writing up that RFC so it'll take some more time unfortunately.

I don't know of any compiler crashes it causes today. The feature should be pretty usable.

However, I could not find any evidence of such a policy. The lint documentation for incomplete_features also only mentions features that are more likely to cause errors.
There are also many other features without an RFC that are not considered incomplete, e.g. macro_metavar_expr_concat, negative_impls or yeet_expr.
The feature does not cause any known ICEs either.

The concrete motivation is to use this feature to replace box_patterns in the compiler and pave the way towards removing that legacy feature.

rustbot · 2026-02-24T16:12:14Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-02-24T16:12:17Z

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jackh726 · 2026-02-24T18:06:43Z

This is indeed more or less current policy. This should get an RFC before being marked as incomplete.

fee1-dead · 2026-03-09T03:37:27Z

If we look at the diagnostic emitted by incomplete_feature:

warning: the feature `deref_patterns` is incomplete and may not be safe to use and/or cause compiler crashes
 --> src/lib.rs:1:12
  |
1 | #![feature(deref_patterns)]
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #87121 <https://github.com/rust-lang/rust/issues/87121> for more information
  = note: `#[warn(incomplete_features)]` on by default

This paints me as a status that moreso reflects the state of the feature in the compiler rather than the language. Given that my memory of incomplete_feature as primarily being used to warn users of unsoundness, ICEs, lack of proper support, etc, I would approve this PR given that deref_patterns appears to have matured and not cause unsoundness/ICEs at present.

cc @Nadrieril who made that comment originally.

@bors r+ rollup

rust-bors · 2026-03-09T03:37:29Z

📌 Commit 06b0bd2 has been approved by fee1-dead

It is now in the queue for this repository.

Nadrieril · 2026-03-09T04:01:38Z

@bors r-

The policy is here: https://lang-team.rust-lang.org/how_to/experiment.html :

The feature gate should be marked as ‘experimental’, so that users get warnings if they try to use it. This flag has to stay until an RFC is accepted, even if the implementation is in good shape.

I consider it important to keep the warning, because this feature may be replaced by something different depending on how the Field Projections work pans out.

Nadrieril · 2026-03-09T04:03:38Z

It's a known annoyance that we use the same "incomplete feature" lint to mark both features that aren't fully implemented and features that aren't yet approved by the lang team, but for now that's the lint we have.

fee1-dead · 2026-03-09T04:08:16Z

/shrug

const traits doesn't have incomplete status either, and it also doesn't have an RFC. The wording on the diagnostic does not match what the lang team prescribes. Someone should do Something I suppose, and change the warnings for these kinds of features from the current wording to one that is like "this feature does not have an accepted RFC", with note "this feature could be majorly changed or outright removed"

Nadrieril · 2026-03-09T04:12:50Z

I consider it important to keep the warning

Arguably "this is a nightly feature" could be enough of a deterrent. I think the lint is a not-super-thorough attempt at signaling to users how risky it is to be making use of that feature in their code.

And, well, for deref patterns I think we're in "not too risky" territory. I wouldn't remove the feature except to replace it with something similar; the overall ergonomics is completely something we want in the language in some form. So maybe it's fair to remove the lint...

Nadrieril · 2026-03-09T04:17:04Z

There are also many other features without an RFC that are not considered incomplete, e.g. macro_metavar_expr_concat, negative_impls or yeet_expr.

const traits doesn't have incomplete status either

Am I the only one respecting that policy x)

Nadrieril · 2026-03-09T12:47:21Z

Alright I've convinced myself, thanks for the PR @cyrgani

@bors r=fee1-dead,Nadrieril

rust-bors · 2026-03-09T12:47:24Z

📌 Commit 06b0bd2 has been approved by fee1-dead,Nadrieril

It is now in the queue for this repository.

…ete, r=fee1-dead,Nadrieril stop marking `deref_patterns` as an incomplete feature This PR removes the `incomplete_feature` warning for `deref_patterns`. The reason given for this in the tracking issue (rust-lang#87121) was > Per policy, the `incomplete_feature` is supposed to stay on until the feature has an accepted RFC. We're slowly working on writing up that RFC so it'll take some more time unfortunately. > > I don't know of any compiler crashes it causes today. The feature should be pretty usable. However, I could not find any evidence of such a policy. The [lint documentation](https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#incomplete-features) for `incomplete_features` also only mentions features that are more likely to cause errors. There are also many other features without an RFC that are not considered incomplete, e.g. `macro_metavar_expr_concat`, `negative_impls` or `yeet_expr`. The feature does not cause any known ICEs either. The concrete motivation is to use this feature to replace `box_patterns` in the compiler and pave the way towards removing that legacy feature.

…uwer Rollup of 4 pull requests Successful merges: - #147834 (Always make tuple elements a coercion site) - #150446 (miri/const eval: support `MaybeDangling`) - #153053 (stop marking `deref_patterns` as an incomplete feature) - #153398 (fix ICE in `const_c_variadic` when passing ZSTs)

Rollup merge of #153053 - cyrgani:deref-patterns-not-imcomplete, r=fee1-dead,Nadrieril stop marking `deref_patterns` as an incomplete feature This PR removes the `incomplete_feature` warning for `deref_patterns`. The reason given for this in the tracking issue (#87121) was > Per policy, the `incomplete_feature` is supposed to stay on until the feature has an accepted RFC. We're slowly working on writing up that RFC so it'll take some more time unfortunately. > > I don't know of any compiler crashes it causes today. The feature should be pretty usable. However, I could not find any evidence of such a policy. The [lint documentation](https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#incomplete-features) for `incomplete_features` also only mentions features that are more likely to cause errors. There are also many other features without an RFC that are not considered incomplete, e.g. `macro_metavar_expr_concat`, `negative_impls` or `yeet_expr`. The feature does not cause any known ICEs either. The concrete motivation is to use this feature to replace `box_patterns` in the compiler and pave the way towards removing that legacy feature.

…uwer Rollup of 4 pull requests Successful merges: - rust-lang/rust#147834 (Always make tuple elements a coercion site) - rust-lang/rust#150446 (miri/const eval: support `MaybeDangling`) - rust-lang/rust#153053 (stop marking `deref_patterns` as an incomplete feature) - rust-lang/rust#153398 (fix ICE in `const_c_variadic` when passing ZSTs)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-clippy Relevant to the Clippy team. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 24, 2026

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stop marking deref_patterns as an incomplete feature

06b0bd2

rust-cloud-vms bot force-pushed the deref-patterns-not-imcomplete branch from 635d644 to 06b0bd2 Compare February 24, 2026 17:43

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JonathanBrouwer mentioned this pull request Mar 9, 2026

Rollup of 4 pull requests #153617

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rust-bors bot merged commit 8120cc4 into rust-lang:main Mar 9, 2026
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cyrgani deleted the deref-patterns-not-imcomplete branch March 9, 2026 20:35

cyrgani mentioned this pull request Mar 10, 2026

allow incomplete_features in UI tests rust-lang/compiler-team#974

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