Match Ergonomics 2024: update old-edition behavior of feature gates #136093

dianne · 2025-01-26T12:57:26Z

This updates the behavior of the feature gates ref_pat_eat_one_layer_2024_structural and ref_pat_eat_one_layer_2024 in Editions 2021 and earlier to correspond to the left and right typing rules compared here, respectively. Compared to the stable_rust rules:

they both allow reference patterns to match a lone inherited ref,
they both allow & patterns to eat &mut reference types (and lone &mut inherited refs) as if they're shared,
they both allow &mut patterns to eat & reference types when there's a &mut inherited reference to also eat,
and the left ruleset has RFC 3627's Rule 3: after encountering a shared reference type in the scrutinee, the default binding mode will be treated as by-shared-ref when it would otherwise be by-mutable-ref.

I think there's already tests for all of those typing rules, so I've added revisions to use the existing tests with the new rulesets. Additionally, I've added a few tests to make sure we handle mixed-edition patterns appropriately, and I've added references to the unstable book.

Relevant tracking issue: #123076

r? @ghost

dianne · 2025-01-31T00:07:56Z

This should now be ready for review, I think!

r? @Nadrieril

bors · 2025-02-07T21:34:39Z

☔ The latest upstream changes (presumably #136697) made this pull request unmergeable. Please resolve the merge conflicts.

Nadrieril

This looks good! I'm sold on the fallback-to-outer (eat both) change. I have a nit about the comments, to make them clearer to readers who don't have all the context in their heads.

There are conflicts in the tests with your other recent PR, once that's fixed I'll merge this!

compiler/rustc_hir_typeck/src/pat.rs

Nadrieril · 2025-02-16T16:47:44Z

compiler/rustc_hir_typeck/src/pat.rs

+                        if fallback_to_outer && inh_mut.is_mut() {
+                            // If we can fall back to matching the inherited reference, the expected
+                            // type is a reference type (of any mutability), and the inherited
+                            // reference is mutable, we'll always be able to match. We handle that
+                            // here to avoid adding fallback-to-outer to the common logic below.
+                            // NB: This way of phrasing the logic will catch more cases than those
+                            // that need to fall back to matching the inherited reference. However,
+                            // as long as `&` patterns can match mutable (inherited) references
+                            // (RFC 3627, Rule 5) this should be sound.
+                            debug_assert!(ref_pat_matches_mut_ref);
+                            self.check_pat(inner, inner_ty, pat_info);
+                            return expected;


Hmmmm this feels a bit too clever, I'm not sure if we may accidentally break that with a future feature like deref patterns. What would it look like to do this the boring way?

It does feel a bit too clever.. I've made it a bit less clever here: b0f337d

That said, I personally don't enjoy any of the fallthrough-type control flow there where some cases use some common logic below and some cases return early. Once there's only a couple of typing rulesets to worry about, my preference would be to find some way to simplify all of that.

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/auxiliary/mixed-editions-macros.rs

compiler/rustc_hir_typeck/src/pat.rs

Nadrieril · 2025-02-16T17:44:18Z

@rustbot author

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/mixed-editions.rs

dianne · 2025-02-17T02:57:17Z

@rustbot ready

Nadrieril · 2025-02-17T21:56:52Z

let's gooo @bors r+

bors · 2025-02-17T21:56:55Z

📌 Commit b0f337d has been approved by Nadrieril

It is now in the queue for this repository.

dianne · 2025-02-17T21:58:41Z

oh if it's not too late: I think this will conflict with #137161

Nadrieril · 2025-02-17T22:00:14Z

which one would you prefer merged first?

dianne · 2025-02-17T22:01:00Z

let's go with #137161, since it fixes a diagnostic issue

Nadrieril · 2025-02-17T22:02:05Z

👍 @bors r-

This also adds `#[cfg]` attributes to tests for bindings' types, to make it visually clearer which revisions type successfully.

These are superseded by the old-edition revisions on the shared tests.

…one deref rules

My reasoning: the ruleset implemented by the same feature gate in Edition 2024 always tries to eat the inherited reference first. For consistency, it makes sense to me to say across all editions that users should consider the inherited reference's mutability when wondering if a `&mut` pattern will type.

Co-authored-by: Nadrieril <[email protected]>

dianne · 2025-02-19T02:05:25Z

The conflicting test should now be fixed @rustbot ready

Nadrieril · 2025-02-19T12:09:05Z

let's gooo @bors r+

bors · 2025-02-19T12:09:08Z

📌 Commit 0a15bfb has been approved by Nadrieril

It is now in the queue for this repository.

…, r=Nadrieril Match Ergonomics 2024: update old-edition behavior of feature gates This updates the behavior of the feature gates `ref_pat_eat_one_layer_2024_structural` and `ref_pat_eat_one_layer_2024` in Editions 2021 and earlier to correspond to the left and right typing rules compared [here](https://nadrieril.github.io/typing-rust-patterns/?opts1=AQEBAQIBAQEBAAAAAAAAAAAAAAAAAAA%3D&style=UserVisible&compare=true&opts2=AQEBAQIBAQABAAAAAQEBAAEBAAABAAA%3D&mode=rules), respectively. Compared to the `stable_rust` rules: - they both allow reference patterns to match a lone inherited ref, - they both allow `&` patterns to eat `&mut` reference types (and lone `&mut` inherited refs) as if they're shared, - they both allow `&mut` patterns to eat `&` reference types when there's a `&mut` inherited reference to also eat, - and the left ruleset has RFC 3627's Rule 3: after encountering a shared reference type in the scrutinee, the default binding mode will be treated as by-shared-ref when it would otherwise be by-mutable-ref. I think there's already tests for all of those typing rules, so I've added revisions to use the existing tests with the new rulesets. Additionally, I've added a few tests to make sure we handle mixed-edition patterns appropriately, and I've added references to the unstable book. Relevant tracking issue: rust-lang#123076 r? `@ghost`

…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#120580 (Add `MAX_LEN_UTF8` and `MAX_LEN_UTF16` Constants) - rust-lang#132268 (Impl TryFrom<Vec<u8>> for String) - rust-lang#136093 (Match Ergonomics 2024: update old-edition behavior of feature gates) - rust-lang#136344 (Suggest replacing `.` with `::` in more error diagnostics.) - rust-lang#136690 (Use more explicit and reliable ptr select in sort impls) - rust-lang#136815 (CI: Stop /msys64/bin from being prepended to PATH in msys2 shell) - rust-lang#136923 (Lint `#[must_use]` attributes applied to methods in trait impls) - rust-lang#137155 (Organize `OsString`/`OsStr` shims) - rust-lang#137225 (vectorcall ABI: require SSE2) Failed merges: - rust-lang#136780 (std: move stdio to `sys`) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#120580 (Add `MAX_LEN_UTF8` and `MAX_LEN_UTF16` Constants) - rust-lang#132268 (Impl TryFrom<Vec<u8>> for String) - rust-lang#136093 (Match Ergonomics 2024: update old-edition behavior of feature gates) - rust-lang#136344 (Suggest replacing `.` with `::` in more error diagnostics.) - rust-lang#136690 (Use more explicit and reliable ptr select in sort impls) - rust-lang#136815 (CI: Stop /msys64/bin from being prepended to PATH in msys2 shell) - rust-lang#136923 (Lint `#[must_use]` attributes applied to methods in trait impls) - rust-lang#137155 (Organize `OsString`/`OsStr` shims) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#136093 - dianne:match-2024-for-edition-2021, r=Nadrieril Match Ergonomics 2024: update old-edition behavior of feature gates This updates the behavior of the feature gates `ref_pat_eat_one_layer_2024_structural` and `ref_pat_eat_one_layer_2024` in Editions 2021 and earlier to correspond to the left and right typing rules compared [here](https://nadrieril.github.io/typing-rust-patterns/?opts1=AQEBAQIBAQEBAAAAAAAAAAAAAAAAAAA%3D&style=UserVisible&compare=true&opts2=AQEBAQIBAQABAAAAAQEBAAEBAAABAAA%3D&mode=rules), respectively. Compared to the `stable_rust` rules: - they both allow reference patterns to match a lone inherited ref, - they both allow `&` patterns to eat `&mut` reference types (and lone `&mut` inherited refs) as if they're shared, - they both allow `&mut` patterns to eat `&` reference types when there's a `&mut` inherited reference to also eat, - and the left ruleset has RFC 3627's Rule 3: after encountering a shared reference type in the scrutinee, the default binding mode will be treated as by-shared-ref when it would otherwise be by-mutable-ref. I think there's already tests for all of those typing rules, so I've added revisions to use the existing tests with the new rulesets. Additionally, I've added a few tests to make sure we handle mixed-edition patterns appropriately, and I've added references to the unstable book. Relevant tracking issue: rust-lang#123076 r? ``@ghost``

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#120580 (Add `MAX_LEN_UTF8` and `MAX_LEN_UTF16` Constants) - rust-lang#132268 (Impl TryFrom<Vec<u8>> for String) - rust-lang#136093 (Match Ergonomics 2024: update old-edition behavior of feature gates) - rust-lang#136344 (Suggest replacing `.` with `::` in more error diagnostics.) - rust-lang#136690 (Use more explicit and reliable ptr select in sort impls) - rust-lang#136815 (CI: Stop /msys64/bin from being prepended to PATH in msys2 shell) - rust-lang#136923 (Lint `#[must_use]` attributes applied to methods in trait impls) - rust-lang#137155 (Organize `OsString`/`OsStr` shims) r? `@ghost` `@rustbot` modify labels: rollup

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. labels Jan 26, 2025

dianne force-pushed the match-2024-for-edition-2021 branch 3 times, most recently from d37a4d4 to 29626d0 Compare January 31, 2025 00:05

dianne marked this pull request as ready for review January 31, 2025 00:06

rustbot assigned Nadrieril Jan 31, 2025

Nadrieril approved these changes Feb 16, 2025

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rustbot 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-review Status: Awaiting review from the assignee but also interested parties. labels Feb 16, 2025

dianne force-pushed the match-2024-for-edition-2021 branch from 24a95bf to b0f337d Compare February 17, 2025 02:48

dianne commented Feb 17, 2025

View reviewed changes

tests/ui/pattern/rfc-3627-match-ergonomics-2024/experimental/mixed-editions.rs Outdated Show resolved Hide resolved

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 17, 2025

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 Feb 17, 2025

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 Feb 17, 2025

dianne added 2 commits February 18, 2025 17:44

add test revisions for old-edition behavior of feature gates

e24833a

This also adds `#[cfg]` attributes to tests for bindings' types, to make it visually clearer which revisions type successfully.

remove old edition-2021-specific tests

3e77657

These are superseded by the old-edition revisions on the shared tests.

dianne and others added 9 commits February 18, 2025 17:44

"classic2021" and "structural2021" rulesets: add eat-inherited-ref-al…

8dc64a4

…one deref rules

"structural2021" ruleset: add fallback-to-outer (eat both) deref rule

443c51d

add mixed-edition tests

1ed74aa

update unstable book

2c595d6

add FIXMEs for diagnostic improvements

799e0f7

clarify wording on doc comment

37bcc1c

Co-authored-by: Nadrieril <[email protected]>

rename consider_inherited_ref_first -> consider_inherited_ref

0e758c4

simplify fallback-to-outer condition on old editions

0a15bfb

dianne force-pushed the match-2024-for-edition-2021 branch from b0f337d to 0a15bfb Compare February 19, 2025 02:03

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 19, 2025

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 Feb 19, 2025

matthiaskrgr mentioned this pull request Feb 19, 2025

Rollup of 9 pull requests #137283

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matthiaskrgr mentioned this pull request Feb 19, 2025

Rollup of 8 pull requests #137290

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bors merged commit 659838e into rust-lang:master Feb 20, 2025
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Match Ergonomics 2024: update old-edition behavior of feature gates #136093

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Match Ergonomics 2024: update old-edition behavior of feature gates #136093

Match Ergonomics 2024: update old-edition behavior of feature gates #136093

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