user0/rust
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions
rust/tests/ui/pattern
History
Matthias Krüger a37fa37281
Rollup merge of #118803 - Nadrieril:min-exhaustive-patterns, r=compiler-errors 
Add the `min_exhaustive_patterns` feature gate

## Motivation

Pattern-matching on empty types is tricky around unsafe code. For that reason, current stable rust conservatively requires arms for empty types in all but the simplest case. It has long been the intention to allow omitting empty arms when it's safe to do so. The [`exhaustive_patterns`](https://github.com/rust-lang/rust/issues/51085) feature allows the omission of all empty arms, but hasn't been stabilized because that was deemed dangerous around unsafe code.

## Proposal

This feature aims to stabilize an uncontroversial subset of exhaustive_patterns. Namely: when `min_exhaustive_patterns` is enabled and the data we're matching on is guaranteed to be valid by rust's operational semantics, then we allow empty arms to be omitted. E.g.:

```rust
let x: Result<T, !> = foo();
match x { // ok
    Ok(y) => ...,
}
let Ok(y) = x; // ok
```

If the place is not guaranteed to hold valid data (namely ptr dereferences, ref dereferences (conservatively) and union field accesses), then we keep stable behavior i.e. we (usually) require arms for the empty cases.

```rust
unsafe {
    let ptr: *const Result<u32, !> = ...;
    match *ptr {
        Ok(x) => { ... }
        Err(_) => { ... } // still required
    }
}
let foo: Result<u32, &!> = ...;
match foo {
    Ok(x) => { ... }
    Err(&_) => { ... } // still required because of the dereference
}
unsafe {
    let ptr: *const ! = ...;
    match *ptr {} // already allowed on stable
}
```

Note that we conservatively consider that a valid reference can point to invalid data, hence we don't allow arms of type `&!` and similar cases to be omitted. This could eventually change depending on [opsem decisions](https://github.com/rust-lang/unsafe-code-guidelines/issues/413). Whenever opsem is undecided on a case, we conservatively keep today's stable behavior.

I proposed this behavior in the [`never_patterns`](https://github.com/rust-lang/rust/issues/118155) feature gate but it makes sense on its own and could be stabilized more quickly. The two proposals nicely complement each other.

## Unresolved Questions

Part of the question is whether this requires an RFC. I'd argue this doesn't need one since there is no design question beyond the intent to omit unreachable patterns, but I'm aware the problem can be framed in ways that require design (I'm thinking of the [original never patterns proposal](https://smallcultfollowing.com/babysteps/blog/2018/08/13/never-patterns-exhaustive-matching-and-uninhabited-types-oh-my/), which would frame this behavior as "auto-nevering" happening).

EDIT: I initially proposed a future-compatibility lint as part of this feature, I don't anymore.
2024-01-26 06:36:36 +01:00
..
auxiliary Move /src/test to /tests 2023-01-11 09:32:08 +00:00
bindings-after-at Show number in error message even for one error 2023-11-24 19:15:52 +01:00
move-ref-patterns Show number in error message even for one error 2023-11-24 19:15:52 +01:00
usefulness Rollup merge of #118803 - Nadrieril:min-exhaustive-patterns, r=compiler-errors 2024-01-26 06:36:36 +01:00
byte-string-inference.rs Revert "Structurally resolve correctly in check_pat_lit" 2023-06-24 18:41:27 +00:00
for-loop-bad-item.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
for-loop-bad-item.stderr Modify primary span label for E0308 2023-01-30 20:12:19 +00:00
ignore-all-the-things.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
incorrect-placement-of-pattern-modifiers.fixed Account for ref and mut in the wrong place for pattern ident renaming 2023-10-30 00:15:49 +00:00
incorrect-placement-of-pattern-modifiers.rs Account for ref and mut in the wrong place for pattern ident renaming 2023-10-30 00:15:49 +00:00
incorrect-placement-of-pattern-modifiers.stderr Account for ref and mut in the wrong place for pattern ident renaming 2023-10-30 00:15:49 +00:00
integer-range-binding.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-6449.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-8351-1.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-8351-2.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-10392.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-11577.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-12582.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-14221.rs Change bindings_with_variant_name to deny-by-default 2023-01-20 02:26:12 -05:00
issue-14221.stderr Change bindings_with_variant_name to deny-by-default 2023-01-20 02:26:12 -05:00
issue-15080.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-17718-patterns.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-17718-patterns.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-22546.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-27320.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-52240.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-52240.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-66270-pat-struct-parser-recovery.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-66270-pat-struct-parser-recovery.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-67037-pat-tup-scrut-ty-diff-less-fields.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-67037-pat-tup-scrut-ty-diff-less-fields.stderr Modify primary span label for E0308 2023-01-30 20:12:19 +00:00
issue-67776-match-same-name-enum-variant-refs.rs Change bindings_with_variant_name to deny-by-default 2023-01-20 02:26:12 -05:00
issue-67776-match-same-name-enum-variant-refs.stderr Change bindings_with_variant_name to deny-by-default 2023-01-20 02:26:12 -05:00
issue-68393-let-pat-assoc-constant.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-68393-let-pat-assoc-constant.stderr Perform match checking on THIR. 2023-04-03 15:59:21 +00:00
issue-72565.rs Avoid emitting the non_exhaustive error if other errors already occurred 2023-10-11 12:49:57 +00:00
issue-72565.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-72574-1.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-72574-1.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-72574-2.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-72574-2.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-74539.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-74539.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-74702.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-74702.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-74954.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-80186-mut-binding-help-suggestion.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-80186-mut-binding-help-suggestion.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-88074-pat-range-type-inference-err.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-88074-pat-range-type-inference-err.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-88074-pat-range-type-inference.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-92074-macro-ice.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-92074-macro-ice.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-94866.rs Move tests 2023-05-24 19:35:59 -03:00
issue-94866.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-95878.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
issue-95878.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-106552.rs suggest fix for attempted integer identifier in patterns 2023-01-14 12:51:20 +13:00
issue-106552.stderr Perform match checking on THIR. 2023-04-03 15:59:21 +00:00
issue-106862.fixed error-msg: impl better suggestion for E0532 2023-03-15 22:19:54 +13:00
issue-106862.rs error-msg: impl better suggestion for E0532 2023-03-15 22:19:54 +13:00
issue-106862.stderr error-msg: impl better suggestion for E0532 2023-03-15 22:19:54 +13:00
issue-110508.rs add regression test 2023-07-01 02:28:15 -04:00
issue-114896.rs fixes #114896 2023-09-07 11:07:33 +08:00
issue-114896.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
issue-115599.rs remove StructuralEq trait 2024-01-24 07:56:23 +01:00
issue-115599.stderr remove StructuralEq trait 2024-01-24 07:56:23 +01:00
issue-117626.rs add test for #117626 2023-12-29 01:13:54 +08:00
non-constant-in-const-path.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
non-constant-in-const-path.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
non-structural-match-types.rs Remove revisions for THIR unsafeck 2024-01-05 09:30:27 +00:00
non-structural-match-types.stderr Remove revisions for THIR unsafeck 2024-01-05 09:30:27 +00:00
pat-shadow-in-nested-binding.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-shadow-in-nested-binding.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
pat-struct-field-expr-has-type.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-struct-field-expr-has-type.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
pat-tuple-bad-type.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-tuple-bad-type.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-tuple-field-count-cross.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-tuple-field-count-cross.stderr resolve: Remove struct_field_names_untracked 2023-03-13 17:31:55 +04:00
pat-tuple-overfield.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-tuple-overfield.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-tuple-underfield.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-tuple-underfield.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-type-err-formal-param.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-type-err-formal-param.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
pat-type-err-let-stmt.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pat-type-err-let-stmt.stderr Modify primary span label for E0308 2023-01-30 20:12:19 +00:00
patkind-litrange-no-expr.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
patkind-litrange-no-expr.stderr Add a note to duplicate diagnostics 2023-10-05 01:04:41 +00:00
pattern-bad-ref-box-order.fixed Suggest swapping the order of ref and box 2023-11-27 21:38:19 +09:00
pattern-bad-ref-box-order.rs Suggest swapping the order of ref and box 2023-11-27 21:38:19 +09:00
pattern-bad-ref-box-order.stderr Suggest swapping the order of ref and box 2023-11-27 21:38:19 +09:00
pattern-binding-disambiguation.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pattern-binding-disambiguation.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pattern-error-continue.rs Modify primary span label for E0308 2023-01-30 20:12:19 +00:00
pattern-error-continue.stderr refactor(resolve): clean up the early error return caused by non-call 2023-05-10 22:35:01 +08:00
pattern-ident-path-generics.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pattern-ident-path-generics.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
pattern-tyvar-2.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pattern-tyvar-2.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
pattern-tyvar.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
pattern-tyvar.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
range-pattern-meant-to-be-slice-rest-pattern.rs On resolve error of [rest..], suggest [rest @ ..] 2023-11-17 00:55:55 +00:00
range-pattern-meant-to-be-slice-rest-pattern.stderr Bless tests 2024-01-13 12:46:58 -05:00
rest-pat-semantic-disallowed.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
rest-pat-semantic-disallowed.stderr Move /src/test to /tests 2023-01-11 09:32:08 +00:00
rest-pat-syntactic.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
rest-pat-syntactic.stderr Bless tests 2024-01-13 12:46:58 -05:00
size-and-align.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
slice-array-infer.rs add more tests 2023-07-17 22:06:32 +00:00
slice-pattern-refutable.rs address review 2023-07-17 22:06:32 +00:00
slice-pattern-refutable.stderr address review 2023-07-17 22:06:32 +00:00
slice-patterns-ambiguity.rs add tests for refutable patterns 2023-07-17 22:02:09 +00:00
slice-patterns-ambiguity.stderr add tests for refutable patterns 2023-07-17 22:02:09 +00:00
slice-patterns-irrefutable.rs address review 2023-07-28 11:20:11 +00:00
slice-patterns-irrefutable.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00
slice-patterns-nested.rs add test for nested pattern 2023-07-17 22:06:32 +00:00
suggest-adding-appropriate-missing-pattern-excluding-comments.fixed Perform match checking on THIR. 2023-04-03 15:59:21 +00:00
suggest-adding-appropriate-missing-pattern-excluding-comments.rs Move /src/test to /tests 2023-01-11 09:32:08 +00:00
suggest-adding-appropriate-missing-pattern-excluding-comments.stderr Show number in error message even for one error 2023-11-24 19:15:52 +01:00