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Explain why we require _ for empty patterns

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This commit is contained in:
Nadrieril 2024-07-21 15:18:10 +02:00
parent 710add58e2
commit 8a49d83db7
3 changed files with 14 additions and 0 deletions
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4
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
View File

@ -1019,6 +1019,10 @@ fn report_non_exhaustive_match<'p, 'tcx>(
err.note("`&str` cannot be matched exhaustively, so a wildcard `_` is necessary");
} else if cx.is_foreign_non_exhaustive_enum(ty) {
err.note(format!("`{ty}` is marked as non-exhaustive, so a wildcard `_` is necessary to match exhaustively"));
} else if cx.is_uninhabited(ty.inner()) && cx.tcx.features().min_exhaustive_patterns {
// The type is uninhabited yet there is a witness: we must be in the `MaybeInvalid`
// case.
err.note(format!("`{ty}` is uninhabited but is not being matched by value, so a wildcard `_` is required"));
}
}
}

9
tests/ui/pattern/usefulness/empty-types.min_exh_pats.stderr
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@ -204,6 +204,7 @@ note: `Option<Void>` defined here
|
= note: not covered
= note: the matched value is of type `Option<Void>`
= note: `Void` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ None => {},
@ -349,6 +350,7 @@ LL | match slice_never {
| ^^^^^^^^^^^ pattern `&[_, ..]` not covered
|
= note: the matched value is of type `&[!]`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ [] => {},
@ -484,6 +486,7 @@ note: `Option<!>` defined here
|
= note: not covered
= note: the matched value is of type `&Option<!>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ &None => {},
@ -502,6 +505,7 @@ note: `Option<!>` defined here
|
= note: not covered
= note: the matched value is of type `Option<!>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ None => {},
@ -520,6 +524,7 @@ note: `Result<!, !>` defined here
|
= note: not covered
= note: the matched value is of type `Result<!, !>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ Ok(_) => {},
@ -538,6 +543,7 @@ note: `Result<!, !>` defined here
|
= note: not covered
= note: the matched value is of type `Result<!, !>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ Ok(_a) => {},
@ -589,6 +595,7 @@ LL | match ref_never {
| ^^^^^^^^^ pattern `&_` not covered
|
= note: the matched value is of type `&!`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
= note: references are always considered inhabited
= note: match arms with guards don't count towards exhaustivity
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
@ -609,6 +616,7 @@ note: `Result<!, !>` defined here
|
= note: not covered
= note: the matched value is of type `Result<!, !>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ Err(_) => {},
@ -627,6 +635,7 @@ note: `Option<Result<!, !>>` defined here
|
= note: not covered
= note: the matched value is of type `Option<Result<!, !>>`
= note: `Result<!, !>` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ None => {},

1
tests/ui/pattern/usefulness/slice_of_empty.min_exhaustive_patterns.stderr
View File

@ -5,6 +5,7 @@ LL | match nevers {
| ^^^^^^ pattern `&[_, ..]` not covered
|
= note: the matched value is of type `&[!]`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ &[] => (),