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Rollup merge of #121823 - Nadrieril:never-witnesses, r=compiler-errors

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never patterns: suggest `!` patterns on non-exhaustive matches

When a match is non-exhaustive we now suggest never patterns whenever it makes sense.

r? ``@compiler-errors``
This commit is contained in:
Matthias Krüger 2024-03-18 22:24:36 +01:00 • committed by GitHub
commit 2d3dcfaade
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11 changed files with 982 additions and 242 deletions
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39
compiler/rustc_pattern_analysis/src/constructor.rs
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@ -678,15 +678,19 @@ pub enum Constructor<Cx: PatCx> {
Or,
/// Wildcard pattern.
Wildcard,
/// Never pattern. Only used in `WitnessPat`. An actual never pattern should be lowered as
/// `Wildcard`.
Never,
/// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
/// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
/// for those types for which we cannot list constructors explicitly, like `f64` and `str`. Only
/// used in `WitnessPat`.
NonExhaustive,
/// Fake extra constructor for variants that should not be mentioned in diagnostics.
/// We use this for variants behind an unstable gate as well as
/// `#[doc(hidden)]` ones.
/// Fake extra constructor for variants that should not be mentioned in diagnostics. We use this
/// for variants behind an unstable gate as well as `#[doc(hidden)]` ones. Only used in
/// `WitnessPat`.
Hidden,
/// Fake extra constructor for constructors that are not seen in the matrix, as explained at the
/// top of the file.
/// top of the file. Only used for specialization.
Missing,
/// Fake extra constructor that indicates and empty field that is private. When we encounter one
/// we skip the column entirely so we don't observe its emptiness. Only used for specialization.
@ -708,6 +712,7 @@ impl<Cx: PatCx> Clone for Constructor<Cx> {
Constructor::Str(value) => Constructor::Str(value.clone()),
Constructor::Opaque(inner) => Constructor::Opaque(inner.clone()),
Constructor::Or => Constructor::Or,
Constructor::Never => Constructor::Never,
Constructor::Wildcard => Constructor::Wildcard,
Constructor::NonExhaustive => Constructor::NonExhaustive,
Constructor::Hidden => Constructor::Hidden,
@ -1040,10 +1045,32 @@ impl<Cx: PatCx> ConstructorSet<Cx> {
// In a `MaybeInvalid` place even an empty pattern may be reachable. We therefore
// add a dummy empty constructor here, which will be ignored if the place is
// `ValidOnly`.
missing_empty.push(NonExhaustive);
missing_empty.push(Never);
}
}
SplitConstructorSet { present, missing, missing_empty }
}
/// Whether this set only contains empty constructors.
pub(crate) fn all_empty(&self) -> bool {
match self {
ConstructorSet::Bool
| ConstructorSet::Integers { .. }
| ConstructorSet::Ref
| ConstructorSet::Union
| ConstructorSet::Unlistable => false,
ConstructorSet::NoConstructors => true,
ConstructorSet::Struct { empty } => *empty,
ConstructorSet::Variants { variants, non_exhaustive } => {
!*non_exhaustive
&& variants
.iter()
.all(|visibility| matches!(visibility, VariantVisibility::Empty))
}
ConstructorSet::Slice { array_len, subtype_is_empty } => {
*subtype_is_empty && matches!(array_len, Some(1..))
}
}
}
}