mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Introduce Constructor::NonExhaustive

Browse Source 
It counts as an extra constructor for types that are not allowed to be
matched exhaustively.
This commit is contained in:
Nadrieril 2019-11-12 12:44:00 +00:00
parent eb99c73e04
commit 357d53c4ce
1 changed files with 57 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

113
src/librustc_mir/hair/pattern/_match.rs
View File

@ -590,6 +590,8 @@ enum Constructor<'tcx> {
FixedLenSlice(u64),
/// Slice patterns. Captures any array constructor of `length >= i + j`.
VarLenSlice(u64, u64),
/// Fake extra constructor for enums that aren't allowed to be matched exhaustively.
NonExhaustive,
}
// Ignore spans when comparing, they don't carry semantic information as they are only for lints.
@ -597,6 +599,7 @@ impl<'tcx> std::cmp::PartialEq for Constructor<'tcx> {
fn eq(&self, other: &Self) -> bool {
match (self, other) {
(Constructor::Single, Constructor::Single) => true,
(Constructor::NonExhaustive, Constructor::NonExhaustive) => true,
(Constructor::Variant(a), Constructor::Variant(b)) => a == b,
(Constructor::ConstantValue(a, _), Constructor::ConstantValue(b, _)) => a == b,
(
@ -771,6 +774,8 @@ impl<'tcx> Constructor<'tcx> {
// ranges have been omitted.
remaining_ctors
}
// This constructor is never covered by anything else
NonExhaustive => vec![NonExhaustive],
}
}
@ -842,7 +847,7 @@ impl<'tcx> Constructor<'tcx> {
}
_ => bug!("bad slice pattern {:?} {:?}", self, ty),
},
ConstantValue(..) | ConstantRange(..) => vec![],
ConstantValue(..) | ConstantRange(..) | NonExhaustive => vec![],
}
}
@ -865,7 +870,7 @@ impl<'tcx> Constructor<'tcx> {
},
FixedLenSlice(length) => *length,
VarLenSlice(prefix, suffix) => prefix + suffix,
ConstantValue(..) | ConstantRange(..) => 0,
ConstantValue(..) | ConstantRange(..) | NonExhaustive => 0,
}
}
@ -932,6 +937,7 @@ impl<'tcx> Constructor<'tcx> {
hi: ty::Const::from_bits(cx.tcx, hi, ty::ParamEnv::empty().and(ty)),
end,
}),
NonExhaustive => PatKind::Wild,
};
Pat { ty, span: DUMMY_SP, kind: Box::new(pat) }
@ -1193,6 +1199,36 @@ fn all_constructors<'a, 'tcx>(
}
}
};
// FIXME: currently the only way I know of something can
// be a privately-empty enum is when the exhaustive_patterns
// feature flag is not present, so this is only
// needed for that case.
let is_privately_empty = ctors.is_empty() && !cx.is_uninhabited(pcx.ty);
let is_declared_nonexhaustive = cx.is_non_exhaustive_enum(pcx.ty) && !cx.is_local(pcx.ty);
let is_non_exhaustive = is_privately_empty
|| is_declared_nonexhaustive
|| (pcx.ty.is_ptr_sized_integral() && !cx.tcx.features().precise_pointer_size_matching);
if is_non_exhaustive {
// If our scrutinee is *privately* an empty enum, we must treat it as though it had an
// "unknown" constructor (in that case, all other patterns obviously can't be variants) to
// avoid exposing its emptyness. See the `match_privately_empty` test for details.
//
// If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an additionnal
// "unknown" constructor. However there is no point in enumerating all possible variants,
// because the user can't actually match against them themselves. So we return only the
// fictitious constructor.
// E.g., in an example like:
// ```
// let err: io::ErrorKind = ...;
// match err {
// io::ErrorKind::NotFound => {},
// }
// ```
// we don't want to show every possible IO error, but instead have only `_` as the witness.
return vec![NonExhaustive];
}
ctors
}
@ -1591,9 +1627,6 @@ pub fn is_useful<'p, 'a, 'tcx>(
let all_ctors = all_constructors(cx, pcx);
debug!("all_ctors = {:#?}", all_ctors);
let is_privately_empty = all_ctors.is_empty() && !cx.is_uninhabited(pcx.ty);
let is_declared_nonexhaustive = cx.is_non_exhaustive_enum(pcx.ty) && !cx.is_local(pcx.ty);
// `missing_ctors` is the set of constructors from the same type as the
// first column of `matrix` that are matched only by wildcard patterns
// from the first column.
@ -1601,38 +1634,15 @@ pub fn is_useful<'p, 'a, 'tcx>(
// Therefore, if there is some pattern that is unmatched by `matrix`,
// it will still be unmatched if the first constructor is replaced by
// any of the constructors in `missing_ctors`
//
// However, if our scrutinee is *privately* an empty enum, we
// must treat it as though it had an "unknown" constructor (in
// that case, all other patterns obviously can't be variants)
// to avoid exposing its emptyness. See the `match_privately_empty`
// test for details.
//
// FIXME: currently the only way I know of something can
// be a privately-empty enum is when the exhaustive_patterns
// feature flag is not present, so this is only
// needed for that case.
// Missing constructors are those that are not matched by any
// non-wildcard patterns in the current column. To determine if
// the set is empty, we can check that `.peek().is_none()`, so
// we only fully construct them on-demand, because they're rarely used and can be big.
// Missing constructors are those that are not matched by any non-wildcard patterns in the
// current column. We only fully construct them on-demand, because they're rarely used and
// can be big.
let missing_ctors = MissingConstructors::new(cx.tcx, cx.param_env, all_ctors, used_ctors);
debug!(
"missing_ctors.empty()={:#?} is_privately_empty={:#?} is_declared_nonexhaustive={:#?}",
missing_ctors.is_empty(),
is_privately_empty,
is_declared_nonexhaustive
);
debug!("missing_ctors.empty()={:#?}", missing_ctors.is_empty(),);
// For privately empty and non-exhaustive enums, we work as if there were an "extra"
// `_` constructor for the type, so we can never match over all constructors.
let is_non_exhaustive = is_privately_empty
|| is_declared_nonexhaustive
|| (pcx.ty.is_ptr_sized_integral() && !cx.tcx.features().precise_pointer_size_matching);
if missing_ctors.is_empty() && !is_non_exhaustive {
if missing_ctors.is_empty() {
let (all_ctors, _) = missing_ctors.into_inner();
split_grouped_constructors(cx.tcx, cx.param_env, pcx, all_ctors, matrix, DUMMY_SP, None)
.into_iter()
@ -1661,26 +1671,9 @@ pub fn is_useful<'p, 'a, 'tcx>(
//
// we can report 3 witnesses: `S`, `E`, and `W`.
//
// However, there are 2 cases where we don't want
// However, there is a case where we don't want
// to do this and instead report a single `_` witness:
//
// 1) If the user is matching against a non-exhaustive
// enum, there is no point in enumerating all possible
// variants, because the user can't actually match
// against them themselves, e.g., in an example like:
// ```
// let err: io::ErrorKind = ...;
// match err {
// io::ErrorKind::NotFound => {},
// }
// ```
// we don't want to show every possible IO error,
// but instead have `_` as the witness (this is
// actually *required* if the user specified *all*
// IO errors, but is probably what we want in every
// case).
//
// 2) If the user didn't actually specify a constructor
// if the user didn't actually specify a constructor
// in this arm, e.g., in
// ```
// let x: (Direction, Direction, bool) = ...;
@ -1690,7 +1683,7 @@ pub fn is_useful<'p, 'a, 'tcx>(
// `(<direction-1>, <direction-2>, true)` - we are
// satisfied with `(_, _, true)`. In this case,
// `used_ctors` is empty.
if is_non_exhaustive || missing_ctors.all_ctors_are_missing() {
if missing_ctors.all_ctors_are_missing() {
// All constructors are unused. Add a wild pattern
// rather than each individual constructor.
usefulness.apply_wildcard(pcx.ty)
@ -2217,13 +2210,21 @@ fn patterns_for_variant<'p, 'a: 'p, 'tcx>(
/// fields filled with wild patterns.
fn specialize_one_pattern<'p, 'a: 'p, 'q: 'p, 'tcx>(
cx: &mut MatchCheckCtxt<'a, 'tcx>,
pat: &'q Pat<'tcx>,
mut pat: &'q Pat<'tcx>,
constructor: &Constructor<'tcx>,
ctor_wild_subpatterns: &[&'p Pat<'tcx>],
) -> Option<PatStack<'p, 'tcx>> {
while let PatKind::AscribeUserType { ref subpattern, .. } = *pat.kind {
pat = subpattern;
}
if let NonExhaustive = constructor {
// Only a wildcard pattern can match the special extra constructor
return if pat.is_wildcard() { Some(PatStack::default()) } else { None };
}
let result = match *pat.kind {
PatKind::AscribeUserType { ref subpattern, .. } => PatStack::from_pattern(subpattern)
.specialize_constructor(cx, constructor, ctor_wild_subpatterns),
PatKind::AscribeUserType { .. } => bug!(), // Handled above
PatKind::Binding { .. } | PatKind::Wild => {
Some(PatStack::from_slice(ctor_wild_subpatterns))