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Fix explanation of handling of empty enums

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This commit is contained in:
Nadrieril 2019-11-30 15:41:27 +00:00
parent 86fb2ef2e1
commit 063d74f5d9
1 changed files with 7 additions and 16 deletions
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23
src/librustc_mir/hair/pattern/_match.rs
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@ -1267,23 +1267,14 @@ fn all_constructors<'a, 'tcx>(
let is_declared_nonexhaustive =
def.is_variant_list_non_exhaustive() && !cx.is_local(pcx.ty);
// 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.
let is_privately_empty = if cx.tcx.features().exhaustive_patterns {
// This cannot happen because we have already filtered out uninhabited variants.
false
} else {
// FIXME: this is fishy
def.variants.is_empty()
};
// If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
// as though it had an "unknown" constructor to avoid exposing its emptyness. Note that
// an empty match will still be considered exhaustive because that case is handled
// separately in `check_match`.
let is_secretly_empty =
def.variants.is_empty() && !cx.tcx.features().exhaustive_patterns;
if is_privately_empty || is_declared_nonexhaustive {
vec![NonExhaustive]
} else {
ctors
}
if is_secretly_empty || is_declared_nonexhaustive { vec![NonExhaustive] } else { ctors }
}
ty::Char => {
vec![