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Only special-case empty matches when exhaustive_patterns is off

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When the feature is on, the special casing is not needed. That way when
we stabilize the feature this `if` can just be removed.
This commit is contained in:
Nadrieril 2019-12-04 16:13:19 +00:00
parent bfb556f97d
commit a591ede2e2
1 changed files with 14 additions and 17 deletions
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31
src/librustc_mir/hair/pattern/check_match.rs
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@ -168,6 +168,8 @@ impl<'tcx> MatchVisitor<'_, 'tcx> {
// Fifth, check if the match is exhaustive.
let scrut_ty = self.tables.node_type(scrut.hir_id);
// Note: An empty match isn't the same as an empty matrix for diagnostics purposes,
// since an empty matrix can occur when there are arms, if those arms all have guards.
let is_empty_match = inlined_arms.is_empty();
check_exhaustive(cx, scrut_ty, scrut.span, &matrix, scrut.hir_id, is_empty_match);
})
@ -435,27 +437,22 @@ fn check_exhaustive<'p, 'tcx>(
hir_id: HirId,
is_empty_match: bool,
) {
// If the match has no arms, check whether the scrutinee is uninhabited.
// Note: An empty match isn't the same as an empty matrix for diagnostics purposes, since an
// empty matrix can occur when there are arms, if those arms all have guards.
let scrutinee_is_visibly_uninhabited = if cx.tcx.features().exhaustive_patterns {
let module = cx.tcx.hir().get_module_parent(hir_id);
cx.tcx.is_ty_uninhabited_from(module, scrut_ty)
} else {
match scrut_ty.kind {
// In the absence of the `exhaustive_patterns` feature, empty matches are not detected by
// `is_useful` to exhaustively match uninhabited types, so we manually check here.
if is_empty_match && !cx.tcx.features().exhaustive_patterns {
let scrutinee_is_visibly_uninhabited = match scrut_ty.kind {
ty::Never => true,
ty::Adt(def, _) if def.is_enum() => {
def.variants.is_empty() && !cx.is_foreign_non_exhaustive_enum(scrut_ty)
ty::Adt(def, _) => {
def.is_enum()
&& def.variants.is_empty()
&& !cx.is_foreign_non_exhaustive_enum(scrut_ty)
}
_ => false,
};
if scrutinee_is_visibly_uninhabited {
// If the type *is* uninhabited, an empty match is vacuously exhaustive.
return;
}
};
if is_empty_match && scrutinee_is_visibly_uninhabited {
// If the type *is* uninhabited, it's vacuously exhaustive.
// This early return is only needed here because in the absence of the
// `exhaustive_patterns` feature, empty matches are not detected by `is_useful`
// to exhaustively match uninhabited types.
return;
}
let witnesses = match check_not_useful(cx, scrut_ty, matrix, hir_id) {