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Move empty match check to check_exhaustive

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This commit is contained in:
Nadrieril 2019-12-03 18:59:50 +00:00
parent 3532835738
commit d289f55b0c
1 changed files with 56 additions and 53 deletions
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109
src/librustc_mir/hair/pattern/check_match.rs
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@ -166,60 +166,10 @@ impl<'tcx> MatchVisitor<'_, 'tcx> {
// Fourth, check for unreachable arms.
let matrix = check_arms(cx, &inlined_arms, source);
// Then, if the match has no arms, check whether the scrutinee
// is uninhabited.
let scrut_ty = self.tables.node_type(scrut.hir_id);
if inlined_arms.is_empty() {
let scrutinee_is_visibly_uninhabited = if self.tcx.features().exhaustive_patterns {
let module = self.tcx.hir().get_module_parent(scrut.hir_id);
self.tcx.is_ty_uninhabited_from(module, scrut_ty)
} else {
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)
}
_ => false,
}
};
if 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;
} else {
// We know the type is inhabited, so this must be wrong
let (def_span, non_empty_enum) = match scrut_ty.kind {
ty::Adt(def, _) if def.is_enum() => {
(self.tcx.hir().span_if_local(def.did), !def.variants.is_empty())
}
_ => (None, false),
};
if non_empty_enum {
// Continue to the normal code path to display missing variants.
} else {
let mut err = create_e0004(
self.tcx.sess,
scrut.span,
format!("non-exhaustive patterns: type `{}` is non-empty", scrut_ty),
);
err.help(
"ensure that all possible cases are being handled, \
possibly by adding wildcards or more match arms",
);
if let Some(sp) = def_span {
err.span_label(sp, format!("`{}` defined here", scrut_ty));
}
err.emit();
return;
}
}
}
// Fifth, check if the match is exhaustive.
check_exhaustive(cx, scrut_ty, scrut.span, &matrix, scrut.hir_id);
let scrut_ty = self.tables.node_type(scrut.hir_id);
let is_empty_match = inlined_arms.is_empty();
check_exhaustive(cx, scrut_ty, scrut.span, &matrix, scrut.hir_id, is_empty_match);
})
}
@ -483,7 +433,60 @@ fn check_exhaustive<'p, 'tcx>(
sp: Span,
matrix: &Matrix<'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.
if is_empty_match {
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 {
ty::Never => true,
ty::Adt(def, _) if 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, 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;
} else {
// We know the type is inhabited, so this must be wrong
let (def_span, non_empty_enum) = match scrut_ty.kind {
ty::Adt(def, _) if def.is_enum() => {
(cx.tcx.hir().span_if_local(def.did), !def.variants.is_empty())
}
_ => (None, false),
};
if non_empty_enum {
// Continue to the normal code path to display missing variants.
} else {
let mut err = create_e0004(
cx.tcx.sess,
sp,
format!("non-exhaustive patterns: type `{}` is non-empty", scrut_ty),
);
err.help(
"ensure that all possible cases are being handled, \
possibly by adding wildcards or more match arms",
);
if let Some(sp) = def_span {
err.span_label(sp, format!("`{}` defined here", scrut_ty));
}
err.emit();
return;
}
}
}
let witnesses = match check_not_useful(cx, scrut_ty, matrix, hir_id) {
Ok(_) => return,
Err(err) => err,