bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Merge unreachable subpatterns correctly

Browse source
This commit is contained in:
Nadrieril 2020-12-17 01:25:53 +00:00
parent 2d71a0b9b9
commit 6319d737e0
3 changed files with 36 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

31
compiler/rustc_mir_build/src/thir/pattern/usefulness.rs
View file

@ -788,13 +788,32 @@ impl<'tcx> Usefulness<'tcx> {
/// When trying several branches and each returns a `Usefulness`, we need to combine the
/// results together.
fn merge_split_constructors(usefulnesses: impl Iterator<Item = Self>) -> Self {
// If we have detected some unreachable sub-branches, we only want to keep them when they
// were unreachable in _all_ branches. So we take a big intersection.
// Is `None` when no branch was useful. Will often be `Some(Spanset::new())` because the
// sets are only non-empty in the diagnostic path.
let mut unreachables: Option<SpanSet> = None;
// Witnesses of usefulness, if any.
let mut witnesses = Vec::new();
for u in usefulnesses {
match u {
Useful(..) => {
return u;
Useful(spans) if spans.is_empty() => {
// Once we reach the empty set, more intersections won't change the result.
return Useful(SpanSet::new());
}
Useful(spans) => {
if let Some(unreachables) = &mut unreachables {
if !unreachables.is_empty() {
unreachables.intersection_mut(&spans);
}
if unreachables.is_empty() {
return Useful(SpanSet::new());
}
} else {
unreachables = Some(spans);
}
}
NotUseful => {}
UsefulWithWitness(wits) => {
@ -803,7 +822,13 @@ impl<'tcx> Usefulness<'tcx> {
}
}
if !witnesses.is_empty() { UsefulWithWitness(witnesses) } else { NotUseful }
if !witnesses.is_empty() {
UsefulWithWitness(witnesses)
} else if let Some(unreachables) = unreachables {
Useful(unreachables)
} else {
NotUseful
}
}
fn apply_constructor<'p>(