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is_union returns ty to avoid computing it twice #61261

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merged 2 commits into from
May 29, 2019
Merged

is_union returns ty to avoid computing it twice #61261

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1b86bd7
is_union returns ty to avoid computing it twice
spastorino May 28, 2019
bb94fc0
Use closure to avoid self.describe_place(...).unwrap_or_else(...) rep…
spastorino May 28, 2019
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51 changes: 24 additions & 27 deletions src/librustc_mir/borrow_check/conflict_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -595,12 +595,11 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
) -> (String, String, String, String) {
// Define a small closure that we can use to check if the type of a place
// is a union.
let is_union = |place: &Place<'tcx>| -> bool {
place.ty(self.mir, self.infcx.tcx).ty
.ty_adt_def()
.map(|adt| adt.is_union())
.unwrap_or(false)
let union_ty = |place: &Place<'tcx>| -> Option<Ty<'tcx>> {
let ty = place.ty(self.mir, self.infcx.tcx).ty;
ty.ty_adt_def().filter(|adt| adt.is_union()).map(|_| ty)
};
let describe_place = |place| self.describe_place(place).unwrap_or_else(|| "_".to_owned());

// Start with an empty tuple, so we can use the functions on `Option` to reduce some
// code duplication (particularly around returning an empty description in the failure
Expand All @@ -619,7 +618,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
let mut current = first_borrowed_place;
while let Place::Projection(box Projection { base, elem }) = current {
match elem {
ProjectionElem::Field(field, _) if is_union(base) => {
ProjectionElem::Field(field, _) if union_ty(base).is_some() => {
return Some((base, field));
},
_ => current = base,
Expand All @@ -632,34 +631,32 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
// borrowed place and look for a access to a different field of the same union.
let mut current = second_borrowed_place;
while let Place::Projection(box Projection { base, elem }) = current {
match elem {
ProjectionElem::Field(field, _) if {
is_union(base) && field != target_field && base == target_base
} => {
let desc_base = self.describe_place(base)
.unwrap_or_else(|| "_".to_owned());
let desc_first = self.describe_place(first_borrowed_place)
.unwrap_or_else(|| "_".to_owned());
let desc_second = self.describe_place(second_borrowed_place)
.unwrap_or_else(|| "_".to_owned());

// Also compute the name of the union type, eg. `Foo` so we
// can add a helpful note with it.
let ty = base.ty(self.mir, self.infcx.tcx).ty;

return Some((desc_base, desc_first, desc_second, ty.to_string()));
},
_ => current = base,
if let ProjectionElem::Field(field, _) = elem {
if let Some(union_ty) = union_ty(base) {
if field != target_field && base == target_base {
return Some((
describe_place(base),
describe_place(first_borrowed_place),
describe_place(second_borrowed_place),
union_ty.to_string(),
));
}
}
}

current = base;
}
None
})
.unwrap_or_else(|| {
// If we didn't find a field access into a union, or both places match, then
// only return the description of the first place.
let desc_place = self.describe_place(first_borrowed_place)
.unwrap_or_else(|| "_".to_owned());
(desc_place, "".to_string(), "".to_string(), "".to_string())
(
describe_place(first_borrowed_place),
"".to_string(),
"".to_string(),
"".to_string(),
)
})
}

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