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Adjust and document 'Pat::to_ty' accordingly.

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This commit is contained in:
Mazdak Farrokhzad 2019-07-09 09:23:51 +02:00
parent b02941f2a6
commit 8ba5f49f6f
1 changed files with 11 additions and 4 deletions
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15
src/libsyntax/ast.rs
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@ -519,21 +519,28 @@ impl fmt::Debug for Pat {
}
impl Pat {
/// Attempt reparsing the pattern as a type.
/// This is intended for use by diagnostics.
pub(super) fn to_ty(&self) -> Option<P<Ty>> {
let node = match &self.node {
// In a type expression `_` is an inference variable.
PatKind::Wild => TyKind::Infer,
// An IDENT pattern with no binding mode would be valid as path to a type. E.g. `u32`.
PatKind::Ident(BindingMode::ByValue(Mutability::Immutable), ident, None) => {
TyKind::Path(None, Path::from_ident(*ident))
}
PatKind::Path(qself, path) => TyKind::Path(qself.clone(), path.clone()),
PatKind::Mac(mac) => TyKind::Mac(mac.clone()),
// `&mut? P` can be reinterpreted as `&mut? T` where `T` is `P` reparsed as a type.
PatKind::Ref(pat, mutbl) => pat
.to_ty()
.map(|ty| TyKind::Rptr(None, MutTy { ty, mutbl: *mutbl }))?,
PatKind::Slice(pats, None, _) if pats.len() == 1 => {
pats[0].to_ty().map(TyKind::Slice)?
}
PatKind::Tuple(pats, None) => {
// A slice/array pattern `[P]` can be reparsed as `[T]`, an unsized array,
// when `P` can be reparsed as a type `T`.
PatKind::Slice(pats) if pats.len() == 1 => pats[0].to_ty().map(TyKind::Slice)?,
// A tuple pattern `(P0, .., Pn)` can be reparsed as `(T0, .., Tn)`
// assuming `T0` to `Tn` are all syntactically valid as types.
PatKind::Tuple(pats) => {
let mut tys = Vec::with_capacity(pats.len());
// FIXME(#48994) - could just be collected into an Option<Vec>
for pat in pats {