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implement pattern-binding-modes RFC

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See the [RFC] and [tracking issue].

[tracking issue]: https://github.com/rust-lang/rust/issues/42640
[RFC]: 491e0af/text/2005-match-ergonomics.md
This commit is contained in:
Tobias Schottdorf 2017-10-06 16:30:23 -04:00
parent a8feaee5b6
commit de55b4f077
46 changed files with 1406 additions and 75 deletions
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38
src/librustc_const_eval/pattern.rs
View file

@ -301,6 +301,44 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
}
pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
// When implicit dereferences have been inserted in this pattern, the unadjusted lowered
// pattern has the type that results *after* dereferencing. For example, in this code:
//
// ```
// match &&Some(0i32) {
// Some(n) => { ... },
// _ => { ... },
// }
// ```
//
// the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
// determined in rustc_typeck::check::match). The adjustments would be
//
// `vec![&&Option<i32>, &Option<i32>]`.
//
// Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
// we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
// adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
// gets the least-dereferenced type).
let unadjusted_pat = self.lower_pattern_unadjusted(pat);
self.tables
.pat_adjustments()
.get(pat.hir_id)
.unwrap_or(&vec![])
.iter()
.rev()
.fold(unadjusted_pat, |pat, ref_ty| {
debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
Pattern {
span: pat.span,
ty: ref_ty,
kind: Box::new(PatternKind::Deref { subpattern: pat }),
}
},
)
}
fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
let mut ty = self.tables.node_id_to_type(pat.hir_id);
let kind = match pat.node {