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resolve: more declarative fresh_binding #66639

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Nov 23, 2019
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resolve: more declarative fresh_binding #66639

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22 changes: 7 additions & 15 deletions src/librustc_resolve/late.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,7 @@ impl PatternSource {
/// Denotes whether the context for the set of already bound bindings is a `Product`
/// or `Or` context. This is used in e.g., `fresh_binding` and `resolve_pattern_inner`.
/// See those functions for more information.
#[derive(PartialEq)]
enum PatBoundCtx {
/// A product pattern context, e.g., `Variant(a, b)`.
Product,
Expand Down Expand Up @@ -1417,21 +1418,12 @@ impl<'a, 'b> LateResolutionVisitor<'a, '_> {
// later passes make about or-patterns.)
let ident = ident.modern_and_legacy();

// Walk outwards the stack of products / or-patterns and
// find out if the identifier has been bound in any of these.
let mut already_bound_and = false;
let mut already_bound_or = false;
for (is_sum, set) in bindings.iter_mut().rev() {
match (is_sum, set.get(&ident).cloned()) {
// Already bound in a product pattern, e.g. `(a, a)` which is not allowed.
(PatBoundCtx::Product, Some(..)) => already_bound_and = true,
// Already bound in an or-pattern, e.g. `V1(a) | V2(a)`.
// This is *required* for consistency which is checked later.
(PatBoundCtx::Or, Some(..)) => already_bound_or = true,
// Not already bound here.
_ => {}
}
}
let mut bound_iter = bindings.iter().filter(|(_, set)| set.contains(&ident));
// Already bound in a product pattern? e.g. `(a, a)` which is not allowed.
let already_bound_and = bound_iter.clone().any(|(ctx, _)| *ctx == PatBoundCtx::Product);
// Already bound in an or-pattern? e.g. `V1(a) | V2(a)`.
// This is *required* for consistency which is checked later.
let already_bound_or = bound_iter.any(|(ctx, _)| *ctx == PatBoundCtx::Or);

if already_bound_and {
// Overlap in a product pattern somewhere; report an error.
Expand Down