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Avoid repeated trait bounds in derived impls #27134

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Aug 3, 2015
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Avoid repeated trait bounds in derived impls #27134

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11 changes: 11 additions & 0 deletions src/libsyntax/ext/deriving/generic/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,7 @@ pub use self::SubstructureFields::*;
use self::StructType::*;

use std::cell::RefCell;
use std::collections::HashSet;
use std::vec;

use abi::Abi;
Expand Down Expand Up @@ -549,10 +550,20 @@ impl<'a> TraitDef<'a> {
.map(|ty_param| ty_param.ident.name)
.collect();

let mut processed_field_types = HashSet::new();
for field_ty in field_tys {
let tys = find_type_parameters(&*field_ty, &ty_param_names);

for ty in tys {
// if we have already handled this type, skip it
if let ast::TyPath(_, ref p) = ty.node {
if p.segments.len() == 1
&& ty_param_names.contains(&p.segments[0].identifier.name)
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Maybe we could just add these to the process_fields_types HashSet to begin with; processed_field_types.extend(ty_param_names.iter().cloned()).

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I don't think so, unless I'm misunderstanding your comment. ty_param_names are ast::Names, while the elements of processed_field_types are Vec<ast::PathSegment>. It's not clear to me that we can somehow convert one into the other for comparison.

|| processed_field_types.contains(&p.segments) {
continue;
};
processed_field_types.insert(p.segments.clone());
}
let mut bounds: Vec<_> = self.additional_bounds.iter().map(|p| {
cx.typarambound(p.to_path(cx, self.span, type_ident, generics))
}).collect();
Expand Down