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Allow nested generics for the last field of structs in unsizing.

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This commit is contained in:
Eduard Burtescu 2015-06-05 20:49:23 +03:00
parent 19a39710c4
commit 01dee1b77e
2 changed files with 36 additions and 15 deletions
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46
src/librustc/middle/traits/select.rs
View file

@ -2523,41 +2523,57 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
ty::lookup_field_type_unsubstituted(tcx, def_id, f.id)
}).collect::<Vec<_>>();
// FIXME(#25351) The last field of the structure has to exist and be a
// type parameter (for now, to avoid tracking edge cases).
let i = if let Some(&ty::ty_param(p)) = fields.last().map(|ty| &ty.sty) {
assert!(p.space == TypeSpace);
p.idx as usize
// The last field of the structure has to exist and contain type parameters.
let field = if let Some(&field) = fields.last() {
field
} else {
return Err(Unimplemented);
};
let mut ty_params = vec![];
ty::walk_ty(field, |ty| {
if let ty::ty_param(p) = ty.sty {
assert!(p.space == TypeSpace);
let idx = p.idx as usize;
if !ty_params.contains(&idx) {
ty_params.push(idx);
}
}
});
if ty_params.is_empty() {
return Err(Unimplemented);
}
// Replace the type parameter chosen for unsizing with
// ty_err and ensure it does not affect any other fields.
// Replace type parameters used in unsizing with
// ty_err and ensure they do not affect any other fields.
// This could be checked after type collection for any struct
// with a potentially unsized trailing field.
let mut new_substs = substs_a.clone();
new_substs.types.get_mut_slice(TypeSpace)[i] = tcx.types.err;
for &i in &ty_params {
new_substs.types.get_mut_slice(TypeSpace)[i] = tcx.types.err;
}
for &ty in fields.init() {
if ty::type_is_error(ty.subst(tcx, &new_substs)) {
return Err(Unimplemented);
}
}
// Extract T and U from Struct<T> and Struct<U>.
let inner_source = *substs_a.types.get(TypeSpace, i);
let inner_target = *substs_b.types.get(TypeSpace, i);
// Extract Field<T> and Field<U> from Struct<T> and Struct<U>.
let inner_source = field.subst(tcx, substs_a);
let inner_target = field.subst(tcx, substs_b);
// Check that all the source structure with the unsized
// type parameter is a subtype of the target.
new_substs.types.get_mut_slice(TypeSpace)[i] = inner_target;
// Check that the source structure with the target's
// type parameters is a subtype of the target.
for &i in &ty_params {
let param_b = *substs_b.types.get(TypeSpace, i);
new_substs.types.get_mut_slice(TypeSpace)[i] = param_b;
}
let new_struct = ty::mk_struct(tcx, def_id, tcx.mk_substs(new_substs));
let origin = infer::Misc(obligation.cause.span);
if self.infcx.sub_types(false, origin, new_struct, target).is_err() {
return Err(Unimplemented);
}
// Construct the nested T: Unsize<U> predicate.
// Construct the nested Field<T>: Unsize<Field<U>> predicate.
nested.push(util::predicate_for_trait_def(tcx,
obligation.cause.clone(),
obligation.predicate.def_id(),

5
src/test/run-pass/dst-coerce-rc.rs
View file

@ -12,6 +12,7 @@
#![feature(core)]
use std::cell::RefCell;
use std::rc::Rc;
trait Baz {
@ -36,4 +37,8 @@ fn main() {
assert_eq!(b.get(), 42);
let _c = b.clone();
let a: Rc<RefCell<i32>> = Rc::new(RefCell::new(42));
let b: Rc<RefCell<Baz>> = a.clone();
assert_eq!(b.borrow().get(), 42);
}