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Be less eager about implicit borrowing when doing method resolution. Closes #2796.

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This commit is contained in:
Michael Sullivan 2012-07-06 15:50:50 -07:00
parent ceac155211
commit 038f925586
2 changed files with 67 additions and 15 deletions
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39
src/rustc/middle/typeck/check/method.rs
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@ -77,16 +77,20 @@ class lookup {
// loop for impls in scope. Note: I don't love these
// semantics, but that's what we had so I am preserving
// it.
if self.candidates.len() > 0u {
break;
}
if self.candidates.len() > 0u { break; }
self.add_candidates_from_scope();
// now look for impls in scope, but don't look for impls that
// would require doing an implicit borrow of the lhs.
self.add_candidates_from_scope(false);
// if we found anything, stop before trying borrows
if self.candidates.len() > 0u { break; }
// now look for impls in scope that might require a borrow
self.add_candidates_from_scope(true);
// if we found anything, stop before attempting auto-deref.
if self.candidates.len() > 0u {
break;
}
if self.candidates.len() > 0u { break; }
// check whether we can autoderef and if so loop around again.
alt ty::deref(self.tcx(), self.self_ty, false) {
@ -290,7 +294,7 @@ class lookup {
*/
}
fn add_candidates_from_scope() {
fn add_candidates_from_scope(use_assignability: bool) {
let impls_vecs = self.fcx.ccx.impl_map.get(self.expr.id);
let mut added_any = false;
@ -306,13 +310,18 @@ class lookup {
let {substs: impl_substs, ty: impl_ty} =
impl_self_ty(self.fcx, im.did);
// if we can assign the caller to the callee, that's a
// potential match. Collect those in the vector.
let can_assign = self.fcx.can_mk_assignty(
self.self_expr, self.borrow_scope,
self.self_ty, impl_ty);
#debug["can_assign = %?", can_assign];
alt can_assign {
// Depending on our argument, we find potential
// matches either by checking subtypability or
// type assignability. Collect the matches.
let matches = if use_assignability {
self.fcx.can_mk_assignty(
self.self_expr, self.borrow_scope,
self.self_ty, impl_ty)
} else {
self.fcx.can_mk_subty(self.self_ty, impl_ty)
};
#debug["matches = %?", matches];
alt matches {
result::err(_) { /* keep looking */ }
result::ok(_) {
if !self.candidate_impls.contains_key(im.did) {