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Special-case some error messages about Sized

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The error messages still aren’t as good as they were before DST, but they better
describe the actual problem, not mentioning `Sized` at all (because that bound
is normally implied, not explicitly stated).

Closes #17567.
Closes #18040.
Closes #18159.
This commit is contained in:
P1start 2014-10-28 21:04:08 +13:00
parent 14398f2929
commit 737e39696b
4 changed files with 34 additions and 12 deletions
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28
src/librustc/middle/typeck/check/vtable.rs
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@ -303,15 +303,25 @@ pub fn maybe_report_ambiguity(fcx: &FnCtxt, obligation: &Obligation) {
// has_errors() to be sure that compilation isn't happening
// anyway. In that case, why inundate the user.
if !fcx.tcx().sess.has_errors() {
fcx.tcx().sess.span_err(
obligation.cause.span,
format!(
"unable to infer enough type information to \
locate the impl of the trait `{}` for \
the type `{}`; type annotations required",
trait_ref.user_string(fcx.tcx()),
self_ty.user_string(fcx.tcx())).as_slice());
note_obligation_cause(fcx, obligation);
if fcx.ccx.tcx.lang_items.sized_trait()
.map_or(false, |sized_id| sized_id == trait_ref.def_id) {
fcx.tcx().sess.span_err(
obligation.cause.span,
format!(
"unable to infer enough type information about `{}`; type annotations \
required",
self_ty.user_string(fcx.tcx())).as_slice());
} else {
fcx.tcx().sess.span_err(
obligation.cause.span,
format!(
"unable to infer enough type information to \
locate the impl of the trait `{}` for \
the type `{}`; type annotations required",
trait_ref.user_string(fcx.tcx()),
self_ty.user_string(fcx.tcx())).as_slice());
note_obligation_cause(fcx, obligation);
}
}
} else if !fcx.tcx().sess.has_errors() {
// Ambiguity. Coherence should have reported an error.