diff options
| -rw-r--r-- | src/librustc/middle/traits/error_reporting.rs | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/src/librustc/middle/traits/error_reporting.rs b/src/librustc/middle/traits/error_reporting.rs index 7d69df73cd2..ea29c48983f 100644 --- a/src/librustc/middle/traits/error_reporting.rs +++ b/src/librustc/middle/traits/error_reporting.rs @@ -57,8 +57,10 @@ pub fn report_projection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>, let predicate = infcx.resolve_type_vars_if_possible(&obligation.predicate); // The ty_err created by normalize_to_error can end up being unified - // into all obligations - we still have to report an error in that - // case. + // into all obligations: for example, if our obligation is something + // like `$X = <() as Foo<$X>>::Out` and () does not implement Foo<_>, + // then $X will be unified with ty_err, but the error still needs to be + // reported. if !infcx.tcx.sess.has_errors() || !predicate.references_error() { span_err!(infcx.tcx.sess, obligation.cause.span, E0271, "type mismatch resolving `{}`: {}", |