mir: improve polymorphic constant bug

This commit changes the span and content of the "collection encountered
polymorphic constant" bug in monomorphization collection to point to the
use of the constant rather than the definition.

Signed-off-by: David Wood <david@davidtw.co>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/librustc_mir/monomorphize/collector.rs b/src/librustc_mir/monomorphize/collector.rs
index 0b5f27fc17a..e724180f4d8 100644
--- a/src/librustc_mir/monomorphize/collector.rs
+++ b/src/librustc_mir/monomorphize/collector.rs
@@ -627,8 +627,9 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
                     Ok(val) => collect_const_value(self.tcx, val, self.output),
                     Err(ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted) => {}
                     Err(ErrorHandled::TooGeneric) => span_bug!(
-                        self.tcx.def_span(def.did),
-                        "collection encountered polymorphic constant",
+                        self.body.source_info(location).span,
+                        "collection encountered polymorphic constant: {}",
+                        substituted_constant
                     ),
                 }
             }