Replace calls to Const::eval in mir build

1 files changed, 3 insertions, 1 deletions

diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index d78e1f5da09..04e921ecc2e 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -441,7 +441,9 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             ty::Slice(..) => PatKind::Slice { prefix, slice, suffix },
             // Fixed-length array, `[T; len]`.
             ty::Array(_, len) => {
-                let len = len.eval_target_usize(self.tcx, self.param_env);
+                let len = len
+                    .try_to_target_usize(self.tcx)
+                    .expect("expected len of array pat to be definite");
                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
                 PatKind::Array { prefix, slice, suffix }
             }