Rollup merge of #80734 - abonander:ab/issue-66693, r=oli-obk

check that first arg to `panic!()` in const is `&str`

closes #66693

~~TODO: regression test~~

cc `@RalfJung` for error message wording

compiler/rustc_mir/src/transform/check_consts/ops.rs

@@ -377,6 +377,18 @@ impl NonConstOp for Panic {
     }
 }
 
+/// A call to a `panic()` lang item where the first argument is _not_ a `&str`.
+#[derive(Debug)]
+pub struct PanicNonStr;
+impl NonConstOp for PanicNonStr {
+    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
+        ccx.tcx.sess.struct_span_err(
+            span,
+            "argument to `panic!()` in a const context must have type `&str`",
+        )
+    }
+}
+
 #[derive(Debug)]
 pub struct RawPtrComparison;
 impl NonConstOp for RawPtrComparison {