check if const is ADT or not

compiler/rustc_transmute/src/lib.rs

@@ -115,7 +115,7 @@ mod rustc {
             tcx: TyCtxt<'tcx>,
             param_env: ParamEnv<'tcx>,
             c: Const<'tcx>,
-        ) -> Self {
+        ) -> Option<Self> {
             use rustc_middle::ty::ScalarInt;
             use rustc_middle::ty::TypeVisitable;
             use rustc_span::symbol::sym;
@@ -123,10 +123,15 @@ mod rustc {
             let c = c.eval(tcx, param_env);
 
             if let Some(err) = c.error_reported() {
-                return Self { alignment: true, lifetimes: true, safety: true, validity: true };
+                return Some(Self {
+                    alignment: true,
+                    lifetimes: true,
+                    safety: true,
+                    validity: true,
+                });
             }
 
-            let adt_def = c.ty().ty_adt_def().expect("The given `Const` must be an ADT.");
+            let adt_def = c.ty().ty_adt_def()?;
 
             assert_eq!(
                 tcx.require_lang_item(LangItem::TransmuteOpts, None),
@@ -148,12 +153,12 @@ mod rustc {
                 fields[field_idx].unwrap_leaf() == ScalarInt::TRUE
             };
 
-            Self {
+            Some(Self {
                 alignment: get_field(sym::alignment),
                 lifetimes: get_field(sym::lifetimes),
                 safety: get_field(sym::safety),
                 validity: get_field(sym::validity),
-            }
+            })
         }
     }
 }