Relax validation now

compiler/rustc_const_eval/src/transform/validate.rs

@@ -105,14 +105,16 @@ impl<'tcx> MirPass<'tcx> for Validator {
             && let Some(by_move_body) = body.coroutine_by_move_body()
             && let Some(by_move_layout) = by_move_body.coroutine_layout_raw()
         {
-            if layout != by_move_layout {
+            // FIXME(async_closures): We could do other validation here?
+            if layout.variant_fields.len() != by_move_layout.variant_fields.len() {
                 // If this turns out not to be true, please let compiler-errors know.
                 // It is possible to support, but requires some changes to the layout
                 // computation code.
                 cfg_checker.fail(
                     Location::START,
                     format!(
-                        "Coroutine layout differs from by-move coroutine layout:\n\
+                        "Coroutine layout has different number of variant fields from \
+                        by-move coroutine layout:\n\
                         layout: {layout:#?}\n\
                         by_move_layout: {by_move_layout:#?}",
                     ),

compiler/rustc_middle/src/ty/sty.rs

@@ -694,8 +694,6 @@ impl<'tcx> CoroutineArgs<'tcx> {
     #[inline]
     pub fn variant_range(&self, def_id: DefId, tcx: TyCtxt<'tcx>) -> Range<VariantIdx> {
         // FIXME requires optimized MIR
-        // FIXME(async_closures): We should assert all coroutine layouts have
-        // the same number of variants.
         FIRST_VARIANT
             ..tcx.coroutine_layout(def_id, tcx.types.unit).unwrap().variant_fields.next_index()
     }