TODO(fmease): Debug-assert that default traits are "simple"

Author: fmease

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -339,6 +339,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let tcx = self.tcx();
 
         if tcx.is_lang_item(def_id, hir::LangItem::Sized) || tcx.is_default_trait(def_id) {
+            // FIXME(fmease): Debug-assert that the trait doesn't have any generic parameters
+            //                (except `Self`) or associated items since we wouldn't be able to
+            //                wfcheck args & constraints passed to it.
+            //                E.g., `?BadDefaultTrait<Vec<str>`.
+            //                NOTE: Alternatively / additionally, introduce a validation step for
+            //                      traits marked `#[default_trait]` in AST validation / lowering.
             return;
         }