don't call type_of on generic params

Author: y21

clippy_lints/src/missing_fields_in_debug.rs

@@ -207,6 +207,11 @@ impl<'tcx> LateLintPass<'tcx> for MissingFieldsInDebug {
         if let ItemKind::Impl(Impl { of_trait: Some(trait_ref), self_ty, items, .. }) = item.kind
             && let Res::Def(DefKind::Trait, trait_def_id) = trait_ref.path.res
             && let TyKind::Path(QPath::Resolved(_, self_path)) = &self_ty.kind
+            // don't trigger if self is a generic parameter, e.g. `impl<T> Debug for T`
+            // this can only happen in core itself, where the trait is defined,
+            // but it caused ICEs in the past:
+            // https://github.com/rust-lang/rust-clippy/issues/10887
+            && !matches!(self_path.res, Res::Def(DefKind::TyParam, _))
             && cx.match_def_path(trait_def_id, &[sym::core, sym::fmt, sym::Debug])
             // don't trigger if this impl was derived
             && !cx.tcx.has_attr(item.owner_id, sym::automatically_derived)