Rework point-at-arg

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -117,11 +117,21 @@ pub enum TraitQueryMode {
 
 /// Creates predicate obligations from the generic bounds.
 pub fn predicates_for_generics<'tcx>(
-    cause: ObligationCause<'tcx>,
+    cause: impl Fn(usize, Span) -> ObligationCause<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     generic_bounds: ty::InstantiatedPredicates<'tcx>,
 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
-    util::predicates_for_generics(cause, 0, param_env, generic_bounds)
+    let generic_bounds = generic_bounds;
+    debug!("predicates_for_generics(generic_bounds={:?})", generic_bounds);
+
+    std::iter::zip(generic_bounds.predicates, generic_bounds.spans).enumerate().map(
+        move |(idx, (predicate, span))| Obligation {
+            cause: cause(idx, span),
+            recursion_depth: 0,
+            param_env: param_env,
+            predicate,
+        },
+    )
 }
 
 /// Determines whether the type `ty` is known to meet `bound` and