Revert "Auto merge of #92007 - oli-obk:lazy_tait2, r=nikomatsakis"

This reverts commit e7cc3bddbe, reversing
changes made to 734368a200.

compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs

@@ -3,7 +3,7 @@ use crate::infer::{InferCtxt, InferOk};
 use crate::traits::engine::TraitEngineExt as _;
 use crate::traits::query::type_op::TypeOpOutput;
 use crate::traits::query::Fallible;
-use crate::traits::TraitEngine;
+use crate::traits::{ObligationCause, TraitEngine};
 use rustc_infer::traits::TraitEngineExt as _;
 use rustc_span::source_map::DUMMY_SP;
 
@@ -60,6 +60,7 @@ fn scrape_region_constraints<'tcx, Op: super::TypeOp<'tcx, Output = R>, R>(
     op: impl FnOnce() -> Fallible<InferOk<'tcx, R>>,
 ) -> Fallible<TypeOpOutput<'tcx, Op>> {
     let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
+    let dummy_body_id = ObligationCause::dummy().body_id;
 
     // During NLL, we expect that nobody will register region
     // obligations **except** as part of a custom type op (and, at the
@@ -74,6 +75,7 @@ fn scrape_region_constraints<'tcx, Op: super::TypeOp<'tcx, Output = R>, R>(
     );
 
     let InferOk { value, obligations } = infcx.commit_if_ok(|_| op())?;
+    debug_assert!(obligations.iter().all(|o| o.cause.body_id == dummy_body_id));
     fulfill_cx.register_predicate_obligations(infcx, obligations);
     let errors = fulfill_cx.select_all_or_error(infcx);
     if !errors.is_empty() {