From 801dd1d061bc6db31547d45c64a32bbd9b4f6124 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Mon, 26 Feb 2024 15:58:53 +0000
Subject: [PATCH] Remove cause

---
 compiler/rustc_infer/src/infer/mod.rs         |  1 -
 .../rustc_infer/src/infer/relate/combine.rs   |  1 -
 .../src/infer/relate/type_relating.rs         | 24 ++-----------------
 compiler/rustc_middle/src/ty/relate.rs        | 17 +++++--------
 4 files changed, 8 insertions(+), 35 deletions(-)

diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 6f52ded3551..b99ea35c22c 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -836,7 +836,6 @@ impl<'tcx> InferCtxt<'tcx> {
         CombineFields {
             infcx: self,
             trace,
-            cause: None,
             param_env,
             obligations: PredicateObligations::new(),
             define_opaque_types,
diff --git a/compiler/rustc_infer/src/infer/relate/combine.rs b/compiler/rustc_infer/src/infer/relate/combine.rs
index 0a550660f94..749c50b57b5 100644
--- a/compiler/rustc_infer/src/infer/relate/combine.rs
+++ b/compiler/rustc_infer/src/infer/relate/combine.rs
@@ -42,7 +42,6 @@ use rustc_span::Span;
 pub struct CombineFields<'infcx, 'tcx> {
     pub infcx: &'infcx InferCtxt<'tcx>,
     pub trace: TypeTrace<'tcx>,
-    pub cause: Option<ty::relate::Cause>,
     pub param_env: ty::ParamEnv<'tcx>,
     pub obligations: PredicateObligations<'tcx>,
     pub define_opaque_types: DefineOpaqueTypes,
diff --git a/compiler/rustc_infer/src/infer/relate/type_relating.rs b/compiler/rustc_infer/src/infer/relate/type_relating.rs
index c4de324e6ff..ddc4bf9a514 100644
--- a/compiler/rustc_infer/src/infer/relate/type_relating.rs
+++ b/compiler/rustc_infer/src/infer/relate/type_relating.rs
@@ -4,12 +4,10 @@ use crate::infer::{
 };
 use crate::traits::{Obligation, PredicateObligations};
 
-use rustc_middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
-use rustc_middle::ty::visit::TypeVisitableExt;
+use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::TyVar;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::Span;
-use std::mem;
 
 /// Enforce that `a` is equal to or a subtype of `b`.
 pub struct TypeRelating<'combine, 'a, 'tcx> {
@@ -43,18 +41,6 @@ impl<'tcx> TypeRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
         self.a_is_expected
     }
 
-    fn with_cause<F, R>(&mut self, cause: Cause, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R,
-    {
-        debug!("sub with_cause={:?}", cause);
-        let old_cause = mem::replace(&mut self.fields.cause, Some(cause));
-        let r = f(self);
-        debug!("sub old_cause={:?}", old_cause);
-        self.fields.cause = old_cause;
-        r
-    }
-
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
         variance: ty::Variance,
@@ -84,12 +70,6 @@ impl<'tcx> TypeRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
 
         match (a.kind(), b.kind()) {
             (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
-                // Shouldn't have any LBR here, so we can safely put
-                // this under a binder below without fear of accidental
-                // capture.
-                assert!(!a.has_escaping_bound_vars());
-                assert!(!b.has_escaping_bound_vars());
-
                 match self.ambient_variance {
                     ty::Covariant => {
                         // can't make progress on `A <: B` if both A and B are
@@ -191,7 +171,7 @@ impl<'tcx> TypeRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
         a: ty::Region<'tcx>,
         b: ty::Region<'tcx>,
     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
-        debug!("{}.regions({:?}, {:?}) self.cause={:?}", self.tag(), a, b, self.fields.cause);
+        debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
 
         // FIXME -- we have more fine-grained information available
         // from the "cause" field, we could perhaps give more tailored
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 303f285b00c..abd39914cfd 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -30,13 +30,6 @@ pub trait TypeRelation<'tcx>: Sized {
     /// relation. Just affects error messages.
     fn a_is_expected(&self) -> bool;
 
-    fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R,
-    {
-        f(self)
-    }
-
     /// Generic relation routine suitable for most anything.
     fn relate<T: Relate<'tcx>>(&mut self, a: T, b: T) -> RelateResult<'tcx, T> {
         Relate::relate(self, a, b)
@@ -452,10 +445,12 @@ pub fn structurally_relate_tys<'tcx, R: TypeRelation<'tcx>>(
         (&ty::Dynamic(a_obj, a_region, a_repr), &ty::Dynamic(b_obj, b_region, b_repr))
             if a_repr == b_repr =>
         {
-            let region_bound = relation.with_cause(Cause::ExistentialRegionBound, |relation| {
-                relation.relate(a_region, b_region)
-            })?;
-            Ok(Ty::new_dynamic(tcx, relation.relate(a_obj, b_obj)?, region_bound, a_repr))
+            Ok(Ty::new_dynamic(
+                tcx,
+                relation.relate(a_obj, b_obj)?,
+                relation.relate(a_region, b_region)?,
+                a_repr,
+            ))
         }
 
         (&ty::Coroutine(a_id, a_args), &ty::Coroutine(b_id, b_args)) if a_id == b_id => {