From ef977767916c473662e593407a059f8d89de6314 Mon Sep 17 00:00:00 2001
From: Alan Egerton <eggyal@gmail.com>
Date: Sun, 26 Feb 2023 00:31:37 +0000
Subject: [PATCH] Derive traversable impls for Obligation

Ever since folding was first added in c5754f397, obligations have not
folded or visited their causes the ObligationCauseCode potentially
containing types that may be of interest to a folder or visitor.

By using the derive macro to implement the visitable traits, we ensure
that all contained types of interest are folded/visited.
---
 compiler/rustc_infer/src/traits/mod.rs        |  2 +-
 .../src/traits/structural_impls.rs            | 33 +------------------
 2 files changed, 2 insertions(+), 33 deletions(-)

diff --git a/compiler/rustc_infer/src/traits/mod.rs b/compiler/rustc_infer/src/traits/mod.rs
index 77c67c14ecc55..e4fe32bb181ca 100644
--- a/compiler/rustc_infer/src/traits/mod.rs
+++ b/compiler/rustc_infer/src/traits/mod.rs
@@ -34,7 +34,7 @@ pub use rustc_middle::traits::*;
 /// either identifying an `impl` (e.g., `impl Eq for i32`) that
 /// satisfies the obligation, or else finding a bound that is in
 /// scope. The eventual result is usually a `Selection` (defined below).
-#[derive(Clone, PartialEq, Eq, Hash)]
+#[derive(Clone, PartialEq, Eq, Hash, TypeFoldable, TypeVisitable)]
 pub struct Obligation<'tcx, T> {
     /// The reason we have to prove this thing.
     pub cause: ObligationCause<'tcx>,
diff --git a/compiler/rustc_infer/src/traits/structural_impls.rs b/compiler/rustc_infer/src/traits/structural_impls.rs
index 3a5273b0359e4..d823e8b78cb31 100644
--- a/compiler/rustc_infer/src/traits/structural_impls.rs
+++ b/compiler/rustc_infer/src/traits/structural_impls.rs
@@ -1,11 +1,8 @@
 use crate::traits;
 use crate::traits::project::Normalized;
-use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFoldable};
-use rustc_middle::ty::visit::{TypeVisitable, TypeVisitor};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty;
 
 use std::fmt;
-use std::ops::ControlFlow;
 
 // Structural impls for the structs in `traits`.
 
@@ -57,31 +54,3 @@ impl<'tcx> fmt::Debug for traits::MismatchedProjectionTypes<'tcx> {
         write!(f, "MismatchedProjectionTypes({:?})", self.err)
     }
 }
-
-///////////////////////////////////////////////////////////////////////////
-// TypeFoldable implementations.
-
-impl<'tcx, O: TypeFoldable<TyCtxt<'tcx>>> TypeFoldable<TyCtxt<'tcx>>
-    for traits::Obligation<'tcx, O>
-{
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(traits::Obligation {
-            cause: self.cause,
-            recursion_depth: self.recursion_depth,
-            predicate: self.predicate.try_fold_with(folder)?,
-            param_env: self.param_env.try_fold_with(folder)?,
-        })
-    }
-}
-
-impl<'tcx, O: TypeVisitable<TyCtxt<'tcx>>> TypeVisitable<TyCtxt<'tcx>>
-    for traits::Obligation<'tcx, O>
-{
-    fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
-        self.predicate.visit_with(visitor)?;
-        self.param_env.visit_with(visitor)
-    }
-}