From ddae395583ccad7cfacf1ee8e7bfeb5fca200c90 Mon Sep 17 00:00:00 2001
From: lcnr <rust@lcnr.de>
Date: Mon, 19 Jul 2021 14:05:13 +0200
Subject: [PATCH] ignore const substs in `implicit_infer`

---
 compiler/rustc_middle/src/ty/walk.rs          | 31 +++++++++++++------
 .../src/outlives/implicit_infer.rs            |  7 ++++-
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/walk.rs b/compiler/rustc_middle/src/ty/walk.rs
index 3cab813f12ad0..73985cf31e0f9 100644
--- a/compiler/rustc_middle/src/ty/walk.rs
+++ b/compiler/rustc_middle/src/ty/walk.rs
@@ -11,7 +11,7 @@ use smallvec::{self, SmallVec};
 type TypeWalkerStack<'tcx> = SmallVec<[GenericArg<'tcx>; 8]>;
 
 pub struct TypeWalker<'tcx> {
-    tcx: TyCtxt<'tcx>,
+    expose_default_const_substs: Option<TyCtxt<'tcx>>,
     stack: TypeWalkerStack<'tcx>,
     last_subtree: usize,
     pub visited: SsoHashSet<GenericArg<'tcx>>,
@@ -26,8 +26,13 @@ pub struct TypeWalker<'tcx> {
 /// It maintains a set of visited types and
 /// skips any types that are already there.
 impl<'tcx> TypeWalker<'tcx> {
-    fn new(tcx: TyCtxt<'tcx>, root: GenericArg<'tcx>) -> Self {
-        Self { tcx, stack: smallvec![root], last_subtree: 1, visited: SsoHashSet::new() }
+    fn new(expose_default_const_substs: Option<TyCtxt<'tcx>>, root: GenericArg<'tcx>) -> Self {
+        Self {
+            expose_default_const_substs,
+            stack: smallvec![root],
+            last_subtree: 1,
+            visited: SsoHashSet::new(),
+        }
     }
 
     /// Skips the subtree corresponding to the last type
@@ -56,7 +61,7 @@ impl<'tcx> Iterator for TypeWalker<'tcx> {
             let next = self.stack.pop()?;
             self.last_subtree = self.stack.len();
             if self.visited.insert(next) {
-                push_inner(self.tcx, &mut self.stack, next);
+                push_inner(self.expose_default_const_substs, &mut self.stack, next);
                 debug!("next: stack={:?}", self.stack);
                 return Some(next);
             }
@@ -76,7 +81,7 @@ impl GenericArg<'tcx> {
     /// [isize] => { [isize], isize }
     /// ```
     pub fn walk(self, tcx: TyCtxt<'tcx>) -> TypeWalker<'tcx> {
-        TypeWalker::new(tcx, self)
+        TypeWalker::new(Some(tcx), self)
     }
 
     /// Iterator that walks the immediate children of `self`. Hence
@@ -92,13 +97,17 @@ impl GenericArg<'tcx> {
         visited: &mut SsoHashSet<GenericArg<'tcx>>,
     ) -> impl Iterator<Item = GenericArg<'tcx>> {
         let mut stack = SmallVec::new();
-        push_inner(tcx, &mut stack, self);
+        push_inner(Some(tcx), &mut stack, self);
         stack.retain(|a| visited.insert(*a));
         stack.into_iter()
     }
 }
 
 impl<'tcx> super::TyS<'tcx> {
+    pub fn walk_ignoring_default_const_substs(&'tcx self) -> TypeWalker<'tcx> {
+        TypeWalker::new(None, self.into())
+    }
+
     /// Iterator that walks `self` and any types reachable from
     /// `self`, in depth-first order. Note that just walks the types
     /// that appear in `self`, it does not descend into the fields of
@@ -110,7 +119,7 @@ impl<'tcx> super::TyS<'tcx> {
     /// [isize] => { [isize], isize }
     /// ```
     pub fn walk(&'tcx self, tcx: TyCtxt<'tcx>) -> TypeWalker<'tcx> {
-        TypeWalker::new(tcx, self.into())
+        TypeWalker::new(Some(tcx), self.into())
     }
 }
 
@@ -121,7 +130,7 @@ impl<'tcx> super::TyS<'tcx> {
 /// natural order one would expect (basically, the order of the
 /// types as they are written).
 fn push_inner<'tcx>(
-    tcx: TyCtxt<'tcx>,
+    expose_default_const_substs: Option<TyCtxt<'tcx>>,
     stack: &mut TypeWalkerStack<'tcx>,
     parent: GenericArg<'tcx>,
 ) {
@@ -202,7 +211,11 @@ fn push_inner<'tcx>(
                 | ty::ConstKind::Error(_) => {}
 
                 ty::ConstKind::Unevaluated(ct) => {
-                    stack.extend(ct.substs(tcx).iter().rev());
+                    if let Some(tcx) = expose_default_const_substs {
+                        stack.extend(ct.substs(tcx).iter().rev());
+                    } else if let Some(substs) = ct.substs_ {
+                        stack.extend(substs.iter().rev());
+                    }
                 }
             }
         }
diff --git a/compiler/rustc_typeck/src/outlives/implicit_infer.rs b/compiler/rustc_typeck/src/outlives/implicit_infer.rs
index 1c7f88c0bb611..f3f22cb05670c 100644
--- a/compiler/rustc_typeck/src/outlives/implicit_infer.rs
+++ b/compiler/rustc_typeck/src/outlives/implicit_infer.rs
@@ -114,7 +114,12 @@ fn insert_required_predicates_to_be_wf<'tcx>(
     required_predicates: &mut RequiredPredicates<'tcx>,
     explicit_map: &mut ExplicitPredicatesMap<'tcx>,
 ) {
-    for arg in field_ty.walk(tcx) {
+    // We must not look into the default substs of consts
+    // as computing those depends on the results of `predicates_of`.
+    //
+    // Luckily the only types contained in default substs are type
+    // parameters which don't matter here.
+    for arg in field_ty.walk_ignoring_default_const_substs() {
         let ty = match arg.unpack() {
             GenericArgKind::Type(ty) => ty,