From 012910dab253e8b64dd06e2a91de1943d518439b Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 7 Jan 2022 09:13:00 -0800
Subject: [PATCH] Canonicalize const variables correctly

---
 compiler/rustc_infer/src/infer/canonical/canonicalizer.rs | 2 +-
 compiler/rustc_infer/src/infer/canonical/mod.rs           | 7 ++-----
 compiler/rustc_middle/src/infer/canonical.rs              | 8 ++++----
 compiler/rustc_traits/src/chalk/mod.rs                    | 8 ++++----
 4 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 60239736653..f29aaf56150 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -425,7 +425,7 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
                         // FIXME: perf problem described in #55921.
                         ui = ty::UniverseIndex::ROOT;
                         return self.canonicalize_const_var(
-                            CanonicalVarInfo { kind: CanonicalVarKind::Const(ui) },
+                            CanonicalVarInfo { kind: CanonicalVarKind::Const(ui, ct.ty) },
                             ct,
                         );
                     }
diff --git a/compiler/rustc_infer/src/infer/canonical/mod.rs b/compiler/rustc_infer/src/infer/canonical/mod.rs
index 0c26639e9b0..2d2edb07d9e 100644
--- a/compiler/rustc_infer/src/infer/canonical/mod.rs
+++ b/compiler/rustc_infer/src/infer/canonical/mod.rs
@@ -137,12 +137,9 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
                 self.tcx.mk_region(ty::RePlaceholder(placeholder_mapped)).into()
             }
 
-            CanonicalVarKind::Const(ui) => self
+            CanonicalVarKind::Const(ui, ty) => self
                 .next_const_var_in_universe(
-                    self.next_ty_var_in_universe(
-                        TypeVariableOrigin { kind: TypeVariableOriginKind::MiscVariable, span },
-                        universe_map(ui),
-                    ),
+                    ty,
                     ConstVariableOrigin { kind: ConstVariableOriginKind::MiscVariable, span },
                     universe_map(ui),
                 )
diff --git a/compiler/rustc_middle/src/infer/canonical.rs b/compiler/rustc_middle/src/infer/canonical.rs
index 605fff671db..28217aeab13 100644
--- a/compiler/rustc_middle/src/infer/canonical.rs
+++ b/compiler/rustc_middle/src/infer/canonical.rs
@@ -23,7 +23,7 @@
 
 use crate::infer::MemberConstraint;
 use crate::ty::subst::GenericArg;
-use crate::ty::{self, BoundVar, List, Region, TyCtxt};
+use crate::ty::{self, BoundVar, List, Region, Ty, TyCtxt};
 use rustc_index::vec::IndexVec;
 use rustc_macros::HashStable;
 use smallvec::SmallVec;
@@ -104,7 +104,7 @@ impl<'tcx> CanonicalVarInfo<'tcx> {
             CanonicalVarKind::PlaceholderTy(_) => false,
             CanonicalVarKind::Region(_) => true,
             CanonicalVarKind::PlaceholderRegion(..) => false,
-            CanonicalVarKind::Const(_) => true,
+            CanonicalVarKind::Const(..) => true,
             CanonicalVarKind::PlaceholderConst(_) => false,
         }
     }
@@ -130,7 +130,7 @@ pub enum CanonicalVarKind<'tcx> {
     PlaceholderRegion(ty::PlaceholderRegion),
 
     /// Some kind of const inference variable.
-    Const(ty::UniverseIndex),
+    Const(ty::UniverseIndex, Ty<'tcx>),
 
     /// A "placeholder" that represents "any const".
     PlaceholderConst(ty::PlaceholderConst<'tcx>),
@@ -147,7 +147,7 @@ impl<'tcx> CanonicalVarKind<'tcx> {
             CanonicalVarKind::PlaceholderTy(placeholder) => placeholder.universe,
             CanonicalVarKind::Region(ui) => ui,
             CanonicalVarKind::PlaceholderRegion(placeholder) => placeholder.universe,
-            CanonicalVarKind::Const(ui) => ui,
+            CanonicalVarKind::Const(ui, _) => ui,
             CanonicalVarKind::PlaceholderConst(placeholder) => placeholder.universe,
         }
     }
diff --git a/compiler/rustc_traits/src/chalk/mod.rs b/compiler/rustc_traits/src/chalk/mod.rs
index a4d844e2eb8..09bfdabf473 100644
--- a/compiler/rustc_traits/src/chalk/mod.rs
+++ b/compiler/rustc_traits/src/chalk/mod.rs
@@ -85,7 +85,7 @@ crate fn evaluate_goal<'tcx>(
                         chalk_ir::VariableKind::Lifetime,
                         chalk_ir::UniverseIndex { counter: ui.index() },
                     ),
-                    CanonicalVarKind::Const(_ui) => unimplemented!(),
+                    CanonicalVarKind::Const(_ui, _ty) => unimplemented!(),
                     CanonicalVarKind::PlaceholderConst(_pc) => unimplemented!(),
                 }),
             ),
@@ -127,9 +127,9 @@ crate fn evaluate_goal<'tcx>(
                     chalk_ir::VariableKind::Lifetime => CanonicalVarKind::Region(
                         ty::UniverseIndex::from_usize(var.skip_kind().counter),
                     ),
-                    chalk_ir::VariableKind::Const(_) => CanonicalVarKind::Const(
-                        ty::UniverseIndex::from_usize(var.skip_kind().counter),
-                    ),
+                    // FIXME(compiler-errors): We don't currently have a way of turning
+                    // a Chalk ty back into a rustc ty, right?
+                    chalk_ir::VariableKind::Const(_) => todo!(),
                 };
                 CanonicalVarInfo { kind }
             })