From 27af8e45852536fd14817464610866c84ad838b0 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 3 Jun 2022 13:14:23 -0700
Subject: [PATCH] Normalize consts' tys when relating with adt_const_params

---
 compiler/rustc_middle/src/ty/relate.rs    | 13 ++--
 src/test/ui/const-generics/issue-97007.rs | 88 +++++++++++++++++++++++
 2 files changed, 97 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/const-generics/issue-97007.rs

diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 8677405eebeda..9712d66b30a22 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -579,10 +579,15 @@ pub fn super_relate_consts<'tcx, R: TypeRelation<'tcx>>(
     debug!("{}.super_relate_consts(a = {:?}, b = {:?})", relation.tag(), a, b);
     let tcx = relation.tcx();
 
-    // FIXME(oli-obk): once const generics can have generic types, this assertion
-    // will likely get triggered. Move to `normalize_erasing_regions` at that point.
-    let a_ty = tcx.erase_regions(a.ty());
-    let b_ty = tcx.erase_regions(b.ty());
+    let a_ty;
+    let b_ty;
+    if relation.tcx().features().adt_const_params {
+        a_ty = tcx.normalize_erasing_regions(relation.param_env(), a.ty());
+        b_ty = tcx.normalize_erasing_regions(relation.param_env(), b.ty());
+    } else {
+        a_ty = tcx.erase_regions(a.ty());
+        b_ty = tcx.erase_regions(b.ty());
+    }
     if a_ty != b_ty {
         relation.tcx().sess.delay_span_bug(
             DUMMY_SP,
diff --git a/src/test/ui/const-generics/issue-97007.rs b/src/test/ui/const-generics/issue-97007.rs
new file mode 100644
index 0000000000000..7036834c4b119
--- /dev/null
+++ b/src/test/ui/const-generics/issue-97007.rs
@@ -0,0 +1,88 @@
+// check-pass
+
+#![feature(adt_const_params, generic_const_exprs)]
+#![allow(incomplete_features)]
+
+mod lib {
+    const N_ISLANDS: usize = 4;
+    const N_BRIDGES: usize = 7;
+    const BRIDGES: [(usize, usize); 7] = [(0, 1), (0, 1), (0, 2), (0, 3), (0, 3), (1, 2), (2, 3)];
+
+    pub type Matrix = [[usize; N_ISLANDS]; N_ISLANDS];
+
+    const EMPTY_MATRIX: Matrix = [[0; N_ISLANDS]; N_ISLANDS];
+
+    const fn build(mut matrix: Matrix, (to, from): (usize, usize)) -> Matrix {
+        matrix[to][from] += 1;
+        matrix[from][to] += 1;
+        matrix
+    }
+
+    pub const fn walk(mut matrix: Matrix, from: usize, to: usize) -> Matrix {
+        matrix[from][to] -= 1;
+        matrix[to][from] -= 1;
+        matrix
+    }
+
+    const fn to_matrix(bridges: [(usize, usize); N_BRIDGES]) -> Matrix {
+        let matrix = EMPTY_MATRIX;
+
+        let matrix = build(matrix, bridges[0]);
+        let matrix = build(matrix, bridges[1]);
+        let matrix = build(matrix, bridges[2]);
+        let matrix = build(matrix, bridges[3]);
+        let matrix = build(matrix, bridges[4]);
+        let matrix = build(matrix, bridges[5]);
+        let matrix = build(matrix, bridges[6]);
+
+        matrix
+    }
+
+    const BRIDGE_MATRIX: [[usize; N_ISLANDS]; N_ISLANDS] = to_matrix(BRIDGES);
+
+    pub struct Walk<const CURRENT: usize, const REMAINING: Matrix> {
+        _p: (),
+    }
+
+    impl Walk<0, BRIDGE_MATRIX> {
+        pub const fn new() -> Self {
+            Self { _p: () }
+        }
+    }
+
+    impl<const CURRENT: usize, const REMAINING: Matrix> Walk<CURRENT, REMAINING> {
+        pub fn proceed_to<const NEXT: usize>(
+            self,
+        ) -> Walk<NEXT, { walk(REMAINING, CURRENT, NEXT) }> {
+            Walk { _p: () }
+        }
+    }
+
+    pub struct Trophy {
+        _p: (),
+    }
+
+    impl<const CURRENT: usize> Walk<CURRENT, EMPTY_MATRIX> {
+        pub fn collect_prize(self) -> Trophy {
+            Trophy { _p: () }
+        }
+    }
+}
+
+pub use lib::{Trophy, Walk};
+
+fn main() {
+    // Example, taking the first step
+    let _ = Walk::new().proceed_to::<1>();
+
+    // Don't be so eager to collect the trophy
+    // let trophy = Walk::new()
+    //     .proceed_to::<1>()
+    //     .proceed_to::<0>()
+    //     .collect_prize();
+
+    // Can't just make a Trophy out of thin air, you must earn it
+    // let trophy: Trophy = Trophy { _p: () };
+
+    // Can you collect the Trophy?
+}