From 64a54df86faf1f55148433753296dc2bc2a7e31d Mon Sep 17 00:00:00 2001
From: Bryan Garza <1396101+bryangarza@users.noreply.github.com>
Date: Wed, 7 Jun 2023 08:17:58 -0700
Subject: [PATCH] Safe Transmute: Disable coinduction support

This patch just removes the `#[rustc_coinductive]` annotation from `BikeshedIntrinsicFrom` and flips the related tests to `check-fail`. Once an FCP for setting the annotation on the trait is approved, it could be enabled again.
---
 library/core/src/mem/transmutability.rs       |  1 -
 .../recursive-wrapper-types-bit-compatible.rs |  5 ++--
 ...ursive-wrapper-types-bit-compatible.stderr | 25 +++++++++++++++++++
 .../references/recursive-wrapper-types.rs     |  5 ++--
 .../references/recursive-wrapper-types.stderr | 25 +++++++++++++++++++
 5 files changed, 56 insertions(+), 5 deletions(-)
 create mode 100644 tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.stderr
 create mode 100644 tests/ui/transmutability/references/recursive-wrapper-types.stderr

diff --git a/library/core/src/mem/transmutability.rs b/library/core/src/mem/transmutability.rs
index d0c30e715d5..87ae30619c6 100644
--- a/library/core/src/mem/transmutability.rs
+++ b/library/core/src/mem/transmutability.rs
@@ -5,7 +5,6 @@
 /// notwithstanding whatever safety checks you have asked the compiler to [`Assume`] are satisfied.
 #[unstable(feature = "transmutability", issue = "99571")]
 #[lang = "transmute_trait"]
-#[rustc_coinductive]
 pub unsafe trait BikeshedIntrinsicFrom<Src, Context, const ASSUME: Assume = { Assume::NOTHING }>
 where
     Src: ?Sized,
diff --git a/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.rs b/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.rs
index 709d8cdc762..3ea80173afa 100644
--- a/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.rs
+++ b/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.rs
@@ -1,4 +1,5 @@
-// check-pass
+// check-fail
+// FIXME(bryangarza): Change to check-pass when coinduction is supported for BikeshedIntrinsicFrom
 #![feature(transmutability)]
 
 mod assert {
@@ -21,5 +22,5 @@ mod assert {
 fn main() {
     #[repr(C)] struct A(bool, &'static A);
     #[repr(C)] struct B(u8, &'static B);
-    assert::is_maybe_transmutable::<&'static A, &'static B>();
+    assert::is_maybe_transmutable::<&'static A, &'static B>(); //~ ERROR overflow evaluating the requirement
 }
diff --git a/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.stderr b/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.stderr
new file mode 100644
index 00000000000..fae332e6af9
--- /dev/null
+++ b/tests/ui/transmutability/references/recursive-wrapper-types-bit-compatible.stderr
@@ -0,0 +1,25 @@
+error[E0275]: overflow evaluating the requirement `B: BikeshedIntrinsicFrom<A, assert::Context, Assume { alignment: true, lifetimes: false, safety: true, validity: false }>`
+  --> $DIR/recursive-wrapper-types-bit-compatible.rs:25:5
+   |
+LL |     assert::is_maybe_transmutable::<&'static A, &'static B>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: required by a bound in `is_maybe_transmutable`
+  --> $DIR/recursive-wrapper-types-bit-compatible.rs:11:14
+   |
+LL |       pub fn is_maybe_transmutable<Src, Dst>()
+   |              --------------------- required by a bound in this function
+LL |       where
+LL |           Dst: BikeshedIntrinsicFrom<Src, Context, {
+   |  ______________^
+LL | |             Assume {
+LL | |                 alignment: true,
+LL | |                 lifetimes: false,
+...  |
+LL | |             }
+LL | |         }>
+   | |__________^ required by this bound in `is_maybe_transmutable`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.
diff --git a/tests/ui/transmutability/references/recursive-wrapper-types.rs b/tests/ui/transmutability/references/recursive-wrapper-types.rs
index 090c1fea6db..59d1ad84a5d 100644
--- a/tests/ui/transmutability/references/recursive-wrapper-types.rs
+++ b/tests/ui/transmutability/references/recursive-wrapper-types.rs
@@ -1,4 +1,5 @@
-// check-pass
+// check-fail
+// FIXME(bryangarza): Change to check-pass when coinduction is supported for BikeshedIntrinsicFrom
 #![feature(transmutability)]
 
 mod assert {
@@ -21,6 +22,6 @@ mod assert {
 fn main() {
     #[repr(C)] struct A(&'static B);
     #[repr(C)] struct B(&'static A);
-    assert::is_maybe_transmutable::<&'static A, &'static B>();
+    assert::is_maybe_transmutable::<&'static A, &'static B>(); //~ overflow evaluating the requirement
     assert::is_maybe_transmutable::<&'static B, &'static A>();
 }
diff --git a/tests/ui/transmutability/references/recursive-wrapper-types.stderr b/tests/ui/transmutability/references/recursive-wrapper-types.stderr
new file mode 100644
index 00000000000..35a60c22643
--- /dev/null
+++ b/tests/ui/transmutability/references/recursive-wrapper-types.stderr
@@ -0,0 +1,25 @@
+error[E0275]: overflow evaluating the requirement `A: BikeshedIntrinsicFrom<B, assert::Context, Assume { alignment: true, lifetimes: false, safety: true, validity: false }>`
+  --> $DIR/recursive-wrapper-types.rs:25:5
+   |
+LL |     assert::is_maybe_transmutable::<&'static A, &'static B>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: required by a bound in `is_maybe_transmutable`
+  --> $DIR/recursive-wrapper-types.rs:11:14
+   |
+LL |       pub fn is_maybe_transmutable<Src, Dst>()
+   |              --------------------- required by a bound in this function
+LL |       where
+LL |           Dst: BikeshedIntrinsicFrom<Src, Context, {
+   |  ______________^
+LL | |             Assume {
+LL | |                 alignment: true,
+LL | |                 lifetimes: false,
+...  |
+LL | |             }
+LL | |         }>
+   | |__________^ required by this bound in `is_maybe_transmutable`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.