1 files changed, 55 insertions, 0 deletions
diff --git a/src/test/ui/consts/const-mut-refs/mut_ref_in_final.rs b/src/test/ui/consts/const-mut-refs/mut_ref_in_final.rs
new file mode 100644
index 000000000..a7d329f12
--- /dev/null
+++ b/src/test/ui/consts/const-mut-refs/mut_ref_in_final.rs
@@ -0,0 +1,55 @@
+#![feature(const_mut_refs)]
+#![feature(raw_ref_op)]
+
+const NULL: *mut i32 = std::ptr::null_mut();
+const A: *const i32 = &4;
+
+// It could be made sound to allow it to compile,
+// but we do not want to allow this to compile,
+// as that would be an enormous footgun in oli-obk's opinion.
+const B: *mut i32 = &mut 4; //~ ERROR mutable references are not allowed
+
+// Ok, no actual mutable allocation exists
+const B2: Option<&mut i32> = None;
+
+// Not ok, can't prove that no mutable allocation ends up in final value
+const B3: Option<&mut i32> = Some(&mut 42); //~ ERROR temporary value dropped while borrowed
+
+const fn helper(x: &mut i32) -> Option<&mut i32> { Some(x) }
+const B4: Option<&mut i32> = helper(&mut 42); //~ ERROR temporary value dropped while borrowed
+
+// Ok, because no references to mutable data exist here, since the `{}` moves
+// its value and then takes a reference to that.
+const C: *const i32 = &{
+    let mut x = 42;
+    x += 3;
+    x
+};
+
+use std::cell::UnsafeCell;
+struct NotAMutex<T>(UnsafeCell<T>);
+
+unsafe impl<T> Sync for NotAMutex<T> {}
+
+const FOO: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
+//~^ ERROR temporary value dropped while borrowed
+
+static FOO2: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
+//~^ ERROR temporary value dropped while borrowed
+
+static mut FOO3: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
+//~^ ERROR temporary value dropped while borrowed
+
+// `BAR` works, because `&42` promotes immediately instead of relying on
+// the enclosing scope rule.
+const BAR: NotAMutex<&i32> = NotAMutex(UnsafeCell::new(&42));
+
+fn main() {
+    println!("{}", unsafe { *A });
+    unsafe { *B = 4 } // Bad news
+
+    unsafe {
+        **FOO.0.get() = 99;
+        assert_eq!(**FOO.0.get(), 99);
+    }
+}