make sure we do not promote things with interior mutability

Author: RalfJung

src/test/ui/consts/promote-not.rs

@@ -3,6 +3,8 @@
 #![allow(unconditional_panic, const_err)]
 #![feature(const_fn, const_fn_union)]
 
+use std::cell::Cell;
+
 // We do not promote mutable references.
 static mut TEST1: Option<&mut [i32]> = Some(&mut [1, 2, 3]); //~ ERROR temporary value dropped while borrowed
 
@@ -32,4 +34,7 @@ const TEST_UNION: () = {
     let _x: &'static i32 = &unsafe { U { x: 0 }.x }; //~ ERROR temporary value dropped while borrowed
 };
 
-fn main() {}
+fn main() {
+    // We must not promote things with interior mutability.
+    let _val: &'static _ = &(Cell::new(1), 2).0; //~ ERROR temporary value dropped while borrowed
+}

src/test/ui/consts/promote-not.stderr

@@ -1,5 +1,5 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:7:50
+  --> $DIR/promote-not.rs:9:50
    |
 LL | static mut TEST1: Option<&mut [i32]> = Some(&mut [1, 2, 3]);
    |                                        ----------^^^^^^^^^-
@@ -9,7 +9,7 @@ LL | static mut TEST1: Option<&mut [i32]> = Some(&mut [1, 2, 3]);
    |                                        using this value as a static requires that borrow lasts for `'static`
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:10:18
+  --> $DIR/promote-not.rs:12:18
    |
 LL |     let x = &mut [1,2,3];
    |                  ^^^^^^^ creates a temporary which is freed while still in use
@@ -19,7 +19,7 @@ LL | };
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:19:32
+  --> $DIR/promote-not.rs:21:32
    |
 LL |         let _x: &'static () = &foo();
    |                 -----------    ^^^^^ creates a temporary which is freed while still in use
@@ -29,7 +29,7 @@ LL |     }
    |     - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:27:29
+  --> $DIR/promote-not.rs:29:29
    |
 LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
    |             ------------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
@@ -39,7 +39,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:32:29
+  --> $DIR/promote-not.rs:34:29
    |
 LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
    |             ------------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
@@ -48,6 +48,16 @@ LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
 LL | };
    | - temporary value is freed at the end of this statement
 
-error: aborting due to 5 previous errors
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promote-not.rs:39:29
+   |
+LL |     let _val: &'static _ = &(Cell::new(1), 2).0;
+   |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
+   |               |
+   |               type annotation requires that borrow lasts for `'static`
+LL | }
+   | - temporary value is freed at the end of this statement
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0716`.