add comment and test: we do not do value-based reasoning for promotion of unions

3 files changed, 46 insertions, 25 deletions

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
index 7eb3c181d69..1847847d9d2 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -284,6 +284,7 @@ where
                 if Q::in_adt_inherently(cx, def, args) {
                     return true;
                 }
+                // Don't do any value-based reasoning for unions.
                 if def.is_union() && Q::in_any_value_of_ty(cx, rvalue.ty(cx.body, cx.tcx)) {
                     return true;
                 }
diff --git a/tests/ui/consts/promote-not.rs b/tests/ui/consts/promote-not.rs
index 47a06e8a72b..e0f02354354 100644
--- a/tests/ui/consts/promote-not.rs
+++ b/tests/ui/consts/promote-not.rs
@@ -3,6 +3,7 @@
 #![allow(unconditional_panic)]
 
 use std::cell::Cell;
+use std::mem::ManuallyDrop;
 
 // We do not promote mutable references.
 static mut TEST1: Option<&mut [i32]> = Some(&mut [1, 2, 3]); //~ ERROR temporary value dropped while borrowed
@@ -69,4 +70,12 @@ fn main() {
     let _val: &'static _ = &[&TEST_DROP; 1];
     //~^ ERROR temporary value dropped while borrowed
     //~| ERROR temporary value dropped while borrowed
+
+    // Make sure there is no value-based reasoning for unions.
+    union UnionWithCell {
+        f1: i32,
+        f2: ManuallyDrop<Cell<i32>>,
+    }
+    let x: &'static _ = &UnionWithCell { f1: 0 };
+    //~^ ERROR temporary value dropped while borrowed
 }
diff --git a/tests/ui/consts/promote-not.stderr b/tests/ui/consts/promote-not.stderr
index 67ac5922efd..9dbd703d489 100644
--- a/tests/ui/consts/promote-not.stderr
+++ b/tests/ui/consts/promote-not.stderr
@@ -1,5 +1,5 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:8:50
+  --> $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:11:18
+  --> $DIR/promote-not.rs:12:18
    |
 LL |     let x = &mut [1,2,3];
    |                  ^^^^^^^ creates a temporary value 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:33:29
+  --> $DIR/promote-not.rs:34:29
    |
 LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
    |             ------------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value 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:39:29
+  --> $DIR/promote-not.rs:40:29
    |
 LL |     let _val: &'static _ = &(Cell::new(1), 2).1;
    |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary value 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:20:32
+  --> $DIR/promote-not.rs:21:32
    |
 LL |         let _x: &'static () = &foo();
    |                 -----------    ^^^^^ creates a temporary value which is freed while still in use
@@ -49,7 +49,7 @@ LL |     }
    |     - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:28:29
+  --> $DIR/promote-not.rs:29:29
    |
 LL |     let _x: &'static i32 = &unsafe { U { x: 0 }.x };
    |             ------------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -59,7 +59,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:46:29
+  --> $DIR/promote-not.rs:47:29
    |
 LL |     let _val: &'static _ = &(Cell::new(1), 2).0;
    |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -70,7 +70,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:47:29
+  --> $DIR/promote-not.rs:48:29
    |
 LL |     let _val: &'static _ = &(Cell::new(1), 2).1;
    |               ----------    ^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -81,7 +81,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:50:29
+  --> $DIR/promote-not.rs:51:29
    |
 LL |     let _val: &'static _ = &(1/0);
    |               ----------    ^^^^^ creates a temporary value which is freed while still in use
@@ -92,7 +92,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:51:29
+  --> $DIR/promote-not.rs:52:29
    |
 LL |     let _val: &'static _ = &(1/(1-1));
    |               ----------    ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -103,7 +103,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:52:29
+  --> $DIR/promote-not.rs:53:29
    |
 LL |     let _val: &'static _ = &((1+1)/(1-1));
    |               ----------    ^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -114,7 +114,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:53:29
+  --> $DIR/promote-not.rs:54:29
    |
 LL |     let _val: &'static _ = &(i32::MIN/-1);
    |               ----------    ^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -125,7 +125,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:54:29
+  --> $DIR/promote-not.rs:55:29
    |
 LL |     let _val: &'static _ = &(i32::MIN/(0-1));
    |               ----------    ^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -136,7 +136,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:55:29
+  --> $DIR/promote-not.rs:56:29
    |
 LL |     let _val: &'static _ = &(-128i8/-1);
    |               ----------    ^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -147,7 +147,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:56:29
+  --> $DIR/promote-not.rs:57:29
    |
 LL |     let _val: &'static _ = &(1%0);
    |               ----------    ^^^^^ creates a temporary value which is freed while still in use
@@ -158,7 +158,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:57:29
+  --> $DIR/promote-not.rs:58:29
    |
 LL |     let _val: &'static _ = &(1%(1-1));
    |               ----------    ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -169,7 +169,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:58:29
+  --> $DIR/promote-not.rs:59:29
    |
 LL |     let _val: &'static _ = &([1,2,3][4]+1);
    |               ----------    ^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -180,7 +180,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:61:29
+  --> $DIR/promote-not.rs:62:29
    |
 LL |     let _val: &'static _ = &TEST_DROP;
    |               ----------    ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -191,7 +191,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:63:29
+  --> $DIR/promote-not.rs:64:29
    |
 LL |     let _val: &'static _ = &&TEST_DROP;
    |               ----------    ^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -202,7 +202,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:63:30
+  --> $DIR/promote-not.rs:64:30
    |
 LL |     let _val: &'static _ = &&TEST_DROP;
    |               ----------     ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -213,7 +213,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:66:29
+  --> $DIR/promote-not.rs:67:29
    |
 LL |     let _val: &'static _ = &(&TEST_DROP,);
    |               ----------    ^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -224,7 +224,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:66:31
+  --> $DIR/promote-not.rs:67:31
    |
 LL |     let _val: &'static _ = &(&TEST_DROP,);
    |               ----------      ^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -235,7 +235,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:69:29
+  --> $DIR/promote-not.rs:70:29
    |
 LL |     let _val: &'static _ = &[&TEST_DROP; 1];
    |               ----------    ^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
@@ -246,7 +246,7 @@ LL | }
    | - temporary value is freed at the end of this statement
 
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/promote-not.rs:69:31
+  --> $DIR/promote-not.rs:70:31
    |
 LL |     let _val: &'static _ = &[&TEST_DROP; 1];
    |               ----------      ^^^^^^^^^    - temporary value is freed at the end of this statement
@@ -254,6 +254,17 @@ LL |     let _val: &'static _ = &[&TEST_DROP; 1];
    |               |               creates a temporary value which is freed while still in use
    |               type annotation requires that borrow lasts for `'static`
 
-error: aborting due to 24 previous errors
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promote-not.rs:79:26
+   |
+LL |     let x: &'static _ = &UnionWithCell { f1: 0 };
+   |            ----------    ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
+   |            |
+   |            type annotation requires that borrow lasts for `'static`
+LL |
+LL | }
+   | - temporary value is freed at the end of this statement
+
+error: aborting due to 25 previous errors
 
 For more information about this error, try `rustc --explain E0716`.