make sure raw ptr casts in 'const' context are unsafe

Author: RalfJung

src/test/ui/cast/cast-ptr-to-int-const.rs

@@ -1,11 +1,25 @@
 // gate-test-const_raw_ptr_to_usize_cast
+// revisions: with_feature without_feature
+
+#![cfg_attr(with_feature, feature(const_raw_ptr_to_usize_cast))]
 
 fn main() {
-    const X: u32 = unsafe {
-        main as u32 //~ ERROR casting pointers to integers in constants is unstable
+    const X: usize = unsafe {
+        main as usize //[without_feature]~ ERROR casting pointers to integers in constants is unstable
     };
     const Y: u32 = 0;
-    const Z: u32 = unsafe {
-        &Y as *const u32 as u32 //~ ERROR is unstable
+    const Z: usize = unsafe {
+        &Y as *const u32 as usize //[without_feature]~ ERROR is unstable
+    };
+    // Cast in `const` without `unsafe` block
+    const SAFE: usize = {
+        &Y as *const u32 as usize //[without_feature]~ ERROR is unstable
+        //[with_feature]~^ ERROR cast of pointer to int is unsafe and requires unsafe
     };
 }
+
+// Cast in `const fn` without `unsafe` block
+const fn test() -> usize {
+    &0 as *const i32 as usize //[without_feature]~ ERROR is unstable
+    //[with_feature]~^ ERROR cast of pointer to int is unsafe and requires unsafe
+}

src/test/ui/cast/cast-ptr-to-int-const.stderr

@@ -0,0 +1,19 @@
+error[E0133]: cast of pointer to int is unsafe and requires unsafe function or block
+  --> $DIR/cast-ptr-to-int-const.rs:16:9
+   |
+LL |         &Y as *const u32 as usize
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^ cast of pointer to int
+   |
+   = note: casting pointers to integers in constants
+
+error[E0133]: cast of pointer to int is unsafe and requires unsafe function or block
+  --> $DIR/cast-ptr-to-int-const.rs:23:5
+   |
+LL |     &0 as *const i32 as usize
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ cast of pointer to int
+   |
+   = note: casting pointers to integers in constants
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0133`.

src/test/ui/cast/cast-ptr-to-int-const.with_feature.stderr

@@ -0,0 +1,39 @@
+error[E0658]: casting pointers to integers in constants is unstable
+  --> $DIR/cast-ptr-to-int-const.rs:8:9
+   |
+LL |         main as usize
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #51910 <https://github.com/rust-lang/rust/issues/51910> for more information
+   = help: add `#![feature(const_raw_ptr_to_usize_cast)]` to the crate attributes to enable
+
+error[E0658]: casting pointers to integers in constants is unstable
+  --> $DIR/cast-ptr-to-int-const.rs:12:9
+   |
+LL |         &Y as *const u32 as usize
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51910 <https://github.com/rust-lang/rust/issues/51910> for more information
+   = help: add `#![feature(const_raw_ptr_to_usize_cast)]` to the crate attributes to enable
+
+error[E0658]: casting pointers to integers in constants is unstable
+  --> $DIR/cast-ptr-to-int-const.rs:16:9
+   |
+LL |         &Y as *const u32 as usize
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51910 <https://github.com/rust-lang/rust/issues/51910> for more information
+   = help: add `#![feature(const_raw_ptr_to_usize_cast)]` to the crate attributes to enable
+
+error[E0658]: casting pointers to integers in constant functions is unstable
+  --> $DIR/cast-ptr-to-int-const.rs:23:5
+   |
+LL |     &0 as *const i32 as usize
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51910 <https://github.com/rust-lang/rust/issues/51910> for more information
+   = help: add `#![feature(const_raw_ptr_to_usize_cast)]` to the crate attributes to enable
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.