Merge pull request #231 from madsmtm/extern-class-verify-zst

Statically verify that the user only uses ZSTs in `extern_class!`

Author: madsmtm

objc2/src/__macro_helpers.rs

@@ -9,6 +9,7 @@ pub use crate::cache::CachedSel;
 pub use core::borrow::{Borrow, BorrowMut};
 pub use core::cell::UnsafeCell;
 pub use core::convert::{AsMut, AsRef};
+pub use core::mem::size_of;
 pub use core::ops::{Deref, DerefMut};
 pub use core::option::Option::{self, None, Some};
 pub use core::primitive::{bool, str, u8};

objc2/src/macros/extern_class.rs

@@ -47,8 +47,6 @@
 /// standard memory management messages (this is upheld if [`NSObject`] is
 /// part of its inheritance chain).
 ///
-/// Additionally, any fields (if specified) must be zero-sized.
-///
 /// [`NSObject`]: crate::foundation::NSObject
 ///
 ///
@@ -107,6 +105,7 @@ macro_rules! extern_class {
         $(#[$m:meta])*
         unsafe $v:vis struct $name:ident: $superclass:ty $(, $inheritance_rest:ty)*;
     ) => {
+        // Just shorthand syntax for the following
         $crate::extern_class! {
             $(#[$m])*
             unsafe $v struct $name: $superclass $(, $inheritance_rest)* {}
@@ -124,6 +123,16 @@ macro_rules! extern_class {
                 $($field_vis $field: $field_ty,)*
             }
         }
+
+        const _: () = {
+            if $crate::__macro_helpers::size_of::<$name>() != 0 {
+                panic!(concat!(
+                    "the struct ",
+                    stringify!($name),
+                    " is not zero-sized!",
+                ))
+            }
+        };
     };
 }
 
@@ -181,14 +190,14 @@ macro_rules! __inner_extern_class {
     (
         $(#[$m:meta])*
         unsafe $v:vis struct $name:ident<$($t:ident $(: $b:ident)?),*>: $($inheritance_chain:ty),+ {
-            $($p:ident: $pty:ty,)*
+            $($field_vis:vis $field:ident: $field_ty:ty,)*
         }
     ) => {
         $crate::__inner_extern_class! {
             @__inner
             $(#[$m])*
             unsafe $v struct $name<$($t $(: $b)?),*>: $($inheritance_chain,)+ $crate::runtime::Object {
-                $($p: $pty,)*
+                $($field_vis $field: $field_ty,)*
             }
         }
 
@@ -209,7 +218,7 @@ macro_rules! __inner_extern_class {
         @__inner
         $(#[$m:meta])*
         unsafe $v:vis struct $name:ident<$($t:ident $(: $b:ident)?),*>: $superclass:ty $(, $inheritance_rest:ty)* {
-            $($p_v:vis $p:ident: $pty:ty,)*
+            $($field_vis:vis $field:ident: $field_ty:ty,)*
         }
     ) => {
         $(#[$m])*
@@ -218,7 +227,7 @@ macro_rules! __inner_extern_class {
         $v struct $name<$($t $(: $b)?),*> {
             __inner: $superclass,
             // Additional fields (should only be zero-sized PhantomData or ivars).
-            $($p_v $p: $pty),*
+            $($field_vis $field: $field_ty,)*
         }
 
         // SAFETY:

test-ui/ui/extern_class_not_zst.rs

@@ -0,0 +1,10 @@
+use objc2::extern_class;
+use objc2::foundation::NSObject;
+
+extern_class! {
+    unsafe pub struct NSNumber: NSObject {
+        var: u32,
+    }
+}
+
+fn main() {}

test-ui/ui/extern_class_not_zst.stderr

@@ -0,0 +1,11 @@
+error[E0080]: evaluation of constant value failed
+ --> ui/extern_class_not_zst.rs
+  |
+  | / extern_class! {
+  | |     unsafe pub struct NSNumber: NSObject {
+  | |         var: u32,
+  | |     }
+  | | }
+  | |_^ the evaluated program panicked at 'the struct NSNumber is not zero-sized!', $DIR/ui/extern_class_not_zst.rs:4:1
+  |
+  = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `extern_class` (in Nightly builds, run with -Z macro-backtrace for more info)