Change extern_class! syntax

Instead of specifying `impl ClassType for ...`, we instead parse the
custom attributes `#[unsafe(super(...))]`, `#[thread_kind = ...]` and
`#[name = ...]`.

This is nice because:
- It's more concise.
- It more closely matches what we might end up with once it can become
  and attribute macro:
  rust-lang/rfcs#3697
- We need to parse the attributes anyhow to override derives:
  #267

  (The extern_class! part of that issue is now resolved).
- It makes it easier to change ClassType in the future without having to
  change the macro API as well.

Additionally, this commit also adds incomplete support for generics, to
avoid the framework crates depending on an internal macro, and it
improves rust-analyzer support in extern_class! by having more relaxed
parsing.

crates/block2/src/lib.rs

@@ -65,12 +65,9 @@
 //! #
 //! # use objc2::ClassType;
 //! # objc2::extern_class!(
+//! #     #[unsafe(super(objc2::runtime::NSObject))]
+//! #     #[name = "NSObject"]
 //! #     struct MyClass;
-//! #
-//! #     unsafe impl ClassType for MyClass {
-//! #         type Super = objc2::runtime::NSObject;
-//! #         const NAME: &'static str = "NSObject";
-//! #     }
 //! # );
 //!
 //! extern_methods!(

crates/header-translator/src/stmt.rs

@@ -1658,18 +1658,23 @@ impl Stmt {
                         return Ok(());
                     }
 
-                    let macro_name = if generics.is_empty() {
-                        "extern_class"
-                    } else {
-                        "__inner_extern_class"
-                    };
-
-                    let (superclass, superclasses_rest) = superclasses.split_at(1);
-                    let (superclass, superclass_generics) = superclass
-                        .first()
-                        .expect("must have a least one superclass");
-
-                    writeln!(f, "{macro_name}!(")?;
+                    writeln!(f, "extern_class!(")?;
+                    write!(f, "    #[unsafe(super(")?;
+                    for (i, (superclass, generics)) in superclasses.iter().enumerate() {
+                        if 0 < i {
+                            write!(f, ", ")?;
+                        }
+                        write!(
+                            f,
+                            "{}{}",
+                            superclass.path_in_relation_to(id.location()),
+                            GenericTyHelper(generics)
+                        )?;
+                    }
+                    writeln!(f, "))]")?;
+                    if *main_thread_only {
+                        writeln!(f, "    #[thread_kind = MainThreadOnly]")?;
+                    }
                     writeln!(f, "    {derives}")?;
                     write!(f, "    {}", self.cfg_gate_ln(config))?;
                     write!(f, "    {availability}")?;
@@ -1681,74 +1686,7 @@ impl Stmt {
                         }
                         write!(f, ">")?;
                     };
-                    if generics.is_empty() {
-                        writeln!(f, ";")?;
-                    } else {
-                        writeln!(f, " {{")?;
-                        writeln!(
-                            f,
-                            "__superclass: {}{},",
-                            superclass.path_in_relation_to(id.location()),
-                            GenericTyHelper(superclass_generics),
-                        )?;
-                        for (i, generic) in generics.iter().enumerate() {
-                            // Invariant over the generic by default
-                            writeln!(f, "_inner{i}: PhantomData<*mut {generic}>,")?;
-                        }
-                        writeln!(f, "notunwindsafe: PhantomData<&'static mut ()>,")?;
-                        writeln!(f, "}}")?;
-                    }
-
-                    writeln!(f)?;
-
-                    write!(f, "    {}", self.cfg_gate_ln(config))?;
-                    writeln!(
-                        f,
-                        "    unsafe impl{} ClassType for {}{} {{",
-                        GenericParamsHelper(generics, "?Sized + Message"),
-                        id.name,
-                        GenericTyHelper(generics),
-                    )?;
-                    if !superclasses_rest.is_empty() {
-                        write!(f, "        #[inherits(")?;
-                        let mut iter = superclasses_rest.iter();
-                        // Using generics in here is not technically correct, but
-                        // should work for our use-cases.
-                        if let Some((superclass, generics)) = iter.next() {
-                            write!(
-                                f,
-                                "{}{}",
-                                superclass.path_in_relation_to(id.location()),
-                                GenericTyHelper(generics)
-                            )?;
-                        }
-                        for (superclass, generics) in iter {
-                            write!(
-                                f,
-                                ", {}{}",
-                                superclass.path_in_relation_to(id.location()),
-                                GenericTyHelper(generics)
-                            )?;
-                        }
-                        writeln!(f, ")]")?;
-                    }
-                    writeln!(
-                        f,
-                        "        type Super = {}{};",
-                        superclass.path_in_relation_to(id.location()),
-                        GenericTyHelper(superclass_generics),
-                    )?;
-                    if *main_thread_only {
-                        writeln!(f, "        type ThreadKind = dyn MainThreadOnly;")?;
-                    }
-                    if !generics.is_empty() {
-                        writeln!(f)?;
-                        writeln!(
-                            f,
-                            "        fn as_super(&self) -> &Self::Super {{ &self.__superclass }}"
-                        )?;
-                    }
-                    writeln!(f, "    }}")?;
+                    writeln!(f, ";")?;
                     writeln!(f, ");")?;
 
                     if *sendable && generics.is_empty() {

crates/objc2/src/__framework_prelude.rs

@@ -17,8 +17,8 @@ pub use crate::runtime::{
     AnyClass, AnyObject, Bool, NSObject, NSObjectProtocol, ProtocolObject, Sel,
 };
 pub use crate::{
-    MainThreadOnly, __inner_extern_class, extern_category, extern_class, extern_methods,
-    extern_protocol, ClassType, MainThreadMarker, Message, ProtocolType,
+    extern_category, extern_class, extern_methods, extern_protocol, ClassType, MainThreadMarker,
+    MainThreadOnly, Message, ProtocolType,
 };
 
 // TODO

crates/objc2/src/__macro_helpers/class.rs

@@ -54,54 +54,39 @@ mod tests {
     use crate::runtime::NSObject;
 
     extern_class!(
+        #[unsafe(super(NSObject))]
+        #[thread_kind = AllocAnyThread]
+        #[name = "NSObject"]
         struct SetAnyThread;
-
-        unsafe impl ClassType for SetAnyThread {
-            type Super = NSObject;
-            type ThreadKind = dyn AllocAnyThread;
-            const NAME: &'static str = "NSObject";
-        }
     );
 
     extern_class!(
+        #[unsafe(super(NSObject))]
+        #[thread_kind = AllocAnyThread]
+        #[name = "NSObject"]
         struct SendSync;
-
-        unsafe impl ClassType for SendSync {
-            type Super = NSObject;
-            type ThreadKind = dyn AllocAnyThread;
-            const NAME: &'static str = "NSObject";
-        }
     );
 
     unsafe impl Send for SendSync {}
     unsafe impl Sync for SendSync {}
 
     extern_class!(
+        #[unsafe(super(NSObject))]
+        #[thread_kind = MainThreadOnly]
+        #[name = "NSObject"]
         struct OnlyMain;
-
-        unsafe impl ClassType for OnlyMain {
-            type Super = NSObject;
-            type ThreadKind = dyn MainThreadOnly;
-            const NAME: &'static str = "NSObject";
-        }
     );
 
     extern_class!(
+        #[unsafe(super(OnlyMain))]
+        #[name = "NSObject"]
         struct OnlyMainSubDefault;
-
-        unsafe impl ClassType for OnlyMainSubDefault {
-            type Super = OnlyMain;
-            const NAME: &'static str = "NSObject";
-        }
     );
 
     extern_class!(
+        #[unsafe(super(OnlyMain))]
+        #[thread_kind = MainThreadOnly]
+        #[name = "NSObject"]
         struct OnlyMainSubExplicit;
-
-        unsafe impl ClassType for OnlyMainSubExplicit {
-            type Super = OnlyMain;
-            type ThreadKind = dyn MainThreadOnly;
-            const NAME: &'static str = "NSObject";
-        }
     );
 }

crates/objc2/src/__macro_helpers/mod.rs

@@ -1,7 +1,10 @@
 pub use core::borrow::Borrow;
 pub use core::cell::UnsafeCell;
+pub use core::cmp::{Eq, PartialEq};
 pub use core::convert::AsRef;
 pub use core::default::Default;
+pub use core::fmt;
+pub use core::hash::{Hash, Hasher};
 pub use core::marker::{PhantomData, Sized};
 pub use core::mem::{size_of, ManuallyDrop, MaybeUninit};
 pub use core::ops::Deref;