Use NSMutableData::from_vec in tests

NSData::from_vec is broken in GNUStep, see gnustep/libs-base#213

Author: madsmtm

objc2_foundation/src/data.rs

@@ -7,8 +7,6 @@ use core::{ffi::c_void, ptr::NonNull};
 use super::{INSCopying, INSMutableCopying, INSObject, NSRange};
 use objc2::msg_send;
 use objc2::rc::{Id, Owned};
-#[cfg(feature = "block")]
-use objc2_block::{Block, ConcreteBlock};
 
 pub trait INSData: INSObject {
     fn len(&self) -> usize {
@@ -22,12 +20,11 @@ pub trait INSData: INSObject {
     fn bytes(&self) -> &[u8] {
         let ptr: *const c_void = unsafe { msg_send![self, bytes] };
         // The bytes pointer may be null for length zero
-        let (ptr, len) = if ptr.is_null() {
-            (0x1 as *const u8, 0)
+        if ptr.is_null() {
+            &[]
         } else {
-            (ptr as *const u8, self.len())
-        };
-        unsafe { slice::from_raw_parts(ptr, len) }
+            unsafe { slice::from_raw_parts(ptr as *const u8, self.len()) }
+        }
     }
 
     fn with_bytes(bytes: &[u8]) -> Id<Self, Owned> {
@@ -46,6 +43,8 @@ pub trait INSData: INSObject {
 
     #[cfg(feature = "block")]
     fn from_vec(bytes: Vec<u8>) -> Id<Self, Owned> {
+        use objc2_block::{Block, ConcreteBlock};
+
         let capacity = bytes.capacity();
         let dealloc = ConcreteBlock::new(move |bytes: *mut c_void, len: usize| unsafe {
             // Recreate the Vec and let it drop
@@ -56,6 +55,23 @@ pub trait INSData: INSObject {
 
         let mut bytes = bytes;
         let bytes_ptr = bytes.as_mut_ptr() as *mut c_void;
+
+        // GNUStep's NSData `initWithBytesNoCopy:length:deallocator:` has a
+        // bug; it forgets to assign the input buffer and length to the
+        // instance before it swizzles to NSDataWithDeallocatorBlock.
+        // See https://github.com/gnustep/libs-base/pull/213
+        // So we just use NSDataWithDeallocatorBlock directly.
+        // TODO
+        // #[cfg(feature = "gnustep")]
+        // let cls = {
+        //     let cls = Self::class();
+        //     if cls == class!(NSData) {
+        //         class!(NSDataWithDeallocatorBlock)
+        //     } else {
+        //         cls
+        //     }
+        // };
+        // #[cfg(not(feature = "gnustep"))]
         let cls = Self::class();
         unsafe {
             let obj: *mut Self = msg_send![cls, alloc];
@@ -215,7 +231,8 @@ mod tests {
         let bytes = vec![3, 7, 16];
         let bytes_ptr = bytes.as_ptr();
 
-        let data = NSData::from_vec(bytes);
-        assert!(data.bytes().as_ptr() == bytes_ptr);
+        // This functionality on NSData is broken on GNUStep
+        let data = NSMutableData::from_vec(bytes);
+        assert_eq!(data.bytes().as_ptr(), bytes_ptr);
     }
 }