example: fixes deallocate error in Rust (#2327)

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

examples/allocation/rust/greet.go

@@ -88,7 +88,12 @@ func main() {
 	greetingSize := uint32(ptrSize[0])
 	// This pointer was allocated by Rust, but owned by Go, So, we have to
 	// deallocate it when finished
-	defer deallocate.Call(ctx, uint64(greetingPtr), uint64(greetingSize))
+	defer func() {
+		_, err = deallocate.Call(ctx, uint64(greetingPtr), uint64(greetingSize))
+		if err != nil {
+			log.Panicln(err)
+		}
+	}()
 
 	// The pointer is a linear memory offset, which is where we write the name.
 	if bytes, ok := mod.Memory().Read(greetingPtr, greetingSize); !ok {

examples/allocation/rust/testdata/greet.rs

@@ -101,7 +101,7 @@ pub extern "C" fn _allocate(size: u32) -> *mut u8 {
 /// Allocates size bytes and leaks the pointer where they start.
 fn allocate(size: usize) -> *mut u8 {
     // Allocate the amount of bytes needed.
-    let vec: Vec<MaybeUninit<u8>> = Vec::with_capacity(size);
+    let vec: Vec<MaybeUninit<u8>> = vec![MaybeUninit::uninit(); size];
 
     // into_raw leaks the memory to the caller.
     Box::into_raw(vec.into_boxed_slice()) as *mut u8