fix: Allow null pointers as empty slices (#79)

Author: DataTriny

include/accesskit.h

@@ -2204,7 +2204,8 @@ struct accesskit_custom_actions *accesskit_node_custom_actions(
     const struct accesskit_node *node);
 
 /**
- * Caller is responsible for freeing each `custom_action` in the array.
+ * Caller is responsible for freeing each `custom_action` in the array
+ * as well as the `values` array itself.
  */
 void accesskit_node_set_custom_actions(
     struct accesskit_node *node, size_t length,

src/common.rs

@@ -63,12 +63,16 @@ macro_rules! array_setter {
             #[no_mangle]
             pub extern "C" fn $c_setter(node: *mut node, length: usize, values: *const $ffi_type) {
                 let node = mut_from_ptr(node);
-                let values = unsafe {
-                    slice::from_raw_parts(values, length)
-                        .iter()
-                        .cloned()
-                        .map(From::from)
-                        .collect::<Vec<$rust_type>>()
+                let values = if length == 0 {
+                    Vec::new()
+                } else {
+                    unsafe {
+                        slice::from_raw_parts(values, length)
+                            .iter()
+                            .cloned()
+                            .map(From::from)
+                            .collect::<Vec<$rust_type>>()
+                    }
                 };
                 node.$setter(values);
             }
@@ -157,8 +161,13 @@ macro_rules! slice_struct {
         }
         impl From<$struct_name> for Vec<$rust_type> {
             fn from(values: $struct_name) -> Self {
-                unsafe {
-                    slice::from_raw_parts(values.values as *mut $rust_type, values.length).to_vec()
+                if values.length == 0 {
+                    Vec::new()
+                } else {
+                    unsafe {
+                        slice::from_raw_parts(values.values as *mut $rust_type, values.length)
+                            .to_vec()
+                    }
                 }
             }
         }
@@ -795,19 +804,24 @@ impl node {
         BoxCastPtr::to_mut_ptr(node.custom_actions().into())
     }
 
-    /// Caller is responsible for freeing each `custom_action` in the array.
+    /// Caller is responsible for freeing each `custom_action` in the array
+    /// as well as the `values` array itself.
     #[no_mangle]
     pub extern "C" fn accesskit_node_set_custom_actions(
         node: *mut node,
         length: usize,
         values: *const *mut custom_action,
     ) {
         let node = mut_from_ptr(node);
-        let values = unsafe {
-            slice::from_raw_parts(values, length)
-                .iter()
-                .map(|ptr| ref_from_ptr(*ptr).clone())
-                .collect::<Vec<CustomAction>>()
+        let values = if length == 0 {
+            Vec::new()
+        } else {
+            unsafe {
+                slice::from_raw_parts(values, length)
+                    .iter()
+                    .map(|ptr| ref_from_ptr(*ptr).clone())
+                    .collect::<Vec<CustomAction>>()
+            }
         };
         node.set_custom_actions(values);
     }

src/lib.rs

@@ -194,5 +194,9 @@ where
 }
 
 unsafe fn string_from_c_slice(value: *const c_char, length: usize) -> String {
-    String::from_utf8_lossy(slice::from_raw_parts(value as *const u8, length)).into_owned()
+    if length == 0 {
+        String::new()
+    } else {
+        String::from_utf8_lossy(slice::from_raw_parts(value as *const u8, length)).into_owned()
+    }
 }