[memory-leak] Fix double-free in HarfBuzzSharp.Buffer.UnicodeFunctions getter

binding/HarfBuzzSharp/Buffer.cs

@@ -132,7 +132,9 @@ public int Length {
 
 		public UnicodeFunctions UnicodeFunctions {
 			get {
-				var r = new UnicodeFunctions (HarfBuzzApi.hb_buffer_get_unicode_funcs (Handle));
+				// hb_buffer_get_unicode_funcs returns a borrowed (transfer-none) reference
+				// owned by the buffer, so the wrapper must not destroy it on dispose.
+				var r = new UnicodeFunctions (HarfBuzzApi.hb_buffer_get_unicode_funcs (Handle), owns: false);
 				GC.KeepAlive (this);
 				return r;
 			}

binding/HarfBuzzSharp/UnicodeFunctions.cs

@@ -16,11 +16,21 @@ public unsafe class UnicodeFunctions : NativeObject
 
 		public static UnicodeFunctions Empty => emptyFunctions.Value;
 
+		// true when this wrapper owns the native handle and must destroy it on dispose;
+		// false when it merely borrows a handle owned by another object (e.g. a buffer).
+		private readonly bool owns = true;
+
 		internal UnicodeFunctions (IntPtr handle)
 			: base (handle)
 		{
 		}
 
+		internal UnicodeFunctions (IntPtr handle, bool owns)
+			: base (handle)
+		{
+			this.owns = owns;
+		}
+
 		public UnicodeFunctions (UnicodeFunctions parent) : base (IntPtr.Zero)
 		{
 			if (parent == null)
@@ -196,7 +206,7 @@ protected override void Dispose (bool disposing) =>
 
 		protected override void DisposeHandler ()
 		{
-			if (Handle != IntPtr.Zero) {
+			if (owns && Handle != IntPtr.Zero) {
 				HarfBuzzApi.hb_unicode_funcs_destroy (Handle);
 			}
 		}

tests/Tests/HarfBuzzSharp/HBUnicodeFuncsTest.cs

@@ -146,5 +146,28 @@ public void ShouldSetDecomposeDelegate()
 				Assert.Equal(7331, second);
 			}
 		}
+
+		[Fact]
+		public void BufferUnicodeFunctionsGetterDoesNotOwnBorrowedHandle()
+		{
+			// hb_buffer_get_unicode_funcs returns a borrowed (transfer-none) reference
+			// owned by the buffer. Disposing the wrapper returned by the getter must not
+			// destroy that shared handle out from under the still-alive buffer.
+			var destroyed = false;
+
+			var unicodeFunctions = new UnicodeFunctions(UnicodeFunctions.Default);
+			unicodeFunctions.SetScriptDelegate((f, cp) => Script.Unknown, () => destroyed = true);
+
+			// The buffer is kept alive (via using) so its funcs reference stays valid
+			// through the assertion, and is disposed cleanly at the end of the scope.
+			using var buffer = new Buffer();
+			buffer.UnicodeFunctions = unicodeFunctions;
+
+			var borrowed = buffer.UnicodeFunctions;
+			borrowed.Dispose();
+			unicodeFunctions.Dispose();
+
+			Assert.False(destroyed, "buffer.UnicodeFunctions getter over-freed a borrowed handle.");
+		}
 	}
 }