`block.zig`: `descCopyHelper` parameters are swapped.

[ulzu]

zig-objc/src/block.zig

Lines 123 to 135 in f356ed0

	fn descCopyHelper(src: *anyopaque, dst: *anyopaque) callconv(.c) void {
	const real_src: *Context = @ptrCast(@alignCast(src));
	const real_dst: *Context = @ptrCast(@alignCast(dst));
	inline for (captures_info.fields) |field| {
	if (field.type == objc.c.id) {
	_Block_object_assign(
	@ptrCast(&@field(real_dst, field.name)),
	@field(real_src, field.name),
	.object,
	);
	}
	}
	}

this function must correspond to the signature of

zig-objc/src/block.zig

Line 260 in f356ed0

copy_helper: *const fn (dst: *anyopaque, src: *anyopaque) callconv(.c) void,

(as per void (*copy_helper)(void *dst, void *src)

Its signature is instead fn (src: *anyopaque, dst: *anyopaque) callconv(.c) void – the parameters are swapped.

I could not find the definition of _Block_object_assign, but in its uses, the first argument does come from dst, the second comes from src, so the call in descCopyHelper seems to be correct.

[mitchellh]

Thanks, an obviously easy fix but we should guard this with a unit test to verify the bug and prevent regressions.