clippy: Fix several warnings in components/script/dom/bindings

[azharcodeit]

Fixed warnings triggered by following checks:

• https://rust-lang.github.io/rust-clippy/master/index.html#from_raw_with_void_ptr
• https://rust-lang.github.io/rust-clippy/master/index.html#zero_ptr
• https://rust-lang.github.io/rust-clippy/master/index.html#useless_transmute
• https://rust-lang.github.io/rust-clippy/master/index.html#non_canonical_clone_impl

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes are part of Fix as many clippy problems as possible #31500

• These changes do not require tests because they do not modify functionality

[eerii]

I think this change was talked about in #31894 (comment) but it wasn't applied in the end. In that discussion, @mrobinson proposed doing this instead to avoid removing the assert:

Suggested change

	*self
	assert_in_layout();
	{ *self }

[azharcodeit]

Thanks, @eerii, very helpful!

I double checked for this particular warning, it still persisted after proposed change.

Since assert_in_layout() needed to be kept, I decided to allow it.

Considering those changes and formatting, I decided to create a new commit rather than committing your suggestion, if you don't mind :)

[eerii]

You're right, sorry for not realizing before! The error still persist because Clone has the assert but Copy doesn't, see #31894 (comment). Maybe the Copy trait should be removed like it says in the comment? Probably a good idea to wait to hear from a maintainer to see what to do, since this is a bit trickier than it seemed.

And no problem at all about the commit!

[mrobinson]

It does sound like the appropriate thing to do here might be to remove the Copy trait implementation...but only if that's possible. Does Servo still compile with that removed?

[azharcodeit]

@mrobinson removing the Copy trait implementation (impl<T> Copy for LayoutDom<'_, T> {}) caused following compile errors:

error[E0204]: the trait `std::marker::Copy` cannot be implemented for this type
  --> components/script/layout_dom/document.rs:34:54
   |
23 |     document: LayoutDom<'dom, Document>,
   |     ----------------------------------- this field does not implement `std::marker::Copy`
...
34 | impl<'dom, LayoutDataType: LayoutDataTrait> Copy for ServoLayoutDocument<'dom, LayoutDataType> {}
   |                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0204]: the trait `std::marker::Copy` cannot be implemented for this type
  --> components/script/layout_dom/element.rs:68:54
   |
55 |     element: LayoutDom<'dom, Element>,
   |     --------------------------------- this field does not implement `std::marker::Copy`
...
68 | impl<'dom, LayoutDataType: LayoutDataTrait> Copy for ServoLayoutElement<'dom, LayoutDataType> {}
   |                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0204]: the trait `std::marker::Copy` cannot be implemented for this type
  --> components/script/layout_dom/node.rs:73:54
   |
51 |     pub(super) node: LayoutDom<'dom, Node>,
   |     -------------------------------------- this field does not implement `std::marker::Copy`
...
73 | impl<'dom, LayoutDataType: LayoutDataTrait> Copy for ServoLayoutNode<'dom, LayoutDataType> {}
   |                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0204]: the trait `std::marker::Copy` cannot be implemented for this type
  --> components/script/layout_dom/shadow_root.rs:30:54
   |
19 |     shadow_root: LayoutDom<'dom, ShadowRoot>,
   |     ---------------------------------------- this field does not implement `std::marker::Copy`
...
30 | impl<'dom, LayoutDataType: LayoutDataTrait> Copy for ServoShadowRoot<'dom, LayoutDataType> {}
   |                                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0204`.
error: could not compile `script` (lib) due to 4 previous errors

[Loirooriol]

What was the warning, why is *const _ better than _?

[azharcodeit]

@Loirooriol, I used *const, because from_raw function receives *const T type as an argument

pub unsafe fn from_raw(ptr: *const T) -> Self {
        unsafe { Arc::from_raw_in(ptr, Global) }
    }

the warning was:

warning: creating a `Arc` from a void raw pointer
   --> components/script/dom/bindings/buffer_source.rs:421:17
    |
421 |         let _ = Arc::from_raw(free_user_data as _);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
help: cast this to a pointer of the appropriate type
   --> components/script/dom/bindings/buffer_source.rs:421:31
    |
421 |         let _ = Arc::from_raw(free_user_data as _);
    |                               ^^^^^^^^^^^^^^^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#from_raw_with_void_ptr
    = note: `#[warn(clippy::from_raw_with_void_ptr)]` on by default