Address issues uncovered by rust-1.78 beta (#32130)

This change makes changes to allow Servo to compile with the 1.78
version of Rust:

 - Dead code is removd (Rust seems to have gotten better at detecting
   it).
 - The `FlowRef` `DerefMut` is updated according to @SimonSapin's advice
   [^1].
 - The `imports.rs` now explicitly silences warnings about unused
   imports.

[^1]: https://github.com/servo/servo/issues/6503#issuecomment-2066088179

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---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they should not change
behavior.

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components/script/dom/bindings/import.rs

@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+#[allow(unused_imports)]
 pub mod base {
     pub use std::ptr;
     pub use std::rc::Rc;
@@ -41,6 +42,7 @@ pub mod base {
     pub use crate::script_runtime::JSContext as SafeJSContext;
 }
 
+#[allow(unused_imports)]
 pub mod module {
     pub use std::cmp;
     pub use std::ffi::CString;

components/script/dom/bindings/root.rs

@@ -31,8 +31,7 @@ use std::marker::PhantomData;
 use std::ops::Deref;
 use std::{mem, ptr};
 
-use js::jsapi::{Heap, JSObject, JSTracer};
-use js::rust::GCMethods;
+use js::jsapi::{JSObject, JSTracer};
 use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use script_layout_interface::TrustedNodeAddress;
 use style::thread_state;
@@ -772,32 +771,3 @@ where
         &*(slice as *const [Dom<T>] as *const [LayoutDom<T>])
     }
 }
-
-/// Helper trait for safer manipulations of `Option<Heap<T>>` values.
-pub trait OptionalHeapSetter {
-    type Value;
-    /// Update this optional heap value with a new value.
-    fn set(&mut self, v: Option<Self::Value>);
-}
-
-impl<T: GCMethods + Copy> OptionalHeapSetter for Option<Heap<T>>
-where
-    Heap<T>: Default,
-{
-    type Value = T;
-    fn set(&mut self, v: Option<T>) {
-        let v = match v {
-            None => {
-                *self = None;
-                return;
-            },
-            Some(v) => v,
-        };
-
-        if self.is_none() {
-            *self = Some(Heap::default());
-        }
-
-        self.as_ref().unwrap().set(v);
-    }
-}

components/script/dom/htmlimageelement.rs

@@ -1376,7 +1376,6 @@ impl MicrotaskRunnable for ImageElementMicrotask {
 }
 
 pub trait LayoutHTMLImageElementHelpers {
-    fn image(self) -> Option<Arc<Image>>;
     fn image_url(self) -> Option<ServoUrl>;
     fn image_density(self) -> Option<f64>;
     fn image_data(self) -> (Option<Arc<Image>>, Option<ImageMetadata>);
@@ -1392,10 +1391,6 @@ impl<'dom> LayoutDom<'dom, HTMLImageElement> {
 }
 
 impl LayoutHTMLImageElementHelpers for LayoutDom<'_, HTMLImageElement> {
-    fn image(self) -> Option<Arc<Image>> {
-        self.current_request().image.clone()
-    }
-
     fn image_url(self) -> Option<ServoUrl> {
         self.current_request().parsed_url.clone()
     }

components/script/dom/htmlinputelement.rs

@@ -974,8 +974,6 @@ pub trait LayoutHTMLInputElementHelpers<'dom> {
     fn value_for_layout(self) -> Cow<'dom, str>;
     fn size_for_layout(self) -> u32;
     fn selection_for_layout(self) -> Option<Range<usize>>;
-    fn checked_state_for_layout(self) -> bool;
-    fn indeterminate_state_for_layout(self) -> bool;
 }
 
 #[allow(unsafe_code)]
@@ -1077,18 +1075,6 @@ impl<'dom> LayoutHTMLInputElementHelpers<'dom> for LayoutDom<'dom, HTMLInputElem
             _ => None,
         }
     }
-
-    fn checked_state_for_layout(self) -> bool {
-        self.upcast::<Element>()
-            .get_state_for_layout()
-            .contains(ElementState::CHECKED)
-    }
-
-    fn indeterminate_state_for_layout(self) -> bool {
-        self.upcast::<Element>()
-            .get_state_for_layout()
-            .contains(ElementState::INDETERMINATE)
-    }
 }
 
 impl TextControlElement for HTMLInputElement {

components/script/dom/node.rs

@@ -1329,8 +1329,6 @@ pub trait LayoutNodeHelpers<'dom> {
     unsafe fn get_flag(self, flag: NodeFlags) -> bool;
     unsafe fn set_flag(self, flag: NodeFlags, value: bool);
 
-    fn children_count(self) -> u32;
-
     fn style_data(self) -> Option<&'dom StyleData>;
     fn layout_data(self) -> Option<&'dom GenericLayoutData>;
 
@@ -1473,11 +1471,6 @@ impl<'dom> LayoutNodeHelpers<'dom> for LayoutDom<'dom, Node> {
         (this).flags.set(flags);
     }
 
-    #[inline]
-    fn children_count(self) -> u32 {
-        self.unsafe_get().children_count.get()
-    }
-
     // FIXME(nox): How we handle style and layout data needs to be completely
     // revisited so we can do that more cleanly and safely in layout 2020.
     #[inline]

components/script/dom/webgl_extensions/wrapper.rs

@@ -2,7 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use std::any::Any;
 use std::ptr::NonNull;
 
 use js::jsapi::JSObject;
@@ -27,7 +26,6 @@ pub trait WebGLExtensionWrapper: JSTraceable + MallocSizeOf {
     fn is_enabled(&self) -> bool;
     fn enable(&self, ext: &WebGLExtensions);
     fn name(&self) -> &'static str;
-    fn as_any(&self) -> &dyn Any;
 }
 
 #[crown::unrooted_must_root_lint::must_root]
@@ -86,8 +84,4 @@ where
     fn name(&self) -> &'static str {
         T::name()
     }
-
-    fn as_any(&self) -> &dyn Any {
-        self
-    }
 }

components/script/dom/webglrenderingcontext.rs

@@ -4960,16 +4960,6 @@ impl WebGLMessageSender {
     }
 }
 
-pub trait Size2DExt {
-    fn to_u64(&self) -> Size2D<u64>;
-}
-
-impl Size2DExt for Size2D<u32> {
-    fn to_u64(&self) -> Size2D<u64> {
-        Size2D::new(self.width as u64, self.height as u64)
-    }
-}
-
 fn array_buffer_type_to_sized_type(type_: Type) -> Option<SizedDataType> {
     match type_ {
         Type::Uint8 | Type::Uint8Clamped => Some(SizedDataType::Uint8),

components/script/euclidext.rs

@@ -1,21 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-
-use euclid::default::Rect;
-
-pub trait RectExt {
-    fn to_u64(&self) -> Rect<u64>;
-}
-
-impl RectExt for Rect<f64> {
-    fn to_u64(&self) -> Rect<u64> {
-        self.cast()
-    }
-}
-
-impl RectExt for Rect<u32> {
-    fn to_u64(&self) -> Rect<u64> {
-        self.cast()
-    }
-}

components/script/lib.rs

@@ -42,7 +42,6 @@ pub mod document_loader;
 mod dom;
 #[warn(deprecated)]
 mod canvas_state;
-mod euclidext;
 #[warn(deprecated)]
 pub mod fetch;
 #[warn(deprecated)]