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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16 files changed, 6 insertions, 146 deletions

diff --git a/components/layout/flow_ref.rs b/components/layout/flow_ref.rs
index 4657db77040..b9827bb7eb6 100644
--- a/components/layout/flow_ref.rs
+++ b/components/layout/flow_ref.rs
@@ -51,7 +51,7 @@ impl FlowRef {
     #[allow(unsafe_code)]
     #[allow(clippy::should_implement_trait)]
     pub fn deref_mut(this: &mut FlowRef) -> &mut dyn Flow {
-        let ptr: *const dyn Flow = &*this.0;
+        let ptr: *const dyn Flow = Arc::as_ptr(&this.0);
         unsafe { &mut *(ptr as *mut dyn Flow) }
     }
 }
diff --git a/components/layout_2020/flow/float.rs b/components/layout_2020/flow/float.rs
index c2c88128e84..5cf4f87d7d3 100644
--- a/components/layout_2020/flow/float.rs
+++ b/components/layout_2020/flow/float.rs
@@ -7,7 +7,7 @@
 //! See CSS 2.1 § 9.5.1: <https://www.w3.org/TR/CSS2/visuren.html#float-position>
 
 use std::collections::VecDeque;
-use std::fmt::{Debug, Formatter, Result as FmtResult};
+use std::fmt::Debug;
 use std::mem;
 use std::ops::Range;
 
@@ -24,7 +24,7 @@ use crate::context::LayoutContext;
 use crate::dom::NodeExt;
 use crate::dom_traversal::{Contents, NodeAndStyleInfo};
 use crate::formatting_contexts::IndependentFormattingContext;
-use crate::fragment_tree::{BoxFragment, CollapsedBlockMargins, CollapsedMargin, FloatFragment};
+use crate::fragment_tree::{BoxFragment, CollapsedBlockMargins, CollapsedMargin};
 use crate::geom::{LogicalRect, LogicalVec2};
 use crate::positioned::PositioningContext;
 use crate::style_ext::{ComputedValuesExt, DisplayInside, PaddingBorderMargin};
@@ -867,12 +867,6 @@ impl FloatBandLink {
     }
 }
 
-impl Debug for FloatFragment {
-    fn fmt(&self, formatter: &mut Formatter) -> FmtResult {
-        write!(formatter, "FloatFragment")
-    }
-}
-
 impl FloatBox {
     /// Creates a new float box.
     pub fn construct<'dom>(
diff --git a/components/layout_2020/fragment_tree/fragment.rs b/components/layout_2020/fragment_tree/fragment.rs
index 1fdff504072..2aaf4775499 100644
--- a/components/layout_2020/fragment_tree/fragment.rs
+++ b/components/layout_2020/fragment_tree/fragment.rs
@@ -49,11 +49,6 @@ pub(crate) enum Fragment {
 }
 
 #[derive(Serialize)]
-pub(crate) struct FloatFragment {
-    pub box_fragment: BoxFragment,
-}
-
-#[derive(Serialize)]
 pub(crate) struct CollapsedBlockMargins {
     pub collapsed_through: bool,
     pub start: CollapsedMargin,
diff --git a/components/layout_2020/style_ext.rs b/components/layout_2020/style_ext.rs
index 3430d2ffd8b..7674e053ce8 100644
--- a/components/layout_2020/style_ext.rs
+++ b/components/layout_2020/style_ext.rs
@@ -137,8 +137,6 @@ impl PaddingBorderMargin {
 }
 
 pub(crate) trait ComputedValuesExt {
-    fn inline_size_is_length(&self) -> bool;
-    fn inline_box_offsets_are_both_non_auto(&self) -> bool;
     fn box_offsets(
         &self,
         containing_block: &ContainingBlock,
@@ -198,28 +196,6 @@ pub(crate) trait ComputedValuesExt {
 }
 
 impl ComputedValuesExt for ComputedValues {
-    fn inline_size_is_length(&self) -> bool {
-        let position = self.get_position();
-        // FIXME: this is the wrong writing mode but we plan to remove eager content size computation.
-        let size = if self.writing_mode.is_horizontal() {
-            &position.width
-        } else {
-            &position.height
-        };
-        matches!(size, Size::LengthPercentage(lp) if lp.0.to_length().is_some())
-    }
-
-    fn inline_box_offsets_are_both_non_auto(&self) -> bool {
-        let position = self.get_position();
-        // FIXME: this is the wrong writing mode but we plan to remove eager content size computation.
-        let (a, b) = if self.writing_mode.is_horizontal() {
-            (&position.left, &position.right)
-        } else {
-            (&position.top, &position.bottom)
-        };
-        !a.is_auto() && !b.is_auto()
-    }
-
     fn box_offsets(
         &self,
         containing_block: &ContainingBlock,
diff --git a/components/script/dom/bindings/import.rs b/components/script/dom/bindings/import.rs
index 34ac97fd31a..f2c6a5e2b81 100644
--- a/components/script/dom/bindings/import.rs
+++ b/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;
diff --git a/components/script/dom/bindings/root.rs b/components/script/dom/bindings/root.rs
index de325707ee5..f9b302fab5f 100644
--- a/components/script/dom/bindings/root.rs
+++ b/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);
-    }
-}
diff --git a/components/script/dom/htmlimageelement.rs b/components/script/dom/htmlimageelement.rs
index 90a4a981710..d2bb0d57408 100644
--- a/components/script/dom/htmlimageelement.rs
+++ b/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()
     }
diff --git a/components/script/dom/htmlinputelement.rs b/components/script/dom/htmlinputelement.rs
index d077e46aec0..20649baa774 100755
--- a/components/script/dom/htmlinputelement.rs
+++ b/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 {
diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index 2ddd18f9503..b3b7fca3904 100644
--- a/components/script/dom/node.rs
+++ b/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]
diff --git a/components/script/dom/webgl_extensions/wrapper.rs b/components/script/dom/webgl_extensions/wrapper.rs
index 8549f87e766..fc9b6074e8e 100644
--- a/components/script/dom/webgl_extensions/wrapper.rs
+++ b/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
-    }
 }
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index 6f7d53c28bc..cf827726906 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/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),
diff --git a/components/script/euclidext.rs b/components/script/euclidext.rs
deleted file mode 100644
index c6eb72f89fc..00000000000
--- a/components/script/euclidext.rs
+++ /dev/null
@@ -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()
-    }
-}
diff --git a/components/script/lib.rs b/components/script/lib.rs
index 2bfde9ecde0..4d984dd5990 100644
--- a/components/script/lib.rs
+++ b/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)]
diff --git a/ports/servoshell/headed_window.rs b/ports/servoshell/headed_window.rs
index 540bb2a3fce..8a006a7e878 100644
--- a/ports/servoshell/headed_window.rs
+++ b/ports/servoshell/headed_window.rs
@@ -283,10 +283,6 @@ impl WindowPortsMethods for Window {
         std::mem::take(&mut *self.event_queue.borrow_mut())
     }
 
-    fn has_events(&self) -> bool {
-        !self.event_queue.borrow().is_empty()
-    }
-
     fn device_hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
         Scale::new(self.winit_window.scale_factor() as f32)
     }
diff --git a/ports/servoshell/headless_window.rs b/ports/servoshell/headless_window.rs
index 93ff68da0b8..3f7499548cb 100644
--- a/ports/servoshell/headless_window.rs
+++ b/ports/servoshell/headless_window.rs
@@ -69,14 +69,6 @@ impl WindowPortsMethods for Window {
         }
     }
 
-    fn has_events(&self) -> bool {
-        self.event_queue
-            .read()
-            .ok()
-            .map(|queue| !queue.is_empty())
-            .unwrap_or(false)
-    }
-
     fn id(&self) -> winit::window::WindowId {
         unsafe { winit::window::WindowId::dummy() }
     }
diff --git a/ports/servoshell/window_trait.rs b/ports/servoshell/window_trait.rs
index 04d5db60fc8..490ec0415dc 100644
--- a/ports/servoshell/window_trait.rs
+++ b/ports/servoshell/window_trait.rs
@@ -21,7 +21,6 @@ pub const LINE_HEIGHT: f32 = 38.0;
 pub trait WindowPortsMethods: WindowMethods {
     fn get_events(&self) -> Vec<EmbedderEvent>;
     fn id(&self) -> winit::window::WindowId;
-    fn has_events(&self) -> bool;
     fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
         self.device_pixel_ratio_override()
             .unwrap_or_else(|| match opts::get().output_file {