Set the placeholder canvas element of offscreenCanvas to a weak reference in transferControlToOffscreen() (#37764)

Set the placeholder canvas element of offscreenCanvas to a weak
reference in transferControlToOffscreen()

Testing: I do not understand how to test it, suggestions appreciated 
Fixes: https://github.com/servo/servo/issues/35626

---------

Signed-off-by: Rodion Borovyk <rodion.borovyk@gmail.com>

components/script/canvas_context.rs

@@ -7,7 +7,7 @@
 use euclid::default::Size2D;
 use layout_api::HTMLCanvasData;
 use pixels::Snapshot;
-use script_bindings::root::Dom;
+use script_bindings::root::{Dom, DomRoot};
 use webrender_api::ImageKey;
 
 use crate::dom::bindings::codegen::UnionTypes::HTMLCanvasElementOrOffscreenCanvas;
@@ -81,7 +81,7 @@ pub(crate) trait CanvasContext {
 
 pub(crate) trait CanvasHelpers {
     fn size(&self) -> Size2D<u32>;
-    fn canvas(&self) -> Option<&HTMLCanvasElement>;
+    fn canvas(&self) -> Option<DomRoot<HTMLCanvasElement>>;
 }
 
 impl CanvasHelpers for HTMLCanvasElementOrOffscreenCanvas {
@@ -94,9 +94,9 @@ impl CanvasHelpers for HTMLCanvasElementOrOffscreenCanvas {
         }
     }
 
-    fn canvas(&self) -> Option<&HTMLCanvasElement> {
+    fn canvas(&self) -> Option<DomRoot<HTMLCanvasElement>> {
         match self {
-            HTMLCanvasElementOrOffscreenCanvas::HTMLCanvasElement(canvas) => Some(canvas),
+            HTMLCanvasElementOrOffscreenCanvas::HTMLCanvasElement(canvas) => Some(canvas.clone()),
             HTMLCanvasElementOrOffscreenCanvas::OffscreenCanvas(canvas) => canvas.placeholder(),
         }
     }

components/script/dom/canvasrenderingcontext2d.rs

@@ -348,15 +348,25 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-filltext
     fn FillText(&self, text: DOMString, x: f64, y: f64, max_width: Option<f64>, can_gc: CanGc) {
-        self.canvas_state
-            .fill_text(self.canvas.canvas(), text, x, y, max_width, can_gc);
+        self.canvas_state.fill_text(
+            self.canvas.canvas().as_deref(),
+            text,
+            x,
+            y,
+            max_width,
+            can_gc,
+        );
         self.mark_as_dirty();
     }
 
     // https://html.spec.whatwg.org/multipage/#textmetrics
     fn MeasureText(&self, text: DOMString, can_gc: CanGc) -> DomRoot<TextMetrics> {
-        self.canvas_state
-            .measure_text(&self.global(), self.canvas.canvas(), text, can_gc)
+        self.canvas_state.measure_text(
+            &self.global(),
+            self.canvas.canvas().as_deref(),
+            text,
+            can_gc,
+        )
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-font
@@ -367,7 +377,7 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-font
     fn SetFont(&self, value: DOMString, can_gc: CanGc) {
         self.canvas_state
-            .set_font(self.canvas.canvas(), value, can_gc)
+            .set_font(self.canvas.canvas().as_deref(), value, can_gc)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-textalign
@@ -403,7 +413,7 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage(&self, image: CanvasImageSource, dx: f64, dy: f64) -> ErrorResult {
         self.canvas_state
-            .draw_image(self.canvas.canvas(), image, dx, dy)
+            .draw_image(self.canvas.canvas().as_deref(), image, dx, dy)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
@@ -416,7 +426,7 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
         dh: f64,
     ) -> ErrorResult {
         self.canvas_state
-            .draw_image_(self.canvas.canvas(), image, dx, dy, dw, dh)
+            .draw_image_(self.canvas.canvas().as_deref(), image, dx, dy, dw, dh)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
@@ -432,8 +442,18 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
         dw: f64,
         dh: f64,
     ) -> ErrorResult {
-        self.canvas_state
-            .draw_image__(self.canvas.canvas(), image, sx, sy, sw, sh, dx, dy, dw, dh)
+        self.canvas_state.draw_image__(
+            self.canvas.canvas().as_deref(),
+            image,
+            sx,
+            sy,
+            sw,
+            sh,
+            dx,
+            dy,
+            dw,
+            dh,
+        )
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-moveto
@@ -506,7 +526,7 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
     fn SetStrokeStyle(&self, value: StringOrCanvasGradientOrCanvasPattern, can_gc: CanGc) {
         self.canvas_state
-            .set_stroke_style(self.canvas.canvas(), value, can_gc)
+            .set_stroke_style(self.canvas.canvas().as_deref(), value, can_gc)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
@@ -517,7 +537,7 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-strokestyle
     fn SetFillStyle(&self, value: StringOrCanvasGradientOrCanvasPattern, can_gc: CanGc) {
         self.canvas_state
-            .set_fill_style(self.canvas.canvas(), value, can_gc)
+            .set_fill_style(self.canvas.canvas().as_deref(), value, can_gc)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-createimagedata
@@ -717,6 +737,6 @@ impl CanvasRenderingContext2DMethods<crate::DomTypeHolder> for CanvasRenderingCo
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-shadowcolor
     fn SetShadowColor(&self, value: DOMString, can_gc: CanGc) {
         self.canvas_state
-            .set_shadow_color(self.canvas.canvas(), value, can_gc)
+            .set_shadow_color(self.canvas.canvas().as_deref(), value, can_gc)
     }
 }

components/script/dom/htmlcanvaselement.rs

@@ -23,6 +23,7 @@ use js::error::throw_type_error;
 use js::rust::{HandleObject, HandleValue};
 use layout_api::HTMLCanvasData;
 use pixels::{Snapshot, SnapshotAlphaMode, SnapshotPixelFormat};
+use script_bindings::weakref::WeakRef;
 use servo_media::streams::MediaStreamType;
 use servo_media::streams::registry::MediaStreamId;
 use style::attr::AttrValue;
@@ -675,7 +676,7 @@ impl HTMLCanvasElementMethods<crate::DomTypeHolder> for HTMLCanvasElement {
             None,
             self.Width().into(),
             self.Height().into(),
-            Some(&Dom::from_ref(self)),
+            Some(WeakRef::new(self)),
             can_gc,
         );
 

components/script/dom/offscreencanvas.rs

@@ -8,6 +8,7 @@ use dom_struct::dom_struct;
 use euclid::default::Size2D;
 use js::rust::{HandleObject, HandleValue};
 use pixels::Snapshot;
+use script_bindings::weakref::WeakRef;
 
 use crate::canvas_context::{CanvasContext, OffscreenRenderingContext};
 use crate::dom::bindings::cell::{DomRefCell, Ref};
@@ -38,21 +39,21 @@ pub(crate) struct OffscreenCanvas {
     context: DomRefCell<Option<OffscreenRenderingContext>>,
 
     /// <https://html.spec.whatwg.org/multipage/#offscreencanvas-placeholder>
-    placeholder: Option<Dom<HTMLCanvasElement>>,
+    placeholder: Option<WeakRef<HTMLCanvasElement>>,
 }
 
 impl OffscreenCanvas {
     pub(crate) fn new_inherited(
         width: u64,
         height: u64,
-        placeholder: Option<&HTMLCanvasElement>,
+        placeholder: Option<WeakRef<HTMLCanvasElement>>,
     ) -> OffscreenCanvas {
         OffscreenCanvas {
             eventtarget: EventTarget::new_inherited(),
             width: Cell::new(width),
             height: Cell::new(height),
             context: DomRefCell::new(None),
-            placeholder: placeholder.map(Dom::from_ref),
+            placeholder,
         }
     }
 
@@ -61,7 +62,7 @@ impl OffscreenCanvas {
         proto: Option<HandleObject>,
         width: u64,
         height: u64,
-        placeholder: Option<&HTMLCanvasElement>,
+        placeholder: Option<WeakRef<HTMLCanvasElement>>,
         can_gc: CanGc,
     ) -> DomRoot<OffscreenCanvas> {
         reflect_dom_object_with_proto(
@@ -126,8 +127,10 @@ impl OffscreenCanvas {
         Some(context)
     }
 
-    pub(crate) fn placeholder(&self) -> Option<&HTMLCanvasElement> {
-        self.placeholder.as_deref()
+    pub(crate) fn placeholder(&self) -> Option<DomRoot<HTMLCanvasElement>> {
+        self.placeholder
+            .as_ref()
+            .and_then(|placeholder| placeholder.root())
     }
 }
 
@@ -181,8 +184,8 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
             canvas_context.resize();
         }
 
-        if let Some(canvas) = &self.placeholder {
-            canvas.set_natural_width(value as _, can_gc);
+        if let Some(canvas) = self.placeholder() {
+            canvas.set_natural_width(value as _, can_gc)
         }
     }
 
@@ -199,8 +202,8 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
             canvas_context.resize();
         }
 
-        if let Some(canvas) = &self.placeholder {
-            canvas.set_natural_height(value as _, can_gc);
+        if let Some(canvas) = self.placeholder() {
+            canvas.set_natural_height(value as _, can_gc)
         }
     }
 }

components/script_bindings/codegen/Bindings.conf

@@ -345,6 +345,7 @@ DOMInterfaces = {
 
 'HTMLCanvasElement': {
     'canGc': ['CaptureStream', 'GetContext', 'SetHeight', 'SetWidth', 'TransferControlToOffscreen'],
+    'weakReferenceable': True,
 },
 
 'HTMLDataListElement': {