Add cleanup code to web backend, mostly web-sys (#1715)

* web-sys: Impl. event listeners removal for canvas

* web-sys: Impl. media query listeners cleanup

* web: Emit WindowEvent::Destroyed after Window is dropped

* web-sys: Fix unload event closure being dropped early

* web: Impl. cleanup on ControlFlow::Exit

- Drops the Runner, which causes the event handler closure to be
  dropped.
- (web-sys only:) Remove event listeners from DOM.

* web: Do not remove canvas from DOM when dropping Window

The canvas was inserted by the user, so it should be up to the user
whether the canvas should be removed.

* Update changelog

src/platform_impl/web/window.rs

@@ -8,15 +8,17 @@ use raw_window_handle::web::WebHandle;
 
 use super::{backend, monitor, EventLoopWindowTarget};
 
-use std::cell::RefCell;
+use std::cell::{Ref, RefCell};
 use std::collections::vec_deque::IntoIter as VecDequeIter;
 use std::collections::VecDeque;
+use std::rc::Rc;
 
 pub struct Window {
-    canvas: backend::Canvas,
+    canvas: Rc<RefCell<backend::Canvas>>,
     previous_pointer: RefCell<&'static str>,
     id: Id,
     register_redraw_request: Box<dyn Fn()>,
+    destroy_fn: Option<Box<dyn FnOnce()>>,
 }
 
 impl Window {
@@ -29,17 +31,22 @@ impl Window {
 
         let id = target.generate_id();
 
-        let mut canvas = backend::Canvas::create(platform_attr)?;
+        let canvas = backend::Canvas::create(platform_attr)?;
+        let mut canvas = Rc::new(RefCell::new(canvas));
 
         let register_redraw_request = Box::new(move || runner.request_redraw(RootWI(id)));
 
         target.register(&mut canvas, id);
 
+        let runner = target.runner.clone();
+        let destroy_fn = Box::new(move || runner.notify_destroy_window(RootWI(id)));
+
         let window = Window {
             canvas,
             previous_pointer: RefCell::new("auto"),
             id,
             register_redraw_request,
+            destroy_fn: Some(destroy_fn),
         };
 
         window.set_inner_size(attr.inner_size.unwrap_or(Size::Logical(LogicalSize {
@@ -54,12 +61,12 @@ impl Window {
         Ok(window)
     }
 
-    pub fn canvas(&self) -> &backend::Canvas {
-        &self.canvas
+    pub fn canvas<'a>(&'a self) -> Ref<'a, backend::Canvas> {
+        self.canvas.borrow()
     }
 
     pub fn set_title(&self, title: &str) {
-        self.canvas.set_attribute("alt", title);
+        self.canvas.borrow().set_attribute("alt", title);
     }
 
     pub fn set_visible(&self, _visible: bool) {
@@ -71,7 +78,11 @@ impl Window {
     }
 
     pub fn outer_position(&self) -> Result<PhysicalPosition<i32>, NotSupportedError> {
-        Ok(self.canvas.position().to_physical(self.scale_factor()))
+        Ok(self
+            .canvas
+            .borrow()
+            .position()
+            .to_physical(self.scale_factor()))
     }
 
     pub fn inner_position(&self) -> Result<PhysicalPosition<i32>, NotSupportedError> {
@@ -82,14 +93,15 @@ impl Window {
     pub fn set_outer_position(&self, position: Position) {
         let position = position.to_logical::<f64>(self.scale_factor());
 
-        self.canvas.set_attribute("position", "fixed");
-        self.canvas.set_attribute("left", &position.x.to_string());
-        self.canvas.set_attribute("top", &position.y.to_string());
+        let canvas = self.canvas.borrow();
+        canvas.set_attribute("position", "fixed");
+        canvas.set_attribute("left", &position.x.to_string());
+        canvas.set_attribute("top", &position.y.to_string());
     }
 
     #[inline]
     pub fn inner_size(&self) -> PhysicalSize<u32> {
-        self.canvas.size()
+        self.canvas.borrow().size()
     }
 
     #[inline]
@@ -100,7 +112,7 @@ impl Window {
 
     #[inline]
     pub fn set_inner_size(&self, size: Size) {
-        backend::set_canvas_size(self.canvas.raw(), size);
+        backend::set_canvas_size(self.canvas.borrow().raw(), size);
     }
 
     #[inline]
@@ -165,7 +177,7 @@ impl Window {
             CursorIcon::RowResize => "row-resize",
         };
         *self.previous_pointer.borrow_mut() = text;
-        backend::set_canvas_style_property(self.canvas.raw(), "cursor", text);
+        backend::set_canvas_style_property(self.canvas.borrow().raw(), "cursor", text);
     }
 
     #[inline]
@@ -181,9 +193,10 @@ impl Window {
     #[inline]
     pub fn set_cursor_visible(&self, visible: bool) {
         if !visible {
-            self.canvas.set_attribute("cursor", "none");
+            self.canvas.borrow().set_attribute("cursor", "none");
         } else {
             self.canvas
+                .borrow()
                 .set_attribute("cursor", *self.previous_pointer.borrow());
         }
     }
@@ -200,7 +213,7 @@ impl Window {
 
     #[inline]
     pub fn fullscreen(&self) -> Option<Fullscreen> {
-        if self.canvas.is_fullscreen() {
+        if self.canvas.borrow().is_fullscreen() {
             Some(Fullscreen::Borderless(self.current_monitor_inner()))
         } else {
             None
@@ -210,8 +223,8 @@ impl Window {
     #[inline]
     pub fn set_fullscreen(&self, monitor: Option<Fullscreen>) {
         if monitor.is_some() {
-            self.canvas.request_fullscreen();
-        } else if self.canvas.is_fullscreen() {
+            self.canvas.borrow().request_fullscreen();
+        } else if self.canvas.borrow().is_fullscreen() {
             backend::exit_fullscreen();
         }
     }
@@ -277,6 +290,14 @@ impl Window {
     }
 }
 
+impl Drop for Window {
+    fn drop(&mut self) {
+        if let Some(destroy_fn) = self.destroy_fn.take() {
+            destroy_fn();
+        }
+    }
+}
+
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Id(pub(crate) u32);