Add old props to fn changed() (#2851)

* Adding old_props to fn changed()

* Change old_props type to &Self::Properties

* Update examples that use fn changed() and want old_props

* Fix tests

* Fix invalid test flags

* cargo fmt

* Oops wrong regex

* Revert change for older version

* Remove unnecessary clone

* Add migration guide

* Oh wow the test was not running xD

examples/boids/src/simulation.rs

@@ -25,7 +25,6 @@ pub struct Props {
 pub struct Simulation {
     boids: Vec<Boid>,
     interval: Interval,
-    settings: Settings,
     generation: usize,
 }
 impl Component for Simulation {
@@ -49,7 +48,6 @@ impl Component for Simulation {
         Self {
             boids,
             interval,
-            settings,
             generation,
         }
     }
@@ -73,10 +71,10 @@ impl Component for Simulation {
         }
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, old_props: &Self::Properties) -> bool {
         let props = ctx.props();
-        let should_reset = self.settings != props.settings || self.generation != props.generation;
-        self.settings = props.settings.clone();
+        let should_reset =
+            old_props.settings != props.settings || self.generation != props.generation;
         self.generation = props.generation;
         if should_reset {
             self.boids.clear();

examples/router/src/components/author_card.rs

@@ -23,7 +23,7 @@ impl Component for AuthorCard {
         }
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
         self.author = Author::generate_from_seed(ctx.props().seed);
         true
     }

examples/router/src/components/post_card.rs

@@ -23,7 +23,7 @@ impl Component for PostCard {
         }
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
         self.post = PostMeta::generate_from_seed(ctx.props().seed);
         true
     }

examples/router/src/pages/author.rs

@@ -21,7 +21,7 @@ impl Component for Author {
         }
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
         self.author = content::Author::generate_from_seed(ctx.props().seed);
         true
     }

examples/router/src/pages/post.rs

@@ -23,7 +23,7 @@ impl Component for Post {
         }
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
         self.post = content::Post::generate_from_seed(ctx.props().seed);
         true
     }

packages/yew-macro/src/function_component.rs

@@ -298,7 +298,7 @@ impl FunctionComponent {
                 }
 
                 #[inline]
-                fn changed(&mut self, _ctx: &::yew::html::Context<Self>) -> ::std::primitive::bool {
+                fn changed(&mut self, _ctx: &::yew::html::Context<Self>, _old_props: &Self::Properties) -> ::std::primitive::bool {
                     true
                 }
 

packages/yew/src/context.rs

@@ -91,7 +91,7 @@ impl<T: Clone + PartialEq + 'static> Component for ContextProvider<T> {
         }
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
         let props = ctx.props();
         let should_render = if self.children == props.children {
             false

packages/yew/src/dom_bundle/bcomp.rs

@@ -314,7 +314,7 @@ mod tests {
             unimplemented!();
         }
 
-        fn changed(&mut self, _ctx: &Context<Self>) -> bool {
+        fn changed(&mut self, _ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
             unimplemented!();
         }
 

packages/yew/src/html/component/lifecycle.rs

@@ -205,8 +205,8 @@ where
         };
 
         if self.context.props != props {
-            self.context.props = props;
-            self.component.changed(&self.context)
+            let old_props = std::mem::replace(&mut self.context.props, props);
+            self.component.changed(&self.context, &*old_props)
         } else {
             false
         }
@@ -791,7 +791,7 @@ mod tests {
             false
         }
 
-        fn changed(&mut self, _ctx: &Context<Self>) -> bool {
+        fn changed(&mut self, _ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
             false
         }
 
@@ -851,7 +851,7 @@ mod tests {
             msg
         }
 
-        fn changed(&mut self, ctx: &Context<Self>) -> bool {
+        fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
             self.lifecycle = Rc::clone(&ctx.props().lifecycle);
             self.lifecycle.borrow_mut().push("change".into());
             false

packages/yew/src/html/component/mod.rs

@@ -100,7 +100,7 @@ pub trait BaseComponent: Sized + 'static {
     fn update(&mut self, ctx: &Context<Self>, msg: Self::Message) -> bool;
 
     /// React to changes of component properties.
-    fn changed(&mut self, ctx: &Context<Self>) -> bool;
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool;
 
     /// Returns a component layout to be rendered.
     fn view(&self, ctx: &Context<Self>) -> HtmlResult;
@@ -154,7 +154,7 @@ pub trait Component: Sized + 'static {
     ///
     /// By default, this function will return true and thus make the component re-render.
     #[allow(unused_variables)]
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, ctx: &Context<Self>, _old_props: &Self::Properties) -> bool {
         true
     }
 
@@ -206,8 +206,8 @@ where
         Component::update(self, ctx, msg)
     }
 
-    fn changed(&mut self, ctx: &Context<Self>) -> bool {
-        Component::changed(self, ctx)
+    fn changed(&mut self, ctx: &Context<Self>, old_props: &Self::Properties) -> bool {
+        Component::changed(self, ctx, old_props)
     }
 
     fn view(&self, ctx: &Context<Self>) -> HtmlResult {
@@ -228,6 +228,7 @@ where
 }
 
 #[cfg(test)]
+#[cfg(any(feature = "ssr", feature = "csr"))]
 mod tests {
     use super::*;
 
@@ -258,6 +259,6 @@ mod tests {
             prepared_state: None,
         };
         assert!(Component::update(&mut comp, &ctx, ()));
-        assert!(Component::changed(&mut comp, &ctx));
+        assert!(Component::changed(&mut comp, &ctx, &Rc::new(())));
     }
 }

packages/yew/src/tests/layout_tests.rs

@@ -22,7 +22,7 @@ impl Component for Comp {
         unimplemented!();
     }
 
-    fn changed(&mut self, _ctx: &Context<Self>) -> bool {
+    fn changed(&mut self, _ctx: &Context<Self>, _: &Self::Properties) -> bool {
         unimplemented!()
     }
 

website/docs/migration-guides/yew/from-0_19_0-to-0_20_0.mdx

@@ -58,3 +58,27 @@ will result in a compile error
 Previously node ref passed to a component was bound to the first element rendered by it.
 If this behavior is still desired, it is recommended to use add a `r#ref` field to the
 component's properties and bind it manually
+
+## `changed` Method on Components
+
+The method `fn changed()` has now a new argument to provide the old properties
+to the function.
+
+The old method's signature was:
+
+```rust ,ignore
+fn changed(&mut self, ctx: &Context<Self>) -> bool
+```
+
+The new method's signature is now:
+
+```rust ,ignore
+fn changed(&mut self, ctx: &Context<Self>, old_props: &Self::Properties) -> bool
+```
+
+This can be adjusted automatically in your code using this bash script (save
+your code before running this!):
+
+```bash
+perl -p -i -e  's/fn changed\(&mut self, (\w+): &Context<Self>\)/fn changed(&mut self, $1: &Context<Self>, _old_props: &Self::Properties)/g' $(find . -name \*.rs)
+```