Merge #525

525: Breaking change: add support for required props r=jstarry a=jstarry

#### Problem
Before this change, properties must implement default which means that even if a prop always gets passed in by value to a component, it still needs a default state in props. No longer!

#### Solution
This breaking change allows annotating prop fields as required by using a procedural derive macro.

#### Notes
- If a prop is required, it does not need to implement `Default`.
- If a prop is optional (not required), it must now implement `Default`.
- If a required prop is not passed into a component, your app will not compile.
- Props with lifetime parameters are not supported
- Props with generics are supported!

#### Breaking changes:
1. Properties must now implement the `Properties` trait by adding `#[derive(Properties)]` to their prop structs
2. Non-required prop fields must implement `Default`
3. Callback props created through the closure syntax will no longer return an `Option` type

Depends on #518

Co-authored-by: Justin Starry <[email protected]>

README.md

@@ -204,11 +204,27 @@ Components live in an Angular-like scopes with **parent-to-child** *(properties)
 Properties are also pure Rust types with strict type-checking during the compilation.
 
 ```rust
+// my_button.rs
+
+#[derive(Properties, PartialEq)]
+pub struct Properties {
+    pub hidden: bool,
+    #[props(required)]
+    pub color: Color,
+    #[props(required)]
+    pub onclick: Callback<()>,
+}
+
+```
+
+```rust
+// confirm_dialog.rs
+
 html! {
-    <nav class="menu">
-        <MyButton color=Color::Red />
-        <MyButton onclick=|_| ParentMsg::DoIt />
-    </nav>
+    <div class="confirm-dialog">
+        <MyButton onclick=|_| DialogMsg::Cancel color=Color::Red hidden=true />
+        <MyButton onclick=|_| DialogMsg::Submit color=Color::Blue />
+    </div>
 }
 ```
 

ci/run_tests.sh

@@ -26,9 +26,15 @@ cargo web test --features web_test --target=wasm32-unknown-emscripten
 echo "Testing for wasm32-unknown-unknown..."
 cargo test --target=wasm32-unknown-unknown
 
-echo "Testing macro..."
+echo "Testing html macro..."
 cargo test --test macro_test
 
+echo "Testing derive props macro..."
+cargo test --test derive_props_test
+
+echo "Testing macro docs..."
+(cd crates/macro && cargo test)
+
 check_example() {
     echo "Checking example [$2]"
     pushd $2 > /dev/null

crates/macro/Cargo.toml

@@ -27,3 +27,6 @@ syn = { version = "^0.15.34", features = ["full"] }
 
 [dev-dependencies]
 yew = { path = "../.." }
+
+[build-dependencies]
+autocfg = "0.1.3"

crates/macro/build.rs

@@ -0,0 +1,7 @@
+extern crate autocfg;
+
+pub fn main() {
+    if autocfg::new().probe_rustc_version(1, 36) {
+        println!("cargo:rustc-cfg=has_maybe_uninit");
+    }
+}