Add component macro and example

Cargo.toml

@@ -18,7 +18,7 @@ rev = "7a3251b9b89df11af653189f2be04c7304861acf"
 
 [dependencies]
 log = "0.4.11"
-
+crochet-macros = { path = "crochet-macros" }
 async-std = { version = "1.6.4", optional = true }
 futures = "0.3.5"
 

crochet-macros/.gitignore

@@ -0,0 +1,2 @@
+/target
+Cargo.lock

crochet-macros/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "crochet-macros"
+version = "0.1.0"
+authors = ["Maan2003 <manmeetmann2003@gmail.com>"]
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "1.0.41", features = ["full"] }
+quote = "1.0.7"
+proc-macro2 = "1.0.22"

crochet-macros/src/lib.rs

@@ -0,0 +1,51 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, FnArg, Ident, ItemFn, Pat, ReturnType, Type};
+
+#[proc_macro_attribute]
+pub fn component(_args: TokenStream, input: TokenStream) -> TokenStream {
+    let ItemFn { attrs, vis, sig, block } = parse_macro_input!(input as ItemFn);
+    let cx = name_of_cx(&sig.inputs).expect("No argument of type `&mut Cx` found");
+
+    // return_ty is explicit to produce better error for return type mismatch.
+    let return_ty = return_ty_or_unit(&sig.output);
+
+    let tokens = quote! {
+        #[track_caller]
+        #(#attrs)*
+        #vis #sig {
+            ::crochet::Cx::with_loc(
+                #cx, ::std::panic::Location::caller(), move |#cx| #return_ty #block
+            )
+        }
+    };
+    tokens.into()
+}
+
+fn name_of_cx<'a>(args: impl IntoIterator<Item = &'a FnArg>) -> Option<Ident> {
+    for arg in args {
+        if let FnArg::Typed(arg) = arg {
+            if let Type::Reference(ty_ref) = &*arg.ty {
+                if let (Some(_), Type::Path(path)) = (ty_ref.mutability, &*ty_ref.elem) {
+                    if let Some(seg) = path.path.segments.first() {
+                        if seg.ident == "Cx" {
+                            if let Pat::Ident(pat_ident) = &*arg.pat {
+                                return Some(pat_ident.ident.clone());
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+    None
+}
+
+fn return_ty_or_unit(ty: &ReturnType) -> proc_macro2::TokenStream {
+    if ty == &ReturnType::Default {
+        quote! { -> () }
+    } else {
+        quote! { #ty }
+    }
+}

examples/component.rs

@@ -0,0 +1,49 @@
+//! The classic counter example but split up into component
+
+use druid::{AppLauncher, PlatformError, Widget, WindowDesc};
+
+use crochet::{component, AppHolder, Button, Column, Cx, DruidAppData, Label, Row};
+
+fn main() -> Result<(), PlatformError> {
+    let main_window = WindowDesc::new(ui_builder);
+    let data = Default::default();
+    AppLauncher::with_window(main_window)
+        .use_simple_logger()
+        .launch(data)
+}
+
+#[derive(Default)]
+struct MyAppLogic {
+    count1: usize,
+    count2: usize,
+}
+
+impl MyAppLogic {
+    fn run(&mut self, cx: &mut Cx) {
+        Row::new().build(cx, |cx| {
+            counter(&mut self.count1, cx);
+            counter(&mut self.count2, cx);
+        });
+    }
+}
+
+#[component]
+fn counter(count: &mut usize, cx: &mut Cx) {
+    cx.if_changed(*count, |cx| {
+        Column::new().build(cx, |cx| {
+            Label::new(format!("current count: {}", *count)).build(cx);
+            if Button::new("Increment").build(cx) {
+                *count += 1;
+            }
+            if *count > 3 && *count < 6 {
+                Label::new("You did it!").build(cx);
+            }
+        });
+    });
+}
+
+fn ui_builder() -> impl Widget<DruidAppData> {
+    let mut app_logic = MyAppLogic::default();
+
+    AppHolder::new(move |cx| app_logic.run(cx))
+}

src/cx.rs

@@ -77,6 +77,16 @@ impl<'a> Cx<'a> {
         self.mut_cursor.begin_loc(body, loc)
     }
 
+    /// Wrap the callback in begin_loc and end.
+    ///
+    /// This method is used by component attribute macro.
+    pub fn with_loc<T>(&mut self, loc: &'static Location, cb: impl FnOnce(&mut Self) -> T) -> T {
+        self.mut_cursor.begin_loc(Payload::Placeholder, loc);
+        let result = cb(self);
+        self.mut_cursor.end();
+        result
+    }
+
     /// Traverse into a subtree only if the data has changed.
     ///
     /// The supplied callback *must* create only one widget. This is not

src/lib.rs

@@ -25,6 +25,7 @@ mod widget;
 
 pub use any_widget::DruidAppData;
 pub use app_holder::AppHolder;
+pub use crochet_macros::component;
 pub use cx::Cx;
 pub use id::Id;
 pub use list::{List, ListData};