WIP

.gitignore

@@ -10,4 +10,4 @@ config.status
 *.o
 *.swp
 **Cargo.lock
-gtk/tests/*
+# gtk/tests/*

gtk/tests/builder_handlers.rs

@@ -0,0 +1,145 @@
+#[derive(glib::Downgrade)]
+pub struct MyWidget(gtk::Widget);
+
+#[gtk3_macros::builder_handlers]
+impl MyWidget {
+    fn handler0(&self) {}
+
+    fn handler1(&self, _p: u32) {}
+
+    fn handler2(&self, _x: f64, _y: f64) {}
+
+    fn handler3(&self, x: f64, y: f64) -> f64 {
+        x + y
+    }
+
+    // fn handler4(&self, x: f64, y: f64) -> Option<f64> {
+    //     if x >= 0.0 && y >= 0.0 {
+    //         Some(x + y)
+    //     } else {
+    //         None
+    //     }
+    // }
+}
+
+// Generated code
+/*
+impl MyWidget {
+    #[allow(clippy)]
+    fn get_handler(
+        &self,
+        signal: &str,
+    ) -> Option<Box<dyn Fn(&[glib::Value]) -> Option<glib::Value> + 'static>> {
+        match signal {
+            "handler0" => Some({
+                #[allow(unused_variables)]
+                Box::new(
+                    glib::clone!(@weak self as this => move |values: &[glib::Value]| {
+                        this.handler0();
+                        None
+                    }),
+                )
+            }),
+            "handler1" => Some({
+                #[allow(unused_variables)]
+                Box::new(
+                    glib::clone!(@weak self as this => move |values: &[glib::Value]| {
+                        this.handler1(
+                            match values[0usize].get_some() {
+                                Ok(value) => value,
+                                Err(error) => {
+                                    glib::g_critical!(
+                                        "builder handler",
+                                        "Handler {} expects an argument of type {} but received `{:?}`: {}.",
+                                        "handler1", stringify! (u32),
+                                        values[0usize], error
+                                    );
+                                    return None;
+                                },
+                            }
+                        );
+                        None
+                    }),
+                )
+            }),
+            "handler2" => Some({
+                #[allow(unused_variables)]
+                Box::new(
+                    glib::clone!(@weak self as this => move |values: &[glib::Value]| {
+                        this.handler2(
+                            match values[0usize].get_some() {
+                                Ok(value) => value,
+                                Err(error) => {
+                                    glib::g_critical!(
+                                        "builder handler",
+                                        "Handler {} expects an argument of type {} but received `{:?}`: {}.",
+                                        "handler2",
+                                        stringify!(f64),
+                                        values[0usize],
+                                        error
+                                    );
+                                    return None;
+                                },
+                            },
+                            match values[1usize].get_some() {
+                                Ok(value) => value,
+                                Err(error) => {
+                                    glib::g_critical!(
+                                        "builder handler",
+                                        "Handler {} expects an argument of type {} but received `{:?}`: {}.",
+                                        "handler2",
+                                        stringify!(f64),
+                                        values[1usize],
+                                        error
+                                    );
+                                    return None;
+                                },
+                            }
+                        );
+                        None
+                    }),
+                )
+            }),
+            "handler3" => Some({
+                #[allow(unused_variables)]
+                Box::new(
+                    glib::clone!(@weak self as this => move |values: &[glib::Value]| {
+                        let result = this.handler3(
+                            match values[0usize].get_some() {
+                                Ok(value) => value,
+                                Err(error) => {
+                                    glib::g_critical!(
+                                        "builder handler",
+                                        "Handler {} expects an argument of type {} but received `{:?}`: {}.",
+                                        "handler3",
+                                        stringify!(f64),
+                                        values[0usize],
+                                        error
+                                    );
+                                    return None;
+                                },
+                            },
+                            match values[1usize].get_some() {
+                                Ok(value) => value,
+                                Err(error) => {
+                                    glib::g_critical!(
+                                        "builder handler",
+                                        "Handler {} expects an argument of type {} but received `{:?}`: {}.",
+                                        "handler3",
+                                        stringify!(f64),
+                                        values[1usize],
+                                        error
+                                    );
+                                    return None;
+                                },
+                            }
+                        );
+                        Some(glib::value::ToValue::to_value(&result))
+                    }),
+                )
+            }),
+            _ => None,
+        }
+    }
+}
+*/

gtk3-macros/Cargo.toml

@@ -25,3 +25,4 @@ proc-macro2 = "1.0"
 quote = "1.0"
 syn = { version = "1.0", default-features = false, features = ["full"] }
 proc-macro-crate = "1.0"
+darling = "0.12"

gtk3-macros/src/builder_handlers.rs

@@ -0,0 +1,199 @@
+// Take a look at the license at the top of the repository in the LICENSE file.
+
+use darling::FromMeta;
+use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
+use quote::{format_ident, quote, quote_spanned};
+use syn::{
+    parse, spanned::Spanned, Attribute, Error, FnArg, ImplItem, ImplItemMethod, ItemImpl, Meta,
+    MetaList, NestedMeta, PatType, Signature, Type,
+};
+
+#[derive(Debug, Default, FromMeta)]
+#[darling(default)]
+pub struct HandlersImplAttributes {
+    get_handler_fn: Option<String>,
+}
+
+#[derive(Debug, Default, FromMeta)]
+#[darling(default)]
+struct HandlerAttributes {
+    name: Option<String>,
+}
+
+#[derive(Debug)]
+struct HandlerInfo {
+    name: String,
+    sig: Signature,
+}
+
+fn generate_handler(info: &HandlerInfo) -> Result<TokenStream2, Error> {
+    let handler_name = &info.name;
+    let arguments: Vec<TokenStream2> = info.sig.inputs
+        .iter()
+        .skip(1)
+        .enumerate()
+        .map(|(index, arg)| {
+            let arg_type = argument_type(arg)?;
+            Ok(quote_spanned! { arg.span() =>
+                match values[#index].get() {
+                    Ok(value) => value,
+                    Err(error) => {
+                        glib::g_critical!("builder handler", "Handler {} expects an argument of type {} but received `{:?}`: {}.", #handler_name, stringify!(#arg_type), values[#index], error);
+                        return None;
+                    },
+                }
+            })
+        })
+        .collect::<Result<_, Error>>()?;
+
+    let signal = &info.name;
+    let method = &info.sig.ident;
+    let is_unit = matches!(info.sig.output, syn::ReturnType::Default);
+    let handler = if is_unit {
+        quote_spanned! { info.sig.span() =>
+            #signal => Some({
+                Box::new(glib::clone!(@weak self as this => @default-return None, move |values: &[glib::Value]| {
+                    this.#method(#(#arguments),*);
+                    None
+                }))
+            }),
+        }
+    } else {
+        quote_spanned! { info.sig.span() =>
+            #signal => Some({
+                Box::new(glib::clone!(@weak self as this => @default-return None, move |values: &[glib::Value]| {
+                    let result = this.#method(#(#arguments),*);
+                    Some(glib::value::ToValue::to_value(&result))
+                }))
+            }),
+        }
+    };
+    Ok(handler)
+}
+
+fn combine_errors(error_acc: &mut Option<Error>, error: Error) {
+    match error_acc {
+        Some(ref mut error_acc) => {
+            error_acc.combine(error);
+        }
+        None => {
+            error_acc.replace(error);
+        }
+    }
+}
+
+fn attributes_to_metas(attributes: Vec<Attribute>) -> Result<Vec<NestedMeta>, Error> {
+    let mut metas = Vec::new();
+    let mut error = None;
+    for attr in attributes {
+        let meta = attr.parse_meta()?;
+        match meta {
+            Meta::List(MetaList { nested, .. }) => metas.extend(nested),
+            _ => combine_errors(&mut error, Error::new(attr.span(), "Unexpected attribute")),
+        }
+    }
+    if let Some(error) = error {
+        Err(error)
+    } else {
+        Ok(metas)
+    }
+}
+
+fn is_assoc(sig: &Signature) -> bool {
+    sig.inputs
+        .first()
+        .map_or(false, |arg| matches!(arg, FnArg::Receiver(..)))
+}
+
+fn argument_type(arg: &FnArg) -> Result<&Type, Error> {
+    match arg {
+        FnArg::Typed(PatType { ty, .. }) => Ok(&*ty),
+        _ => Err(Error::new(
+            arg.span(),
+            "Cannot extract type of an argument.",
+        )),
+    }
+}
+
+fn generate_connect_method(
+    attrs: &HandlersImplAttributes,
+    actions: &[TokenStream2],
+) -> ImplItemMethod {
+    let get_handler_fn = format_ident!(
+        "{}",
+        attrs.get_handler_fn.as_deref().unwrap_or("get_handler")
+    );
+    let builder_connect_method = quote! {
+        #[allow(clippy)]
+        #[allow(unused_variables, unused_braces)]
+        fn #get_handler_fn(&self, builder: &gtk::Builder, signal: &str) -> Option<Box<dyn Fn(&[glib::Value]) -> Option<glib::Value> + 'static>> {
+            match signal {
+                #(
+                    #actions
+                )*
+                _ => None,
+            }
+        }
+    };
+    parse(builder_connect_method.into()).unwrap()
+}
+
+pub fn handlers(
+    attrs: HandlersImplAttributes,
+    mut input: ItemImpl,
+) -> Result<TokenStream, TokenStream> {
+    let mut handlers: Vec<HandlerInfo> = Vec::new();
+    for item in input.items.iter_mut() {
+        if let ImplItem::Method(method) = item {
+            if !is_assoc(&method.sig) {
+                return Err(Error::new(
+                    method.sig.span(),
+                    "Unsupported signature of method. Only associated methods are supported.",
+                )
+                .to_compile_error()
+                .into());
+            }
+
+            let attributes =
+                extract_from_vec(&mut method.attrs, |attr| attr.path.is_ident("handler"));
+            let metas = attributes_to_metas(attributes).map_err(|err| err.to_compile_error())?;
+            let attrs = HandlerAttributes::from_list(&metas)
+                .map_err(|err| TokenStream::from(err.write_errors()))?;
+
+            let info = HandlerInfo {
+                name: attrs.name.unwrap_or_else(|| method.sig.ident.to_string()),
+                sig: method.sig.clone(),
+            };
+            handlers.push(info);
+        }
+    }
+
+    let connects: Vec<TokenStream2> = handlers
+        .iter()
+        .map(generate_handler)
+        .collect::<Result<_, _>>()
+        .map_err(|err| err.to_compile_error())?;
+
+    let connect_method = generate_connect_method(&attrs, &connects);
+    input.items.push(ImplItem::Method(connect_method));
+
+    let s = quote!(#input);
+    // println!("{}", s);
+    Ok(s.into())
+}
+
+// TODO: Replace this by Vec::drain_filter as soon as it is stabilized.
+fn extract_from_vec<T>(vec: &mut Vec<T>, predicate: impl Fn(&T) -> bool) -> Vec<T> {
+    let mut i = 0;
+    let mut result: Vec<T> = Vec::new();
+    while i != vec.len() {
+        if (predicate)(&vec[i]) {
+            let item = vec.remove(i);
+            result.push(item);
+        } else {
+            i += 1;
+        }
+    }
+    result
+}

gtk3-macros/src/lib.rs

@@ -1,12 +1,15 @@
 // Take a look at the license at the top of the repository in the LICENSE file.
 
 mod attribute_parser;
+mod builder_handlers;
 mod composite_template_derive;
 mod util;
 
+use darling::FromMeta;
 use proc_macro::TokenStream;
 use proc_macro_error::proc_macro_error;
-use syn::{parse_macro_input, DeriveInput};
+use syn::DeriveInput;
+use syn::{parse_macro_input, AttributeArgs, ItemImpl};
 
 /// Derive macro for using a composite template in a widget.
 ///
@@ -61,3 +64,16 @@ pub fn composite_template_derive(input: TokenStream) -> TokenStream {
     let gen = composite_template_derive::impl_composite_template(&input);
     gen.into()
 }
+
+#[proc_macro_attribute]
+pub fn builder_handlers(args: TokenStream, item: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(item as ItemImpl);
+    let attribute_args = parse_macro_input!(args as AttributeArgs);
+    let attrs = match builder_handlers::HandlersImplAttributes::from_list(&attribute_args) {
+        Ok(v) => v,
+        Err(e) => {
+            return TokenStream::from(e.write_errors());
+        }
+    };
+    builder_handlers::handlers(attrs, input).unwrap_or_else(|err| err)
+}