Parse variant

Author: tmandry

trait_transformer/examples/variant.rs

@@ -0,0 +1,19 @@
+// Copyright (c) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use trait_transformer::variant;
+
+#[variant(SendIntFactory: Send)]
+trait IntFactory {
+    async fn make(&self) -> i32;
+    // ..or..
+    fn stream(&self) -> impl Iterator<Item = i32>;
+    fn call(&self) -> u32;
+}
+
+fn main() {}

trait_transformer/src/lib.rs

@@ -7,6 +7,7 @@
 // except according to those terms.
 
 mod transformer;
+mod variant;
 
 #[proc_macro_attribute]
 pub fn trait_transformer(
@@ -15,3 +16,11 @@ pub fn trait_transformer(
 ) -> proc_macro::TokenStream {
     transformer::trait_transformer(attr, item)
 }
+
+#[proc_macro_attribute]
+pub fn variant(
+    attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    variant::variant(attr, item)
+}

trait_transformer/src/variant.rs

@@ -0,0 +1,57 @@
+// Copyright (c) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{
+    parse::{Parse, ParseStream},
+    parse_macro_input,
+    punctuated::Punctuated,
+    token::Comma,
+    Ident, ItemTrait, Path, Result, ReturnType, Token, TraitBound, TraitBoundModifier, TraitItem,
+    Type,
+};
+
+struct Attrs {
+    variant: Variant,
+}
+
+impl Parse for Attrs {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(Self {
+            variant: Variant::parse(input)?,
+        })
+    }
+}
+
+struct Variant {
+    name: Ident,
+    #[allow(unused)]
+    colon: Token![:],
+    supertrait: Path,
+}
+
+impl Parse for Variant {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(Self {
+            name: input.parse()?,
+            colon: input.parse()?,
+            supertrait: input.parse()?,
+        })
+    }
+}
+
+pub fn variant(
+    attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let attrs = parse_macro_input!(attr as Attrs);
+    let item = parse_macro_input!(item as ItemTrait);
+
+    quote! {}.into()
+}

trait_transformer_test/src/main.rs

@@ -6,7 +6,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(async_fn_in_trait, return_position_impl_trait_in_trait, return_type_notation)]
+#![feature(
+    async_fn_in_trait,
+    return_position_impl_trait_in_trait,
+    return_type_notation
+)]
 
 use trait_transformer::trait_transformer;
 
@@ -19,9 +23,9 @@ trait IntFactory {
 }
 
 fn thing(factory: impl SendIntFactory) {
-    tokio::task::spawn(|| async {
+    tokio::task::spawn(async {
         factory.make().await;
-    })
+    });
 }
 
 struct MyFactory;