async_main proc macro

Cargo.toml

@@ -1,9 +1,7 @@
-[package]
-name = "messing_with_async"
-version = "0.1.0"
-edition = "2021"
+[workspace]
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
-[dependencies]
-futures = "0.3"
+members = [
+    "bin",
+    "messing_with_async",
+    "async_main"
+]

async_main/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "async_main"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1.0.15"
+syn = { version = "1.0.86", features = [ "full" ] }

async_main/src/lib.rs

@@ -0,0 +1,51 @@
+extern crate proc_macro;
+
+use core::panic;
+
+use proc_macro::TokenStream;
+use syn::ItemFn;
+use quote::quote;
+
+/// Sets up the given `async fn` to be the entry point.
+/// 
+/// ```no_run
+/// # // i see no way to `use messing_with_async::block_on`, so we cant run this test
+/// #[async_main]
+/// async fn async_main() {
+///     println!("Hello, world!");
+/// }
+/// ```
+#[proc_macro_attribute]
+pub fn async_main(_: TokenStream, item: TokenStream) -> TokenStream {
+    let func = syn::parse::<ItemFn>(item).unwrap_or_else(
+        |_| panic!("`async_main` can only be applied to functions!")
+    );
+    
+    if func.sig.asyncness.is_none() {
+        panic!("`async_main` can only be applied to an `async fn`!");
+    }
+
+    if !func.sig.inputs.is_empty() {
+        panic!("`async_main` cannot be applied to functions with arguments!");
+    }
+
+    if !func.sig.generics.params.is_empty() {
+        panic!("`async_main` cannot be applied to generic functions!");
+    }
+
+    if func.sig.unsafety.is_some() {
+        panic!("`async_main` cannot be applied to unsafe functions!");
+    }
+
+    let ident = func.sig.ident.clone();
+
+    quote! {
+        fn main() {
+            use ::messing_with_async::block_on;
+
+            #func
+
+            let _ = block_on(#ident());
+        }
+    }.into()
+}

bin/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "bin"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+messing_with_async = { path = "../messing_with_async", features = [ "proc-macro" ] }

bin/src/main.rs

@@ -1,6 +1,6 @@
 use messing_with_async::{async_main, all, sleep, FutureExt, stream::{from_iter, StreamExt}};
 
-async_main!(async_main);
+#[async_main]
 async fn async_main() {
     println!("hi!");
     sleep!(1000).await;

messing_with_async/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "messing_with_async"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+# futures = "0.3"
+async_main = { path = "../async_main", optional = true }
+
+[features]
+proc-macro = ["async_main"]

messing_with_async/src/lib.rs

@@ -1,21 +1,6 @@
-/// Sets up the given `async fn` to be the entry point.
-/// 
-/// ```
-/// # use messing_with_async::async_main;
-/// async_main!(async_main);
-/// async fn async_main() {
-///     println!("Hello, world!");
-/// }
-/// # main(); // needed cause the main generated by the macro isnt recognized by doctests
-/// ```
-#[macro_export]
-macro_rules! async_main {
-    ($ident:ident) => {
-        fn main() {
-            let _ = $crate::block_on($ident());
-        }
-    };
-}
+#[doc(inline)]
+#[cfg(feature = "proc-macro")]
+pub use async_main::async_main;
 
 use std::{sync::{mpsc::{SyncSender, self, RecvError}, Arc, Mutex}, pin::Pin, future::Future, task::{Context, Poll}};