executor: add executor selection to #[embassy_executor::main]

2 files changed, 67 insertions, 5 deletions

diff --git a/embassy-executor-macros/src/lib.rs b/embassy-executor-macros/src/lib.rs
index 5f2182f10..8e737db6a 100644
--- a/embassy-executor-macros/src/lib.rs
+++ b/embassy-executor-macros/src/lib.rs
@@ -173,3 +173,27 @@ pub fn main_std(args: TokenStream, item: TokenStream) -> TokenStream {
 pub fn main_wasm(args: TokenStream, item: TokenStream) -> TokenStream {
     main::run(args.into(), item.into(), &main::ARCH_WASM).into()
 }
+
+/// Creates a new `executor` instance and declares an application entry point for an unspecified architecture, spawning the corresponding function body as an async task.
+///
+/// The following restrictions apply:
+///
+/// * The function must accept exactly 1 parameter, an `embassy_executor::Spawner` handle that it can use to spawn additional tasks.
+/// * The function must be declared `async`.
+/// * The function must not use generics.
+/// * Only a single `main` task may be declared.
+///
+/// A user-defined entry macro and executor type must be provided via the `entry` and `executor` arguments of the `main` macro.
+///
+/// ## Examples
+/// Spawning a task:
+/// ``` rust
+/// #[embassy_executor::main(entry = "your_hal::entry", executor = "your_hal::Executor")]
+/// async fn main(_s: embassy_executor::Spawner) {
+///     // Function body
+/// }
+/// ```
+#[proc_macro_attribute]
+pub fn main_unspecified(args: TokenStream, item: TokenStream) -> TokenStream {
+    main::run(args.into(), item.into(), &main::ARCH_UNSPECIFIED).into()
+}
diff --git a/embassy-executor-macros/src/macros/main.rs b/embassy-executor-macros/src/macros/main.rs
index 24f61f30b..95722b19b 100644
--- a/embassy-executor-macros/src/macros/main.rs
+++ b/embassy-executor-macros/src/macros/main.rs
@@ -16,42 +16,57 @@ enum Flavor {
 pub(crate) struct Arch {
     default_entry: Option<&'static str>,
     flavor: Flavor,
+    executor_required: bool,
 }
 
 pub static ARCH_AVR: Arch = Arch {
     default_entry: Some("avr_device::entry"),
     flavor: Flavor::Standard,
+    executor_required: false,
 };
 
 pub static ARCH_RISCV: Arch = Arch {
     default_entry: Some("riscv_rt::entry"),
     flavor: Flavor::Standard,
+    executor_required: false,
 };
 
 pub static ARCH_CORTEX_M: Arch = Arch {
     default_entry: Some("cortex_m_rt::entry"),
     flavor: Flavor::Standard,
+    executor_required: false,
 };
 
 pub static ARCH_SPIN: Arch = Arch {
     default_entry: None,
     flavor: Flavor::Standard,
+    executor_required: false,
 };
 
 pub static ARCH_STD: Arch = Arch {
     default_entry: None,
     flavor: Flavor::Standard,
+    executor_required: false,
 };
 
 pub static ARCH_WASM: Arch = Arch {
     default_entry: Some("wasm_bindgen::prelude::wasm_bindgen(start)"),
     flavor: Flavor::Wasm,
+    executor_required: false,
+};
+
+pub static ARCH_UNSPECIFIED: Arch = Arch {
+    default_entry: None,
+    flavor: Flavor::Standard,
+    executor_required: true,
 };
 
 #[derive(Debug, FromMeta, Default)]
 struct Args {
     #[darling(default)]
     entry: Option<String>,
+    #[darling(default)]
+    executor: Option<String>,
 }
 
 pub fn run(args: TokenStream, item: TokenStream, arch: &Arch) -> TokenStream {
@@ -112,9 +127,10 @@ pub fn run(args: TokenStream, item: TokenStream, arch: &Arch) -> TokenStream {
         error(&mut errors, &f.sig, "main function must have 1 argument: the spawner.");
     }
 
-    let entry = match args.entry.as_deref().or(arch.default_entry) {
-        None => TokenStream::new(),
-        Some(x) => match TokenStream::from_str(x) {
+    let entry = match (args.entry.as_deref(), arch.default_entry.as_deref()) {
+        (None, None) => TokenStream::new(),
+        (Some(x), _) | (None, Some(x)) if x == "" => TokenStream::new(),
+        (Some(x), _) | (None, Some(x)) => match TokenStream::from_str(x) {
             Ok(x) => quote!(#[#x]),
             Err(e) => {
                 error(&mut errors, &f.sig, e);
@@ -123,6 +139,28 @@ pub fn run(args: TokenStream, item: TokenStream, arch: &Arch) -> TokenStream {
         },
     };
 
+    let executor = match (args.executor.as_deref(), arch.executor_required) {
+        (None, true) => {
+            error(
+                &mut errors,
+                &f.sig,
+                "\
+No architecture selected for embassy-executor. Make sure you've enabled one of the `arch-*` features in your Cargo.toml.
+
+Alternatively, if you would like to use a custom executor implementation, specify it with the `executor` argument.
+For example: `#[embassy_executor::main(entry = ..., executor = \"some_crate::Executor\")]",
+            );
+            ""
+        }
+        (Some(x), _) => x,
+        (None, _) => "::embassy_executor::Executor",
+    };
+
+    let executor = TokenStream::from_str(executor).unwrap_or_else(|e| {
+        error(&mut errors, &f.sig, e);
+        TokenStream::new()
+    });
+
     let f_body = f.body;
     let out = &f.sig.output;
 
@@ -134,7 +172,7 @@ pub fn run(args: TokenStream, item: TokenStream, arch: &Arch) -> TokenStream {
                     ::core::mem::transmute(t)
                 }
 
-                let mut executor = ::embassy_executor::Executor::new();
+                let mut executor = #executor::new();
                 let executor = unsafe { __make_static(&mut executor) };
                 executor.run(|spawner| {
                     spawner.must_spawn(__embassy_main(spawner));
@@ -144,7 +182,7 @@ pub fn run(args: TokenStream, item: TokenStream, arch: &Arch) -> TokenStream {
         Flavor::Wasm => (
             quote!(Result<(), wasm_bindgen::JsValue>),
             quote! {
-                let executor = ::std::boxed::Box::leak(::std::boxed::Box::new(::embassy_executor::Executor::new()));
+                let executor = ::std::boxed::Box::leak(::std::boxed::Box::new(#executor::new()));
 
                 executor.start(|spawner| {
                     spawner.must_spawn(__embassy_main(spawner));