12 files changed, 55 insertions, 16 deletions

diff --git a/embassy-macros/src/macros/main.rs b/embassy-macros/src/macros/main.rs
index 18f7c36c4..6ae77398d 100644
--- a/embassy-macros/src/macros/main.rs
+++ b/embassy-macros/src/macros/main.rs
@@ -1,6 +1,7 @@
 use darling::FromMeta;
 use proc_macro2::TokenStream;
 use quote::quote;
+use syn::{ReturnType, Type};
 
 use crate::util::ctxt::Ctxt;
 
@@ -76,6 +77,26 @@ pub fn run(args: syn::AttributeArgs, f: syn::ItemFn, main: TokenStream) -> Resul
     if !f.sig.generics.params.is_empty() {
         ctxt.error_spanned_by(&f.sig, "main function must not be generic");
     }
+    if !f.sig.generics.where_clause.is_none() {
+        ctxt.error_spanned_by(&f.sig, "main function must not have `where` clauses");
+    }
+    if !f.sig.abi.is_none() {
+        ctxt.error_spanned_by(&f.sig, "main function must not have an ABI qualifier");
+    }
+    if !f.sig.variadic.is_none() {
+        ctxt.error_spanned_by(&f.sig, "main function must not be variadic");
+    }
+    match &f.sig.output {
+        ReturnType::Default => {}
+        ReturnType::Type(_, ty) => match &**ty {
+            Type::Tuple(tuple) if tuple.elems.is_empty() => {}
+            Type::Never(_) => {}
+            _ => ctxt.error_spanned_by(
+                &f.sig,
+                "main function must either not return a value, return `()` or return `!`",
+            ),
+        },
+    }
 
     if fargs.len() != 1 {
         ctxt.error_spanned_by(&f.sig, "main function must have 1 argument: the spawner.");
@@ -84,10 +105,11 @@ pub fn run(args: syn::AttributeArgs, f: syn::ItemFn, main: TokenStream) -> Resul
     ctxt.check()?;
 
     let f_body = f.block;
+    let out = &f.sig.output;
 
     let result = quote! {
         #[::embassy_executor::task()]
-        async fn __embassy_main(#fargs) {
+        async fn __embassy_main(#fargs) #out {
             #f_body
         }
 
diff --git a/embassy-macros/src/macros/task.rs b/embassy-macros/src/macros/task.rs
index 90d2cd893..9f30cf43e 100644
--- a/embassy-macros/src/macros/task.rs
+++ b/embassy-macros/src/macros/task.rs
@@ -1,7 +1,7 @@
 use darling::FromMeta;
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
-use syn::{parse_quote, ItemFn};
+use syn::{parse_quote, ItemFn, ReturnType, Type};
 
 use crate::util::ctxt::Ctxt;
 
@@ -24,6 +24,27 @@ pub fn run(args: syn::AttributeArgs, f: syn::ItemFn) -> Result<TokenStream, Toke
     if !f.sig.generics.params.is_empty() {
         ctxt.error_spanned_by(&f.sig, "task functions must not be generic");
     }
+    if !f.sig.generics.where_clause.is_none() {
+        ctxt.error_spanned_by(&f.sig, "task functions must not have `where` clauses");
+    }
+    if !f.sig.abi.is_none() {
+        ctxt.error_spanned_by(&f.sig, "task functions must not have an ABI qualifier");
+    }
+    if !f.sig.variadic.is_none() {
+        ctxt.error_spanned_by(&f.sig, "task functions must not be variadic");
+    }
+    match &f.sig.output {
+        ReturnType::Default => {}
+        ReturnType::Type(_, ty) => match &**ty {
+            Type::Tuple(tuple) if tuple.elems.is_empty() => {}
+            Type::Never(_) => {}
+            _ => ctxt.error_spanned_by(
+                &f.sig,
+                "task functions must either not return a value, return `()` or return `!`",
+            ),
+        },
+    }
+
     if pool_size < 1 {
         ctxt.error_spanned_by(&f.sig, "pool_size must be 1 or greater");
     }
diff --git a/examples/stm32f4/src/bin/i2c.rs b/examples/stm32f4/src/bin/i2c.rs
index 6e51c211d..f8ae0890c 100644
--- a/examples/stm32f4/src/bin/i2c.rs
+++ b/examples/stm32f4/src/bin/i2c.rs
@@ -15,7 +15,7 @@ const ADDRESS: u8 = 0x5F;
 const WHOAMI: u8 = 0x0F;
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     info!("Hello world!");
     let p = embassy_stm32::init(Default::default());
 
diff --git a/examples/stm32f4/src/bin/sdmmc.rs b/examples/stm32f4/src/bin/sdmmc.rs
index 1d0e60cb8..ebdfdb22d 100644
--- a/examples/stm32f4/src/bin/sdmmc.rs
+++ b/examples/stm32f4/src/bin/sdmmc.rs
@@ -14,7 +14,7 @@ use {defmt_rtt as _, panic_probe as _};
 const ALLOW_WRITES: bool = false;
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     let mut config = Config::default();
     config.rcc.sys_ck = Some(mhz(48));
     config.rcc.pll48 = true;
@@ -75,6 +75,4 @@ async fn main(_spawner: Spawner) -> ! {
 
     sdmmc.read_block(block_idx, &mut block).await.unwrap();
     info!("Read: {=[u8]:X}...{=[u8]:X}", block[..8], block[512 - 8..]);
-
-    loop {}
 }
diff --git a/examples/stm32f7/src/bin/eth.rs b/examples/stm32f7/src/bin/eth.rs
index 571a6c1b9..9febb14e6 100644
--- a/examples/stm32f7/src/bin/eth.rs
+++ b/examples/stm32f7/src/bin/eth.rs
@@ -106,7 +106,7 @@ async fn main(spawner: Spawner) -> ! {
             let r = socket.write_all(&buf).await;
             if let Err(e) = r {
                 info!("write error: {:?}", e);
-                return;
+                continue;
             }
             Timer::after(Duration::from_secs(1)).await;
         }
diff --git a/examples/stm32f7/src/bin/sdmmc.rs b/examples/stm32f7/src/bin/sdmmc.rs
index cf8128e27..c050a4002 100644
--- a/examples/stm32f7/src/bin/sdmmc.rs
+++ b/examples/stm32f7/src/bin/sdmmc.rs
@@ -10,7 +10,7 @@ use embassy_stm32::{interrupt, Config};
 use {defmt_rtt as _, panic_probe as _};
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     let mut config = Config::default();
     config.rcc.sys_ck = Some(mhz(200));
     config.rcc.pll48 = true;
@@ -41,6 +41,4 @@ async fn main(_spawner: Spawner) -> ! {
     let card = unwrap!(sdmmc.card());
 
     info!("Card: {:#?}", Debug2Format(card));
-
-    loop {}
 }
diff --git a/examples/stm32h7/src/bin/eth.rs b/examples/stm32h7/src/bin/eth.rs
index cb245c325..541e49762 100644
--- a/examples/stm32h7/src/bin/eth.rs
+++ b/examples/stm32h7/src/bin/eth.rs
@@ -106,7 +106,7 @@ async fn main(spawner: Spawner) -> ! {
             let r = socket.write_all(b"Hello\n").await;
             if let Err(e) = r {
                 info!("write error: {:?}", e);
-                return;
+                continue;
             }
             Timer::after(Duration::from_secs(1)).await;
         }
diff --git a/examples/stm32h7/src/bin/eth_client.rs b/examples/stm32h7/src/bin/eth_client.rs
index cce85a083..b609fa5df 100644
--- a/examples/stm32h7/src/bin/eth_client.rs
+++ b/examples/stm32h7/src/bin/eth_client.rs
@@ -108,7 +108,7 @@ async fn main(spawner: Spawner) -> ! {
             let r = connection.write_all(b"Hello\n").await;
             if let Err(e) = r {
                 info!("write error: {:?}", e);
-                return;
+                continue;
             }
             Timer::after(Duration::from_secs(1)).await;
         }
diff --git a/examples/stm32h7/src/bin/i2c.rs b/examples/stm32h7/src/bin/i2c.rs
index d44319ae6..78e03f014 100644
--- a/examples/stm32h7/src/bin/i2c.rs
+++ b/examples/stm32h7/src/bin/i2c.rs
@@ -14,7 +14,7 @@ const ADDRESS: u8 = 0x5F;
 const WHOAMI: u8 = 0x0F;
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     info!("Hello world!");
     let p = embassy_stm32::init(Default::default());
 
diff --git a/examples/stm32l4/src/bin/i2c.rs b/examples/stm32l4/src/bin/i2c.rs
index d54c080c7..d40d6803d 100644
--- a/examples/stm32l4/src/bin/i2c.rs
+++ b/examples/stm32l4/src/bin/i2c.rs
@@ -14,7 +14,7 @@ const ADDRESS: u8 = 0x5F;
 const WHOAMI: u8 = 0x0F;
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     let p = embassy_stm32::init(Default::default());
     let irq = interrupt::take!(I2C2_EV);
     let mut i2c = I2c::new(
diff --git a/examples/stm32l4/src/bin/i2c_blocking_async.rs b/examples/stm32l4/src/bin/i2c_blocking_async.rs
index 35a86660d..d868cac01 100644
--- a/examples/stm32l4/src/bin/i2c_blocking_async.rs
+++ b/examples/stm32l4/src/bin/i2c_blocking_async.rs
@@ -16,7 +16,7 @@ const ADDRESS: u8 = 0x5F;
 const WHOAMI: u8 = 0x0F;
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     let p = embassy_stm32::init(Default::default());
     let irq = interrupt::take!(I2C2_EV);
     let i2c = I2c::new(
diff --git a/examples/stm32l4/src/bin/i2c_dma.rs b/examples/stm32l4/src/bin/i2c_dma.rs
index 3ce9398a4..7e62ee637 100644
--- a/examples/stm32l4/src/bin/i2c_dma.rs
+++ b/examples/stm32l4/src/bin/i2c_dma.rs
@@ -13,7 +13,7 @@ const ADDRESS: u8 = 0x5F;
 const WHOAMI: u8 = 0x0F;
 
 #[embassy_executor::main]
-async fn main(_spawner: Spawner) -> ! {
+async fn main(_spawner: Spawner) {
     let p = embassy_stm32::init(Default::default());
     let irq = interrupt::take!(I2C2_EV);
     let mut i2c = I2c::new(