Improve #[entry] macro

nds-proc-macros/Cargo.toml

@@ -11,4 +11,4 @@ proc-macro = true
 
 [dependencies]
 syn = { version = "2.0", features = ["full"]}
-quote = "1.0"
+quote = "1.0"

nds-proc-macros/src/lib.rs

@@ -1,21 +1,109 @@
 use proc_macro::TokenStream;
 use quote::quote;
-use syn::{parse_macro_input, ItemFn, Meta, MetaNameValue, ReturnType, Type};
+use syn::{
+    parse_macro_input, spanned::Spanned, Attribute, FnArg, ItemFn, Meta, MetaNameValue, PatType,
+    ReturnType, Type, Visibility,
+};
 
-/// Use it to mark the ROM entry point.
+/// Allows only `fn(Hw) -> !`
+fn check_sig(signature: &syn::Signature) -> Result<(), syn::Error> {
+    let span = signature.span();
+    if let ReturnType::Type(_, ref t) = signature.output {
+        match **t {
+            Type::Never(_) => {}
+            Type::Infer(_) => {
+                return Err(syn::Error::new(
+                    span,
+                    "Add `-> !`. To avoid ambiguity, please specify the return type as `!`",
+                ));
+            }
+            _ => {
+                return Err(syn::Error::new(
+                    span,
+                    "Change to `-> !`. The entry point must be diverging. E.g. `fn() -> !`",
+                ));
+            }
+        }
+    } else {
+        return Err(syn::Error::new(
+            span,
+            "Add `-> !`. To avoid ambiguity, please specify the return type as `!`.",
+        ));
+    }
+
+    if signature.inputs.len() != 1 {
+        return Err(syn::Error::new(
+            span,
+            "Incorrect arguments. The entry point must take exactly one argument of type `Hw`",
+        ));
+    } else {
+        let arg = signature.inputs.first().unwrap();
+        if let FnArg::Typed(PatType { ty, .. }) = arg {
+            if let Type::Path(ref path) = **ty {
+                if path.path.segments.last().unwrap().ident != "Hw" {
+                    return Err(syn::Error::new(
+                        arg.span(),
+                        "Change type. The entry point must take exactly one argument of type `Hw`",
+                    ));
+                }
+            } else {
+                return Err(syn::Error::new(
+                    arg.span(),
+                    "Change type. The entry point must take exactly one argument of type `Hw`",
+                ));
+            }
+        } else {
+            return Err(syn::Error::new(
+                arg.span(),
+                "Change type. The entry point can not be a method.",
+            ));
+        }
+    }
+
+    Ok(())
+}
+
+/// Allow only `pub` visibility
+fn check_vis(vis: &Visibility) -> Result<(), syn::Error> {
+    if let Visibility::Public(..) = vis {
+        Ok(())
+    } else {
+        Err(syn::Error::new(
+            vis.span(),
+            "Add `pub`. The entry point must be public and without restriction.",
+        ))
+    }
+}
+
+/// Forbids `#[no_mangle]` and `#[link_name = ...]`
+fn check_attr(attrs: &Vec<Attribute>) -> Result<(), syn::Error> {
+    for attr in attrs {
+        match &attr.meta {
+            Meta::NameValue(MetaNameValue { path, .. }) if path.is_ident("export_name") => {
+                return Err(syn::Error::new(path.span(), "Remove this `link_name`. The entry point requires a specific symbol name that it's set by the `entry` attribute."))
+            }
+            Meta::Path(path) if path.is_ident("no_mangle") => {
+                return Err(syn::Error::new(path.span(), "Remove this `no_mangle`. The entry point requires a specific symbol name that it's set by the `entry` attribute."))
+            }
+            _ => {}
+        }
+    }
+
+    Ok(())
+}
+
+/// Use it to mark the entry point of your program.
 ///
-/// Example:
+/// # Example:
 /// ```rust,no_run
 /// #![no_main]
 ///
 /// #[macro_use]
-/// extern crate nds:
+/// extern crate nds_proc_macros:
 ///
 /// #[entry]
-/// fn main(mut hw: nds::Hw) -> ! {
-///     loop {
-///         nds::interrupts::swi_wait_for_v_blank();
-///     }
+/// pub fn main(_: nds::Hw) -> ! {
+///     loop { }
 /// }
 /// ```
 #[proc_macro_attribute]
@@ -24,37 +112,24 @@ pub fn entry(_: TokenStream, input: TokenStream) -> TokenStream {
 
     // Check the signature is correct:
     // - Must be `fn() -> !`
-    // - Must be `pub`
     // - Must have 1 argument
-    // - Must not have `link_name` or `no_mangle` attributes
+    // - Must be `pub`
+    // - Must not have `export_name` or `no_mangle` attributes
 
-    if let ReturnType::Type(_, t) = &input.sig.output {
-        assert!(
-            matches!(**t, Type::Never(_)),
-            "The function must return `!`"
-        );
-    } else {
-        panic!("The function must return `!`");
+    if let Err(e) = check_sig(&input.sig) {
+        return e.to_compile_error().into();
     }
 
-    assert!(matches!(input.vis, syn::Visibility::Public(_)));
+    if let Err(e) = check_vis(&input.vis) {
+        return e.to_compile_error().into();
+    }
 
-    assert_eq!(input.sig.inputs.len(), 1);
-
-    for attr in &input.attrs {
-        match &attr.meta {
-            Meta::NameValue(MetaNameValue { path, .. }) if path.is_ident("link_name") => {
-                panic!("The `link_name` attribute is not allowed here");
-            }
-            Meta::Path(path) if path.is_ident("no_mangle") => {
-                panic!("The `no_mangle` attribute is not allowed here");
-            }
-            _ => {}
-        }
+    if let Err(e) = check_attr(&input.attrs) {
+        return e.to_compile_error().into();
     }
 
     quote! {
-        #[link_name = "rust_main"]
+        #[export_name = "__rust_user_main"]
         #input
     }
     .into()

nds-rt/src/lib.rs

@@ -2,14 +2,19 @@
 
 use nds_rs::Hw;
 
+/// Entry point called from the C runtime
+///
+/// # Safety
+///
+/// Must never be called by user code.
 #[no_mangle]
-pub extern "C" fn main() -> ! {
+pub unsafe extern "C" fn main() -> ! {
     extern "Rust" {
-        #[link_name = "rust_main"]
+        #[link_name = "__rust_user_main"]
         fn main(hw: Hw) -> !;
     }
 
-    let peripherals = Hw::take().unwrap();
+    let peripherals = Hw::take().unwrap_unchecked();
     unsafe {
         main(peripherals);
     }