Add a simple entrypoint macro

agb-entrypoint/Cargo.lock

@@ -0,0 +1,123 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "agb-entrypoint"
+version = "0.6.0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "rand",
+ "syn",
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agb-entrypoint/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "agb-entrypoint"
+version = "0.6.0"
+authors = ["Gwilym Kuiper <gw@ilym.me>"]
+edition = "2018"
+license = "MPL-2.0"
+description = "Macro for declaring the entrypoint for a game using the agb library"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "1.0.73", features = ["full", "extra-traits"] }
+proc-macro2 = "1.0.27"
+quote = "1.0.9"
+rand = "0.8.4"

agb-entrypoint/src/lib.rs

@@ -0,0 +1,60 @@
+// This macro is based very heavily on the entry one in rust-embedded
+use proc_macro::TokenStream;
+
+use proc_macro2::Span;
+use quote::quote;
+use syn::{ItemFn, ReturnType, Type, Visibility, Ident};
+use rand;
+use rand::Rng;
+
+#[proc_macro_attribute]
+pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
+    let f: ItemFn = syn::parse(input).expect("#[agb::entry] must be applied to a function");
+
+    // Check that the function signature is correct
+    assert!(
+        f.sig.constness.is_none()
+            && f.vis == Visibility::Inherited
+            && f.sig.abi.is_none()
+            && f.sig.inputs.is_empty()
+            && f.sig.generics.params.is_empty()
+            && f.sig.generics.where_clause.is_none()
+            && match f.sig.output {
+                ReturnType::Type(_, ref ty) => match **ty {
+                    Type::Never(_) => true,
+                    _ => false,
+                },
+                _ => false,
+            },
+        "#[agb::entry] must have signature [unsafe] fn () -> !"
+    );
+
+    assert!(args.to_string() == "", "Must pass no args to entrypoint");
+
+    let fn_name = random_ident();
+
+    let attrs = f.attrs;
+    let stmts = f.block.stmts;
+
+    quote!(
+        #[export_name = "main"]
+        #(#attrs)*
+        pub fn #fn_name() -> ! {
+            #(#stmts)*
+        }
+    ).into()
+}
+
+fn random_ident() -> Ident {
+    let mut rng = rand::thread_rng();
+    Ident::new(
+        &(0..16).map(|i| {
+            if i == 0 || rng.gen() {
+                ('a' as u8 + rng.gen::<u8>() % 25) as char
+            } else {
+                ('0' as u8 + rng.gen::<u8>() % 10) as char
+            }
+        }).collect::<String>(),
+        Span::call_site()
+    )
+}