[macros] allow multiple inherent impl blocks.

All but one blocks must have the key 'secondary'.

Author: 0x53A

godot-ffi/src/plugins.rs

@@ -33,7 +33,7 @@ macro_rules! plugin_registry {
 #[cfg_attr(rustfmt, rustfmt::skip)]
 // ^ skip: paste's [< >] syntax chokes fmt
 //   cfg_attr: workaround for https://github.com/rust-lang/rust/pull/52234#issuecomment-976702997
-macro_rules! plugin_add_inner_wasm {
+macro_rules! plugin_execute_pre_main_wasm {
     ($gensym:ident,) => {
         // Rust presently requires that statics with a custom `#[link_section]` must be a simple
         // list of bytes on the wasm target (with no extra levels of indirection such as references).
@@ -49,14 +49,15 @@ macro_rules! plugin_add_inner_wasm {
     };
 }
 
+/// Executes a block of code before main, by utilising platform specific linker instructions.
 #[doc(hidden)]
 #[macro_export]
 #[allow(clippy::deprecated_cfg_attr)]
 #[cfg_attr(rustfmt, rustfmt::skip)]
 // ^ skip: paste's [< >] syntax chokes fmt
 //   cfg_attr: workaround for https://github.com/rust-lang/rust/pull/52234#issuecomment-976702997
-macro_rules! plugin_add_inner {
-    ($registry:ident; $plugin:expr; $( $path_tt:tt )* ) => {
+macro_rules! plugin_execute_pre_main {
+    ($body:expr) => {
         const _: () = {
             #[allow(non_upper_case_globals)]
             #[used]
@@ -76,20 +77,35 @@ macro_rules! plugin_add_inner {
                 #[cfg_attr(target_os = "android", link_section = ".text.startup")]
                 #[cfg_attr(target_os = "linux", link_section = ".text.startup")]
                 extern "C" fn __inner_init() {
-                	let mut guard = $crate::paste::paste!( $( $path_tt )* [< __godot_rust_plugin_ $registry >] )
-                        .lock()
-                        .unwrap();
-                    guard.push($plugin);
+                    $body
                 }
                 __inner_init
             };
 
             #[cfg(target_family = "wasm")]
-            $crate::gensym! { $crate::plugin_add_inner_wasm!() }
+            $crate::gensym! { $crate::plugin_execute_pre_main_wasm!() }
         };
     };
 }
 
+/// register a plugin by executing code pre-main that adds the plugin to the plugin registry
+#[doc(hidden)]
+#[macro_export]
+#[allow(clippy::deprecated_cfg_attr)]
+#[cfg_attr(rustfmt, rustfmt::skip)]
+// ^ skip: paste's [< >] syntax chokes fmt
+//   cfg_attr: workaround for https://github.com/rust-lang/rust/pull/52234#issuecomment-976702997
+macro_rules! plugin_add_inner {
+    ($registry:ident; $plugin:expr; $( $path_tt:tt )* ) => {
+        $crate::plugin_execute_pre_main!({
+            let mut guard = $crate::paste::paste!( $( $path_tt )* [< __godot_rust_plugin_ $registry >] )
+                .lock()
+                .unwrap();
+            guard.push($plugin);
+        });
+    };
+}
+
 /// Register a plugin to a registry
 #[doc(hidden)]
 #[macro_export]

godot-macros/src/class/data_models/inherent_impl.rs

@@ -64,8 +64,17 @@ struct FuncAttr {
 
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 
+pub struct InherentImplAttr {
+    /// For implementation reasons, there can be a single 'primary' impl block and 0 or more 'secondary' impl blocks.
+    /// For now this is controlled by a key in the the 'godot_api' attribute
+    pub secondary: bool,
+}
+
 /// Codegen for `#[godot_api] impl MyType`
-pub fn transform_inherent_impl(mut impl_block: venial::Impl) -> ParseResult<TokenStream> {
+pub fn transform_inherent_impl(
+    meta: InherentImplAttr,
+    mut impl_block: venial::Impl,
+) -> ParseResult<TokenStream> {
     let class_name = util::validate_impl(&impl_block, None, "godot_api")?;
     let class_name_obj = util::class_name_obj(&class_name);
     let prv = quote! { ::godot::private };
@@ -93,38 +102,96 @@ pub fn transform_inherent_impl(mut impl_block: venial::Impl) -> ParseResult<Toke
 
     let constant_registration = make_constant_registration(consts, &class_name, &class_name_obj)?;
 
-    let result = quote! {
-        #impl_block
+    let method_storage_name = format_ident!("__registration_methods_{class_name}");
+    let constants_storage_name = format_ident!("__registration_constants_{class_name}");
+
+    let fill_storage = quote! {
+        ::godot::sys::plugin_execute_pre_main!({
+            #method_storage_name.lock().unwrap().push(||{
 
-        impl ::godot::obj::cap::ImplementsGodotApi for #class_name {
-            fn __register_methods() {
                 #( #method_registrations )*
                 #( #signal_registrations )*
-            }
 
-            fn __register_constants() {
-                #constant_registration
-            }
+            });
+            #constants_storage_name.lock().unwrap().push(||{
 
-            #rpc_registrations
-        }
+                #constant_registration
 
-        ::godot::sys::plugin_add!(__GODOT_PLUGIN_REGISTRY in #prv; #prv::ClassPlugin {
-            class_name: #class_name_obj,
-            item: #prv::PluginItem::InherentImpl(#prv::InherentImpl {
-                register_methods_constants_fn: #prv::ErasedRegisterFn {
-                    raw: #prv::callbacks::register_user_methods_constants::<#class_name>,
-                },
-                register_rpcs_fn: Some(#prv::ErasedRegisterRpcsFn {
-                    raw: #prv::callbacks::register_user_rpcs::<#class_name>,
-                }),
-                #docs
-            }),
-            init_level: <#class_name as ::godot::obj::GodotClass>::INIT_LEVEL,
+            });
         });
     };
 
-    Ok(result)
+    if !meta.secondary {
+        // We are the primary `impl` block.
+
+        let storage = quote! {
+            #[allow(non_upper_case_globals)]
+            #[doc(hidden)]
+            static #method_storage_name: std::sync::Mutex<Vec<fn()>> = std::sync::Mutex::new(Vec::new());
+
+            #[allow(non_upper_case_globals)]
+            #[doc(hidden)]
+            static #constants_storage_name: std::sync::Mutex<Vec<fn()>> = std::sync::Mutex::new(Vec::new());
+        };
+
+        let trait_impl = quote! {
+            impl ::godot::obj::cap::ImplementsGodotApi for #class_name {
+                fn __register_methods() {
+                    let guard = #method_storage_name.lock().unwrap();
+                    for f in guard.iter() {
+                        f();
+                    }
+                }
+
+                fn __register_constants() {
+                    let guard = #constants_storage_name.lock().unwrap();
+                    for f in guard.iter() {
+                        f();
+                    }
+                }
+
+                #rpc_registrations
+            }
+        };
+
+        let class_registration = quote! {
+
+            ::godot::sys::plugin_add!(__GODOT_PLUGIN_REGISTRY in #prv; #prv::ClassPlugin {
+                class_name: #class_name_obj,
+                item: #prv::PluginItem::InherentImpl(#prv::InherentImpl {
+                    register_methods_constants_fn: #prv::ErasedRegisterFn {
+                        raw: #prv::callbacks::register_user_methods_constants::<#class_name>,
+                    },
+                    register_rpcs_fn: Some(#prv::ErasedRegisterRpcsFn {
+                        raw: #prv::callbacks::register_user_rpcs::<#class_name>,
+                    }),
+                    #docs
+                }),
+                init_level: <#class_name as ::godot::obj::GodotClass>::INIT_LEVEL,
+            });
+
+        };
+
+        let result = quote! {
+            #impl_block
+            #storage
+            #trait_impl
+            #fill_storage
+            #class_registration
+        };
+
+        Ok(result)
+    } else {
+        // We are in a secondary `impl` block, so most of the work has already been done
+        // and we just need to add our registration functions in the storage defined by the primary `impl` block.
+
+        let result = quote! {
+            #impl_block
+            #fill_storage
+        };
+
+        Ok(result)
+    }
 }
 
 fn process_godot_fns(

godot-macros/src/class/godot_api.rs

@@ -8,10 +8,24 @@
 use proc_macro2::TokenStream;
 
 use crate::class::{transform_inherent_impl, transform_trait_impl};
-use crate::util::bail;
+use crate::util::{bail, venial_parse_meta, KvParser};
 use crate::ParseResult;
 
-pub fn attribute_godot_api(input_decl: venial::Item) -> ParseResult<TokenStream> {
+use quote::{format_ident, quote};
+
+fn parse_inherent_impl_attr(meta: TokenStream) -> Result<super::InherentImplAttr, venial::Error> {
+    let item = venial_parse_meta(&meta, format_ident!("godot_api"), &quote! { fn func(); })?;
+    let mut attr = KvParser::parse_required(item.attributes(), "godot_api", &meta)?;
+    let secondary = attr.handle_alone("secondary")?;
+    attr.finish()?;
+
+    Ok(super::InherentImplAttr { secondary })
+}
+
+pub fn attribute_godot_api(
+    meta: TokenStream,
+    input_decl: venial::Item,
+) -> ParseResult<TokenStream> {
     let decl = match input_decl {
         venial::Item::Impl(decl) => decl,
         _ => bail!(
@@ -32,8 +46,19 @@ pub fn attribute_godot_api(input_decl: venial::Item) -> ParseResult<TokenStream>
     };
 
     if decl.trait_ty.is_some() {
+        // 'meta' contains the parameters to the macro, that is, for `#[godot_api(a, b, x=y)]`, anything inside the braces.
+        // We currently don't accept any parameters for a trait `impl`, so show an error to the user if they added something there.
+        if meta.to_string() != "" {
+            return bail!(
+                meta,
+                "#[godot_api] on a trait implementation currently does not support any parameters"
+            );
+        }
         transform_trait_impl(decl)
     } else {
-        transform_inherent_impl(decl)
+        match parse_inherent_impl_attr(meta) {
+            Ok(meta) => transform_inherent_impl(meta, decl),
+            Err(err) => Err(err),
+        }
     }
 }

godot-macros/src/lib.rs

@@ -21,7 +21,6 @@ mod util;
 
 use proc_macro::TokenStream;
 use proc_macro2::TokenStream as TokenStream2;
-use quote::quote;
 
 use crate::util::{bail, ident, KvParser};
 
@@ -520,6 +519,7 @@ pub fn derive_godot_class(input: TokenStream) -> TokenStream {
 ///   - [Virtual methods](#virtual-methods)
 ///   - [RPC attributes](#rpc-attributes)
 /// - [Constants and signals](#signals)
+/// - [Multiple inherent `impl` blocks](#multiple-inherent-impl-blocks)
 ///
 /// # Constructors
 ///
@@ -749,9 +749,35 @@ pub fn derive_godot_class(input: TokenStream) -> TokenStream {
 /// # Constants and signals
 ///
 /// Please refer to [the book](https://godot-rust.github.io/book/register/constants.html).
+///
+/// # Multiple inherent `impl` blocks
+///
+/// Just like with regular structs, you can have multiple inherent `impl` blocks. This can be useful for code organization or when you want to generate code from a proc-macro.
+/// For implementation reasons, all but one `impl` blocks must have the key `secondary`. There is no difference between implementing all functions in one block or splitting them up between multiple blocks.
+/// ```no_run
+/// # use godot::prelude::*;
+/// # #[derive(GodotClass)]
+/// # #[class(init)]
+/// # struct MyStruct {
+/// #     base: Base<RefCounted>,
+/// # }
+/// #[godot_api]
+/// impl MyStruct {
+///     #[func]
+///     pub fn one(&self) { }
+/// }
+///
+/// #[godot_api(secondary)]
+/// impl MyStruct {
+///     #[func]
+///     pub fn two(&self) { }
+/// }
+/// ```
 #[proc_macro_attribute]
-pub fn godot_api(_meta: TokenStream, input: TokenStream) -> TokenStream {
-    translate(input, class::attribute_godot_api)
+pub fn godot_api(meta: TokenStream, input: TokenStream) -> TokenStream {
+    translate(input, |body| {
+        class::attribute_godot_api(TokenStream2::from(meta), body)
+    })
 }
 
 /// Derive macro for [`GodotConvert`](../builtin/meta/trait.GodotConvert.html) on structs.
@@ -961,13 +987,7 @@ where
     let input2 = TokenStream2::from(input);
     let meta2 = TokenStream2::from(meta);
 
-    // Hack because venial doesn't support direct meta parsing yet
-    let input = quote! {
-        #[#self_name(#meta2)]
-        #input2
-    };
-
-    let result2 = venial::parse_item(input)
+    let result2 = util::venial_parse_meta(&meta2, self_name, &input2)
         .and_then(transform)
         .unwrap_or_else(|e| e.to_compile_error());
 

godot-macros/src/util/mod.rs

@@ -288,3 +288,21 @@ pub fn safe_ident(s: &str) -> Ident {
          _ => ident(s)
     }
 }
+
+// ----------------------------------------------------------------------------------------------------------------------------------------------
+
+/// Parses a `meta` TokenStream, that is, the tokens in parameter position of a proc-macro (between the braces).
+/// Because venial can't actually parse a meta item directly, this is done by reconstructing the full macro attribute on top of some content and then parsing *that*.
+pub fn venial_parse_meta(
+    meta: &TokenStream,
+    self_name: Ident,
+    content: &TokenStream,
+) -> Result<venial::Item, venial::Error> {
+    // Hack because venial doesn't support direct meta parsing yet
+    let input = quote! {
+        #[#self_name(#meta)]
+        #content
+    };
+
+    venial::parse_item(input)
+}

itest/rust/src/register_tests/mod.rs

@@ -10,6 +10,7 @@ mod conversion_test;
 mod derive_godotconvert_test;
 mod func_test;
 mod gdscript_ffi_test;
+mod multiple_impl_blocks_test;
 mod naming_tests;
 mod option_ffi_test;
 mod register_docs_test;