Allow functions with return type '-> ()' to be bound

examples/example-deno-runtime/tests.ts

@@ -23,6 +23,7 @@ import type {
   SerdeVariantRenaming,
   StructWithGenerics,
 } from "../example-protocol/bindings/ts-runtime/types.ts";
+import {Result} from "../example-protocol/bindings/ts-runtime/types.ts";
 
 let voidFunctionCalled = false;
 
@@ -203,6 +204,15 @@ const imports: Imports = {
     voidFunctionCalled = true;
   },
 
+  importVoidFunctionEmptyResult: (): Result<void, number> => {
+    return {
+      Ok: undefined
+    };
+  },
+
+  importVoidFunctionEmptyReturn: (): void => {
+  },
+
   log: (message: string): void => {
     // The plugin is not expected to log anything unless it panics:
     fail("Plugin panic: " + message);

examples/example-protocol/src/assets/rust_plugin_test/expected_import.rs

@@ -84,6 +84,12 @@ pub fn import_timestamp(arg: MyDateTime) -> MyDateTime;
 #[fp_bindgen_support::fp_import_signature]
 pub fn import_void_function();
 
+#[fp_bindgen_support::fp_import_signature]
+pub fn import_void_function_empty_result() -> Result<(), u32>;
+
+#[fp_bindgen_support::fp_import_signature]
+pub fn import_void_function_empty_return();
+
 /// Logs a message to the (development) console.
 #[fp_bindgen_support::fp_import_signature]
 pub fn log(message: String);

examples/example-protocol/src/assets/rust_wasmer_runtime_test/expected_bindings.rs

@@ -795,6 +795,8 @@ fn create_import_object(store: &Store, env: &RuntimeInstanceData) -> ImportObjec
            "__fp_gen_import_string" => Function :: new_native_with_env (store , env . clone () , _import_string) ,
            "__fp_gen_import_timestamp" => Function :: new_native_with_env (store , env . clone () , _import_timestamp) ,
            "__fp_gen_import_void_function" => Function :: new_native_with_env (store , env . clone () , _import_void_function) ,
+           "__fp_gen_import_void_function_empty_result" => Function :: new_native_with_env (store , env . clone () , _import_void_function_empty_result) ,
+           "__fp_gen_import_void_function_empty_return" => Function :: new_native_with_env (store , env . clone () , _import_void_function_empty_return) ,
            "__fp_gen_log" => Function :: new_native_with_env (store , env . clone () , _log) ,
            "__fp_gen_make_http_request" => Function :: new_native_with_env (store , env . clone () , _make_http_request) ,
         }
@@ -1005,6 +1007,15 @@ pub fn _import_void_function(env: &RuntimeInstanceData) {
     let result = super::import_void_function();
 }
 
+pub fn _import_void_function_empty_result(env: &RuntimeInstanceData) -> FatPtr {
+    let result = super::import_void_function_empty_result();
+    export_to_guest(env, &result)
+}
+
+pub fn _import_void_function_empty_return(env: &RuntimeInstanceData) {
+    let result = super::import_void_function_empty_return();
+}
+
 pub fn _log(env: &RuntimeInstanceData, message: FatPtr) {
     let message = import_from_guest::<String>(env, message);
     let result = super::log(message);

examples/example-protocol/src/assets/ts_runtime_test/expected_index.ts

@@ -72,6 +72,8 @@ export type Imports = {
     importString: (arg: string) => string;
     importTimestamp: (arg: MyDateTime) => MyDateTime;
     importVoidFunction: () => void;
+    importVoidFunctionEmptyResult: () => Result<void, number>;
+    importVoidFunctionEmptyReturn: () => void;
     log: (message: string) => void;
     makeHttpRequest: (request: Request) => Promise<HttpResult>;
 };
@@ -345,6 +347,12 @@ export async function createRuntime(
             __fp_gen_import_void_function: () => {
                 importFunctions.importVoidFunction();
             },
+            __fp_gen_import_void_function_empty_result: (): FatPtr => {
+                return serializeObject(importFunctions.importVoidFunctionEmptyResult());
+            },
+            __fp_gen_import_void_function_empty_return: () => {
+                importFunctions.importVoidFunctionEmptyReturn();
+            },
             __fp_gen_log: (message_ptr: FatPtr) => {
                 const message = parseObject<string>(message_ptr);
                 importFunctions.log(message);

examples/example-protocol/src/assets/ts_runtime_test/expected_types.ts

@@ -217,11 +217,11 @@ export type Response = {
 };
 
 /**
- * A result that can be either successful (`Ok)` or represent an error (`Err`).
+ * A result that can be either successful (`Ok`) or represent an error (`Err`).
  */
 export type Result<T, E> =
     /**
-     * Represents a succesful result.
+     * Represents a successful result.
      */
     | { Ok: T }
     /**

examples/example-protocol/src/main.rs

@@ -39,6 +39,12 @@ fp_import! {
     // No arguments, no return type:
     fn import_void_function();
 
+    // No arguments, empty return type:
+    fn import_void_function_empty_return() -> ();
+
+    // No arguments, generic empty result type:
+    fn import_void_function_empty_result() -> Result<(), u32>;
+
     // Passing primitives:
     fn import_primitive_bool(arg: bool) -> bool;
     fn import_primitive_f32(arg: f32) -> f32;

examples/example-rust-runtime/src/spec/mod.rs

@@ -8,6 +8,10 @@ use time::OffsetDateTime;
 use types::*;
 
 fn import_void_function() {}
+fn import_void_function_empty_result() -> Result<(), u32> {
+    Ok(())
+}
+fn import_void_function_empty_return() -> () {}
 
 fn import_primitive_bool(arg: bool) -> bool {
     todo!()
@@ -103,7 +107,6 @@ fn log(msg: String) {
 }
 
 async fn make_http_request(opts: Request) -> Result<Response, RequestError> {
-
     Ok(Response {
         body: ByteBuf::from(r#"status: "confirmed"#.to_string()),
         headers: opts.headers,

fp-bindgen/src/functions.rs

@@ -1,7 +1,8 @@
+use crate::utils::normalize_return_type;
 use crate::{docs::get_doc_lines, types::TypeIdent};
 use quote::{format_ident, quote, ToTokens};
 use std::{collections::BTreeSet, convert::TryFrom};
-use syn::{token::Async, FnArg, ForeignItemFn, ReturnType};
+use syn::{token::Async, FnArg, ForeignItemFn};
 
 /// Maps from function name to the stringified function declaration.
 #[derive(Debug, Default)]
@@ -71,13 +72,10 @@ impl Function {
                 },
             })
             .collect();
-        let return_type = match &item.sig.output {
-            ReturnType::Default => None,
-            ReturnType::Type(_, return_type) => Some(
-                TypeIdent::try_from(return_type.as_ref())
-                    .unwrap_or_else(|_| panic!("Invalid return type for function {}", name)),
-            ),
-        };
+        let return_type = normalize_return_type(&item.sig.output).map(|return_type| {
+            TypeIdent::try_from(return_type)
+                .unwrap_or_else(|_| panic!("Invalid return type for function {}", name))
+        });
         let is_async = item.sig.asyncness.is_some();
 
         Self {

fp-bindgen/src/generators/rust_plugin/mod.rs

@@ -261,7 +261,7 @@ fn format_type_with_ident(ty: &Type, ident: &TypeIdent, types: &TypeMap) -> Stri
                 .collect::<Vec<_>>()
                 .join(", ")
         ),
-        Type::Unit => "void".to_owned(),
+        Type::Unit => "()".to_owned(),
         _ => ident.to_string(),
     }
 }

fp-bindgen/src/lib.rs

@@ -342,6 +342,7 @@ mod serializable;
 pub mod prelude;
 pub mod primitives;
 pub mod types;
+mod utils;
 
 use fp_bindgen_macros::primitive_impls;
 use prelude::*;

fp-bindgen/src/serializable/mod.rs

@@ -215,7 +215,7 @@ where
                 Variant {
                     name: "Ok".to_owned(),
                     ty: Type::Tuple(vec![TypeIdent::from("T")]),
-                    doc_lines: vec![" Represents a succesful result.".to_owned()],
+                    doc_lines: vec![" Represents a successful result.".to_owned()],
                     attrs: VariantAttrs::default(),
                 },
                 Variant {
@@ -226,7 +226,7 @@ where
                 },
             ],
             doc_lines: vec![
-                " A result that can be either successful (`Ok)` or represent an error (`Err`)."
+                " A result that can be either successful (`Ok`) or represent an error (`Err`)."
                     .to_owned(),
             ],
             options: EnumOptions::default(),
@@ -240,6 +240,16 @@ where
     }
 }
 
+impl Serializable for () {
+    fn ident() -> TypeIdent {
+        TypeIdent::from("()")
+    }
+
+    fn ty() -> Type {
+        Type::Unit
+    }
+}
+
 impl Serializable for String {
     fn ident() -> TypeIdent {
         TypeIdent::from("String")

fp-bindgen/src/types/type_ident.rs

@@ -6,7 +6,7 @@ use std::{
     fmt::Display,
     str::FromStr,
 };
-use syn::{PathArguments, TypePath};
+use syn::{PathArguments, TypePath, TypeTuple};
 
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct TypeIdent {
@@ -111,30 +111,43 @@ impl TryFrom<&syn::Type> for TypeIdent {
 
     fn try_from(ty: &syn::Type) -> Result<Self, Self::Error> {
         match ty {
-            syn::Type::Path(TypePath { path, qself }) if qself.is_none() => Ok(Self {
-                name: path
-                    .segments
-                    .iter()
-                    .map(|segment| segment.ident.to_string())
-                    .collect::<Vec<_>>()
-                    .join("::"),
-                generic_args: path
-                    .segments
-                    .last()
-                    .and_then(|segment| match &segment.arguments {
-                        PathArguments::AngleBracketed(args) => Some(
-                            args.args
-                                .iter()
-                                .flat_map(|arg| match arg {
-                                    syn::GenericArgument::Type(ty) => TypeIdent::try_from(ty),
-                                    arg => Err(format!("Unsupported generic argument: {:?}", arg)),
-                                })
-                                .collect(),
-                        ),
-                        _ => None,
-                    })
-                    .unwrap_or_default(),
-            }),
+            syn::Type::Path(TypePath { path, qself }) if qself.is_none() => {
+                let mut generic_args = vec![];
+                if let Some(segment) = path.segments.last() {
+                    match &segment.arguments {
+                        PathArguments::AngleBracketed(args) => {
+                            for arg in &args.args {
+                                match arg {
+                                    syn::GenericArgument::Type(ty) => {
+                                        generic_args.push(TypeIdent::try_from(ty)?);
+                                    }
+                                    arg => {
+                                        return Err(format!(
+                                            "Unsupported generic argument: {:?}",
+                                            arg
+                                        ));
+                                    }
+                                }
+                            }
+                        }
+                        _ => {}
+                    }
+                }
+
+                Ok(Self {
+                    name: path
+                        .segments
+                        .iter()
+                        .map(|segment| segment.ident.to_string())
+                        .collect::<Vec<_>>()
+                        .join("::"),
+                    generic_args,
+                })
+            }
+            syn::Type::Tuple(TypeTuple {
+                elems,
+                paren_token: _,
+            }) if elems.is_empty() => Ok(TypeIdent::from("()")),
             ty => Err(format!("Unsupported type: {:?}", ty)),
         }
     }

fp-bindgen/src/utils.rs

@@ -0,0 +1,17 @@
+use syn::{ReturnType, Type};
+
+// This is the same as the one in macros/src/lib.rs, which we unfortunately cannot export.
+pub(crate) fn normalize_return_type(ty: &ReturnType) -> Option<&Type> {
+    match ty {
+        ReturnType::Default => None,
+        ReturnType::Type(_, ty) => {
+            match ty.as_ref() {
+                Type::Tuple(tuple) if tuple.elems.is_empty() => {
+                    /* An empty '-> ()' return value */
+                    None
+                }
+                r => Some(r),
+            }
+        }
+    }
+}

macros/src/lib.rs

@@ -10,7 +10,7 @@ use syn::{
     AttributeArgs, FnArg, ForeignItemFn, GenericParam, ItemFn, ItemType, ItemUse, Pat, PatPath,
     Path, PathArguments, PathSegment, ReturnType,
 };
-use utils::flatten_using_statement;
+use utils::{flatten_using_statement, normalize_return_type};
 
 mod primitives;
 mod serializable;
@@ -128,19 +128,14 @@ fn parse_statements(token_stream: TokenStream) -> ParsedStatements {
                         }
                     }
 
-                    match &function.sig.output {
-                        ReturnType::Default => { /* No return value. */ }
-                        ReturnType::Type(_, ty) => {
-                            type_paths.insert(extract_path_from_type(ty.as_ref()).unwrap_or_else(
-                                || {
-                                    panic!(
-                                        "Only value types are supported. \
+                    if let Some(ty) = normalize_return_type(&function.sig.output) {
+                        type_paths.insert(extract_path_from_type(ty).unwrap_or_else(|| {
+                            panic!(
+                                "Only value types are supported. \
                                             Incompatible return type in function declaration: {:?}",
-                                        function.sig
-                                    )
-                                },
-                            ));
-                        }
+                                function.sig
+                            )
+                        }));
                     }
 
                     functions.push(function.into_token_stream().to_string());

macros/src/utils.rs

@@ -3,7 +3,8 @@ use std::collections::VecDeque;
 use proc_macro::TokenStream;
 use proc_macro2::Ident;
 use syn::{
-    punctuated::Punctuated, Generics, Item, ItemUse, Path, PathArguments, PathSegment, Type,
+    punctuated::Punctuated, Generics, Item, ItemUse, Path, PathArguments, PathSegment, ReturnType,
+    Type,
 };
 
 pub(crate) fn extract_path_from_type(ty: &Type) -> Option<Path> {
@@ -80,3 +81,18 @@ pub(crate) fn flatten_using_statement(using: ItemUse) -> impl Iterator<Item = Pa
 
     result.into_iter()
 }
+
+pub(crate) fn normalize_return_type(ty: &ReturnType) -> Option<&Type> {
+    match ty {
+        ReturnType::Default => None,
+        ReturnType::Type(_, ty) => {
+            match ty.as_ref() {
+                Type::Tuple(tuple) if tuple.elems.is_empty() => {
+                    /* An empty '-> ()' return value */
+                    None
+                }
+                r => Some(r),
+            }
+        }
+    }
+}