Implement #[wasm_bindgen(main)]

.github/workflows/main.yml

@@ -219,7 +219,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v3
-    - run: rustup update --no-self-update 1.56.0 && rustup default 1.56.0
+    - run: rustup update --no-self-update 1.61.0 && rustup default 1.61.0
     - run: cargo test -p wasm-bindgen-macro
 
   build_examples:

crates/macro-support/src/parser.rs

@@ -10,7 +10,7 @@ use proc_macro2::{Delimiter, Ident, Span, TokenStream, TokenTree};
 use quote::ToTokens;
 use syn::parse::{Parse, ParseStream, Result as SynResult};
 use syn::spanned::Spanned;
-use syn::Lit;
+use syn::{ItemFn, Lit, ReturnType};
 
 thread_local!(static ATTRS: AttributeParseState = Default::default());
 
@@ -80,6 +80,7 @@ macro_rules! attrgen {
             (variadic, Variadic(Span)),
             (typescript_custom_section, TypescriptCustomSection(Span)),
             (skip_typescript, SkipTypescript(Span)),
+            (main, Main(Span)),
             (start, Start(Span)),
             (skip, Skip(Span)),
             (typescript_type, TypeScriptType(Span, String, Span)),
@@ -933,6 +934,13 @@ impl<'a> MacroParse<(Option<BindgenAttrs>, &'a mut TokenStream)> for syn::Item {
     ) -> Result<(), Diagnostic> {
         match self {
             syn::Item::Fn(mut f) => {
+                let opts = opts.unwrap_or_default();
+
+                if opts.main().is_some() {
+                    opts.check_used();
+                    return main(f, tokens);
+                }
+
                 let no_mangle = f
                     .attrs
                     .iter()
@@ -951,7 +959,6 @@ impl<'a> MacroParse<(Option<BindgenAttrs>, &'a mut TokenStream)> for syn::Item {
                 // `dead_code` warning. So, add `#[allow(dead_code)]` before it to avoid that.
                 tokens.extend(quote::quote! { #[allow(dead_code)] });
                 f.to_tokens(tokens);
-                let opts = opts.unwrap_or_default();
                 if opts.start().is_some() {
                     if f.sig.generics.params.len() > 0 {
                         bail_span!(&f.sig.generics, "the start function cannot have generics",);
@@ -1689,6 +1696,59 @@ pub fn link_to(opts: BindgenAttrs) -> Result<ast::LinkToModule, Diagnostic> {
     Ok(ast::LinkToModule(program))
 }
 
+fn main(mut f: ItemFn, tokens: &mut TokenStream) -> Result<(), Diagnostic> {
+    if f.sig.ident != "main" {
+        bail_span!(&f.sig.ident, "the main function has to be called main");
+    }
+    if let Some(constness) = f.sig.constness {
+        bail_span!(&constness, "the main function cannot be const");
+    }
+    if !f.sig.generics.params.is_empty() {
+        bail_span!(&f.sig.generics, "the main function cannot have generics");
+    }
+    if !f.sig.inputs.is_empty() {
+        bail_span!(&f.sig.inputs, "the main function cannot have arguments");
+    }
+
+    let r#return = f.sig.output;
+    f.sig.output = ReturnType::Default;
+    let body = f.block;
+
+    if f.sig.asyncness.take().is_some() {
+        f.block = Box::new(
+            syn::parse2(quote::quote! {
+                {
+                    async fn __wasm_bindgen_generated_main() #r#return #body
+                    wasm_bindgen_futures::spawn_local(
+                        async move {
+                            use wasm_bindgen::__rt::Main;
+                            let __ret = __wasm_bindgen_generated_main();
+                            (&mut wasm_bindgen::__rt::MainWrapper(Some(__ret.await))).__wasm_bindgen_main()
+                        },
+                    )
+                }
+            })
+            .unwrap(),
+        );
+    } else {
+        f.block = Box::new(
+            syn::parse2(quote::quote! {
+                {
+                    fn __wasm_bindgen_generated_main() #r#return #body
+                    use wasm_bindgen::__rt::Main;
+                    let __ret = __wasm_bindgen_generated_main();
+                    (&mut wasm_bindgen::__rt::MainWrapper(Some(__ret))).__wasm_bindgen_main()
+                }
+            })
+            .unwrap(),
+        );
+    }
+
+    f.to_tokens(tokens);
+
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     #[test]

crates/macro/ui-tests/async-errors.stderr

@@ -7,11 +7,6 @@ error[E0277]: the trait bound `Result<(), ()>: IntoJsResult` is not satisfied
    = help: the following implementations were found:
              <Result<(), E> as IntoJsResult>
              <Result<T, E> as IntoJsResult>
-note: required by `into_js_result`
-  --> $WORKSPACE/src/lib.rs
-   |
-   |         fn into_js_result(self) -> Result<JsValue, JsValue>;
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `wasm_bindgen` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `Result<(), BadType>: IntoJsResult` is not satisfied
@@ -23,11 +18,6 @@ error[E0277]: the trait bound `Result<(), BadType>: IntoJsResult` is not satisfi
    = help: the following implementations were found:
              <Result<(), E> as IntoJsResult>
              <Result<T, E> as IntoJsResult>
-note: required by `into_js_result`
-  --> $WORKSPACE/src/lib.rs
-   |
-   |         fn into_js_result(self) -> Result<JsValue, JsValue>;
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `wasm_bindgen` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `wasm_bindgen::JsValue: From<BadType>` is not satisfied
@@ -44,11 +34,6 @@ error[E0277]: the trait bound `wasm_bindgen::JsValue: From<BadType>` is not sati
            and $N others
    = note: required because of the requirements on the impl of `Into<wasm_bindgen::JsValue>` for `BadType`
    = note: required because of the requirements on the impl of `IntoJsResult` for `BadType`
-note: required by `into_js_result`
-  --> $WORKSPACE/src/lib.rs
-   |
-   |         fn into_js_result(self) -> Result<JsValue, JsValue>;
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `wasm_bindgen` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `Result<BadType, wasm_bindgen::JsValue>: IntoJsResult` is not satisfied
@@ -60,9 +45,4 @@ error[E0277]: the trait bound `Result<BadType, wasm_bindgen::JsValue>: IntoJsRes
    = help: the following implementations were found:
              <Result<(), E> as IntoJsResult>
              <Result<T, E> as IntoJsResult>
-note: required by `into_js_result`
-  --> $WORKSPACE/src/lib.rs
-   |
-   |         fn into_js_result(self) -> Result<JsValue, JsValue>;
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `wasm_bindgen` (in Nightly builds, run with -Z macro-backtrace for more info)

crates/macro/ui-tests/invalid-methods.stderr

@@ -1,61 +1,61 @@
 error: #[wasm_bindgen] default impls are not supported
- --> $DIR/invalid-methods.rs:7:1
+ --> ui-tests/invalid-methods.rs:7:1
   |
 7 | default impl A {
   | ^^^^^^^
 
 error: #[wasm_bindgen] unsafe impls are not supported
-  --> $DIR/invalid-methods.rs:11:1
+  --> ui-tests/invalid-methods.rs:11:1
    |
 11 | unsafe impl A {
    | ^^^^^^
 
 error: #[wasm_bindgen] trait impls are not supported
-  --> $DIR/invalid-methods.rs:15:6
+  --> ui-tests/invalid-methods.rs:15:6
    |
 15 | impl Clone for A {
    |      ^^^^^
 
 error: #[wasm_bindgen] generic impls aren't supported
-  --> $DIR/invalid-methods.rs:19:5
+  --> ui-tests/invalid-methods.rs:19:5
    |
 19 | impl<T> A {
    |     ^^^
 
 error: unsupported self type in #[wasm_bindgen] impl
-  --> $DIR/invalid-methods.rs:23:6
+  --> ui-tests/invalid-methods.rs:23:6
    |
 23 | impl &'static A {
    |      ^^^^^^^^^^
 
 error: const definitions aren't supported with #[wasm_bindgen]
-  --> $DIR/invalid-methods.rs:30:5
+  --> ui-tests/invalid-methods.rs:30:5
    |
 30 |     const X: u32 = 3;
    |     ^^^^^^^^^^^^^^^^^
 
 error: type definitions in impls aren't supported with #[wasm_bindgen]
-  --> $DIR/invalid-methods.rs:31:5
+  --> ui-tests/invalid-methods.rs:31:5
    |
 31 |     type Y = u32;
    |     ^^^^^^^^^^^^^
 
 error: macros in impls aren't supported
-  --> $DIR/invalid-methods.rs:32:5
+  --> ui-tests/invalid-methods.rs:32:5
    |
 32 |     x!();
    |     ^^^^^
 
 error: can only #[wasm_bindgen] non-const functions
-  --> $DIR/invalid-methods.rs:39:9
+  --> ui-tests/invalid-methods.rs:39:9
    |
 39 |     pub const fn foo() {}
    |         ^^^^^
 
-warning: unused macro definition
-  --> $DIR/invalid-methods.rs:26:1
+warning: unused macro definition: `x`
+  --> ui-tests/invalid-methods.rs:26:14
    |
 26 | macro_rules! x { () => () }
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |              ^
    |
    = note: `#[warn(unused_macros)]` on by default

crates/macro/ui-tests/main-async.rs

@@ -0,0 +1,7 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+async fn main() {}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main-async.stderr

@@ -0,0 +1,5 @@
+error: the main function has to be called main
+ --> ui-tests/main-async.rs:7:4
+  |
+7 | fn fail() {}
+  |    ^^^^

crates/macro/ui-tests/main-debug.rs

@@ -0,0 +1,18 @@
+use std::fmt;
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+fn main() -> Result<(), Test> {
+    unimplemented!()
+}
+
+struct Test;
+
+impl fmt::Debug for Test {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        unimplemented!()
+    }
+}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main-debug.stderr

@@ -0,0 +1,5 @@
+error: the main function has to be called main
+  --> ui-tests/main-debug.rs:18:4
+   |
+18 | fn fail() {}
+   |    ^^^^

crates/macro/ui-tests/main-infallible.rs

@@ -0,0 +1,10 @@
+use std::convert::Infallible;
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+fn main() -> Infallible {
+    unimplemented!()
+}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main-infallible.stderr

@@ -0,0 +1,5 @@
+error: the main function has to be called main
+  --> ui-tests/main-infallible.rs:10:4
+   |
+10 | fn fail() {}
+   |    ^^^^

crates/macro/ui-tests/main-jsvalue.rs

@@ -0,0 +1,9 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+fn main() -> Result<(), JsValue> {
+    unimplemented!()
+}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main-jsvalue.stderr

@@ -0,0 +1,5 @@
+error: the main function has to be called main
+ --> ui-tests/main-jsvalue.rs:9:4
+  |
+9 | fn fail() {}
+  |    ^^^^

crates/macro/ui-tests/main-termination.rs

@@ -0,0 +1,18 @@
+use std::process;
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+fn main() -> Result<(), Test> {
+    unimplemented!()
+}
+
+struct Test;
+
+impl process::Termination for Test {
+    fn report(self) -> process::ExitCode {
+        unimplemented!()
+    }
+}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main-termination.stderr

@@ -0,0 +1,36 @@
+error: the main function has to be called main
+  --> ui-tests/main-termination.rs:18:4
+   |
+18 | fn fail() {}
+   |    ^^^^
+
+error[E0599]: the method `__wasm_bindgen_main` exists for mutable reference `&mut MainWrapper<Result<(), Test>>`, but its trait bounds were not satisfied
+ --> ui-tests/main-termination.rs:4:1
+  |
+4 |   #[wasm_bindgen(main)]
+  |   ^^^^^^^^^^^^^^^^^^^^^ method cannot be called on `&mut MainWrapper<Result<(), Test>>` due to unsatisfied trait bounds
+...
+9 |   struct Test;
+  |   ------------
+  |   |
+  |   doesn't satisfy `Test: Debug`
+  |   doesn't satisfy `Test: Into<JsValue>`
+  |
+ ::: $WORKSPACE/src/lib.rs
+  |
+  |       pub struct MainWrapper<T>(pub Option<T>);
+  |       ----------------------------------------- doesn't satisfy `MainWrapper<Result<(), Test>>: Main`
+  |
+  = note: the following trait bounds were not satisfied:
+          `Test: Debug`
+          which is required by `&mut MainWrapper<Result<(), Test>>: Main`
+          `Result<(), Test>: Termination`
+          which is required by `&mut &mut MainWrapper<Result<(), Test>>: Main`
+          `Test: Into<JsValue>`
+          which is required by `MainWrapper<Result<(), Test>>: Main`
+note: the following trait must be implemented
+  = note: this error originates in the attribute macro `wasm_bindgen` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Test` with `#[derive(Debug)]`
+     |
+9    | #[derive(Debug)]
+     |

crates/macro/ui-tests/main-unit.rs

@@ -0,0 +1,7 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+fn main() -> () {}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main-unit.stderr

@@ -0,0 +1,5 @@
+error: the main function has to be called main
+ --> ui-tests/main-unit.rs:7:4
+  |
+7 | fn fail() {}
+  |    ^^^^

crates/macro/ui-tests/main.rs

@@ -0,0 +1,7 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen(main)]
+fn main() {}
+
+#[wasm_bindgen(main)]
+fn fail() {}

crates/macro/ui-tests/main.stderr

@@ -0,0 +1,5 @@
+error: the main function has to be called main
+ --> ui-tests/main.rs:7:4
+  |
+7 | fn fail() {}
+  |    ^^^^

crates/macro/ui-tests/missing-catch.stderr

@@ -3,15 +3,3 @@ error[E0277]: the trait bound `Result<wasm_bindgen::JsValue, wasm_bindgen::JsVal
   |
 6 |     pub fn foo() -> Result<JsValue, JsValue>;
   |            ^^^ the trait `FromWasmAbi` is not implemented for `Result<wasm_bindgen::JsValue, wasm_bindgen::JsValue>`
-  |
-note: required by a bound in `FromWasmAbi`
- --> $WORKSPACE/src/convert/traits.rs
-  |
-  | / pub trait FromWasmAbi: WasmDescribe {
-  | |     /// The wasm ABI type that this converts from when coming back out from the
-  | |     /// ABI boundary.
-  | |     type Abi: WasmAbi;
-... |
-  | |     unsafe fn from_abi(js: Self::Abi) -> Self;
-  | | }
-  | |_^ required by this bound in `FromWasmAbi`