Support C-Style enums with custom int values

crates/wasm-bindgen-cli-support/src/js.rs

@@ -1434,10 +1434,8 @@ impl<'a, 'b> SubContext<'a, 'b> {
     pub fn generate_enum(&mut self, enum_: &shared::Enum) {
         let mut variants = String::new();
 
-        let mut value = 0;
         for variant in enum_.variants.iter() {
-            variants.push_str(&format!("{}:{},", variant.name, value));
-            value = value + 1;
+            variants.push_str(&format!("{}:{},", variant.name, variant.value));
         }
         self.cx.globals.push_str(&format!("export const {} = {{", enum_.name));
         self.cx.globals.push_str(&variants);

crates/wasm-bindgen-macro/src/ast.rs

@@ -50,7 +50,7 @@ pub struct Struct {
 
 pub struct Enum {
     pub name: syn::Ident,
-    pub variants: Vec<syn::Ident>
+    pub variants: Vec<(syn::Ident, u32)>
 }
 
 pub enum Type {
@@ -212,12 +212,25 @@ impl Program {
             _ => panic!("only public enums are allowed"),
         }
 
+        let mut i = 0;
         let variants = item.variants.iter().map(|ref v| {
             match v.fields {
                 syn::Fields::Unit => (),
                 _ => panic!("Only C-Style enums allowed")
             }
-            v.ident
+            let value = match v.discriminant {
+                Some((_, syn::Expr::Lit(syn::ExprLit {attrs: _, lit: syn::Lit::Int(ref int_lit)}))) => {
+                    if int_lit.value() > <u32>::max_value() as u64 {
+                        panic!("Enums can only support numbers that can be represented as u32");
+                    }
+                    int_lit.value() as u32
+                },
+                None => i,
+                _ => panic!("Enums may only have number literal values")
+            };
+
+            i = i + 1;
+            (v.ident, value)
         }).collect();
         self.enums.push(Enum {
             name: item.ident,
@@ -670,7 +683,9 @@ impl Enum {
         a.fields(&[
                  ("name", &|a| a.str(self.name.as_ref())),
                  ("variants", &|a| a.list(&self.variants, |v, a| {
-                     a.fields(&[("name", &|a| a.str(v.as_ref()))])
+                     let &(name, value) = v;
+                     a.fields(&[("name", &|a| a.str(name.as_ref())),
+                                ("value", &|a| a.append(&format!("{}", value)))])
                  })),
         ]);
     }

crates/wasm-bindgen-macro/src/lib.rs

@@ -515,27 +515,28 @@ fn bindgen_import(import: &ast::Import, tokens: &mut Tokens) {
 }
 
 fn bindgen_enum(e: &ast::Enum, into: &mut Tokens) {
-    let name = &e.name;
+    let enum_name = &e.name;
     let c = shared::TYPE_ENUM as u32;
     let incoming_u32 = quote! { n };
-    let name_as_string = name.to_string();
-    let cast_clauses = e.variants.iter().map(|ident| {
+    let enum_name_as_string = enum_name.to_string();
+    let cast_clauses = e.variants.iter().map(|variant| {
+        let &(variant_name, _) = variant;
         quote! {
-            if #incoming_u32 == #name::#ident as u32 {
-                #name::#ident
+            if #incoming_u32 == #enum_name::#variant_name as u32 {
+                #enum_name::#variant_name
             }
         }
     });
     (my_quote! {
-        impl #name {
-            fn from_u32(#incoming_u32: u32) -> #name {
+        impl #enum_name {
+            fn from_u32(#incoming_u32: u32) -> #enum_name {
                 #(#cast_clauses else)* {
-                    wasm_bindgen::throw(&format!("Could not cast {} as {}", #incoming_u32, #name_as_string));
+                    wasm_bindgen::throw(&format!("Could not cast {} as {}", #incoming_u32, #enum_name_as_string));
                 }
             }
         }
 
-        impl ::wasm_bindgen::convert::WasmBoundary for #name {
+        impl ::wasm_bindgen::convert::WasmBoundary for #enum_name {
             type Js = u32;
             const DESCRIPTOR: u32 = #c;
 
@@ -544,7 +545,7 @@ fn bindgen_enum(e: &ast::Enum, into: &mut Tokens) {
             }
 
             unsafe fn from_js(js: u32) -> Self {
-                #name::from_u32(js)
+                #enum_name::from_u32(js)
             }
         }
     }).to_tokens(into);

crates/wasm-bindgen-shared/src/lib.rs

@@ -41,7 +41,8 @@ pub struct Enum {
 
 #[derive(Deserialize)]
 pub struct EnumVariant {
-    pub name: String
+    pub name: String,
+    pub value: u32
 }
 
 #[derive(Deserialize)]