From 45543c545e772dc5c4040b9fdfe821f0ab6a0a71 Mon Sep 17 00:00:00 2001
From: Ryan Levick <ryan.levick@gmail.com>
Date: Thu, 22 Feb 2018 10:55:44 +0100
Subject: [PATCH] Pass numbers in js as enums to Rust successfully

---
 crates/wasm-bindgen-cli-support/src/js.rs |  3 ++-
 crates/wasm-bindgen-macro/src/ast.rs      | 22 ++++++++---------
 crates/wasm-bindgen-macro/src/lib.rs      | 29 +++++++++++++++--------
 3 files changed, 31 insertions(+), 23 deletions(-)

diff --git a/crates/wasm-bindgen-cli-support/src/js.rs b/crates/wasm-bindgen-cli-support/src/js.rs
index 3108beb6..37ec69fc 100644
--- a/crates/wasm-bindgen-cli-support/src/js.rs
+++ b/crates/wasm-bindgen-cli-support/src/js.rs
@@ -1051,7 +1051,8 @@ impl<'a, 'b> SubContext<'a, 'b> {
                 passed_args.push_str(arg);
             };
             match *arg {
-                shared::TYPE_NUMBER => {
+                shared::TYPE_ENUM | shared::TYPE_NUMBER => {
+                    // TODO: TS for Enum
                     dst_ts.push_str(": number");
                     if self.cx.config.debug {
                         self.cx.expose_assert_num();
diff --git a/crates/wasm-bindgen-macro/src/ast.rs b/crates/wasm-bindgen-macro/src/ast.rs
index 1899a6dc..2904ed0c 100644
--- a/crates/wasm-bindgen-macro/src/ast.rs
+++ b/crates/wasm-bindgen-macro/src/ast.rs
@@ -49,7 +49,8 @@ pub struct Struct {
 }
 
 pub struct Enum {
-    pub name: syn::Ident
+    pub name: syn::Ident,
+    pub variants: Vec<syn::Ident>
 }
 
 pub enum Type {
@@ -211,20 +212,17 @@ impl Program {
             _ => panic!("only public enums are allowed"),
         }
 
-        let all_fields_unit = item.variants.iter().all(|ref v| {
+        let variants = item.variants.iter().map(|ref v| {
             match v.fields {
-                syn::Fields::Unit => true,
-                _ => false
+                syn::Fields::Unit => (),
+                _ => panic!("Only C-Style enums allowed")
             }
+            v.ident
+        }).collect();
+        self.enums.push(Enum {
+            name: item.ident,
+            variants
         });
-        if all_fields_unit {
-            self.enums.push(Enum {
-                name: item.ident
-            });
-
-        } else {
-            panic!("Only C-Style enums allowed")
-        }
     }
 
     pub fn push_foreign_fn(&mut self,
diff --git a/crates/wasm-bindgen-macro/src/lib.rs b/crates/wasm-bindgen-macro/src/lib.rs
index 039d23ff..c47d362e 100644
--- a/crates/wasm-bindgen-macro/src/lib.rs
+++ b/crates/wasm-bindgen-macro/src/lib.rs
@@ -516,26 +516,35 @@ fn bindgen_import(import: &ast::Import, tokens: &mut Tokens) {
 
 fn bindgen_enum(e: &ast::Enum, into: &mut Tokens) {
     let name = &e.name;
-    let c = shared::name_to_descriptor(name.as_ref()) as u32;
-    (my_quote! {
-        impl #name {
-            fn from_usize(n: usize) -> #name {
-                #name::Blue
+    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| {
+        quote! {
+            if #incoming_u32 == #name::#ident as u32 {
+                #name::#ident
             }
         }
+    });
+    (my_quote! {
+        impl #name {
+            fn from_u32(#incoming_u32: u32) -> #name {
+                #(#cast_clauses else)* {
+                    wasm_bindgen::throw(&format!("Could not cast {} as {}", #incoming_u32, #name_as_string));
+                }
+            }
+        }
+
         impl ::wasm_bindgen::convert::WasmBoundary for #name {
             type Js = u32;
             const DESCRIPTOR: u32 = #c;
 
             fn into_js(self) -> u32 {
-                Box::into_raw(Box::new(self as u32)) as u32
+                self as u32
             }
 
             unsafe fn from_js(js: u32) -> Self {
-                let js = js as *mut usize;
-                ::wasm_bindgen::__rt::assert_not_null(js);
-                let js = Box::from_raw(js);
-                #name::from_usize(*js)
+                #name::from_u32(js)
             }
         }
     }).to_tokens(into);