feat(export): add option to export wasm code as X

X can be
🐣 'buffer' will export wasm code as Buffer class
🐥 'module' will export wasm code as WebAssembly.Module
🐤 'instance' will export wasm code as WebAssembly.Instance
🐔 'promise' will "instantiate" wasm code asynchronously

first attempt, no test yet, so [skip ci]

Author: DrSensor

flow-typed/rollupPluginRustDef.js

@@ -1,4 +1,5 @@
 declare type Options = {
+  export: 'buffer' | 'instance' | 'module' | 'promise',
   include?: string[] | string, // rollup recommend to add this
   exclude?: string[] | string // rollup recommend to add this
 };

src/main.js

@@ -1,11 +1,12 @@
 // @flow
 import { createFilter } from 'rollup-pluginutils';
+import wrap from './wrapper';
 import predef from './options';
 
 const extension = /\.rs$/; // rust file extension
 
 export default function(options: Options = predef) {
-  options = Object.assign(options, predef); // diff and merge with predefined options
+  options = Object.assign(predef, options); // diff and merge with predefined options
   const filter = createFilter(options.include, options.exclude);
 
   return {
@@ -14,17 +15,17 @@ export default function(options: Options = predef) {
       if (!extension.test(id)) return;
       if (!filter(id)) return;
 
-      const wasmCode = Buffer.from([
-        0x00,
-        0x61,
-        0x73,
-        0x6d,
-        0x01,
-        0,
-        0,
-        0
-      ]).toJSON().data;
-      return `export default Buffer.from([${wasmCode.toString()}])`;
+      const wasmCode = Buffer.from([0x00, 0x61, 0x73, 0x6d, 0x01, 0, 0, 0]);
+      switch (options.export) {
+        case 'buffer':
+          return wrap(wasmCode).asBuffer;
+        case 'instance':
+          return wrap(wasmCode).asWebAssembly.Instance;
+        case 'module':
+          return wrap(wasmCode).asWebAssembly.Module;
+        case 'promise':
+          return wrap(wasmCode).promiseWebAssembly;
+      }
     }
   };
 }

src/options.js

@@ -1,6 +1,7 @@
 // @flow
 /** Default options */
 export default ({
+  export: 'promise',
   include: ['**/*.rs'],
   exclude: ['node_modules/**', 'target/**']
 }: Options);

src/wrapper.js

@@ -0,0 +1,26 @@
+// @flow
+
+/** Wrap binary data as es6 module so it can be imported by rollup
+ * @param buffer raw binary data to be wrapped as es6 module
+ * @return chainable object which represent `wrap this data as...`
+ * @example return wrap(arrayBuffer).asWebAssembly.Module
+ */
+export default function(buffer: Buffer) {
+  const data = buffer.toJSON().data.toString();
+  return {
+    asBuffer: `export default Buffer.from([${data}])`,
+    asWebAssembly: {
+      Module: `export default new WebAssembly.Module(
+        Buffer.from([${data}])
+      )`,
+      Instance: `export default new WebAssembly.Instance(
+        new WebAssembly.Module(
+          Buffer.from([${data}])
+        )
+      )`
+    },
+    promiseWebAssembly: `export default WebAssembly.instantiate(
+      Buffer.from([${data}])
+    )`
+  };
+}