Add support for optional dependencies (#788)

Put a `require` call inside a try…catch block, and it becomes optional. If that dependency cannot be resolved, it will throw a runtime error instead of a build time one.

src/Bundler.js

@@ -328,6 +328,10 @@ class Bundler extends EventEmitter {
  let thrown = err;
 
  if (thrown.message.indexOf(`Cannot find module '${dep.name}'`) === 0) {
+ if (dep.optional) {
+ return;
+ }
+
  thrown.message = `Cannot resolve dependency '${dep.name}'`;
 
  // Add absolute path to the error message if the dependency specifies a relative path
@@ -403,7 +407,10 @@ class Bundler extends EventEmitter {
  this.watch(dep.name, asset);
  } else {
  let assetDep = await this.resolveDep(asset, dep);
- await this.loadAsset(assetDep);
+ if (assetDep) {
+ await this.loadAsset(assetDep);
+ }
+
  return assetDep;
  }
  })

src/assets/JSAsset.js

@@ -87,7 +87,7 @@ class JSAsset extends Asset {
  }
 
  collectDependencies() {
- this.traverseFast(collectDependencies);
+ walk.ancestor(this.ast, collectDependencies, this);
  }
 
  async pretransform() {

src/visitors/dependencies.js

@@ -30,7 +30,7 @@ module.exports = {
  asset.isES6Module = true;
  },
 
- CallExpression(node, asset) {
+ CallExpression(node, asset, ancestors) {
  let {callee, arguments: args} = node;
 
  let isRequire =
@@ -40,7 +40,8 @@ module.exports = {
  types.isStringLiteral(args[0]);
 
  if (isRequire) {
- addDependency(asset, args[0]);
+ let optional = ancestors.some(a => types.isTryStatement(a)) || undefined;
+ addDependency(asset, args[0], {optional});
  return;
  }
 

test/integration/optional-dep/index.js

@@ -0,0 +1,5 @@
+try {
+ require('optional-dep');
+} catch (err) {
+ module.exports = err;
+}

test/javascript.js

@@ -676,4 +676,25 @@ describe('javascript', function() {
  let file = fs.readFileSync(__dirname + '/dist/index.js', 'utf8');
  assert(file.includes('h("div"'));
  });
+
+ it('should support optional dependencies in try...catch blocks', async function() {
+ let b = await bundle(__dirname + '/integration/optional-dep/index.js');
+
+ assertBundleTree(b, {
+ name: 'index.js',
+ assets: ['index.js'],
+ childBundles: [
+ {
+ type: 'map'
+ }
+ ]
+ });
+
+ let output = run(b);
+
+ let err = new Error('Cannot find module "optional-dep"');
+ err.code = 'MODULE_NOT_FOUND';
+
+ assert.deepEqual(output, err);
+ });
 });