Prevent circular deps from causing a stack overflow in HMR runtime

packages/core/integration-tests/test/hmr.js

@@ -287,6 +287,37 @@ describe('hmr', function() {
     assert.deepEqual(outputs, [3, 10]);
   });
 
+  it('should work with circular dependencies', async function() {
+    await ncp(
+      path.join(__dirname, '/integration/hmr-circular'),
+      path.join(__dirname, '/input')
+    );
+
+    b = bundler(path.join(__dirname, '/input/index.js'), {
+      watch: true,
+      hmr: true
+    });
+    let bundle = await b.bundle();
+    let outputs = [];
+
+    await run(bundle, {
+      output(o) {
+        outputs.push(o);
+      }
+    });
+
+    assert.deepEqual(outputs, [3]);
+
+    await sleep(100);
+    fs.writeFile(
+      path.join(__dirname, '/input/local.js'),
+      "var other = require('./index.js'); exports.a = 5; exports.b = 5;"
+    );
+
+    await nextEvent(b, 'bundled');
+    assert.deepEqual(outputs, [3, 10]);
+  });
+
   it('should call dispose and accept callbacks', async function() {
     await ncp(
       path.join(__dirname, '/integration/hmr-callbacks'),

packages/core/integration-tests/test/integration/hmr-circular/index.js

@@ -0,0 +1,9 @@
+var local = require('./local');
+
+function run() {
+  output(local.a + local.b);
+}
+
+run();
+
+module.exports = 'value';

packages/core/integration-tests/test/integration/hmr-circular/local.js

@@ -0,0 +1,4 @@
+var other = require('./index.js');
+
+exports.a = 1;
+exports.b = 2;

packages/core/parcel-bundler/src/builtins/hmr-runtime.js

@@ -20,13 +20,16 @@ function Module(moduleName) {
 }
 
 module.bundle.Module = Module;
+var updatedAssets;
 
 var parent = module.bundle.parent;
 if ((!parent || !parent.isParcelRequire) && typeof WebSocket !== 'undefined') {
   var hostname = process.env.HMR_HOSTNAME || location.hostname;
   var protocol = location.protocol === 'https:' ? 'wss' : 'ws';
   var ws = new WebSocket(protocol + '://' + hostname + ':' + process.env.HMR_PORT + '/');
   ws.onmessage = function(event) {
+    updatedAssets = {};
+
     var data = JSON.parse(event.data);
 
     if (data.type === 'update') {
@@ -147,6 +150,11 @@ function hmrAccept(bundle, id) {
     return hmrAccept(bundle.parent, id);
   }
 
+  if (updatedAssets[id]) {
+    return;
+  }
+  updatedAssets[id] = true;
+
   var cached = bundle.cache[id];
   bundle.hotData = {};
   if (cached) {