Do not optimize away async/gen arrow functions (#7319)

* Do not optimize away async/gen arrow functions

* Node version 8

packages/babel-plugin-proposal-pipeline-operator/src/index.js

@@ -14,7 +14,10 @@ export default function() {
         if (operator !== "|>") return;
 
         let optimizeArrow =
-          t.isArrowFunctionExpression(right) && t.isExpression(right.body);
+          t.isArrowFunctionExpression(right) &&
+          t.isExpression(right.body) &&
+          !right.async &&
+          !right.generator;
         let param;
 
         if (optimizeArrow) {

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/pipeline-operator/async-arrow/exec.js

@@ -0,0 +1,13 @@
+function then(fn) {
+  return async (value) => {
+    return fn(await value);
+  };
+}
+
+var result = 1
+  |> (async (x) => await x + 1)
+  |> then((x) => x + 1);
+
+result.then(val => {
+  assert.equal(val, 3);
+});

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/pipeline-operator/async-arrow/input.js

@@ -0,0 +1,13 @@
+function then(fn) {
+  return async (value) => {
+    return fn(await value);
+  };
+}
+
+var result = 1
+  |> (async (x) => await x + 1)
+  |> then((x) => x + 1);
+
+result.then(val => {
+  assert.equal(val, 3);
+});

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/pipeline-operator/async-arrow/options.json

@@ -0,0 +1,3 @@
+{
+  "minNodeVersion": "8.0.0"
+}

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/pipeline-operator/async-arrow/output.js

@@ -0,0 +1,12 @@
+var _ref, _;
+
+function then(fn) {
+  return async value => {
+    return fn((await value));
+  };
+}
+
+var result = (_ref = (_ = 1, (async x => (await x) + 1)(_)), then(x => x + 1)(_ref));
+result.then(val => {
+  assert.equal(val, 3);
+});