Allow patterns as argument of RestElement (#8414)

packages/babel-plugin-transform-parameters/src/rest.js

@@ -228,10 +228,20 @@ export default function convertFunctionRest(path) {
   const { node, scope } = path;
   if (!hasRest(node)) return false;
 
-  const rest = node.params.pop().argument;
+  let rest = node.params.pop().argument;
 
   const argsId = t.identifier("arguments");
 
+  if (t.isPattern(rest)) {
+    const pattern = rest;
+    rest = scope.generateUidIdentifier("ref");
+
+    const declar = t.variableDeclaration("let", [
+      t.variableDeclarator(pattern, rest),
+    ]);
+    node.body.body.unshift(declar);
+  }
+
   // check and optimise for extremely common cases
   const state = {
     references: [],

packages/babel-plugin-transform-parameters/test/fixtures/parameters/rest-patterns/exec.js

@@ -0,0 +1,5 @@
+function foo(...{ length }) {
+  return length;
+}
+
+expect(foo(1, 2, 3)).toEqual(3);

packages/babel-plugin-transform-parameters/test/fixtures/parameters/rest-patterns/input.js

@@ -0,0 +1 @@
+function foo(...[a]) {}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/rest-patterns/output.js

@@ -0,0 +1,7 @@
+function foo() {
+  for (var _len = arguments.length, _ref = new Array(_len), _key = 0; _key < _len; _key++) {
+    _ref[_key] = arguments[_key];
+  }
+
+  var a = _ref[0];
+}