Use Object Spread Syntax (babel#7777)

* Use Object Spread Syntax

* Nits

Author: jridgewell

codemods/babel-plugin-codemod-object-assign-to-object-spread/.npmignore

@@ -0,0 +1,3 @@
+src
+test
+*.log

codemods/babel-plugin-codemod-object-assign-to-object-spread/README.md

@@ -0,0 +1,57 @@
+# @babel/plugin-codemod-object-assign-to-object-spread
+
+Transforms old code that uses `Object.assign` with an Object Literal as
+the first param to use Object Spread syntax.
+
+## Examples
+
+```js
+const obj = Object.assign({
+  test1: 1,
+}, other, {
+  test2: 2,
+}, other2);
+```
+
+Is transformed to:
+
+```js
+const obj = {
+  test1: 1,
+  ...other,
+  test2: 2,
+  ...other2,
+};
+```
+
+## Installation
+
+```sh
+npm install --save-dev @babel/plugin-codemod-object-assign-to-object-spread
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "plugins": ["@babel/plugin-codemod-object-assign-to-object-spread"]
+}
+```
+
+### Via CLI
+
+```sh
+babel --plugins @babel/plugin-codemod-object-assign-to-object-spread script.js
+```
+
+### Via Node API
+
+```javascript
+require("@babel/core").transform("code", {
+  plugins: ["@babel/plugin-codemod-object-assign-to-object-spread"]
+});
+```

codemods/babel-plugin-codemod-object-assign-to-object-spread/package.json

@@ -0,0 +1,22 @@
+{
+  "name": "@babel/plugin-codemod-object-assign-to-object-spread",
+  "version": "7.0.0-beta.44",
+  "description": "Transforms Object.assign into object spread syntax",
+  "repository": "https://github.com/babel/babel/tree/master/codemods/babel-plugin-codemod-object-assign-to-object-spread",
+  "license": "MIT",
+  "main": "lib/index.js",
+  "keywords": [
+    "@babel/codemod",
+    "@babel/plugin"
+  ],
+  "dependencies": {
+    "@babel/plugin-syntax-object-rest-spread": "7.0.0-beta.44"
+  },
+  "peerDependencies": {
+    "@babel/core": "7.0.0-beta.44"
+  },
+  "devDependencies": {
+    "@babel/core": "7.0.0-beta.44",
+    "@babel/helper-plugin-test-runner": "7.0.0-beta.44"
+  }
+}

codemods/babel-plugin-codemod-object-assign-to-object-spread/src/index.js

@@ -0,0 +1,35 @@
+import syntaxObjectRestSpread from "@babel/plugin-syntax-object-rest-spread";
+
+export default function({ types: t }) {
+  return {
+    inherits: syntaxObjectRestSpread,
+
+    visitor: {
+      CallExpression(path) {
+        if (!path.get("callee").matchesPattern("Object.assign")) return;
+
+        const args = path.get("arguments");
+        if (args.length === 0) return;
+
+        const [objPath] = args;
+        if (!objPath.isObjectExpression()) return;
+
+        const obj = objPath.node;
+        const { properties } = obj;
+
+        for (let i = 1; i < args.length; i++) {
+          const arg = args[i];
+          const { node } = arg;
+
+          if (arg.isObjectExpression()) {
+            properties.push(...node.properties);
+          } else {
+            properties.push(t.spreadElement(node));
+          }
+        }
+
+        path.replaceWith(obj);
+      },
+    },
+  };
+}

codemods/babel-plugin-codemod-object-assign-to-object-spread/test/fixtures/object-assign-to-object-spread/multiple-objects/input.js

@@ -0,0 +1 @@
+Object.assign({test: 1}, {test: 2});

codemods/babel-plugin-codemod-object-assign-to-object-spread/test/fixtures/object-assign-to-object-spread/multiple-objects/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["../../../../lib"]
+}

codemods/babel-plugin-codemod-object-assign-to-object-spread/test/fixtures/object-assign-to-object-spread/multiple-objects/output.js

@@ -0,0 +1,4 @@
+({
+  test: 1,
+  test: 2
+});

codemods/babel-plugin-codemod-object-assign-to-object-spread/test/fixtures/object-assign-to-object-spread/multiple/input.js

@@ -0,0 +1 @@
+Object.assign({test: 1}, test2, {test: 2}, test3);

codemods/babel-plugin-codemod-object-assign-to-object-spread/test/fixtures/object-assign-to-object-spread/multiple/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["../../../../lib"]
+}

codemods/babel-plugin-codemod-object-assign-to-object-spread/test/fixtures/object-assign-to-object-spread/multiple/output.js

@@ -0,0 +1,6 @@
+({
+  test: 1,
+  ...test2,
+  test: 2,
+  ...test3
+});