move some babel-plugins into the main repo

packages/babel-plugin-react-constant-elements/.npmignore

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+node_modules
+*.log
+src

packages/babel-plugin-react-constant-elements/README.md

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+# babel-plugin-react-constant-elements
+
+Treat React JSX elements as value types and hoist them to the highest scope
+
+## Installation
+
+```sh
+$ npm install babel-plugin-react-constant-elements
+```
+
+## Usage
+
+### Via `.babelrc` (Recommended)
+
+**.babelrc**
+
+```json
+{
+  "plugins": ["react-constant-elements"]
+}
+```
+
+### Via CLI
+
+```sh
+$ babel --plugins react-constant-elements script.js
+```
+
+### Via Node API
+
+```javascript
+require("babel-core").transform("code", {
+  plugins: ["react-constant-elements"]
+});
+```

packages/babel-plugin-react-constant-elements/package.json

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+{
+  "name": "babel-plugin-react-constant-elements",
+  "version": "1.0.3",
+  "description": "Treat React JSX elements as value types and hoist them to the highest scope",
+  "repository": "babel-plugins/babel-plugin-react-constant-elements",
+  "license": "MIT",
+  "main": "lib/index.js",
+  "keywords": [
+    "babel-plugin"
+  ]
+}

packages/babel-plugin-react-constant-elements/src/index.js

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+export default function ({ Plugin }) {
+  var immutabilityVisitor = {
+    enter(node, parent, scope, state) {
+      var stop = () => {
+        state.isImmutable = false;
+        this.stop();
+      };
+
+      if (this.isJSXClosingElement()) {
+        this.skip();
+        return;
+      }
+
+      if (this.isJSXIdentifier({ name: "ref" }) && this.parentPath.isJSXAttribute({ name: node })) {
+        return stop();
+      }
+
+      if (this.isJSXIdentifier() || this.isIdentifier() || this.isJSXMemberExpression()) {
+        return;
+      }
+
+      if (!this.isImmutable()) stop();
+    }
+  };
+
+  return new Plugin("react-constant-elements", {
+    metadata: {
+      group: "builtin-basic"
+    },
+
+    visitor: {
+      JSXElement(node) {
+        if (node._hoisted) return;
+
+        var state = { isImmutable: true };
+        this.traverse(immutabilityVisitor, state);
+
+        if (state.isImmutable) {
+          this.hoist();
+        } else {
+          node._hoisted = true;
+        }
+      }
+    }
+  });
+}