Implement @babel/plugin-transform-react-pure-annotations (#11428)

The new plugin is also enabled in `@babel/preset-react`

packages/babel-plugin-transform-react-pure-annotations/src/index.js

@@ -0,0 +1,79 @@
+import { declare } from "@babel/helper-plugin-utils";
+import annotateAsPure from "@babel/helper-annotate-as-pure";
+import { types as t } from "@babel/core";
+
+// Mapping of React top-level methods that are pure.
+// This plugin adds a /*#__PURE__#/ annotation to calls to these methods,
+// so that terser and other minifiers can safely remove them during dead
+// code elimination.
+// See https://reactjs.org/docs/react-api.html
+const PURE_CALLS = new Map([
+  [
+    "react",
+    [
+      "cloneElement",
+      "createElement",
+      "createFactory",
+      "createRef",
+      "forwardRef",
+      "isValidElement",
+      "memo",
+      "lazy",
+    ],
+  ],
+  ["react-dom", ["createPortal"]],
+]);
+
+export default declare(api => {
+  api.assertVersion(7);
+
+  return {
+    name: "transform-react-pure-annotations",
+    visitor: {
+      CallExpression(path) {
+        if (isReactCall(path)) {
+          annotateAsPure(path);
+        }
+      },
+    },
+  };
+});
+
+function isReactCall(path) {
+  // If the callee is not a member expression, then check if it matches
+  // a named import, e.g. `import {forwardRef} from 'react'`.
+  if (!t.isMemberExpression(path.node.callee)) {
+    const callee = path.get("callee");
+    for (const [module, methods] of PURE_CALLS) {
+      for (const method of methods) {
+        if (callee.referencesImport(module, method)) {
+          return true;
+        }
+      }
+    }
+
+    return false;
+  }
+
+  // Otherwise, check if the member expression's object matches
+  // a default import (`import React from 'react'`) or namespace
+  // import (`import * as React from 'react'), and check if the
+  // property matches one of the pure methods.
+  for (const [module, methods] of PURE_CALLS) {
+    const object = path.get("callee.object");
+    if (
+      object.referencesImport(module, "default") ||
+      object.referencesImport(module, "*")
+    ) {
+      for (const method of methods) {
+        if (t.isIdentifier(path.node.callee.property, { name: method })) {
+          return true;
+        }
+      }
+
+      return false;
+    }
+  }
+
+  return false;
+}