Move decorators transform to @babel/helper-create-class-features-plugin (#9059)

* Move decorators to @babel/plugin-class-features

* Minor refactoring

* Use the new helper package

packages/babel-helper-create-class-features-plugin/src/decorators.js

@@ -1,3 +1,154 @@
-export function hasDecorators(path) {
-  return !!(path.node.decorators && path.node.decorators.length);
+import { types as t, template } from "@babel/core";
+import ReplaceSupers from "@babel/helper-replace-supers";
+
+export function hasOwnDecorators(node) {
+  return !!(node.decorators && node.decorators.length);
+}
+
+export function hasDecorators(node) {
+  return hasOwnDecorators(node) || node.body.body.some(hasOwnDecorators);
+}
+
+function prop(key, value) {
+  if (!value) return null;
+  return t.objectProperty(t.identifier(key), value);
+}
+
+function value(body, params = [], async, generator) {
+  const method = t.objectMethod("method", t.identifier("value"), params, body);
+  method.async = !!async;
+  method.generator = !!generator;
+  return method;
+}
+
+function takeDecorators(node) {
+  let result;
+  if (node.decorators && node.decorators.length > 0) {
+    result = t.arrayExpression(
+      node.decorators.map(decorator => decorator.expression),
+    );
+  }
+  node.decorators = undefined;
+  return result;
+}
+
+function getKey(node) {
+  if (node.computed) {
+    return node.key;
+  } else if (t.isIdentifier(node.key)) {
+    return t.stringLiteral(node.key.name);
+  } else {
+    return t.stringLiteral(String(node.key.value));
+  }
+}
+
+// NOTE: This function can be easily bound as .bind(file, classRef, superRef)
+//       to make it easier to use it in a loop.
+function extractElementDescriptor(/* this: File, */ classRef, superRef, path) {
+  const { node, scope } = path;
+  const isMethod = path.isClassMethod();
+
+  if (path.isPrivate()) {
+    throw path.buildCodeFrameError(
+      `Private ${
+        isMethod ? "methods" : "fields"
+      } in decorated classes are not supported yet.`,
+    );
+  }
+
+  new ReplaceSupers(
+    {
+      methodPath: path,
+      methodNode: node,
+      objectRef: classRef,
+      isStatic: node.static,
+      superRef,
+      scope,
+      file: this,
+    },
+    true,
+  ).replace();
+
+  const properties = [
+    prop("kind", t.stringLiteral(isMethod ? node.kind : "field")),
+    prop("decorators", takeDecorators(node)),
+    prop("static", node.static && t.booleanLiteral(true)),
+    prop("key", getKey(node)),
+    isMethod
+      ? value(node.body, node.params, node.async, node.generator)
+      : node.value
+      ? value(template.ast`{ return ${node.value} }`)
+      : prop("value", scope.buildUndefinedNode()),
+  ].filter(Boolean);
+
+  path.remove();
+
+  return t.objectExpression(properties);
+}
+
+function addDecorateHelper(file) {
+  try {
+    return file.addHelper("decorate");
+  } catch (err) {
+    if (err.code === "BABEL_HELPER_UNKNOWN") {
+      err.message +=
+        "\n  '@babel/plugin-transform-decorators' in non-legacy mode" +
+        " requires '@babel/core' version ^7.0.2 and you appear to be using" +
+        " an older version.";
+    }
+    throw err;
+  }
+}
+
+export function buildDecoratedClass(ref, path, elements, file) {
+  const { node, scope } = path;
+  const initializeId = scope.generateUidIdentifier("initialize");
+  const isDeclaration = node.id && path.isDeclaration();
+  const isStrict = path.isInStrictMode();
+  const { superClass } = node;
+
+  node.type = "ClassDeclaration";
+  if (!node.id) node.id = t.cloneNode(ref);
+
+  let superId;
+  if (superClass) {
+    superId = scope.generateUidIdentifierBasedOnNode(node.superClass, "super");
+    node.superClass = superId;
+  }
+
+  const classDecorators = takeDecorators(node);
+  const definitions = t.arrayExpression(
+    elements.map(extractElementDescriptor.bind(file, node.id, superId)),
+  );
+
+  let replacement = template.expression.ast`
+    ${addDecorateHelper(file)}(
+      ${classDecorators || t.nullLiteral()},
+      function (${initializeId}, ${superClass ? superId : null}) {
+        ${node}
+        return { F: ${t.cloneNode(node.id)}, d: ${definitions} };
+      },
+      ${superClass}
+    )
+  `;
+  let classPathDesc = "arguments.1.body.body.0";
+
+  if (!isStrict) {
+    replacement.arguments[1].body.directives.push(
+      t.directive(t.directiveLiteral("use strict")),
+    );
+  }
+
+  if (isDeclaration) {
+    replacement = template.ast`let ${ref} = ${replacement}`;
+    classPathDesc = "declarations.0.init." + classPathDesc;
+  }
+
+  return {
+    instanceNodes: [template.statement.ast`${initializeId}(this)`],
+    wrapClass(path) {
+      path.replaceWith(replacement);
+      return path.get(classPathDesc);
+    },
+  };
 }