Add support for TS declare modifier on fields (#10545)

* [parser] Add support for TS declare modifier on fields (#10484)

* [parser] Add support for TS declare modifier on fields

* Use Object.create(null)

* Comment

* Add support for TS declare types to types and generator (#10544)

* Transform TypeScript "declare" fields (#10546)

* Transform TypeScript "declare" fields

* Remove multiple spaces

* declareFields -> allowDeclareFields

* Update after rebase

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

@@ -5,6 +5,8 @@ import ReplaceSupers, {
 import memberExpressionToFunctions from "@babel/helper-member-expression-to-functions";
 import optimiseCall from "@babel/helper-optimise-call-expression";
 
+import * as ts from "./typescript";
+
 export function buildPrivateNamesMap(props) {
   const privateNamesMap = new Map();
   for (const prop of props) {
@@ -556,6 +558,8 @@ export function buildFieldsInitNodes(
   let needsClassRef = false;
 
   for (const prop of props) {
+    ts.assertFieldTransformed(prop);
+
     const isStatic = prop.node.static;
     const isInstance = !isStatic;
     const isPrivate = prop.isPrivate();

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

@@ -0,0 +1,19 @@
+// @flow
+
+import type { NodePath } from "@babel/traverse";
+
+export function assertFieldTransformed(path: NodePath) {
+  // TODO (Babel 8): Also check path.node.definite
+
+  if (path.node.declare) {
+    throw path.buildCodeFrameError(
+      `TypeScript 'declare' fields must first be transformed by ` +
+        `@babel/plugin-transform-typescript.\n` +
+        `If you have already enabled that plugin (or '@babel/preset-typescript'), make sure ` +
+        `that it runs before any plugin related to additional class features:\n` +
+        ` - @babel/plugin-proposal-class-properties\n` +
+        ` - @babel/plugin-proposal-private-methods\n` +
+        ` - @babel/plugin-proposal-decorators`,
+    );
+  }
+}