Implement an official TypeScript compiler plugin.

packages/typescript/README.md

@@ -0,0 +1,98 @@
+# typescript
+[Source code of released version](https://github.com/meteor/meteor/tree/master/packages/typescript) | [Source code of development version](https://github.com/meteor/meteor/tree/devel/packages/typescript)
+***
+
+This plugin package enables the use of
+[TypeScript](https://www.typescriptlang.org) modules with `.ts` or `.tsx`
+file extensions in Meteor applications and packages, alongside `.js`
+modules (or whatever other types of modules you might be using).
+
+## Usage
+
+The `typescript` package registers a compiler plugin that transpiles
+TypeScript to plain ECMAScript, which is then compiled by Babel for
+multiple targets (server, modern browsers, legacy browsers, cordova).
+By default, the `typescript` package is included in the `.meteor/packages`
+file of all new Meteor applications.
+
+To add the `typescript` package to an existing app, run the following
+command from your app directory:
+
+```bash
+meteor add typescript
+```
+
+To add the `typescript` package to an existing package, include the
+statement `api.use('typescript');` in the `Package.onUse` callback in your
+`package.js` file:
+
+```js
+Package.onUse(function (api) {
+  api.use('typescript');
+});
+```
+
+## Supported TypeScript features
+
+Almost all TypeScript syntax is supported, though this plugin currently
+does not attempt to provide type checking (just compilation).
+
+Since the Meteor `typescript` package runs the official TypeScript
+compiler before running Babel, it does not suffer from the same
+[caveats](https://babeljs.io/docs/en/babel-plugin-transform-typescript#caveats)
+known to affect the Babel TypeScript transform. In particular,
+`namespace`s are fully supported.
+
+However, as of this writing, the Meteor `typescript` package compiles
+TypeScript modules individually, using the `transpileModule` function,
+which means that certain cross-file analysis and compilation will not
+work. For example, `export const enum {...}` is not fully supported,
+though `const enum {...}` works when confined to a single module.
+
+Unlike the Babel implementation of TypeScript, there is nothing
+fundamentally preventing Meteor from compiling all TypeScript modules
+together, rather than individually, which would enable full support for
+features like `export const enum`. That's an area for future improvement,
+though we will have to weigh the performance implications carefully.
+
+As of this writing, `tsconfig.json` files are ignored by the plugin.
+There's nothing fundamentally preventing the Meteor `typescript` plugin
+from accepting configuration options from `tsconfig.json`, but for now
+we've kept things simple by avoiding configuration complexities. You may
+still want to have a `tsconfig.json` file in your application root
+directory to configure the behavior of editors like VSCode, but it will
+not be respected by Meteor.
+
+Finally, since the TypeScript compiler runs first, syntax that is not
+understood by the TypeScript compiler, such as experimental ECMAScript
+proposals, may cause the TypeScript parser to reject your code. You can
+use `.babelrc` files to configure Babel compilation, but TypeScript still
+has to accept the code first.
+
+## Areas for improvement
+
+* Compile all TypeScript modules at the same time, rather than compiling
+  them individually, to enable cross-module analysis and compilation. In
+  the meantime, if you need this behavior, consider using
+  [`adornis:typescript`](https://atmospherejs.com/adornis/typescript).
+
+* Use the version of `typescript` installed in the application
+  `node_modules` directory, rather than the one bundled with
+  `meteor-babel`. We will attempt to keep `meteor-babel`'s version of
+  `typescript` up-to-date, but it would be better to leave this decision
+  to the application developer.
+
+* Generate `.d.ts` declaration files that can be consumed by external
+  tools. In particular, a Meteor package that uses TypeScript could
+  generate `.d.ts` files in the `/node_modules/meteor/package-name/`
+  directory, which would allow tools like VSCode to find the right types
+  for the package when importing from `meteor/package-name`.
+
+* Cache the output of the TypeScript compiler separately from the output
+  of Meteor's Babel compiler pipeline. The TypeScript compiler does not
+  compile code differently for different targets (server, modern, legacy,
+  etc.), so its results could theoretically be reused for all targets.
+
+* Make the `typescript` plugin look up `tsconfig.json` files (similar to
+  how `babel-compiler` looks up `.babelrc` files) and obey (some of) the
+  configuration options.

packages/typescript/package.js

@@ -0,0 +1,31 @@
+Package.describe({
+  name: "typescript",
+  version: "3.5.2",
+  summary: "Compiler plugin that compiles TypeScript and ECMAScript in .ts and .tsx files",
+  documentation: "README.md"
+});
+
+Package.registerBuildPlugin({
+  name: "compile-typescript",
+  use: ["babel-compiler"],
+  sources: ["plugin.js"]
+});
+
+Package.onUse(function (api) {
+  api.use("isobuild:compiler-plugin@1.0.0");
+  // The following api.imply calls should match those in
+  // ../ecmascript/package.js.
+  api.imply("modules");
+  api.imply("ecmascript-runtime");
+  api.imply("babel-runtime");
+  api.imply("promise");
+  // Runtime support for Meteor 1.5 dynamic import(...) syntax.
+  api.imply("dynamic-import");
+});
+
+Package.onTest(function (api) {
+  api.use("tinytest");
+  api.use("es5-shim");
+  api.use("typescript");
+  api.mainModule("tests.ts");
+});

packages/typescript/plugin.js

@@ -0,0 +1,19 @@
+Plugin.registerCompiler({
+  extensions: ["ts", "tsx"],
+}, function () {
+  return new TypeScriptCompiler({
+    react: true,
+    typescript: true,
+  });
+});
+
+class TypeScriptCompiler extends BabelCompiler {
+  processFilesForTarget(inputFiles) {
+    return super.processFilesForTarget(inputFiles.filter(
+      // TypeScript .d.ts declaration files look like .ts files, but it's
+      // important that we do not compile them using the TypeScript
+      // compiler, as it will fail with a cryptic error message.
+      file => ! file.getPathInPackage().endsWith(".d.ts")
+    ));
+  }
+}

packages/typescript/tests.ts

@@ -0,0 +1,39 @@
+import { Tinytest } from "meteor/tinytest";
+
+Tinytest.add("TypeScript - basics", test => {
+  test.equal(2 + 2, 4);
+});
+
+Tinytest.add("TypeScript - const enum", test => {
+  const enum Kind {
+    NORMAL,
+    WEIRD,
+  }
+  test.equal(typeof Kind.NORMAL, "number");
+  test.equal(typeof Kind.WEIRD, "number");
+  test.equal(Kind.NORMAL + 1, Kind.WEIRD);
+});
+
+Tinytest.add("TypeScript - constructor member parameters", test => {
+  class Test {
+    constructor(
+      private a: number,
+      public b: string,
+    ) {}
+  }
+  const t = new Test(1234, "asdf");
+  test.equal((t as any).a, 1234);
+  test.equal(t.b, "asdf");
+});
+
+Tinytest.add("TypeScript - namespaces", test => {
+  function foo() {
+    return foo.bar;
+  }
+
+  namespace foo {
+    export const bar = "oyez";
+  }
+
+  test.equal(foo(), "oyez");
+});

tools/static-assets/skel-bare/.meteor/packages

@@ -15,4 +15,5 @@ standard-minifier-css   # CSS minifier run for production mode
 standard-minifier-js    # JS minifier run for production mode
 es5-shim                # ECMAScript 5 compatibility for older browsers
 ecmascript              # Enable ECMAScript2015+ syntax in app code
+typescript              # Enable TypeScript syntax in .ts and .tsx modules
 shell-server            # Server-side component of the `meteor shell` command

tools/static-assets/skel-full/.meteor/packages

@@ -15,6 +15,7 @@ standard-minifier-css   # CSS minifier run for production mode
 standard-minifier-js    # JS minifier run for production mode
 es5-shim                # ECMAScript 5 compatibility for older browsers
 ecmascript              # Enable ECMAScript2015+ syntax in app code
+typescript              # Enable TypeScript syntax in .ts and .tsx modules
 shell-server            # Server-side component of the `meteor shell` command
 
 kadira:flow-router      # FlowRouter is a very simple router for Meteor

tools/static-assets/skel-minimal/.meteor/packages

@@ -10,6 +10,7 @@ standard-minifier-css   # CSS minifier run for production mode
 standard-minifier-js    # JS minifier run for production mode
 es5-shim                # ECMAScript 5 compatibility for older browsers
 ecmascript              # Enable ECMAScript2015+ syntax in app code
+typescript              # Enable TypeScript syntax in .ts and .tsx modules
 shell-server            # Server-side component of the `meteor shell` command
 webapp                  # Serves a Meteor app over HTTP
 server-render           # Support for server-side rendering

tools/static-assets/skel-react/.meteor/packages

@@ -13,6 +13,7 @@ standard-minifier-css   # CSS minifier run for production mode
 standard-minifier-js    # JS minifier run for production mode
 es5-shim                # ECMAScript 5 compatibility for older browsers
 ecmascript              # Enable ECMAScript2015+ syntax in app code
+typescript              # Enable TypeScript syntax in .ts and .tsx modules
 shell-server            # Server-side component of the `meteor shell` command
 
 autopublish             # Publish all data to the clients (for prototyping)

tools/static-assets/skel/.meteor/packages

@@ -15,6 +15,7 @@ standard-minifier-css   # CSS minifier run for production mode
 standard-minifier-js    # JS minifier run for production mode
 es5-shim                # ECMAScript 5 compatibility for older browsers
 ecmascript              # Enable ECMAScript2015+ syntax in app code
+typescript              # Enable TypeScript syntax in .ts and .tsx modules
 shell-server            # Server-side component of the `meteor shell` command
 
 autopublish             # Publish all data to the clients (for prototyping)

tools/tests/apps/modules/.meteor/packages

@@ -27,3 +27,4 @@ underscore@1.0.10
 import-local-json-module
 akryum:vue-component
 dummy-compiler
+typescript

tools/tests/apps/modules/tests.js

@@ -708,6 +708,14 @@ describe("ecmascript miscellany", () => {
   });
 });
 
+describe("TypeScript", () => {
+  it("can be imported", () => {
+    const { Test } = require("./typescript");
+    assert.strictEqual(typeof Test, "function");
+    assert.strictEqual(new Test(1234).value, 1234);
+  });
+});
+
 Meteor.isClient &&
 describe("client/compatibility directories", () => {
   it("should contain bare files", () => {

tools/tests/apps/modules/typescript.ts

@@ -0,0 +1,3 @@
+export class Test<T> {
+  constructor(public readonly value: T) {}
+}

tools/tool-testing/sandbox.js

@@ -566,6 +566,8 @@ const ROOT_PACKAGES_TO_BUILD_IN_SANDBOX = [
   "es5-shim",
   "shell-server",
   "modern-browsers",
+  "ecmascript",
+  "typescript",
 ];
 
 function newSelfTestCatalog() {