feat: Support .cts as configuration file

packages/babel-core/package.json

@@ -74,7 +74,16 @@
     "@types/gensync": "^1.0.0",
     "@types/resolve": "^1.3.2",
     "@types/semver": "^5.4.0",
-    "rimraf": "^3.0.0"
+    "rimraf": "^3.0.0",
+    "ts-node": "^10.9.1"
+  },
+  "peerDependencies": {
+    "@babel/preset-typescript": "^7.0.0"
+  },
+  "peerDependenciesMeta": {
+    "@babel/preset-typescript": {
+      "optional": true
+    }
   },
   "conditions": {
     "BABEL_8_BREAKING": [

packages/babel-core/src/config/files/configuration.ts

@@ -9,7 +9,7 @@ import type { CacheConfigurator } from "../caching";
 import { makeConfigAPI } from "../helpers/config-api";
 import type { ConfigAPI } from "../helpers/config-api";
 import { makeStaticFileCache } from "./utils";
-import loadCjsOrMjsDefault from "./module-types";
+import loadCodeDefault from "./module-types";
 import pathPatternToRegex from "../pattern-to-regex";
 import type { FilePackageData, RelativeConfig, ConfigFile } from "./types";
 import type { CallerMetadata } from "../validation/options";
@@ -28,20 +28,22 @@ export const ROOT_CONFIG_FILENAMES = [
   "babel.config.cjs",
   "babel.config.mjs",
   "babel.config.json",
+  "babel.config.cts",
 ];
 const RELATIVE_CONFIG_FILENAMES = [
   ".babelrc",
   ".babelrc.js",
   ".babelrc.cjs",
   ".babelrc.mjs",
   ".babelrc.json",
+  ".babelrc.cts",
 ];
 
 const BABELIGNORE_FILENAME = ".babelignore";
 
 const LOADING_CONFIGS = new Set();
 
-const readConfigJS = makeStrongCache(function* readConfigJS(
+const readConfigCode = makeStrongCache(function* readConfigCode(
   filepath: string,
   cache: CacheConfigurator<{
     envName: string;
@@ -70,7 +72,7 @@ const readConfigJS = makeStrongCache(function* readConfigJS(
   let options: unknown;
   try {
     LOADING_CONFIGS.add(filepath);
-    options = yield* loadCjsOrMjsDefault(
+    options = yield* loadCodeDefault(
       filepath,
       "You appear to be using a native ECMAScript module configuration " +
         "file, which is only supported when running Babel asynchronously.",
@@ -313,9 +315,15 @@ function readConfig(
   caller: CallerMetadata | undefined,
 ): Handler<ConfigFile | null> {
   const ext = path.extname(filepath);
-  return ext === ".js" || ext === ".cjs" || ext === ".mjs"
-    ? readConfigJS(filepath, { envName, caller })
-    : readConfigJSON5(filepath);
+  switch (ext) {
+    case ".js":
+    case ".cjs":
+    case ".mjs":
+    case ".cts":
+      return readConfigCode(filepath, { envName, caller });
+    default:
+      return readConfigJSON5(filepath);
+  }
 }
 
 export function* resolveShowConfigPath(

packages/babel-core/src/config/files/module-types.ts

@@ -3,11 +3,15 @@ import type { Handler } from "gensync";
 import path from "path";
 import { pathToFileURL } from "url";
 import { createRequire } from "module";
+import fs from "fs";
 import semver from "semver";
 
 import { endHiddenCallStack } from "../../errors/rewrite-stack-trace";
 import ConfigError from "../../errors/config-error";
 
+import { transformSync } from "../../transform";
+import type { InputOptions } from "..";
+
 const require = createRequire(import.meta.url);
 
 let import_: ((specifier: string | URL) => any) | undefined;
@@ -23,38 +27,82 @@ export const supportsESM = semver.satisfies(
   "^12.17 || >=13.2",
 );
 
-export default function* loadCjsOrMjsDefault(
+export default function* loadCodeDefault(
   filepath: string,
   asyncError: string,
   // TODO(Babel 8): Remove this
   fallbackToTranspiledModule: boolean = false,
 ): Handler<unknown> {
-  switch (guessJSModuleType(filepath)) {
-    case "cjs":
+  switch (path.extname(filepath)) {
+    case ".cjs":
       return loadCjsDefault(filepath, fallbackToTranspiledModule);
-    case "unknown":
+    case ".mjs":
+      break;
+    case ".cts":
+      return loadCtsDefault(filepath);
+    default:
       try {
         return loadCjsDefault(filepath, fallbackToTranspiledModule);
       } catch (e) {
         if (e.code !== "ERR_REQUIRE_ESM") throw e;
       }
-    // fall through
-    case "mjs":
-      if (yield* isAsync()) {
-        return yield* waitFor(loadMjsDefault(filepath));
-      }
-      throw new ConfigError(asyncError, filepath);
   }
+  if (yield* isAsync()) {
+    return yield* waitFor(loadMjsDefault(filepath));
+  }
+  throw new ConfigError(asyncError, filepath);
 }
 
-function guessJSModuleType(filename: string): "cjs" | "mjs" | "unknown" {
-  switch (path.extname(filename)) {
-    case ".cjs":
-      return "cjs";
-    case ".mjs":
-      return "mjs";
-    default:
-      return "unknown";
+function loadCtsDefault(filepath: string) {
+  const ext = ".cts";
+  const hasTsSupport = !!(
+    require.extensions[".ts"] ||
+    require.extensions[".cts"] ||
+    require.extensions[".mts"]
+  );
+  if (!hasTsSupport) {
+    const code = fs.readFileSync(filepath, "utf8");
+    const opts: InputOptions = {
+      babelrc: false,
+      configFile: false,
+      filename: path.basename(filepath),
+      sourceType: "script",
+      sourceMaps: "inline",
+      presets: [
+        [
+          "@babel/preset-typescript",
+          process.env.BABEL_8_BREAKING
+            ? {
+                disallowAmbiguousJSXLike: true,
+                allExtensions: true,
+                onlyRemoveTypeImports: true,
+                optimizeConstEnums: true,
+              }
+            : {
+                allowDeclareFields: true,
+                disallowAmbiguousJSXLike: true,
+                allExtensions: true,
+                onlyRemoveTypeImports: true,
+                optimizeConstEnums: true,
+              },
+        ],
+      ],
+    };
+    const result = transformSync(code, opts);
+    require.extensions[ext] = function (m, filename) {
+      if (filename === filepath) {
+        // @ts-expect-error Undocumented API
+        return m._compile(result.code, filename);
+      }
+      return require.extensions[".js"](m, filename);
+    };
+  }
+  try {
+    return endHiddenCallStack(require)(filepath);
+  } finally {
+    if (!hasTsSupport) {
+      delete require.extensions[ext];
+    }
   }
 }
 
@@ -69,8 +117,7 @@ function loadCjsDefault(filepath: string, fallbackToTranspiledModule: boolean) {
 async function loadMjsDefault(filepath: string) {
   if (!import_) {
     throw new ConfigError(
-      "Internal error: Native ECMAScript modules aren't supported" +
-        " by this platform.\n",
+      "Internal error: Native ECMAScript modules aren't supported by this platform.\n",
       filepath,
     );
   }

packages/babel-core/src/config/files/plugins.ts

@@ -6,7 +6,7 @@ import buildDebug from "debug";
 import path from "path";
 import gensync, { type Handler } from "gensync";
 import { isAsync } from "../../gensync-utils/async";
-import loadCjsOrMjsDefault, { supportsESM } from "./module-types";
+import loadCodeDefault, { supportsESM } from "./module-types";
 import { fileURLToPath, pathToFileURL } from "url";
 
 import importMetaResolve from "./import-meta-resolve";
@@ -217,7 +217,7 @@ function* requireModule(type: string, name: string): Handler<unknown> {
     if (!process.env.BABEL_8_BREAKING) {
       LOADING_MODULES.add(name);
     }
-    return yield* loadCjsOrMjsDefault(
+    return yield* loadCodeDefault(
       name,
       `You appear to be using a native ECMAScript module ${type}, ` +
         "which is only supported when running Babel asynchronously.",

packages/babel-core/test/config-ts.js

@@ -0,0 +1,82 @@
+import { loadPartialConfigSync } from "../lib/index.js";
+import path from "path";
+import { fileURLToPath } from "url";
+import { createRequire } from "module";
+import semver from "semver";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const require = createRequire(import.meta.url);
+
+// We skip older versions of node testing for two reasons.
+// 1. ts-node does not support the old version of node.
+// 2. In the old version of node, jest has been registered in `require.extensions`, which will cause babel to disable the transforming as expected.
+
+describe("@babel/core config with ts [dummy]", () => {
+  it("dummy", () => {
+    expect(1).toBe(1);
+  });
+});
+
+semver.gte(process.version, "12.0.0")
+  ? describe
+  : describe.skip("@babel/core config with ts", () => {
+      it("should work with simple .cts", () => {
+        const config = loadPartialConfigSync({
+          configFile: path.join(
+            __dirname,
+            "fixtures/config-ts/simple-cts/babel.config.cts",
+          ),
+        });
+
+        expect(config.options.targets).toMatchInlineSnapshot(`
+      Object {
+        "node": "12.0.0",
+      }
+    `);
+      });
+
+      it("should throw with invalid .ts register", () => {
+        require.extensions[".ts"] = () => {
+          throw new Error("Not support .ts.");
+        };
+        expect(() => {
+          loadPartialConfigSync({
+            configFile: path.join(
+              __dirname,
+              "fixtures/config-ts/invalid-cts-register/babel.config.cts",
+            ),
+          });
+        }).toThrow(/Unexpected identifier.*/);
+        delete require.extensions[".ts"];
+      });
+
+      it("should work with ts-node", async () => {
+        const service = eval("import('ts-node')").register({
+          experimentalResolver: true,
+          compilerOptions: {
+            module: "CommonJS",
+          },
+        });
+        service.enabled(true);
+
+        require(path.join(
+          __dirname,
+          "fixtures/config-ts/simple-cts-with-ts-node/babel.config.cts",
+        ));
+
+        const config = loadPartialConfigSync({
+          configFile: path.join(
+            __dirname,
+            "fixtures/config-ts/simple-cts-with-ts-node/babel.config.cts",
+          ),
+        });
+
+        service.enabled(false);
+
+        expect(config.options.targets).toMatchInlineSnapshot(`
+      Object {
+        "node": "12.0.0",
+      }
+    `);
+      });
+    });

packages/babel-core/test/fixtures/config-ts/invalid-cts-register/babel.config.cts

@@ -0,0 +1,2 @@
+type config = any;
+module.exports = { targets: "node 12.0.0" } as config;

packages/babel-core/test/fixtures/config-ts/simple-cts-with-ts-node/babel.config.cts

@@ -0,0 +1,2 @@
+type config = any;
+module.exports = { targets: "node 12.0.0" } as config;

packages/babel-core/test/fixtures/config-ts/simple-cts/babel.config.cts

@@ -0,0 +1,2 @@
+type config = any;
+module.exports = { targets: "node 12.0.0" } as config;