Rename @babel/core files to .ts (#12929)

packages/babel-core/src/transform.ts

@@ -0,0 +1,44 @@
+// @flow
+
+import gensync from "gensync";
+
+import loadConfig, { type InputOptions, type ResolvedConfig } from "./config";
+import {
+  run,
+  type FileResult,
+  type FileResultCallback,
+} from "./transformation";
+
+type Transform = {
+  (code: string, callback: FileResultCallback): void,
+  (code: string, opts: ?InputOptions, callback: FileResultCallback): void,
+
+  // Here for backward-compatibility. Ideally use ".transformSync" if you want
+  // a synchronous API.
+  (code: string, opts: ?InputOptions): FileResult | null,
+};
+
+const transformRunner = gensync<[string, ?InputOptions], FileResult | null>(
+  function* transform(code, opts) {
+    const config: ResolvedConfig | null = yield* loadConfig(opts);
+    if (config === null) return null;
+
+    return yield* run(config, code);
+  },
+);
+
+export const transform: Transform = (function transform(code, opts, callback) {
+  if (typeof opts === "function") {
+    callback = opts;
+    opts = undefined;
+  }
+
+  // For backward-compat with Babel 6, we allow sync transformation when
+  // no callback is given. Will be dropped in some future Babel major version.
+  if (callback === undefined) return transformRunner.sync(code, opts);
+
+  transformRunner.errback(code, opts, callback);
+}: Function);
+
+export const transformSync = transformRunner.sync;
+export const transformAsync = transformRunner.async;