feat(transformer): async code transformation

CHANGELOG.md

@@ -24,6 +24,7 @@
 - `[jest-transform]` Pass config options defined in Jest's config to transformer's `process` and `getCacheKey` functions ([#10926](https://github.com/facebook/jest/pull/10926))
 - `[jest-transform]` Add support for transformers written in ESM ([#11163](https://github.com/facebook/jest/pull/11163))
 - `[jest-transform]` [**BREAKING**] Do not export `ScriptTransformer` class, instead export the async function `createScriptTransformer` ([#11163](https://github.com/facebook/jest/pull/11163))
+- `[jest-transform]` Async code transformations ([#9889](https://github.com/facebook/jest/pull/9889))
 - `[jest-worker]` Add support for custom task queues and adds a `PriorityQueue` implementation. ([#10921](https://github.com/facebook/jest/pull/10921))
 - `[jest-worker]` Add in-order scheduling policy to jest worker ([10902](https://github.com/facebook/jest/pull/10902))
 

packages/babel-jest/src/index.ts

@@ -17,7 +17,7 @@ import * as fs from 'graceful-fs';
 import slash = require('slash');
 import type {
   TransformOptions as JestTransformOptions,
-  Transformer,
+  SyncTransformer,
 } from '@jest/transform';
 import type {Config} from '@jest/types';
 import {loadPartialConfig} from './loadBabelConfig';
@@ -26,7 +26,7 @@ const THIS_FILE = fs.readFileSync(__filename);
 const jestPresetPath = require.resolve('babel-preset-jest');
 const babelIstanbulPlugin = require.resolve('babel-plugin-istanbul');
 
-type CreateTransformer = Transformer<TransformOptions>['createTransformer'];
+type CreateTransformer = SyncTransformer<TransformOptions>['createTransformer'];
 
 const createTransformer: CreateTransformer = userOptions => {
   const inputOptions = userOptions ?? {};
@@ -160,7 +160,7 @@ const createTransformer: CreateTransformer = userOptions => {
   };
 };
 
-const transformer: Transformer<TransformOptions> = {
+const transformer: SyncTransformer<TransformOptions> = {
   ...createTransformer(),
   // Assigned here so only the exported transformer has `createTransformer`,
   // instead of all created transformers by the function

packages/jest-repl/src/cli/repl.ts

@@ -11,10 +11,11 @@ declare const jestProjectConfig: Config.ProjectConfig;
 import * as path from 'path';
 import * as repl from 'repl';
 import {runInThisContext} from 'vm';
-import type {Transformer} from '@jest/transform';
+import type {SyncTransformer} from '@jest/transform';
 import type {Config} from '@jest/types';
 
-let transformer: Transformer;
+// TODO: support async as well
+let transformer: SyncTransformer;
 let transformerConfig: unknown;
 
 const evalCommand: repl.REPLEval = (