feat: add support for avoiding the module wrapper

Author: SimenB

CHANGELOG.md

@@ -17,6 +17,7 @@
 - `[jest-diff]` Add `changeColor` and `patchColor` options ([#8911](https://github.com/facebook/jest/pull/8911))
 - `[jest-diff]` Add `trailingSpaceFormatter` option and replace cyan with `commonColor` ([#8927](https://github.com/facebook/jest/pull/8927))
 - `[jest-diff]` Add `firstOrLastEmptyLineReplacement` option and export 3 `diffLines` functions ([#8955](https://github.com/facebook/jest/pull/8955))
+- `[jest-environment]` Support compiling a function, rather than using a module wrapper ([#9252](https://github.com/facebook/jest/pull/9252))
 - `[jest-environment-jsdom]` Add `fakeTimersLolex` ([#8925](https://github.com/facebook/jest/pull/8925))
 - `[jest-environment-node]` Add `fakeTimersLolex` ([#8925](https://github.com/facebook/jest/pull/8925))
 - `[jest-environment-node]` Add `queueMicrotask` ([#9140](https://github.com/facebook/jest/pull/9140))
@@ -26,6 +27,7 @@
 - `[jest-reporters]` Export utils for path formatting ([#9162](https://github.com/facebook/jest/pull/9162))
 - `[jest-runner]` Warn if a worker had to be force exited ([#8206](https://github.com/facebook/jest/pull/8206))
 - `[jest-runtime]` [**BREAKING**] Do not export `ScriptTransformer` - it can be imported from `@jest/transform` instead ([#9256](https://github.com/facebook/jest/pull/9256))
+- `[jest-runtime]` Support compiling a function, rather than using a module wrapper ([#9252](https://github.com/facebook/jest/pull/9252))
 - `[jest-snapshot]` Display change counts in annotation lines ([#8982](https://github.com/facebook/jest/pull/8982))
 - `[jest-snapshot]` [**BREAKING**] Improve report when the matcher has properties ([#9104](https://github.com/facebook/jest/pull/9104))
 - `[jest-snapshot]` Improve colors when snapshots are updatable ([#9132](https://github.com/facebook/jest/pull/9132))

packages/jest-environment-node/src/index.ts

@@ -5,7 +5,13 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {Context, Script, createContext, runInContext} from 'vm';
+import {
+  Context,
+  Script,
+  compileFunction,
+  createContext,
+  runInContext,
+} from 'vm';
 import {Config, Global} from '@jest/types';
 import {ModuleMocker} from 'jest-mock';
 import {installCommonGlobals} from 'jest-util';
@@ -110,6 +116,20 @@ class NodeEnvironment implements JestEnvironment {
     }
     return null;
   }
+
+  compileFunction(code: string, params: Array<string>, filename: string) {
+    if (this.context) {
+      return compileFunction(code, params, {
+        filename,
+        parsingContext: this.context,
+      }) as any;
+    }
+    return null;
+  }
+}
+
+if (typeof compileFunction !== 'function') {
+  delete NodeEnvironment.prototype.compileFunction;
 }
 
 export = NodeEnvironment;

packages/jest-environment/src/index.ts

@@ -44,6 +44,11 @@ export declare class JestEnvironment {
   fakeTimersLolex: LolexFakeTimers | null;
   moduleMocker: jestMock.ModuleMocker | null;
   runScript<T = unknown>(script: Script): T | null;
+  compileFunction?<T = unknown>(
+    code: string,
+    params: Array<string>,
+    filename: string,
+  ): T | null;
   setup(): Promise<void>;
   teardown(): Promise<void>;
   handleTestEvent?(event: Circus.Event, state: Circus.State): void;

packages/jest-runtime/src/index.ts

@@ -730,20 +730,41 @@ class Runtime {
       }
     }
 
-    const script = this.createScriptFromCode(transformedFile.code, filename);
+    let compiledFunction: ModuleWrapper | null;
+
+    if (typeof this._environment.compileFunction === 'function') {
+      try {
+        compiledFunction = this._environment.compileFunction<ModuleWrapper>(
+          transformedFile.code,
+          this.constructInjectedModuleParameters(),
+          filename,
+        );
+      } catch (e) {
+        throw handlePotentialSyntaxError(e);
+      }
+    } else {
+      const script = this.createScriptFromCode(transformedFile.code, filename);
 
-    const runScript = this._environment.runScript<RunScriptEvalResult>(script);
+      const runScript = this._environment.runScript<RunScriptEvalResult>(
+        script,
+      );
 
-    if (runScript === null) {
+      if (runScript === null) {
+        compiledFunction = null;
+      } else {
+        compiledFunction = runScript[EVAL_RESULT_VARIABLE];
+      }
+    }
+
+    if (compiledFunction === null) {
       this._logFormattedReferenceError(
         'You are trying to `import` a file after the Jest environment has been torn down.',
       );
       process.exitCode = 1;
       return;
     }
 
-    //Wrapper
-    runScript[EVAL_RESULT_VARIABLE].call(
+    compiledFunction.call(
       localModule.exports,
       localModule as NodeModule, // module object
       localModule.exports, // module exports
@@ -1107,7 +1128,19 @@ class Runtime {
   }
 
   private wrapCodeInModuleWrapper(content: string) {
-    const args = [
+    const args = this.constructInjectedModuleParameters();
+
+    return (
+      '({"' +
+      EVAL_RESULT_VARIABLE +
+      `":function(${args.join(',')}){` +
+      content +
+      '\n}});'
+    );
+  }
+
+  private constructInjectedModuleParameters() {
+    return [
       'module',
       'exports',
       'require',
@@ -1117,14 +1150,6 @@ class Runtime {
       'jest',
       ...this._config.extraGlobals,
     ];
-
-    return (
-      '({"' +
-      EVAL_RESULT_VARIABLE +
-      `":function(${args.join(',')}){` +
-      content +
-      '\n}});'
-    );
   }
 }
 

packages/jest-transform/src/enhanceUnexpectedTokenMessage.ts

@@ -17,7 +17,8 @@ export default function handlePotentialSyntaxError(
   }
 
   if (
-    e instanceof SyntaxError &&
+    // `instanceof` might come from the wrong context
+    e.name === 'SyntaxError' &&
     (e.message.includes('Unexpected token') ||
       e.message.includes('Cannot use import')) &&
     !e.message.includes(' expected')