test: add tests for REPL custom evals

this commit reintroduces the REPL custom eval tests that have
been introduced in nodejs#57691
but reverted in nodejs#57793

the tests turned out problematic before because `getReplOutput`,
the function used to return the repl output, wasn't taking into
account that input processing and output emitting are asynchronous
operation can resolve with a small delay

Author: dario-piotrowicz

lib/repl.js

@@ -302,7 +302,6 @@ function REPLServer(prompt,
     options.useColors = shouldColorize(options.output);
   }
 
-  // TODO(devsnek): Add a test case for custom eval functions.
   const preview = options.terminal &&
     (options.preview !== undefined ? !!options.preview : !eval_);
 

test/parallel/test-repl-custom-eval.js

@@ -0,0 +1,160 @@
+'use strict';
+
+require('../common');
+const ArrayStream = require('../common/arraystream');
+const assert = require('assert');
+const { describe, it } = require('node:test');
+
+const repl = require('repl');
+
+// Processes some input in a REPL instance and resolves to the repl's
+// output when the provided exitCondition is met, or after a certain
+// timeout threshold if the condition is never met
+function getReplOutput(input, exitCondition, replOptions, run = true) {
+  return new Promise((resolve) => {
+    const inputStream = new ArrayStream();
+    const outputStream = new ArrayStream();
+
+    const replServer = repl.start({
+      input: inputStream,
+      output: outputStream,
+      ...replOptions,
+    });
+
+    let output = '';
+
+    const timeoutTimer = setTimeout(() => {
+      replServer.close();
+      resolve(output);
+    }, 3_000);
+
+    outputStream.write = (chunk) => {
+      output += chunk;
+      if (exitCondition(output)) {
+        clearTimeout(timeoutTimer);
+        replServer.close();
+        resolve(output);
+      }
+    };
+
+    inputStream.emit('data', input);
+
+    if (run) {
+      inputStream.run(['']);
+    }
+
+    return output;
+  });
+}
+
+describe('repl with custom eval', { concurrency: true }, () => {
+  it('uses the custom eval function as expected', async () => {
+    const regexp = /Convert this to upper case\r\n'CONVERT THIS TO UPPER CASE\\n'/;
+    const output = await getReplOutput('Convert this to upper case', (output) => regexp.test(output), {
+      terminal: true,
+      eval: (code, _ctx, _replRes, cb) => cb(null, code.toUpperCase()),
+    });
+    assert.match(output, regexp);
+  });
+
+  it('surfaces errors as expected', async () => {
+    const regexp = /Uncaught Error: Testing Error\n/;
+    const output = await getReplOutput('Convert this to upper case',
+                                       (output) => regexp.test(output), {
+                                         terminal: true,
+                                         eval: (_code, _ctx, _replRes, cb) => cb(new Error('Testing Error')),
+                                       });
+    assert.match(output, regexp);
+  });
+
+  it('provides a repl context to the eval callback', async () => {
+    const context = await new Promise((resolve) => {
+      const r = repl.start({
+        eval: (_cmd, context) => resolve(context),
+      });
+      r.context = { foo: 'bar' };
+      r.write('\n.exit\n');
+    });
+    assert.strictEqual(context.foo, 'bar');
+  });
+
+  it('provides the global context to the eval callback', async () => {
+    const context = await new Promise((resolve) => {
+      const r = repl.start({
+        useGlobal: true,
+        eval: (_cmd, context) => resolve(context),
+      });
+      global.foo = 'global_foo';
+      r.write('\n.exit\n');
+    });
+
+    assert.strictEqual(context.foo, 'global_foo');
+    delete global.foo;
+  });
+
+  it('inherits variables from the global context but does not use it afterwords if `useGlobal` is false', async () => {
+    global.bar = 'global_bar';
+    const context = await new Promise((resolve) => {
+      const r = repl.start({
+        useGlobal: false,
+        eval: (_cmd, context) => resolve(context),
+      });
+      global.baz = 'global_baz';
+      r.write('\n.exit\n');
+    });
+
+    assert.strictEqual(context.bar, 'global_bar');
+    assert.notStrictEqual(context.baz, 'global_baz');
+    delete global.bar;
+    delete global.baz;
+  });
+
+  /**
+   * Default preprocessor transforms
+   *  function f() {}  to
+   *  var f = function f() {}
+   * This test ensures that original input is preserved.
+   * Reference: https://github.com/nodejs/node/issues/9743
+   */
+  it('preserves the original input', async () => {
+    const cmd = await new Promise((resolve) => {
+      const r = repl.start({
+        eval: (cmd) => resolve(cmd),
+      });
+      r.write('function f() {}\n.exit\n');
+    });
+    assert.strictEqual(cmd, 'function f() {}\n');
+  });
+
+  it("doesn't show previews by default", async () => {
+    const input = "'Hello custom' + ' eval World!'";
+    const output = await getReplOutput(
+      input,
+      () => false,
+      {
+        terminal: true,
+        eval: (code, _ctx, _replRes, cb) => cb(null, eval(code)),
+      },
+      false
+    );
+    assert.strictEqual(output, input);
+    assert.doesNotMatch(output, /Hello custom eval World!/);
+  });
+
+  it('does show previews if `preview` is set to `true`', async () => {
+    const input = "'Hello custom' + ' eval World!'";
+    const escapedInput = input.replace(/\+/g, '\\+'); // TODO: migrate to `RegExp.escape` when it's available.
+    const regexp = new RegExp(`${escapedInput}\n// 'Hello custom eval World!'`);
+    const output = await getReplOutput(
+      input,
+      (output) => regexp.test(output),
+      {
+        terminal: true,
+        eval: (code, _ctx, _replRes, cb) => cb(null, eval(code)),
+        preview: true,
+      },
+      false
+    );
+    assert.match(output, regexp);
+  });
+});