repl: show lexically scoped vars in tab completion

Use the V8 inspector protocol, if available, to query the list of
lexically scoped variables (defined with `let`, `const` or `class`).

PR-URL: https://github.com/nodejs/node/pull/16591
Fixes: https://github.com/nodejs/node/issues/983
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

1 files changed, 34 insertions, 0 deletions

diff --git a/test/parallel/test-repl-inspector.js b/test/parallel/test-repl-inspector.js
new file mode 100644
index 0000000000..b02f6139e7
--- /dev/null
+++ b/test/parallel/test-repl-inspector.js
@@ -0,0 +1,34 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const repl = require('repl');
+
+common.skipIfInspectorDisabled();
+
+// This test verifies that the V8 inspector API is usable in the REPL.
+
+const putIn = new common.ArrayStream();
+let output = '';
+putIn.write = function(data) {
+  output += data;
+};
+
+const testMe = repl.start('', putIn);
+
+putIn.run(['const myVariable = 42']);
+
+testMe.complete('myVar', common.mustCall((error, data) => {
+  assert.deepStrictEqual(data, [['myVariable'], 'myVar']);
+}));
+
+putIn.run([
+  'const inspector = require("inspector")',
+  'const session = new inspector.Session()',
+  'session.connect()',
+  'session.post("Runtime.evaluate", { expression: "1 + 1" }, console.log)',
+  'session.disconnect()'
+]);
+
+assert(output.includes(
+  "null { result: { type: 'number', value: 2, description: '2' } }"));