lib: disable REPL completion on proxies and getters

the REPL completion logic evaluates code, this is generally ok
but it can be problematic when there are objects with nested
properties since the code evaluation would trigger their potential
getters (e.g. the `obj.foo.b` line would trigger the getter of
`foo`), the changes here disable the completion logic when proxies
and getters are involved thus making sure that code evaluation does
not take place when it can potentially (and surprisingly to the user)
trigger side effectful behaviors

Author: dario-piotrowicz

lib/repl.js

@@ -1311,9 +1311,11 @@ function completeFSFunctions(match) {
 //    -> [['util.print', 'util.debug', 'util.log', 'util.inspect'],
 //        'util.' ]
 //
-// Warning: This eval's code like "foo.bar.baz", so it will run property
-// getter code.
-function complete(line, callback) {
+// Warning: This eval's code like "foo.bar.baz", so it could run property
+// getter code. To avoid potential side-effecful getters the completion
+// logic is skipped when getters or proxies are involved in the expression.
+// (see: https://github.com/nodejs/node/issues/57829).
+async function complete(line, callback) {
   // List of completion lists, one for each inheritance "level"
   let completionGroups = [];
   let completeOn, group;
@@ -1508,6 +1510,12 @@ function complete(line, callback) {
       return;
     }
 
+    if (await includesProxiesOrGetters(match, this.eval, this.context)) {
+      // The expression involves proxies or getters, meaning that it
+      // can trigger side-effectful behaviors, so bail out
+      return completionGroupsLoaded();
+    }
+
     let chaining = '.';
     if (StringPrototypeEndsWith(expr, '?')) {
       expr = StringPrototypeSlice(expr, 0, -1);
@@ -1609,6 +1617,37 @@ function complete(line, callback) {
   }
 }
 
+async function includesProxiesOrGetters(fullExpr, evalFn, context) {
+  const bits = StringPrototypeSplit(fullExpr, '.');
+
+  let currentExpr = '';
+  for (let i = 0; i < bits.length - 1; i++) {
+    currentExpr += `${i===0? '' : '.'}${bits[i]}`;
+    const currentExprIsObject = await evalPromisified(`try { ${currentExpr} !== null && typeof ${currentExpr} === 'object' } catch { false }`);
+    if (!currentExprIsObject) {
+      return false;
+    }
+
+    const currentExprIsProxy = await evalPromisified(`require("node:util/types").isProxy(${currentExpr})`);
+    if (currentExprIsProxy) {
+      return true;
+    }
+
+    const typeOfNextBitGet = await evalPromisified(`typeof Object.getOwnPropertyDescriptor(${currentExpr}, '${bits[i+1]}')?.get`);
+    const nextBitHasGetter = typeOfNextBitGet === 'function';
+    if (nextBitHasGetter) {
+      return true;
+    }
+  }
+
+  function evalPromisified (evalExpr) {
+    return new Promise((resolve, reject) =>
+      evalFn(evalExpr, context, getREPLResourceName(), (_, res) => {
+        resolve(res);
+    }));
+  }
+}
+
 REPLServer.prototype.completeOnEditorMode = (callback) => (err, results) => {
   if (err) return callback(err);
 

test/parallel/test-repl-completion-on-getters-disabled.js

@@ -0,0 +1,119 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('node:assert');
+const { describe, test } = require('node:test');
+
+const ArrayStream = require('../common/arraystream');
+
+const repl = require('node:repl');
+
+function runCompletionTests(replInit, tests) {
+  const stream = new ArrayStream();
+  const testRepl = repl.start({ stream });
+
+  // Some errors are passed to the domain
+  testRepl._domain.on('error', assert.ifError);
+
+  testRepl.write(replInit);
+  testRepl.write('\n');
+
+  tests.forEach(([query, expectedCompletions]) => {
+    testRepl.complete(query, common.mustCall((error, data) => {
+      const actualCompletions = data[0];
+      if (expectedCompletions.length === 0) {
+        assert.deepStrictEqual(actualCompletions, []);
+      } else {
+        expectedCompletions.forEach((expectedCompletion) =>
+          assert(actualCompletions.includes(expectedCompletion), `completion '${expectedCompletion}' not found`)
+        );
+      }
+    }));
+  });
+}
+
+describe('REPL completion in relation of getters', () => {
+  describe('standard behavior without proxies/getters', () => {
+    test('completion of nested properties of an undeclared objects', () => {
+      runCompletionTests('', [
+        ['nonExisting.', []],
+        ['nonExisting.f', []],
+        ['nonExisting.foo', []],
+        ['nonExisting.foo.', []],
+        ['nonExisting.foo.bar.b', []],
+      ]);
+    });
+
+    test('completion of nested properties on plain objects', () => {
+      runCompletionTests('const plainObj = { foo: { bar: { baz: {} } } };', [
+        ['plainObj.', ['plainObj.foo']],
+        ['plainObj.f', ['plainObj.foo']],
+        ['plainObj.foo', ['plainObj.foo']],
+        ['plainObj.foo.', ['plainObj.foo.bar']],
+        ['plainObj.foo.bar.b', ['plainObj.foo.bar.baz']],
+        ['plainObj.fooBar.', []],
+        ['plainObj.fooBar.baz', []],
+      ]);
+    });
+  });
+
+  describe('completions on an object with getters', () => {
+    test(`completions are generated for properties that don't trigger getters`, () => {
+      runCompletionTests(
+        `
+        const objWithGetters = {
+          foo: { bar: { baz: {} }, get gBar() { return { baz: {} } } },
+          get gFoo() { return { bar: { baz: {} } }; }
+        };
+        `, [
+          ['objWithGetters.', ['objWithGetters.foo']],
+          ['objWithGetters.f', ['objWithGetters.foo']],
+          ['objWithGetters.foo', ['objWithGetters.foo']],
+          ['objWithGetters.foo.', ['objWithGetters.foo.bar']],
+          ['objWithGetters.foo.bar.b', ['objWithGetters.foo.bar.baz']],
+          ['objWithGetters.gFo', ['objWithGetters.gFoo']],
+          ['objWithGetters.foo.gB', ['objWithGetters.foo.gBar']],
+        ]);
+    });
+
+    test('no completions are generated for properties that trigger getters', () => {
+      runCompletionTests(
+        `
+        const objWithGetters = {
+          foo: { bar: { baz: {} }, get gBar() { return { baz: {} } } },
+          get gFoo() { return { bar: { baz: {} } }; }
+        };
+        `,
+        [
+          ['objWithGetters.gFoo.', []],
+          ['objWithGetters.gFoo.b', []],
+          ['objWithGetters.gFoo.bar.b', []],
+          ['objWithGetters.foo.gBar.', []],
+          ['objWithGetters.foo.gBar.b', []],
+        ]);
+    });
+  });
+
+  describe('completions on proxies', () => {
+    test('no completions are generated for a proxy object', () => {
+      runCompletionTests('const proxyObj = new Proxy({ foo: { bar: { baz: {} } } }, {});', [
+        ['proxyObj.', []],
+        ['proxyObj.f', []],
+        ['proxyObj.foo', []],
+        ['proxyObj.foo.', []],
+        ['proxyObj.foo.bar.b', []],
+      ]);
+    });
+
+    test('no completions are generated for a proxy present in a standard object', () => {
+      runCompletionTests(
+        'const objWithProxy = { foo: { bar: new Proxy({ baz: {} }, {}) } };', [
+          ['objWithProxy.', ['objWithProxy.foo']],
+          ['objWithProxy.foo', ['objWithProxy.foo']],
+          ['objWithProxy.foo.', ['objWithProxy.foo.bar']],
+          ['objWithProxy.foo.b', ['objWithProxy.foo.bar']],
+          ['objWithProxy.foo.bar.', []],
+        ]);
+    });
+  });
+});