vm: let declaration no longer throws SyntaxError for non-configurable global property in vm context (regression in v26)

Version

v26.3.0

Platform

Darwin 24.6.0 Darwin Kernel Version 24.6.0: xnu-11417.140.69.705.2~1/RELEASE_ARM64_T6041 arm64 (macOS, Apple Silicon)

Subsystem

vm

What steps will reproduce the bug?

A let declaration that collides with a non-configurable property on a vm context's global object is no longer rejected with a SyntaxError. Save as repro.js and run with node repro.js:

const vm = require('vm');
const context = vm.createContext({});

// Define a non-configurable ("restricted") property on the context global.
vm.runInContext(
  "Object.defineProperty(this, 'foo', { value: 1, configurable: false });",
  context
);

// Per ECMA-262 GlobalDeclarationInstantiation step 3.d, a lexical
// declaration colliding with a restricted global property must throw.
try {
  vm.runInContext('let foo;', context);
  console.log('NO ERROR (let foo; was accepted)');
} catch (e) {
  console.log('THREW:', e.constructor.name, '-', e.message);
}

How often does it reproduce? Is there a required condition?

100% reproducible.

What is the expected behavior? Why is that the expected behavior?

let foo; should throw a SyntaxError, because foo is a non-configurable own property of the global object. v24.12.0 behaves correctly: THREW: SyntaxError - Identifier 'foo' has already been declared

What do you see instead?

On v26.3.0 the declaration is silently accepted: NO ERROR (let foo; was accepted)

Additional information

Found via the test262 language/global-code/script-decl-lex-restricted-global.js case.

@legendecas

This might be one of the cases that the behaviour before #63549 was guarding us against (cc @legendecas)

Thanks for the report!

This might be one of the cases that the behaviour before #63549 was guarding us against.

I will try with https://chromium-review.googlesource.com/c/v8/v8/+/7898818.

As a follow-up, I think we could run the part of the test262 global-code in vm to proactively verify vm changes.

[execution] Lookup interceptor for RestrictedGlobalProperty

deps: V8: backport a05321ebd98e

vm: enable interception on global restricted properties

deps: V8: backport a05321ebd98e

vm: enable interception on global restricted properties

deps: V8: backport a05321ebd98e

vm: enable interception on global restricted properties

deps: V8: backport a05321ebd98e

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vm: `let` declaration no longer throws SyntaxError for non-configurable global property in vm context (regression in v26) #63715

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How often does it reproduce? Is there a required condition?

What is the expected behavior? Why is that the expected behavior?

What do you see instead?

Additional information

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vm: let declaration no longer throws SyntaxError for non-configurable global property in vm context (regression in v26) #63715

Description

Version

Platform

Subsystem

What steps will reproduce the bug?

How often does it reproduce? Is there a required condition?

What is the expected behavior? Why is that the expected behavior?

What do you see instead?

Additional information

Activity

Renegade334 commented on Jun 2, 2026

legendecas commented on Jun 3, 2026

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vm: `let` declaration no longer throws SyntaxError for non-configurable global property in vm context (regression in v26) #63715