Bug 257677 – Implementation error in ForStatement with LexicalDeclaration

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: JavaScriptCore

The POC

let cb;
for (let i = (cb = (() => i), 0); i<10;) {
  i++;
}
console.log(cb());

In chrome(V8) and engine262 we got output "0", but WebKit(JSC) we got "1", which is unexpected and completely wrong.
The spec(https://tc39.es/ecma262/#sec-forbodyevaluation) require to call CreatePerIterationEnvironment in every loop iteration, so the i++ in the loop body cannot effect the variable captured from the LexicalDeclaration, it seems jsc reuse the env in the first iteration.

[Radar WebKit Bug Importer]

<rdar://problem/110238901>

[Alexey Shvayka]

Hello, thanks for the report & test case!

As confirmed by naive fix, it is the same issue as https://bugs.webkit.org/show_bug.cgi?id=189799.

*** This bug has been marked as a duplicate of bug 189799 ***

[Alexey Shvayka]

(In reply to Alexey Shvayka from comment #2)
> Hello, thanks for the report & test case!
> 
> As confirmed by naive fix, it is the same issue as
> https://bugs.webkit.org/show_bug.cgi?id=189799.
> 
> *** This bug has been marked as a duplicate of bug 189799 ***

We can't ship the naive fix as it bloats the bytecode size, but we are working on a better solution!