v8: Parse issue with code snippet: "{ a: 1 } { a: 1 }"

[princejwesley]

• Version: master, v6.5.0
• Platform: Darwin Princes-MacBook-Pro.local 15.6.0 Darwin Kernel Version 15.6.0: Mon Aug 29 20:21:34 PDT 2016; root:xnu-3248.60.11~1/RELEASE_X86_64 x86_64
• Subsystem: v8 (version tested: 5.1.281.81 & 5.1.281.82) (vm & repl modules are affected)

While working on #8195, I come across this v8 issue.

// with vm & repl
const vm = require('vm');
const script = vm.createScript("{ a: 1 } { a: 1 }", { displayErrors: true });
const output = script.runInThisContext({ displayErrors: true }); 
console.log(output); // returns 1 instead of throwing syntax error

// when used directly
{ a: 1 } { a: 1 } // no error
// when used with other constructs
console.log({ a: 1 } { a: 1 }) // Throws SyntaxError: missing ) after argument list

Chrome behaviour

Canary (64-bit)(55.0.2856.0) is buggy where as the latest version (52.0.2743.116) works fine.

cc: @nodejs/v8

[addaleax]

I think this is expected behaviour… V8 interprets the {} as code blocks and the a: as labels (MDN), i.e. as:

{
a:
  1;
}
{
a:
  1;
}

That’s valid, even if not very meaningful, JS code. You can’t put arbitrary code blocks as function parameters, so V8 is right to complain about the console.log example.

[princejwesley]

@addaleax so the last chrome browser(v52.0.2743.116) is buggy and the canary has correct behaviour. right? Feel free to close it if you are sure about it 👍

edit: Firefox is also having same behaviour, seems legit.

[addaleax]

I think so, yeah. Firefox also returns 1 for that statement, that seems like a good indicator to me. :)