Division with comment containing '/' - SyntaxError

[dlangerenken]

• Version: 6.9.1, 7.0.0
• Platform: Linux
• Subsystem: Mint 17, Ubuntu 16

Following function fails parsing:

function foo(){
    var bar = 1 / 1; // '/'
}

SyntaxError: Unexpected end of input

tested with:

• docker run -it node:6.9.1,
• docker run -it node:7.0.0,
• local installation

This code parses correctly in some node versions 5.X

[jasnell]

Interesting... I'm able to reproduce only in the REPL and only when the line var bar = 1 / 1; // '/' occurs within a function.

[dlangerenken]

Yes, that's what I found out too. It also does not fail if you use more than one slash. However, it fails even if the comment is not in the same line.

[mscdex]

It works for me with node v6.9.1, even with strict mode.

It looks like this is indeed REPL-specific.

/cc @princejwesley ?

[princejwesley]

It's a LineParser bug. Looking into it.

Update: With our ad-hoc parser, first /(division operator) in var bar = 1 / 1; // '/' is treated as start of regex literal

[princejwesley]

Without proper state machine, Its not easy to deduce whether '/' is a division operator or start of regex literal.

@dlangerenken Worst case, type/paste in .editor mode.

[not-an-aardvark]

I'm investigating this issue now. I think it should be possible to correctly distinguish between division and regex literals in almost all cases, with only a single lookbehind. A regex literal is almost always¹ preceded by (, {, [, ;, }, or the beginning of input. A division operator is almost always² preceded by another character.

¹ An exception is code like this:

function foo() {
  return
  /regex/ // not preceded by ;
}

² An exception is code like this:

({ ok: true } / 3)

Both of these exceptional cases are sort of obselete (they either require dead code, or dividing an object literal by something), so I think using a single-character lookbehind would be an improvement over the current behavior.