Node: Tab completion for block-scoped variables doesn't work in REPL

Created on 27 Feb 2015 · 28Comments · Source: nodejs/node

Using version 1.4.1 REPL mode, it seems that tab completion for block-scoped variables (i.e. let and const statements) doesn't show suggestions, while tab completion for variables declared with var or otherwise just assigned a value without a deceleration, does show up a list of suggestions.

Of course, this happens in strict mode, or else I couldn't use let and const.

confirmed-bug help wanted repl

Source

RB14

👍1

All 28 comments

A test (run with --use_strict):

require('assert').equal(require('vm').runInNewContext(`
  let a = 42;
  this.a
`), 42);

summoning @domenic.

vkurchatkin on 27 Feb 2015

I can reproduce this on v1.4.1 on OSX.

$ ./iojs --use_strict

let foobar = 40;
var bazbar = 100;
foo // hit tab, no autocomplete
baz // hit tab, autocompletes to bazbar

The test @vkurchatkin posted also fails.

benjamingr on 27 Feb 2015

I think this can be explained because of how the REPL does autocompletion: it spawns a nested VM context that contains a copy of the globals from the parent context. var bindings have global scope but let bindings don't, i.e.:

> var x = 1; typeof global['x']  // 'number'
> let y = 1; typeof global['y']  // 'undefined'

I can't think of a good fix off the top of my head.

bnoordhuis on 27 Feb 2015

the question is, this the correct behaviour according to spec?

vkurchatkin on 27 Feb 2015

@vkurchatkin it appears that it is.

benjamingr on 28 Feb 2015

Right, indeed, let and const and class don't add to the global object, but instead to a separate scope contour. Unsure how to deal with this given the implementation details @bnoordhuis mentions.

domenic on 1 Mar 2015

Is this actually an issue then?

Fishrock123 on 1 Jul 2015

Well, as the one who opened this ticket, I still find it odd that auto-complete in REPL would work for only var (or should I say old-style) variables, and not for the new kinds of declarations.
Since auto-complete is a feature of io.js (and node.js), and it's a very useful feature if you ask me, I think this behavior should be fixed (if possible of course).. so I think it should still be considered as an issue.

RB14 on 1 Jul 2015

Appears to be fixed in master. Closing.

jasnell on 2 Apr 2016

Is this actually closed? Tab completion of let and const variables isn't working for me.

cjihrig on 2 Apr 2016

👍1

neither is it for me. I'm on node v6.2.0

philj0st on 30 May 2016

I'll reopen, it doesn't work with master either.

bnoordhuis on 30 May 2016

Can confirm that tab completion isn't working for const or let for me in the latest release (v6.2.2), but interestingly, const (but not let) works in v5.11.1.

kaicataldo on 26 Jun 2016

😕1

Anyone know if there is a way to hook into what variables are in the current scope? VM hacks count.

Would running in/hooking into a new vm module context have this info?

Fishrock123 on 17 Sep 2016

@nodejs/v8?

addaleax on 17 Sep 2016

Anyone know if there is a way to hook into what variables are in the current scope?

You can through the debugger API but you have to fake a breakpoint.

Interestingly though, tab completion for let and const bindings seems to work with master.

bnoordhuis on 18 Sep 2016

Interestingly though, tab completion for let and const bindings seems to work with master.

It doesn't seem to work for me. What did you try ?

targos on 20 Sep 2016

Just confirmed this still doesn't work on master.

Fishrock123 on 18 Oct 2016

cc @fhinkel

Fishrock123 on 18 Oct 2016

I'll check what the debugger does, since it works there.

If that doesn't work for us, here's a workaround we might try: Since vm intercepts all variable declarations anyways (and REPL sends everything through vm), we could also store the variable names in a list, and then do tab completion using that list. /cc @AnnaMag