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

[RB14]

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.

[vkurchatkin]

A test (run with --use_strict):

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

summoning @domenic.

[benjamingr]

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.

[bnoordhuis]

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.

[vkurchatkin]

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

[benjamingr]

@vkurchatkin it appears that it is.

[domenic]

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.

[Fishrock123]

Is this actually an issue then?

[RB14]

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.

[jasnell]

Appears to be fixed in master. Closing.

[cjihrig]

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

[philj0st]

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

[bnoordhuis]

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

[kaicataldo]

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.

[Fishrock123]

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?

[addaleax]

@nodejs/v8?

[bnoordhuis]

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.

[targos]

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 ?

[Fishrock123]

Just confirmed this still doesn't work on master.

[Fishrock123]

cc @fhinkel

[fhinkel]

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

[Fishrock123]

ping @fhinkel did you get anywhere here?

[fhinkel]

Sorry, didn't get too much time on this yet.

[Fishrock123]

ping @fhinkel, were you ever able to look into this? :D

[robahl]

Help us @fhinkel, you're our only hope!

[jasnell]

This appears to no longer be an issue.

[targos]

@jasnell I think it's still an issue. Note that Chrome devtools are also unable to provide completion for let or const variables.

[jasnell]

hmm.... yep, quick verification test shows that I was testing the wrong thing. Thanks for reopening @targos

[jgranduel]

Hi,
node-8.5.0 REPL win10... seems to still be an issue. Any news?