vm misses const definitions after recursive loads (only in v0.11.15)

[paleolitico]

We have a system configured with scripts in a DSL that is loaded with vm module.
This DSL have a "include" action so that a script can load other scripts.
We use "const" to declare constants in the script.
With Node.js upto 0.11.14 everything behaves as expected.
But with 0.11.15, something strange happens with const declarations:
consts before the first include behave as usual,
but consts after the first include disappear and we got an undefined.

We have simplified the DSL to the following program:

//------------------------------------------------------------
// load-conf.js
var vm = require('vm');
var fs = require('fs');

function include(script) {
vm.runInContext(fs.readFileSync(script), ctxt, script);
}

var sandbox = {
include: include,
console: console
};

var ctxt = vm.createContext(sandbox);

for (var i = 2; i < process.argv.length; i++) include(process.argv[i]);

The following configuration scripts can be used to test the problem.

//------------------------------------------------------------
// const-root.conf
console.info("const-root.conf");

function f0(x) {return x;}
const x0 = 10;
var y0 = 20;
console.info("Root before include (0):", f0, x0, y0);

include("const-included.conf");

function f2(x) {return x;}
const x2 = 10;
var y2 = 20;
console.info("Root after include (0):", f0, x0, y0);
console.info("Root after include (2):", f2, x2, y2);

//------------------------------------------------------------
// const-included.conf
console.info("const-included.conf");

function f1(x) {return x;}
const x1 = 10;
var y1 = 20;
console.info("Included (1):", f1, x1, y1);

When executed with node-v0.10.35 or node-v0.11.14, we get the following output:

$ node-v0.11.14/node load-conf.js const-root.conf
const-root.conf
Root before include (0): function f0(x) {return x;} 10 20
const-included.conf
Included (1): function f1(x) {return x;} 10 20
Root after include (0): function f0(x) {return x;} 10 20
Root after include (2): function f2(x) {return x;} 10 20

But when executed with node-0.11.15, we get:

$ node-v0.11.15/node load-conf.js const-root.conf
const-root.conf
Root before include (0): function f0(x) {return x;} 10 20
const-included.conf
Included (1): function f1(x) {return x;} 10 20
Root after include (0): function f0(x) {return x;} 10 20
Root after include (2): function f2(x) {return x;} undefined 20

Note the undefined in the last line of the output!

[misterdjules]

@tjfontaine @cjihrig @chrisdickinson @trevnorris @jasnell Do you have some time to look into it to determine if this needs to be added to the 0.11.16 milestone?

[trevnorris]

@misterdjules Do we know the commit that caused this? If we can get a quick fix for it let's go ahead and throw it on the 0.11.16 milestone.

[misterdjules]

@trevnorris I've been busy with other issues/PRs so I haven't tried to investigate at all.

[misterdjules]

@trevnorris The regression was introduced by the most recent upgrade to V8 (and subsequent commits that fix it). It also happens in io.js, so it's either due to the way node.js/io.js uses the V8's API, or it's still a bug in V8.

I'll try to think of ways to narrow down the issue.

[trevnorris]

@misterdjules excellent work. Thanks for tracking that down.

[trevnorris]

@domenic Pulling you in since this also affects io.js. Any thoughts on why this is happening?

[trevnorris]

This worked in V8 up to 3.28.22. After that this test fails.

[jasnell]

@trevnorris ... any further thoughts on this one?

[trevnorris]

@jasnell Sorry. I only did some bisecting and briefly looked at it. Nothing deep enough to give a proper assessment.

[domenic]

This is on my to-do list to look in to, but pretty far down there. The fact that it broke in V8 is encouraging, and hopefully will lead to a fix similar to that discovered in nodejs/node#1774.

[domenic]

Candidate commit: https://code.google.com/p/v8/source/detail?r=22385 based on @trevnorris's 3.28.22 -> 3.28.23 range.