lib,src: remove vm.runInDebugContext()

[bnoordhuis]

The V8 API it is based on is deprecated and scheduled for removal later this year. Remove it.

The first commit replaces the Debug.MakeMirror() call in lib/util.js with something else.

The most important reason for doing this is of course to have a deprecation warning-free build again!

[addaleax]

I think @joshgav or @ofrobots had the plan of removing this after Node 9 (i.e. in Node 10)?

[bnoordhuis]

The file is whitelisted because the V8 builtins don't lint. They're not legal JS syntax, eslint can't parse them.

[addaleax]

You should be able add comments by starting lines with # – if you comment here in the PR, that sounds like a good indicator that it makes sense to do so. :)

[fhinkel]

There are other lib/internal/v8 files whitelisted. I don't think we need a comment. But either way is fine.

[bnoordhuis]

There is a minor change in behavior here in that the preview is now limited to 100 elements. Before, it would show them all but that is (IMO) rather annoying with large maps and sets (and it's basically equivalent to printing the map or set minus the already iterated over elements.)

I'm planning to follow up with a PR that prints a nice "..." if there are more elements but I can restore the old behavior if people prefer that.

[bnoordhuis]

I think @joshgav or @ofrobots had the plan of removing this after Node 9 (i.e. in Node 10)?

In a LTS release? That doesn't make sense. Removing it in node 9 gives people the chance to update their code bases before entering the next LTS.

[targos]

Documentation says Node 10+: https://github.com/nodejs/node/blob/master/doc/api/deprecations.md#dep0069-vmrunindebugcontextstring

According to our deprecation policy, we should first emit a warning in Node 9 and remove the feature in Node 10 or higher. I guess it would have to be 10 here because V8 will remove the API by the end of the year.

[addaleax]

CITGM: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/845/

I don’t know about the reasons behind not going for a runtime deprecation in Node 8, I was just pretty sure I read somewhere that it was intentional. ¯\_(ツ)_/¯

[targos]

Most of the discussion is here: #12243
PR for the runtime deprecation: #12815

[addaleax]

You should be able add comments by starting lines with # – if you comment here in the PR, that sounds like a good indicator that it makes sense to do so. :)

[addaleax]

You’ll also want to update the entry in deprecations.md to say Type: End-of-Life

[bnoordhuis]

According to our deprecation policy, we should first emit a warning in Node 9 and remove the feature in Node 10 or higher.

That doesn't apply to vm.runInDebugContext(), its documentation has always stated very clearly that it could disappear at any time.

[jasnell]

We really ought to have had a deprecation message added in 8.0.0 for this but it's rather too late now. If the plan is to remove it in 9.0, then we should get a runtime deprecation into an 8.x minor.

[TimothyGu]

For context: the first part of this PR which removes the use of Debug Mirrors is, well, hacky as heck. But there is no other solution as I have found out when investigating #11875, other than convincing V8 devs to add C++ APIs for Map- and SetIterators.

@bnoordhuis can you attach a Fixes: https://github.com/nodejs/node/issues/11875 to the commit message as well?

[TimothyGu]

Can the 0/1/2/3 magic numbers be constants instead? V8 is using

define ITERATOR_KIND_KEYS = 1;
define ITERATOR_KIND_VALUES = 2;
define ITERATOR_KIND_ENTRIES = 3;

which looks good to me.

[TimothyGu]

Can a for-of loop be used directly on the cloned it?

[fhinkel]

LGTM with nit

[fhinkel]

There are other lib/internal/v8 files whitelisted. I don't think we need a comment. But either way is fine.

[fhinkel]

Can we test the SetIterator as well?

[bnoordhuis]

I didn't add a test here, I just updated an existing test that was using internals.

[TimothyGu]

@fhinkel Do you have a better way to preserve the Iterator support w/o using V8 natives syntax?

[fhinkel]

Maybe we could add these methods to the V8 API. Relying on intrinsic functions (%) is somewhat dangerous. They are not part of the API and we might change/delete them without a deprecation period.

[bnoordhuis]

Yes, that's my longer-term goal. Using natives syntax is a short-term + least-effort solution.

[BridgeAR]

This needs a rebase.

[TimothyGu]

LGTM once #13295 (comment) is addressed.

[BridgeAR]

@bnoordhuis do you still want to follow up on this?

[bnoordhuis]

Updated. CI for a change: https://ci.nodejs.org/job/node-test-pull-request/10379/

[ofrobots]

I would like to formally request that we do NOT land this in Node 9. We have been migrating some of the code we use in https://github.com/GoogleCloudPlatform/cloud-debug-nodejs to the inspector module. At this point we do not think the inspector API is a complete replacement for the Debug context, at least for our use cases. See V8 bug: https://bugs.chromium.org/p/v8/issues/detail?id=6945.

Since there is no pressing need to remove the API just yet, let's not accelerate the removal.

[mcollina]

👍 in waiting.

[addaleax]

This would need to be rebased now that the runtime deprecation has been merged.

[BridgeAR]

Ping @bnoordhuis this could land after a rebase

[bnoordhuis]

Done. CI: https://ci.nodejs.org/job/node-test-pull-request/11627/

[targos]

unrelated change?

[jasnell]

grr... this one is becoming quite annoying.

[jasnell]

@bnoordhuis ... the extraneous js-yaml change is causing CI to fail on this.

[bnoordhuis]

With js-yaml change undone: https://ci.nodejs.org/job/node-test-pull-request/11679/

[addaleax]

Btw: This breaks gulp because it uses graceful-fs@3.x and their parsing of process.binding('natives') doesn’t expect the --allow_natives_syntax cleverness.

That’s nothing we can do anything about, we need this patch in order to avoid breakage ourselves, so it’s graceful-fs that needs to work around this, but I wanted to leave that information here.