src: add NODE_VERSION_IS_LTS to node_version.h

[gibfahn]

This is defined in LTS releases, but should really be defined in master too.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

cc/ @nodejs/lts

[jasnell]

FWIW, when these were first introduced, the decision was to not have them in master at all. For the codename, the idea was that if the macro is missing, the value of the process property is undefined rather than an empty string, so someone would be able to determine if a release is LTS simply by checking for the presence of the property (without checking the value).

[gibfahn]

Hmm, okay, so that's to make things easier for core collaborators? I could be wrong, but I don't see how that makes sense.

If you don't define in master, you can do #ifdef NODE_VERSION_IS_LTS to check if it's defined, but if you define it to 0 or 1, you can just do #if NODE_VERSION_IS_LTS, which is true if it's 1, and false if it's 0.

In fact AFAICT NODE_VERSION_IS_LTS is only used in one place in the source, and that already uses #if not #ifdef:

node/src/node.cc

Lines 3172 to 3175 in 3a977fc

	#if NODE_VERSION_IS_LTS
	READONLY_PROPERTY(release, "lts",
	OneByteString(env->isolate(), NODE_VERSION_LTS_CODENAME));
	#endif

[cjihrig]

As a separate commit or separate PR, could you add a note to doc/releases.md about these values. That document already talks about updating the other values in this file.

[gibfahn]

As a separate commit or separate PR, could you add a note to doc/releases.md about these values. That document already talks about updating the other values in this file.

Yep, I'm working on an update to include all the stuff that isn't in that doc that you need to do for a first LTS release, including this!

[jasnell]

heh, I didn't argue that it still makes sense ;-) I just explained the history ;-) ... adding these is fine I think

[rvagg]

I'm not fussed either way but I think I can confirm that this isn't going to break anything if introduced. The only other place I'm aware of it being used is in dist-indexer which makes index.json and index.tab in the download directories and that'll still work fine after this.

iirc pulling in release commits back to master can be a pain when you have to reset src/node_version.h. I seem to remember occasionally having trouble with these missing lines. I'm not sure this will make much of a difference; although it could introduce the possibility of accidentally turning it to 1 and not noticing because a switch from 0 to 1 in a commit is much easier to miss than adding a whole new line or two.

[gibfahn]

CI: https://ci.nodejs.org/job/node-test-commit/13990/
CI 2: https://ci.nodejs.org/job/node-test-commit/14160/