fix(perf): add cache for fs calls when using language service

[topaxi]

Supersedes #940

[topaxi]

lodash.memoize is a devDependency, should I include it in the dependencies? Or do we favor the old PR over this?

[coveralls]

Pull Request Test Coverage Report for Build 3533

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 90.038%

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Totals
Change from base Build 3532:	0.005%
Covered Lines:	1069
Relevant Lines:	1129

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💛 - Coveralls

[ahnpnl]

I think if lodash.memoize is needed for published version then we need to add it to dependencies.

I think I don't have any questions about this. Just you need to check why the CI failed.

Cc @GeeWee @kulshekhar

[GeeWee]

I agree. I didn't see it was a devDependency.
If the CI passes we should merge this in.

[kulshekhar]

One test seems to be failing on linux with node 6. Once that's fixed, this looks good to me

[ahnpnl]

snapshot failed on node 6 looks strange, even though new snapshot looks identical to old snapshot. Would you please check @topaxi

[topaxi]

I'm unable to reproduce this on my machine using node v6.16.0.

[ahnpnl]

hmm, the similar error occurs to #1056 which upgrades upgrade jest to 24.7.1, snapshot also failed even though they were identical. any thoughts @GeeWee @kulshekhar ?

[GeeWee]

That's.. weird. Seems like Node 6 is running through the files in a different order for node 6 here, not identical as in #1056 - I'm thinking maybe we should drop the Node 6 build - latest LTS is node 8 anyways.

[ahnpnl]

I think we should. Not sure if jest already dropped support. We need to check if jest dropped then we will do too.

[ahnpnl]

what should we deal with node 6 failed build here @GeeWee ?

[GeeWee]

I think we should disable it but only @kulshekhar has CI access I think

[Mordred]

I have tried this patch and it will break "watch" mode, because file changes are not reloaded.

[topaxi]

I haven't checked further implications in this PR, I continued the work from #940. Let me know if there is anything left I can do, although this PR isn't very high in my priorities. If anyone else is up for this, feel free to take over or close 👍

[ahnpnl]

If rebasing this branch, CI no longer runs for node 6

[topaxi]

Rebased

[kulshekhar]

thanks @topaxi @ahnpnl