v2.15.0 is leaking memory

[asapach]

After updating to v2.15.0 eslint started running out of memory on our fairly large project.
I was able to reproduce something similar when running the plugin against a dozen copies of lodash-es. I can create a repro case, but it's rather trivial.
One rule is enough to see the difference between v2.14.0 and v2.15.0:

plugins:
  - import

rules:
  import/default: 2

This seems to be caused by 05c3935. I've run some memory profiles, but I can't pinpoint the exact source of the leak other than that it seems to originate in ExportMap.js. It's possible that the leak was always there, but extra parsing and memory allocations made it more evident.

[benmosher]

Thanks for identifying the commit! This is not the first time ExportMap has had a major memory leak after a minor change.

Memory leaks are always my top priority after a release. I'll try to take a look at lunch today.

[sergei-startsev]

@benmosher you might also want to take a look at PR #1271

[benmosher]

@sergei-startsev thanks for that! I think I found the issue though:

For some reason, the function closer for getter in captureDependency is retaining source despite not referencing it. I am still untangling why, but semantically, this code should not need to retain source so I think some refactoring should resolve this without disabling the code entirely.

Also: I'm not sure your PR will actually work in practice; if non-no-deprecated rules run first, they will cache ExportMaps without the docs parsed.

[sergei-startsev]

@benmosher The PR idea is not to parse docs if it's not required, I wouldn't like to build SourceCode instances if no-deprecated rule isn't used.

As for cache, we can distinguish docs was disabled and docs wasn't found.

[benmosher]

Sure, but the SourceCode instances shouldn’t be retained at all to begin with. And I don’t think they cost much CPU-wise.

[benmosher]

Published as 2.16.0. Thanks so much for both of your help on this!