Get rid of createLegacyClass

[timroes]

We have a way to inherit classes in an old fashioned style in legacy_class. Trying to convert some old Mocha tests to Jest (which we compile differently in Babel, because they run in node.js and not the browser) I found some issues with that class.

createLegacyClass currently only works, because we are compiling specific features (in this case class) down to ES5. Since we are not compiling down to ES5, but use babel target node: 'current' for Jest tests, this class does not work in Jest tests. In case we would ever stop compiling class to ES5 (e.g. we decide to no longer support IE11 or such), this class would also not work in the Kibana distributable anymore.

The cause is, that class Foo {} will lead to Foo.prototype being writable: false from its descriptor (Object.getOwnPropertyDescriptor), while the babel compiled code would contain function Foo {} which makes Foo.prototype writable. createLegacyClass tries to overwrite prototype and thus fails if we are not compiling to ES5.

This needs to be fixed before we ever possibly could get rid of compiling class no longer down for Kibana during runtime.

cc @elastic/kibana-platform

[mattkime]

Summarizing and verifying -

1. createLegacyClass is a problem only where its called on a class
2. This is the primary obstacle in porting a large portion of tests from mocha to jest

[epixa]

I'm pretty sure createLegacyClass can just be replaced with native class...extends, in which case this isn't really a platform thing. Teams need to remove their usage of that utility, then we can remove the utility. A quick search shows it's mostly (maybe all) apps and platform.

If we want to park it in the platform queue for lack of an obvious alternative, we can.

[mattkime]

Scope of work - createLegacyClass is used in 20 places. Removal sounds manageable.

[pgayvallet]

Only remaining usages are in the legacy state_management (src/legacy/ui/public/state_management). I guess this would be resolved when we complete legacy removal.

[timroes]

cc @flash1293 Do you know if those state_management utils are going away automatically with legacy removal?

[flash1293]

legacy state_management is only used in timelion which will be migrated away from it soon. This can simply be removed along with the legacy platform.

[lukeelmers]

Pretty sure this has been removed for awhile now -- @flash1293 is this issue safe to close?

[pgayvallet]

createLegacyClass: no occurrence found in master code. Closing.