[PiranhaJS] Remove declaration of the identifier

[mkr-plse]

Is it planned for Piranha to support refactoring/removing the declaration of the identifier argument?
e.g. removing all of the code in this block, instead of just the conditional block:

const featureFlag = "feature-flag"
if (isFlagTreated(featureFlag)) {
 // do stuff
}

If we had that functionality, we could likely make the assumption that the configured API argument index always refers to a string literal and expect the flag name to be a string literal node. Being able to search across multiple files/imports would likely be required for some of the more complex usages of feature flags

Originally posted by @atrakh in #91 (comment)

[anag004]

Not sure if this is relevant, but we might need to make PiranhaJS aware of variable scope here. Without this, the following code

{ var featureFlag = "feature1-flag"; } // scope 1

// ...

{ var featureFlag = "feature2-flag"; } // scope 2

will be refactored incorrectly when cleaning up one of the flags. For example, when cleaning up "feature1-flag", featureFlag will be replaced by "feature1-flag" everywhere.

[msridhar]

The escope library can be helpful for variable scopes:

https://github.com/estools/escope

[atrakh]

Not sure if this is relevant, but we might need to make PiranhaJS aware of variable scope here.

Good point... this is some of the magic I hand-waved away 😄

[ketkarameya]

@atrakh we can now perform this kind of cleanup in polyglot piranha.
However, on-boarding JS of Polyglot Piranha is pending.
I am closing this issue for now, since polyglot piranha allows developers to support for such cleanups.
Feel free to reopen this issue if you have further questions.