JavaScript mutator improvements

[brody4hire]

• JavaScript mutator code improvements
  • use raw string mutations internally whenever possible
  • generate some of the mutations as AST nodes from the Babel types API
  • use some ternaries
  • remove some intermediate const declarations no longer needed
  • remove a couple of internal utility functions no longer needed
• add Arrow Function Mutator for JavaScript (already supported by the existing TypeScript mutator)
• remove lodash.clonedeep from dependencies in packages/javascript-mutator/package.json

These improvements should help reduce the amount of consistency between the JavaScript and TypeScript mutators that I raised in #1893.

/cc @kmdrGroch

[brody4hire]

WIP for now, waiting for PR #1903 to be reviewed and merged before I finish resolving the review comments.

@kmdrGroch it was not clear to me whether we need to go back to if statements for all mutators or not.

[bartekleon]

@brodybits Thanks. I only meant these 2 I review. Simple short if's are ok, but if you have multiple ones, it isn't very clean.
I have looked through and it looks nice

[brody4hire]

I just merged from master and pushed some fixes to ArrayDeclarationMutator.ts:

• revert use of a ternary
• resolve issue with mutating Array() function call
• resolve lint issues on ArrayDeclarationMutator.ts (again)

This PR is no longer WIP.

Thanks again to @kmdrGroch for the review comments, final review would be much appreciated.

Thanks to @simondel for merging the other recent PRs.

[bartekleon]

Looks good to me. One question /.thing to check: is "lodash.deepClone" dependency required after these changes? It could.be removed from package.json if it's not.

[brody4hire]

I just did a clean rebase and removed lodash.clonedeep from dependencies in packages/javascript-mutator/package.json.

[bartekleon]

And it still works. So 1 dependency less 🚀

[brody4hire]

Back to [WIP] again, since it is now expected to have a conflict with PR #1912 and I would like to break the implementation of JavaScriptMutator.mutate() down into smaller parts again (someday).

The one thing is that I find it to be a bit of a waste if I would have to keep working around conflicts due to a slow merge cycle. I am also thinking that if we can unify the JavaScript and TypeScript mutators, as discussed in #1893, it could help reduce the efforts needed for enhancements such as PR #1912 and custom external mutators.

[bartekleon]

@brodybits, I was thinking, if some of the changes introduced here, could be merged into my PR, especially from this file:
packages/javascript-mutator/src/JavaScriptMutator.ts

And I was also looking at your code, and I think, there might be an issue since you are not a coping object in some cases. It can lead to some problems with references. (But I am not sure).

[brody4hire]

@kmdrGroch I would downvote that idea at this point since I think these 2 PRs are really doing different things and should be mostly orthogonal. I think it would be ideal if we could somehow improve the internal interfaces to keep these 2 PRs completely independent.

I think a quicker solution would be to merge this PR now so that you can continue without dealing with a conflict in the future.

[bartekleon]

I rather only meant this part where you consolidate generateMutants and mutate function. But well, yea, it makes sense too

[brody4hire]

Got it. I would (still) favor getting this one merged first, for the sake of maintaining more linear progress.

[bartekleon]

@simondel could you take a look? I guess this PR is ready to be checked and merged

[simondel]

Hi! Thanks for making these changes :)

I'm reviewing this and I'll also do a diff check between a report from the current master branch and your branch to see if anything other than the arrow mutator has changed.