fix(eslint-plugin): [no-magic-numbers] handle UnaryExpression for enums

[bradzacher]

Fixes #1414

Also fixes a consistency issue wherein our extension would include the + when reporting, but the base rule doesn't.
Also reformatted the code a bit:

• moved utility functions outside of create
• used optional chaining

[typescript-eslint]

Thanks for the PR, @bradzacher!

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[codecov]

Codecov Report

Merging #1415 into master will decrease coverage by 0.1%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master    #1415      +/-   ##
==========================================
- Coverage   94.58%   94.48%   -0.11%     
==========================================
  Files         140      140              
  Lines        6057     6055       -2     
  Branches     1723     1721       -2     
==========================================
- Hits         5729     5721       -8     
  Misses        181      181              
- Partials      147      153       +6

Impacted Files	Coverage Δ
...ckages/eslint-plugin/src/rules/no-magic-numbers.ts	82.35% <71.42%> (-11.99%)	⬇️

[armano2]

hmm, i was thinking what to do with node.parent?

parent is always defined in eslint context for nodes (with exception for Program).

[bradzacher]

yeah we should probably fix the types.
I was considering just adding a new type to ts-estree:

type KnownParent<TNode extends Node, TParent extends Node> = TNode & { parent: TParent };

But that type wouldn't doesn't fix cases like this. It would let us express direct parent selectors like VariableDeclaration > VariableDeclarator, so it's probably a nice thing to add as a non-breaking feature.

---

I was considering doing this via generics to make it even more explicit. But this only works if we make it non-optional.

interface BaseNode<TParent extends Node = Node> {
  // ...
  parent: TParent;
}

interface VariableDeclarator<TParent extends Node = Node> extends BaseNode<TParent> {}

interface Program extends BaseNode {
  parent?: never;
}

The problem with making it non-optional is that this complicates the converter code because the converter isn't the one that adds the parent, eslint is.

[armano2]

q: what do you think maybe about adding d.ts with augmentation for type in eslint-utils or plugin itself?

import { Node } from "@typescript-eslint/typescript-estree/dist/ts-estree/ts-estree";

declare module '@typescript-eslint/typescript-estree/dist/ts-estree/ts-estree' {
  export interface BaseNode {
    parent: Node;
  }

  export interface Program {
    parent: never;
  }
}

and dropping parent from ts-estree completely?

---

this is just an idea (should work, but i haven't tested it)