fix(eslint-plugin): [switch-exhaustiveness-check] handle special characters in enum keys

[karishnu]

Fixes #2181

[typescript-eslint]

Thanks for the PR, @karishnu!

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[codecov]

Codecov Report

Merging #2207 into master will decrease coverage by 0.27%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2207      +/-   ##
==========================================
- Coverage   93.39%   93.12%   -0.28%     
==========================================
  Files         173      283     +110     
  Lines        7871     9044    +1173     
  Branches     2247     2477     +230     
==========================================
+ Hits         7351     8422    +1071     
- Misses        247      301      +54     
- Partials      273      321      +48     

Flag	Coverage Δ
#unittest	93.12% <100.00%> (-0.28%)	⬇️

Impacted Files	Coverage Δ
...nt-plugin/src/rules/switch-exhaustiveness-check.ts	98.27% <100.00%> (+0.60%)	⬆️
packages/typescript-estree/src/simple-traverse.ts	75.00% <0.00%> (-20.00%)	⬇️
...-internal/src/rules/no-typescript-estree-import.ts	87.50% <0.00%> (-12.50%)	⬇️
packages/parser/src/scope/scopes.ts	100.00% <0.00%> (ø)
packages/eslint-plugin/src/configs/all.ts	100.00% <0.00%> (ø)
packages/eslint-plugin/src/configs/base.ts	100.00% <0.00%> (ø)
packages/parser/src/scope/scope-manager.ts	100.00% <0.00%> (ø)
packages/eslint-plugin/src/rules/no-namespace.ts	100.00% <0.00%> (ø)
packages/eslint-plugin/src/configs/recommended.ts	100.00% <0.00%> (ø)
packages/typescript-estree/src/ts-estree/index.ts	100.00% <0.00%> (ø)
... and 128 more

[karishnu]

@bradzacher Are any changes required before this can be merged?

[bradzacher]

This PR is in the queue of PRs to reviewed, and will be reviewed when we are able.
https://github.com/typescript-eslint/typescript-eslint/blob/master/CONTRIBUTING.md#addressing-feedback-and-beyond

[bradzacher]

The problem we've got is that a-zA-Z doesn't include all of the "letter-like" characters that are actually allowed in the spec (chinese/japanese/korean/cyrillic/etc characters, accented characters), etc. So for a large number of codebases this regex will actually cause a false match. A false match isn't the end of the world, but it's going to be annoying for non-english speakers.

This is the actual regex of allowed characters within a variable name: https://github.com/estools/esutils/blob/a825f91fd1d1e3a9fff84227cb06c011d8a0b9e8/lib/code.js#L39-L44

It's a mess.

TypeScript needs to parse identifiers itself, and thankfully they export two functions that we can use here: isIdentifierStart and isIdentifierPart.

You can use this function instead to determine if the name requires quoting:

const compilerOptions = service.program.getCompilerOptions();
function requiresQuoting(name: string): boolean {
  if (name.length === 0) {
    return true;
  }
  if (!ts.isIdentifierStart(name.charCodeAt(0), compilerOptions.target)) {
    return true;
  }

  for (let i = 1; i < name.length; i += 1) {
    if (!ts.isIdentifierPart(name.charCodeAt(i), compilerOptions.target)) {
      return true;
    }
  }

  return false;
}

[karishnu]

Thank you! Will make the changes as soon as I can find some time.

[bradzacher]

LGTM.
Thanks for your contribution!