Refactor for better type-checking

[ybiquitous]

Which issue, if any, is this issue related to?

• Related to Fix all types problems #4496

Is there anything in the PR that needs further explanation?

This change aims to improve type-checking and refactor tsconfig.json:

• Add noFallthroughCasesInSwitch. This aims to prevent a fallthrough bug.
• Add noUnusedParameters. This aims to improve readability. If you'd like to avoid the error, add a prefix _.
• Remove noImplicitThis and alwaysStrict. These are enabled by strict: true.

See https://www.typescriptlang.org/tsconfig

[ybiquitous]

I thought it is useful to enable also noUnusedLocals, but the option causes the following errors:

$ npm run lint:types
> stylelint@14.0.0 lint:types
> tsc

types/stylelint/type-test.ts(47,8): error TS6133: 'err' is declared but its value is never read.
types/stylelint/type-test.ts(48,8): error TS6133: 'output' is declared but its value is never read.
types/stylelint/type-test.ts(51,9): error TS6133: 'warnings' is declared but its value is never read.
types/stylelint/type-test.ts(55,7): error TS6133: 'formatter' is declared but its value is never read.
types/stylelint/type-test.ts(62,7): error TS6133: 'problemMessage' is declared but its value is never read.
types/stylelint/type-test.ts(63,7): error TS6133: 'problemFunc' is declared but its value is never read.

I could not find a good way to resolve the errors in types/stylelint/type-test.ts, so I gave up enabling the option. Any help is welcome. 😃

[hudochenkov]

There is already ESLint rule enabled similar to noUnusedLocals. No need to show the same problem in two tools. Also during development is very annoying rule.

[ybiquitous]

Ah, I forgot we are using the ESLint no-unused-vars rule. Surely, noUnusedLocals is unnecessary. 👍🏼

https://github.com/stylelint/eslint-config-stylelint/blob/80cd6392b4be512bd6e1381753b3fc4411d4c043/.eslintrc.js#L49-L54

[jeddy3]

Thanks!