Fix: class-methods-use-this reports 'undefined' names

[mdjermanovic]

What is the purpose of this pull request? (put an "X" next to item)

[X] Bug fix

Tell us about your environment

• ESLint Version: 6.1.0
• Node Version: 10.16.0
• npm Version: 6.9.0

What parser (default, Babel-ESLint, etc.) are you using?

default

Please show your full configuration:

Configuration

module.exports = {
  parserOptions: {
    ecmaVersion: 2015,
  },
};

What did you do? Please include the actual source code causing the issue.

/*eslint class-methods-use-this: "error"*/

class A {
  "foo"() {}
  123() {}
  [f()]() {}
}

What did you expect to happen?

Error messages with method names, where it is possible.

What actually happened? Please include the actual, raw output from ESLint.

  5:8  error  Expected 'this' to be used by class method 'undefined'  class-methods-use-this
  6:6  error  Expected 'this' to be used by class method 'undefined'  class-methods-use-this
  7:8  error  Expected 'this' to be used by class method 'undefined'  class-methods-use-this

What changes did you make? (Give an overview)

Fixed class-methods-use-this to use astUtils.getFunctionNameWithKind(), like other rules.

Is there anything you'd like reviewers to focus on?

In most cases the message before the fix should remain exactly the same after the fix.

The differences are:

• "foo"(){} and 123(){} are fixed to show the name instead of 'undefined'.
• Computed keys such as [f()](){} are fixed to just ... class method. instead of ... class method 'undefined'.
• The previous also applies to computed keys with only an identifier like [a](){}, but the old message was showing 'a'. This is in line with how other rules work, it could be a future enhancement in getFunctionNameWithKind().
• For accessors e.g. getters it's now ... class getter 'foo' instead of class method 'foo'.
• The message can now have additional details, e.g. class generator method 'foo'

There is a new test case with full messages.

[platinumazure]

LGTM, thanks!

[kaicataldo]

LGTM. Thanks!

[platinumazure]

Merged. Thanks for contributing!