Update: add fixer for capitalized-comments

[not-an-aardvark]

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

[x] Add autofixing to a rule

What changes did you make? (Give an overview)

This adds a fixer for capitalized-comments. The fixer works by changing the letter case of the first character of the comment.

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

Nothing in particular.

[mention-bot]

@not-an-aardvark, thanks for your PR! By analyzing the history of the files in this pull request, we identified @platinumazure and @Trott to be potential reviewers.

[eslintbot]

LGTM

[platinumazure]

LGTM, thanks!

[kaicataldo]

LGTM. Thanks!

[mysticatea]

Hmm, I'm afraid that autofix of this rule.
Some tools (include eslint) has directive comments such as eslint-disable. People might use such comments the default ignorePattern does not include, so it can break the code.

[not-an-aardvark]

If ESLint changes a tool's directive comments and the tool parses them case-sensitively, it will break the tool, not the code. This might still be bad enough that we should avoid autofixing, but I think the distinction is important, because autofix doesn't guarantee that other tools will still work afterwards. Of course, it's nice if we can avoid breaking other tools, but in general there's no way to be sure if any given fix will break an external tool. For example:

/* eslint indent: [error, 2], curly: error, brace-style: [error, "1tbs"] */
// jscs:enable requireSpaceAfterKeywords

if(foo) bar() // jscs:ignore

JSCS would normally report an error on this code due to the if statement, but the jscs:ignore comment prevents this from happening.

However, after running eslint --fix on the code, ESLint will output:

/* eslint indent: [error, 2], curly: error, brace-style: [error, "1tbs"] */
// jscs:enable requireSpaceAfterKeywords

if(foo) {
  bar()
} // jscs:ignore

Now JSCS will report an error for the if statement, because the comment is on the wrong line. It's not possible for ESLint to prevent all errors like this, because it can't know what other programs will use comments for.

In general, I think ESLint's autofixer should only need to ensure that the behavior of the code stays the same when a JavaScript engine runs it. It shouldn't be required to preserve other tool-specific directives such as comments. If a user does want to prevent ESLint from reporting and autofixing a particular type of directive comment, they can simply add it to this rule's ignorePattern.

[mysticatea]

Ah, it's fair enough.
Thank you!