max-len ignorePattern should set 'i' and 'u' flags on the RegEx

I think the ignorePattern flag on max-len should set both the unicode and case-insensitive flags. This would simplify the process of writing a RegEx to match things like TODO-style comments and other special characters.

What rule do you want to change? max-len

Does this change cause the rule to produce more or fewer warnings? Fewer

How will the change be implemented? (New option, new default behavior, etc.)? New default behavior.

Please provide some example code that this change will affect:

'max-len': [
    'warn',
    {
        code: 100,
        ignorePattern: '((?:\\/\\/|\\/\\*)\\s*eslint-|(?:\\/\\/|\\/\\*)\\s*(?:@?(?:todo|TODO|fix|FIX|bug|BUG)))',
    },
],

What does the rule currently do for this code? If you want to use the ignorePattern option, you must specify all possible permutations of upper and lower case characters

What will the rule do after it’s changed? The example above could be written as:

'max-len': [
    'warn',
    {
        code: 100,
        ignorePattern: '((?:\\/\\/|\\/\\*)\\s*eslint-|(?:\\/\\/|\\/\\*)\\s*(?:@?(?:todo|fix|bug)))',
    },
],

Are you willing to submit a pull request to implement this change? Certainly

[ljharb]

What about adding ignorePatternFlags: ["u", "i"]? Then it’d default to [], and users could provide any regex flags they want (it’d ofc have to be an array of 'gimsuy'.split() to be valid)

[aladdin-add]

there is a proposal: https://github.com/eslint/eslint/issues/11318 (not accepted yet), might address the issue.