Allow arbitrary nodes to be ignored in the indent rule

[not-an-aardvark]

Problem

People have lots of different indentation preferences, and the indent rule can't realistically support all of them. With other rules, we generally encourage people to make a plugin if they want to enforce their specific preferences, which implies disabling the core rule and using the rule from the plugin instead.

However, the indent rule is big and complicated, and if a user wants to disable it in favor of their plugin, then the plugin needs to reimplement the entire rule. This adds a very large maintenance burden.

Proposal

What rule do you want to change?

indent

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

By default, it produces the same amount.

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

This change adds an ignoredNodes option to the rule, which is an array of AST selectors. Any nodes matching those selectors will be treated the same way as unknown node types -- the indentation of their direct children will be ignored, but the indentation of nested children will still be enforced relative to each other.

Please provide some example code that this change will affect:

/* eslint indent: [
    error,
    4,
    {
        ignoredNodes: ["VariableDeclarator[kind='const']"]
    }
] */

const foo = 1,
      bar = 2,
      baz = 3,
      qux = function() {
          return;
      };

What does the rule currently do for this code?

The rule reports an error because it enforces a style where bar, baz, and qux are indented incorrectly. (We have gotten several feature requests to allow a style like this.)

What will the rule do after it's changed?

The rule will ignore the indentation of bar, baz, and qux, but it will still enforce the alignment of the return statement with qux. This would allow someone to write a plugin that just checks the indentation of bar, baz, and qux, without reimplementing the indentation logic for anything else.