[New] order: allow controlling intragroup spacing of type-only imports via newlines-between-types

[Xunnamius]

Depends on #3104

This PR implements in import/order: a new option analogous to newlines-between but specifically for controlling newlines between type-only imports.

A demo package containing this feature is temporarily available for easy testing:

npm install --save-dev eslint-plugin-import@npm:@-xun/eslint-plugin-import-experimental

Allow controlling intragroup spacing of type-only imports

This is implemented via newlines-between-types. The proposed documentation corresponding to this new feature can be previewed here.

Example

Given this code:

import type A from 'fs';
import type B from 'path';
import type C from '../foo.js';
import type D from './bar.js';
import type E from './';

import a from 'fs';
import b from 'path';

import c from '../foo.js';

import d from './bar.js';

import e from './';

And the following settings, the rule check will fail:

{
  "groups": ["type", "builtin", "parent", "sibling", "index"],
  "sortTypesAmongThemselves": true,
  "newlines-between": "always"
}

With --fix yielding:

import type A from 'fs';
import type B from 'path';

import type C from '../foo.js';

import type D from './bar.js';

import type E from './';

import a from 'fs';
import b from 'path';

import c from '../foo.js';

import d from './bar.js';

import e from './';

However, with the following settings, the rule check will succeed instead:

{
  "groups": ["type", "builtin", "parent", "sibling", "index"],
  "sortTypesAmongThemselves": true,
  "newlines-between": "always",
+ "newlines-between-types": "ignore"
}

sortTypesAmongThemselves allows sorting type-only and normal imports separately. By default, newlines-between will govern all newlines between import statements like normal.

I generally want my type-only imports to be sorted for ease of reference but never have newlines between them (save space) while I want my normal imports (which I tend to visually peruse more often) to be aesthetically pleasing, grouped, and sorted. newlines-between is too coarse-grained for this, so this PR introduces newlines-between-types, a setting identical to newlines-between except it only applies to type-only imports, and only when sortTypesAmongThemselves is enabled (i.e. it is backward-compatible).

When newlines-between and newlines-between-types conflict, newlines-between-types takes precedence for type-only imports. For normal imports, newlines-between-types is ignored entirely.

One issue that might warrant further discussion is which setting governs the newline separating type-only imports from normal imports. Right now, I have it so newlines-between-types controls this space, but perhaps it should be its own setting.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.30%. Comparing base (8b2d570) to head (eba9746).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3127      +/-   ##
==========================================
- Coverage   95.04%   85.30%   -9.74%     
==========================================
  Files          84       84              
  Lines        3634     3662      +28     
  Branches     1279     1302      +23     
==========================================
- Hits         3454     3124     -330     
- Misses        180      538     +358     

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