Custom configs and merge rules not working

[DanPurdy]

Currently custom sass-lint configurations will be ignored when a custom configuration has merge-default-rules set to false. The only way to actually override the defaults is to set merge to true and provide every rule with a 0.

This was brought to light here DanPurdy/linter-sass-lint#9

I'm guessing the reason we haven't picked up on it for so long is that our config file matches the default config file or was set to merge and contained every rule we didn't want to use zeroed out.

To try this out use the config @mik01aj posted

options:
    merge-default-rules: true 

files:
    include: 'mockups/**/*.scss'
    ignore:
          - 'app/styles/legacy/**/*.*'
          - 'mockups/**/vendor/**/*'

rules:
    # ignoring EVERYTHING
    border-zero: 0
    brace-style: 0
    clean-import-paths: 0
    empty-args: 0
    empty-line-between-blocks: 0
    extends-before-declarations: 0
    extends-before-mixins: 0
    final-newline: 0
    force-attribute-nesting: 0
    force-element-nesting: 0
    force-pseudo-nesting: 0
    function-name-format: 0
    hex-length: 0
    hex-notation: 0
    indentation: 0
    leading-zero: 0
    mixin-name-format: 0
    mixins-before-declarations: 0
    nesting-depth: 0
    no-color-keywords: 0
    no-color-literals: 0
    no-css-comments: 0
    no-debug: 0
    no-duplicate-properties: 0
    no-empty-rulesets: 0
    no-extends: 0
    no-ids: 0
    no-important: 0
    no-invalid-hex: 0
    no-mergeable-selectors: 0
    no-misspelled-properties: 0
    no-qualifying-elements: 0
    no-trailing-zero: 0
    no-transition-all: 0
    no-url-protocols: 0
    no-vendor-prefixes: 0
    no-warn: 0
    one-declaration-per-line: 0
    placeholder-in-extend: 0
    placeholder-name-format: 0
    property-sort-order: 0
    quotes: 0
    shorthand-values: 0
    single-line-per-selector: 0
    space-after-bang: 0
    space-after-colon: 0
    space-after-comma: 0
    space-before-bang: 0
    space-before-brace: 0
    space-before-colon: 0
    space-between-parens: 0
    trailing-semicolon: 0
    url-quotes: 0
    variable-for-property: 0
    variable-name-format: 0
    zero-unit: 0

then try this

options:
    merge-default-rules: false 

files:
    include: 'mockups/**/*.scss'
    ignore:
        - 'app/styles/legacy/**/*.*'
        - 'mockups/**/vendor/**/*'

rules:
    no-color-keywords: 0

on this file

a {
  color: red;
}

.test .test {
  color: red;
}

.test {
  color: blue;
}

Looks like an error in checking for configMerge here https://github.com/sasstools/sass-lint/blob/develop/lib/config.js#L77