Add Stylelint

.stylelintrc

@@ -0,0 +1,58 @@
+{
+  "rules": {
+	"indentation": "tab",
+	"color-hex-case": "lower",
+	"color-no-invalid-hex": true,
+
+	"function-calc-no-unspaced-operator": true,
+	"function-comma-space-after": "always-single-line",
+	"function-comma-space-before": "never",
+	"function-name-case": "lower",
+	"function-url-quotes": "always",
+	"function-whitespace-after": "always",
+
+	"number-leading-zero": "always",
+	"number-no-trailing-zeros": true,
+	"length-zero-no-unit": true,
+
+	"string-no-newline": true,
+	"string-quotes": "single",
+
+	"unit-case": "lower",
+	"unit-no-unknown": true,
+	"unit-whitelist": ["px", "%", "deg", "ms", "em", "vh", "vw", "rem", "s", "ex", "pt", "cm"],
+
+	"value-list-comma-space-after": "always-single-line",
+	"value-list-comma-space-before": "never",
+
+	"shorthand-property-no-redundant-values": true,
+
+	"property-case": "lower",
+
+	"declaration-block-no-duplicate-properties": [true, { "severity": "warning" } ],
+	"declaration-block-trailing-semicolon": "always",
+	"declaration-block-single-line-max-declarations": 0,
+	"declaration-block-semicolon-space-before": "never",
+	"declaration-block-semicolon-space-after": "always-single-line",
+	"declaration-block-semicolon-newline-before": "never-multi-line",
+	"declaration-block-semicolon-newline-after": "always-multi-line",
+
+	"block-closing-brace-newline-after": "always",
+	"block-closing-brace-newline-before": "always-multi-line",
+	"block-no-empty": true,
+	"block-opening-brace-newline-after": "always-multi-line",
+	"block-opening-brace-space-before": "always",
+
+	"selector-attribute-brackets-space-inside": "never",
+	"selector-attribute-operator-space-after": "never",
+	"selector-attribute-operator-space-before": "never",
+	"selector-combinator-space-after": "always",
+	"selector-combinator-space-before": "always",
+	"selector-pseudo-class-case": "lower",
+	"selector-pseudo-class-parentheses-space-inside": "always",
+	"selector-pseudo-element-case": "lower",
+	"selector-pseudo-element-colon-notation": "double",
+	"selector-pseudo-element-no-unknown": true,
+	"selector-type-case": "lower"
+  }
+}

Gruntfile.js

@@ -47,6 +47,17 @@ module.exports = function( grunt ) {
 			]
 		},
 
+		// Sass linting with Stylelint.
+		stylelint: {
+			options: {
+				configFile: '.stylelintrc'
+			},
+			all: [
+				'assets/sass/**/*.scss',
+				'!assets/sass/vendors/**/*.scss'
+			]
+		},
+
 		// Minify .js files.
 		uglify: {
 			options: {
@@ -418,6 +429,7 @@ module.exports = function( grunt ) {
 	grunt.loadNpmTasks( 'grunt-rtlcss' );
 	grunt.loadNpmTasks( 'grunt-postcss' );
 	grunt.loadNpmTasks( 'grunt-contrib-compress' );
+	grunt.loadNpmTasks( 'grunt-stylelint' );
 
 
 	// Register tasks

package.json

@@ -27,9 +27,11 @@
     "grunt-postcss": "^0.8.0",
     "grunt-rtlcss": "~2.0.1",
     "grunt-sass": "~2.0.0",
+    "grunt-stylelint": "~0.9.0",
     "grunt-wp-i18n": "^1.0.0",
     "node-bourbon": "~4.2.8",
     "node-sass": "~4.5.2",
+    "stylelint": "~8.2.0",
     "susy": "~2.2.12"
   },
   "engines": {