Set up Stylelint and add custom plugins

stylelint_plugins/declaration-block-multi-line-min-declarations.js

@@ -0,0 +1,54 @@
+const stylelint = require('stylelint');
+const { isNumber } = require('stylelint/lib/utils/validateTypes');
+
+const { report, ruleMessages, validateOptions } = stylelint.utils;
+const ruleName = 'naturalcrit/declaration-block-multi-line-min-declarations';
+const messages = ruleMessages(ruleName, {
+   expected: (decls) => `Rule with ${decls} declaration${decls == 1 ? '' : 's'} should a single line`,
+});
+
+
+module.exports = stylelint.createPlugin(ruleName, function getPlugin(primaryOption, secondaryOptionObject, context) {
+   return function lint(postcssRoot, postcssResult) {
+
+       const validOptions = validateOptions(
+            postcssResult,
+            ruleName,
+            {
+                actual: primaryOption,
+                possible: [isNumber],
+            }
+       );
+
+       if (!validOptions) { //If the options are invalid, don't lint
+           return;
+       }
+       const isAutoFixing = Boolean(context.fix);
+
+       postcssRoot.walkRules(rule => { //Iterate CSS rules
+
+            //Apply rule only if all children are decls (no nested rules)
+            if (rule.nodes.length > primaryOption || !rule.nodes.every((node) => node.type === 'decl')) {
+                return;
+            }
+
+            if (isAutoFixing) { //We are in “fix” mode
+                rule.each((decl) => {
+                    decl.raws.before = " ";
+                });
+                rule.raws.after = ' ';
+            } else {
+                report({
+                    ruleName,
+                    result: postcssResult,
+                    message: messages.expected(rule.nodes.length), // Build the reported message
+                    node: rule, // Specify the reported node
+                    word: rule.selector, // Which exact word caused the error? This positions the error properly
+                });
+            }
+       });
+   };
+});
+
+module.exports.ruleName = ruleName;
+module.exports.messages = messages;