[Draft][No ticket] New linter rule to prevent leaky selectors

.stylelintrc.yml

@@ -1,6 +1,8 @@
 extends:
   - stylelint-config-css-modules
   - stylelint-config-sass-guidelines
+plugins:
+  - ./ember-osf-web-stylelint/no-unlocalized-selectors.js
 rules:
   indentation: 4
   max-nesting-depth: 2
@@ -13,3 +15,4 @@ rules:
     - ignoreProperties:
       - composes
       - compose-with
+  ember-osf-web-stylelint/no-unlocalized-selectors: true

ember-osf-web-stylelint/no-unlocalized-selectors.js

@@ -0,0 +1,42 @@
+// eslint-disable @typescript-eslin/no-var-requires
+const stylelint = require('stylelint');
+
+/*
+    * This rule prevents the use of bare element selectors in CSS
+    * Bare element selectors are selectors that are not wrapped in  or paired with a class or id
+*/
+
+const ruleName = 'ember-osf-web-stylelint/no-unlocalized-selectors';
+const messages = stylelint.utils.ruleMessages(ruleName, {
+    expected: selector => `Rule "${selector}" should be wrapped in or paired with a local-class or ID`,
+});
+
+module.exports = stylelint.createPlugin(ruleName, _ =>
+    (postcssRoot, postcssResult) => {
+        postcssRoot.walkRules(rule => {
+            const selector = rule.selector;
+            const isChildRule = rule.parent.type === 'rule'; // top-level rules have rule.parent.type === 'root'
+            const hasGlobal = selector.includes(':global');
+            if (
+                isChildRule ||
+                (!hasGlobal && (selector.includes('.') || selector.includes('#'))) // has a local-class or local-id
+            ) {
+                return;
+            }
+
+            if (
+                /^[a-z]+/.test(selector) || // starts with a letter
+                /^:global\([a-z]+/.test(selector) // or starts with :global
+            ) {
+                stylelint.utils.report({
+                    ruleName,
+                    result: postcssResult,
+                    message: messages.expected(selector),
+                    node: rule,
+                });
+            }
+        });
+    });
+
+module.exports.ruleName = ruleName;
+module.exports.messages = messages;