Bugfix/selector no union class name nesting

src/rules/selector-no-union-class-name/__tests__/index.js

@@ -95,6 +95,20 @@ testRule(rule, {
       }
       `,
       description: "ignores an ampersand chained with an attribute"
+    },
+    {
+      code: `
+      @mixin demo() {
+        @content;
+      }
+      .a-selector {
+        @include demo() {
+          button:hover & {
+  	        background:purple
+          }
+        }
+      }`,
+      description: "should not throw an error when using nesting (issue #345)"
     }
   ],
 

src/rules/selector-no-union-class-name/index.js

@@ -35,9 +35,15 @@ export default function(actual) {
     root.walkRules(/&/, rule => {
       const parentNodes = [];
 
-      parseSelector(rule.parent.selector, result, rule, fullSelector => {
-        fullSelector.walk(node => parentNodes.push(node));
-      });
+      const selector = getSelectorFromRule(rule.parent);
+
+      if (selector) {
+        parseSelector(selector, result, rule, fullSelector => {
+          fullSelector.walk(node => parentNodes.push(node));
+        });
+      }
+
+      if (parentNodes.length === 0) return;
 
       const lastParentNode = parentNodes[parentNodes.length - 1];
 
@@ -63,3 +69,21 @@ export default function(actual) {
     });
   };
 }
+
+/**
+ * Searches for the closest rule which
+ * has a selector and returns the selector
+ * @returns {string|undefined}
+ */
+function getSelectorFromRule(rule) {
+  // All non at-rules have their own selector
+  if (rule.selector !== undefined) {
+    return rule.selector;
+  }
+
+  // At-rules like @mixin don't have a selector themself
+  // but their parents might have one
+  if (rule.parent) {
+    return getSelectorFromRule(rule.parent);
+  }
+}