Fix false positives for system fonts in font-family-no-missing-generic-family-keyword

lib/reference/keywordSets.js

@@ -78,6 +78,15 @@ keywordSets.camelCaseFunctionNames = new Set([
 
 keywordSets.basicKeywords = new Set(["initial", "inherit", "unset"]);
 
+keywordSets.systemFontValues = uniteSets(keywordSets.basicKeywords, [
+  "caption",
+  "icon",
+  "menu",
+  "message-box",
+  "small-caption",
+  "status-bar"
+]);
+
 keywordSets.fontFamilyKeywords = uniteSets(keywordSets.basicKeywords, [
   "serif",
   "sans-serif",

lib/rules/font-family-no-missing-generic-family-keyword/README.md

@@ -34,12 +34,13 @@ a { font-family: Helvetica, Arial, Verdana, Tahoma, sans-serif; }
 a { font: 1em/1.3 Times, serif; }
 ```
 
-It's also *not* a violation to use a keyword related to property inheritance.
+It's also *not* a violation to use a keyword related to property inheritance or a system font value.
 
 ```css
 a { font: inherit; }
 b { font: initial; }
 i { font: unset; }
+input { font: caption; }
 ```
 
 It's also *not* a violation to use a generic font family anywhere in the list. In other words, the generic font name doesn't need to be the last.

lib/rules/font-family-no-missing-generic-family-keyword/__tests__/index.js

@@ -53,6 +53,27 @@ testRule(rule, {
     },
     {
       code: "@FONT-FACE { font-family: Gentium; }"
+    },
+    {
+      code: "a { font: inherit; }"
+    },
+    {
+      code: "a { font: caption; }"
+    },
+    {
+      code: "a { font: icon; }"
+    },
+    {
+      code: "a { font: menu; }"
+    },
+    {
+      code: "a { font: message-box; }"
+    },
+    {
+      code: "a { font: small-caption; }"
+    },
+    {
+      code: "a { font: status-bar; }"
     }
   ],
 

lib/rules/font-family-no-missing-generic-family-keyword/index.js

@@ -34,6 +34,13 @@ const rule = function(actual) {
         return;
       }
 
+      if (
+        decl.prop === "font" &&
+        keywordSets.systemFontValues.has(decl.value.toLowerCase())
+      ) {
+        return;
+      }
+
       const fontFamilies = findFontFamily(decl.value);
 
       if (fontFamilies.length === 0) {