Add font-family-no-duplicate-names rule

docs/user-guide/example-config.md

@@ -63,6 +63,7 @@ You might want to learn a little about [how rules are named and how they work to
     "declaration-property-value-blacklist": {},
     "declaration-property-value-whitelist": {},
     "font-family-name-quotes": "always-where-required"|"always-where-recommended"|"always-unless-keyword",
+    "font-family-no-duplicate-names": true,    
     "font-weight-notation": "numeric"|"named",
     "function-blacklist": string|[],
     "function-calc-no-unspaced-operator": true,

docs/user-guide/rules.md

@@ -19,6 +19,7 @@ Here are all the rules within stylelint, grouped by the [*thing*](http://apps.wo
 ### Font family
 
 -   [`font-family-name-quotes`](../../src/rules/font-family-name-quotes/README.md): Specify whether or not quotation marks should be used around font family names.
+-   [`font-family-no-duplicate-names`](../../src/rules/font-family-no-duplicate-names/README.md): Disallow duplicate font family names.
 
 ### Font weight
 

src/rules/font-family-no-duplicate-names/README.md

@@ -0,0 +1,47 @@
+# font-family-no-duplicate-names
+
+Disallow duplicate font family names.
+
+```css
+a { font-family: serif, serif; }
+/**              ↑      ↑
+ * These font family names */
+```
+
+This rule checks the `font` and `font-family` properties.
+
+This rule ignores `$sass`, `@less`, and `var(--custom-property)` variable syntaxes.
+
+**Caveat:** This rule will stumble on *unquoted* multi-word font names and *unquoted* font names containing escape sequences. Wrap these font names in quotation marks, and everything should be fine.
+
+## Options
+
+### `true`
+
+The following patterns are considered warnings:
+
+```css
+a { font-family: 'Times', Times, serif; }
+```
+
+```css
+a { font: 1em "Arial", 'Arial', sans-serif; }
+```
+
+```css
+a { font: normal 14px/32px -apple-system, BlinkMacSystemFont, sans-serif, sans-serif; }
+```
+
+The following patterns are *not* considered warnings:
+
+```css
+a { font-family: Times, serif; }
+```
+
+```css
+a { font: 1em "Arial", "sans-serif", sans-serif; }
+```
+
+```css
+a { font: normal 14px/32px -apple-system, BlinkMacSystemFont, sans-serif; }
+```

src/rules/font-family-no-duplicate-names/__tests__/index.js

@@ -0,0 +1,58 @@
+import {
+  messages,
+  ruleName,
+} from ".."
+import rules from "../../../rules"
+import { testRule } from "../../../testUtils"
+
+const rule = rules[ruleName]
+
+testRule(rule, {
+  ruleName,
+  config: [true],
+
+  accept: [ {
+    code: "a { font-family: \"Lucida Grande\", \"Arial\", sans-serif; }",
+  }, {
+    code: "a { font: 1em \"Lucida Grande\", \'Arial\', sans-serif; }",
+  }, {
+    code: "a { font: 1em \"Lucida Grande\", \'Arial\', \"sans-serif\", sans-serif; }",
+  }, {
+    code: "a { font-family: Times, serif; }",
+  }, {
+    code: "b { font: normal 14px/32px -apple-system, BlinkMacSystemFont, sans-serif; }",
+  } ],
+
+  reject: [ {
+    code: "a { font-family: \"Lucida Grande\", \'Arial\', sans-serif, sans-serif; }",
+    message: messages.rejected("sans-serif"),
+    line: 1,
+    column: 56,
+  }, {
+    code: "a { font-family: \'Arial\', \"Lucida Grande\", Arial, sans-serif; }",
+    message: messages.rejected("Arial"),
+    line: 1,
+    column: 44,
+  }, {
+    code: "a { fOnT-fAmIlY: \'  Lucida Grande \', \"Lucida Grande\", sans-serif; }",
+    message: messages.rejected("Lucida Grande"),
+    line: 1,
+    column: 38,
+  }, {
+    code: "a { font-family: \'Times\', Times, \"serif\", serif; }",
+    message: messages.rejected("Times"),
+    line: 1,
+    column: 27,
+  }, {
+    code: "a { FONT: italic 300 16px/30px Arial, \" Arial\", serif; }",
+    message: messages.rejected("Arial"),
+    line: 1,
+    column: 39,
+  }, {
+    code: "b { font: normal 14px/32px -apple-system, BlinkMacSystemFont, sans-serif, sans-serif; }",
+    message: messages.rejected("sans-serif"),
+    line: 1,
+    column: 75,
+  } ],
+
+})

src/rules/font-family-no-duplicate-names/index.js

@@ -0,0 +1,66 @@
+import {
+  declarationValueIndex,
+  findFontFamily,
+  report,
+  ruleMessages,
+  validateOptions,
+  } from "../../utils"
+import { fontFamilyKeywords } from "../../reference/keywordSets"
+
+export const ruleName = "font-family-no-duplicate-names"
+
+export const messages = ruleMessages(ruleName, {
+  rejected: (name) => `Unexpected duplicate name ${name}`,
+})
+
+const isFamilyNameKeyword = (node) => !node.quote && fontFamilyKeywords.has(node.value.toLowerCase())
+
+export default function (actual) {
+  return (root, result) => {
+    const validOptions = validateOptions(result, ruleName, { actual })
+    if (!validOptions) { return }
+
+    root.walkDecls(/^font(-family)?$/i, decl => {
+      const keywords = new Set()
+      const familyNames = new Set()
+
+      const fontFamilies = findFontFamily(decl.value)
+
+      if (fontFamilies.length === 0) { return }
+
+      fontFamilies.forEach(fontFamilyNode => {
+        if (isFamilyNameKeyword(fontFamilyNode)) {
+          const family = fontFamilyNode.value.toLowerCase()
+
+          if (keywords.has(family)) {
+            complain(messages.rejected(family), declarationValueIndex(decl) + fontFamilyNode.sourceIndex, decl)
+            return
+          }
+
+          keywords.add(family)
+          return
+        }
+
+        const family = fontFamilyNode.value.trim()
+
+        if (familyNames.has(family)) {
+          complain(messages.rejected(family), declarationValueIndex(decl) + fontFamilyNode.sourceIndex, decl)
+          return
+        }
+
+        familyNames.add(family)
+      })
+    })
+
+    function complain(message, index, decl) {
+      report({
+        result,
+        ruleName,
+        message,
+        node: decl,
+        index,
+      })
+    }
+  }
+}
+

src/rules/index.js

@@ -54,6 +54,7 @@ import declarationPropertyUnitWhitelist from "./declaration-property-unit-whitel
 import declarationPropertyValueBlacklist from "./declaration-property-value-blacklist"
 import declarationPropertyValueWhitelist from "./declaration-property-value-whitelist"
 import fontFamilyNameQuotes from "./font-family-name-quotes"
+import fontFamilyNoDuplicateNames from "./font-family-no-duplicate-names"
 import fontWeightNotation from "./font-weight-notation"
 import functionBlacklist from "./function-blacklist"
 import functionCalcNoUnspacedOperator from "./function-calc-no-unspaced-operator"
@@ -227,6 +228,7 @@ export default {
   "declaration-property-value-blacklist": declarationPropertyValueBlacklist,
   "declaration-property-value-whitelist": declarationPropertyValueWhitelist,
   "font-family-name-quotes": fontFamilyNameQuotes,
+  "font-family-no-duplicate-names": fontFamilyNoDuplicateNames,
   "font-weight-notation": fontWeightNotation,
   "function-blacklist": functionBlacklist,
   "function-calc-no-unspaced-operator": functionCalcNoUnspacedOperator,