htmlhint · thedaviddias · Jun 10, 2021 · Apr 22, 2021 · Jun 10, 2021 · Jun 10, 2021
diff --git a/src/core/rules/html-lang-require.ts b/src/core/rules/html-lang-require.ts
@@ -0,0 +1,66 @@
+import { Rule } from '../types'
+
+const regular =
+  '(art-lojban|cel-gaulish|no-bok|no-nyn|zh-guoyu|zh-hakka|zh-min|zh-min-nan|zh-xiang)'
+const irregular =
+  '(en-GB-oed|i-ami|i-bnn|i-default|i-enochian|i-hak|i-klingon|i-lux|i-mingo|i-navajo|i-pwn|i-tao|i-tay|i-tsu|sgn-BE-FR|sgn-BE-NL|sgn-CH-DE)'
+const grandfathered = `(?<grandfathered>${irregular}|${regular})`
+const privateUse = '(?<privateUse>x(-[A-Za-z0-9]{1,8})+)'
+const privateUse2 = '(?<privateUse2>x(-[A-Za-z0-9]{1,8})+)'
+const singleton = '[0-9A-WY-Za-wy-z]'
+const extension = `(?<extension>${singleton}(-[A-Za-z0-9]{2,8})+)`
+const variant = '(?<variant>[A-Za-z0-9]{5,8}|[0-9][A-Za-z0-9]{3})'
+const region = '(?<region>[A-Za-z]{2}|[0-9]{3})'
+const script = '(?<script>[A-Za-z]{4})'
+const extlang = '(?<extlang>[A-Za-z]{3}(-[A-Za-z]{3}){0,2})'
+const language = `(?<language>([A-Za-z]{2,3}(-${extlang})?)|[A-Za-z]{4}|[A-Za-z]{5,8})`
+const langtag =
+  `(${language}(-${script})?` +
+  `(-${region})?` +
+  `(-${variant})*` +
+  `(-${extension})*` +
+  `(-${privateUse})?` +
+  ')'
+const languageTag = `(${grandfathered}|${langtag}|${privateUse2})`
+const LANG_VALIDITY_PATTERN = new RegExp(languageTag, 'g')
+
+export default {
+  id: 'html-lang-require',
+  description:
+    'The lang attribute of an <html> element must be present and should be valid.',
+  init(parser, reporter) {
+    parser.addListener('tagstart', (event) => {
+      const tagName = event.tagName.toLowerCase()
+      const mapAttrs = parser.getMapAttrs(event.attrs)
+      const col = event.col + tagName.length + 1
+
+      if (tagName === 'html' && 'lang' in mapAttrs) {
+        if (!mapAttrs['lang']) {
+          reporter.warn(
+            'The lang attribute of <html> element must have a value.',
+            event.line,
+            col,
+            this,
+            event.raw
+          )
+        } else if (!LANG_VALIDITY_PATTERN.test(mapAttrs['lang'])) {
+          reporter.warn(
+            'The lang attribute value of <html> element must be a valid BCP47.',
+            event.line,
+            col,
+            this,
+            event.raw
+          )
+        }
+      } else {
+        reporter.warn(
+          'An lang attribute must be present on <html> elements.',
+          event.line,
+          col,
+          this,
+          event.raw
+        )
+      }
+    })
+  },
+} as Rule
diff --git a/src/core/rules/index.ts b/src/core/rules/index.ts
@@ -11,6 +11,7 @@ export { default as doctypeFirst } from './doctype-first'
 export { default as doctypeHTML5 } from './doctype-html5'
 export { default as headScriptDisabled } from './head-script-disabled'
 export { default as hrefAbsOrRel } from './href-abs-or-rel'
+export { default as htmlLangRequire } from './html-lang-require'
 export { default as idClsasAdDisabled } from './id-class-ad-disabled'
 export { default as idClassValue } from './id-class-value'
 export { default as idUnique } from './id-unique'

diff --git a/test/rules/html-lang-require.spec.js b/test/rules/html-lang-require.spec.js
@@ -0,0 +1,31 @@
+const expect = require('expect.js')
+
+const HTMLHint = require('../../dist/htmlhint.js').HTMLHint
+
+const ruldId = 'html-lang-require'
+const ruleOptions = {}
+
+ruleOptions[ruldId] = true
+
+describe(`Rules: ${ruldId}`, () => {
+  it('HTML tag have no a lang attribute should result in an error', () => {
+    const code = '<html></html>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).to.be(1)
+  })
+  it('HTML tag have an empty lang attribute should result in an error', () => {
+    const code = '<html lang=""></html>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).to.be(1)
+  })
+  it('HTML tag have an invalid lang attribute should result in an error', () => {
+    const code = '<html lang="-"></html>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).to.be(1)
+  })
+  it('HTML tag have an non emtpy and valid lang attribute should not result in an error', () => {
+    const code = '<html lang="en-EN"></html>'
+    const messages = HTMLHint.verify(code, ruleOptions)
+    expect(messages.length).to.be(0)
+  })
+})