Add vnu-jar for HTML validation.

Also, add a GitHub Action which builds the docs and run the validator script.

.github/workflows/docs.yml

@@ -0,0 +1,73 @@
+name: Docs
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - "**"
+
+env:
+  CI: true
+  NODE: 12.x
+  RUBY: 2.6.x
+
+jobs:
+  run:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Clone repository
+        uses: actions/checkout@v2
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: "${{ env.NODE }}"
+
+      - name: Set up Ruby
+        uses: actions/setup-ruby@v1
+        with:
+          ruby-version: ${{ env.RUBY }}
+
+      - name: Disable gem docs
+        run: 'echo "gem: --no-document" > ~/.gemrc'
+
+      - name: Set up npm cache
+        uses: actions/cache@v2
+        with:
+          path: ~/.npm
+          key: ${{ runner.os }}-node-v${{ env.node }}-${{ hashFiles('package.json') }}-${{ hashFiles('package-lock.json') }}}
+          restore-keys: |
+            ${{ runner.OS }}-node-v${{ env.node }}-${{ hashFiles('package.json') }}-${{ hashFiles('package-lock.json') }}
+            ${{ runner.OS }}-node-v${{ env.node }}-
+
+      - name: Set up Ruby cache
+        uses: actions/cache@v2
+        with:
+          path: vendor/bundle
+          key: ${{ runner.os }}-ruby-v${{ env.RUBY }}-${{ hashFiles('Gemfile') }}-${{ hashFiles('Gemfile.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-ruby-v${{ env.RUBY }}-${{ hashFiles('Gemfile') }}-${{ hashFiles('Gemfile.lock') }}
+            ${{ runner.os }}-ruby-v${{ env.RUBY }}-
+
+      - name: Set up Bundler
+        run: gem install bundler -v "~> 1.17"
+
+      - run: ruby --version
+      - run: gem --version
+      - run: bundle --version
+      - run: java -version
+
+      - name: Install npm dependencies
+        run: npm ci
+
+      - name: Install bundler dependencies
+        run: bundle install --gemfile docs/Gemfile --deployment --jobs=4 --retry=3 --clean
+
+      - name: Build docs
+        run: npm run docs-compile
+
+      - name: Run HTML validator
+        run: npm run docs-lint

build/npm/vnu-jar.js

@@ -0,0 +1,55 @@
+#!/usr/bin/env node
+
+/*!
+ * Script to run vnu-jar if Java is available.
+ * Copyright 2017-2020 The Bootstrap Authors
+ * Copyright 2017-2020 Twitter, Inc.
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
+ */
+
+'use strict'
+
+const childProcess = require('child_process')
+const vnu = require('vnu-jar')
+
+childProcess.exec('java -version', (error, stdout, stderr) => {
+  if (error) {
+    console.error('Skipping vnu-jar test; Java is missing.')
+    return
+  }
+
+  const is32bitJava = !/64-Bit/.test(stderr)
+
+  // vnu-jar accepts multiple ignores joined with a `|`.
+  // Also note that the ignores are regular expressions.
+  const ignores = [
+    // "autocomplete" is included in <button> and checkboxes and radio <input>s due to
+    // Firefox's non-standard autocomplete behavior - see https://bugzilla.mozilla.org/show_bug.cgi?id=654072
+    'Attribute “autocomplete” is only allowed when the input type is.*'
+  ].join('|')
+
+  const args = [
+    '-jar',
+    vnu,
+    '--asciiquotes',
+    '--skip-non-html',
+    // Ignore the language code warnings
+    '--no-langdetect',
+    // '--Werror',
+    `--filterpattern "${ignores}"`,
+    './*.html',
+    'docs_html/',
+    'pages/'
+  ]
+
+  // For the 32-bit Java we need to pass `-Xss512k`
+  if (is32bitJava) {
+    args.splice(0, 0, '-Xss512k')
+  }
+
+  return childProcess.spawn('java', args, {
+    shell: true,
+    stdio: 'inherit'
+  })
+    .on('exit', process.exit)
+})

package-lock.json

@@ -11581,6 +11581,12 @@
         "unist-util-stringify-position": "^2.0.0"
       }
     },
+    "vnu-jar": {
+      "version": "20.5.29",
+      "resolved": "https://registry.npmjs.org/vnu-jar/-/vnu-jar-20.5.29.tgz",
+      "integrity": "sha512-//4B+FR0RlMul8YTQCDrC1Xxrm/meFKpD/cNaam6VU/bfjOiFIeNYVpCUsIiUWGqBiNcxtky+K5RIPzO1QSykg==",
+      "dev": true
+    },
     "which": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/which/-/which-2.0.2.tgz",

package.json

@@ -31,6 +31,7 @@
     "compile": "npm-run-all --parallel js css-all",
     "dev": "npm-run-all --parallel watch sync",
     "docs": "npm-run-all --sequential docs-prepare docs-compile",
+    "docs-lint": "node build/npm/vnu-jar.js",
     "docs-compile": "cd docs/ && bundle exec jekyll build -d ../docs_html",
     "docs-serve": "cd docs/ && bundle exec jekyll serve",
     "docs-prepare": "node build/npm/DocsPublish.js -v",
@@ -152,6 +153,7 @@
     "rollup": "^2.12.1",
     "stylelint": "^13.5.0",
     "stylelint-config-twbs-bootstrap": "^2.0.3",
-    "terser": "^4.7.0"
+    "terser": "^4.7.0",
+    "vnu-jar": "^20.5.29"
   }
 }