Replace lint-vars.sh with a node.js script.

Also, include it in the `css` npm script since it's instant.

build/lint-vars.js

@@ -0,0 +1,83 @@
+#!/usr/bin/env node
+
+/*!
+ * Script to find unused Sass variables.
+ *
+ * Copyright 2017 The Bootstrap Authors
+ * Copyright 2017 Twitter, Inc.
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
+ */
+
+'use strict'
+
+const fs = require('fs')
+const path = require('path')
+const glob = require('glob')
+
+// Blame TC39... https://github.com/benjamingr/RegExp.escape/issues/37
+function regExpQuote(str) {
+  return str.replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&')
+}
+
+let globalSuccess = true
+
+function findUnusedVars(dir) {
+  if (!(fs.existsSync(dir) && fs.statSync(dir).isDirectory())) {
+    console.log(`"${dir}": Not a valid directory!`)
+    process.exit(1)
+  }
+
+  console.log(`Finding unused variables in "${dir}"...`)
+
+  // A variable to handle success/failure message in this function
+  let unusedVarsFound = false
+
+  // Array of all Sass files' content
+  const sassFiles = glob.sync(path.join(dir, '**/*.scss'))
+  // String of all Sass files' content
+  let sassFilesString = ''
+
+  sassFiles.forEach((file) => {
+    sassFilesString += fs.readFileSync(file, 'utf8')
+  })
+
+  // Array of all Sass variables
+  const variables = sassFilesString.match(/(^\$[a-zA-Z0-9_-]+[^:])/gm)
+
+  console.log(`There's a total of ${variables.length} variables.`)
+
+  // Loop through each variable
+  variables.forEach((variable) => {
+    const re = new RegExp(regExpQuote(variable), 'g')
+    const count = (sassFilesString.match(re) || []).length
+
+    if (count === 1) {
+      console.log(`Variable "${variable}" is only used once!`)
+      unusedVarsFound = true
+      globalSuccess = false
+    }
+  })
+
+  if (unusedVarsFound === false) {
+    console.log(`No unused variables found in "${dir}".`)
+  }
+}
+
+function main(args) {
+  if (args.length < 1) {
+    console.log('Wrong arguments!')
+    console.log('Usage: lint-vars.js folder [, folder2...]')
+    process.exit(1)
+  }
+
+  args.forEach((arg) => {
+    findUnusedVars(arg)
+  })
+
+  if (globalSuccess === false) {
+    process.exit(1)
+  }
+}
+
+// The first and second args are: path/to/node script.js
+main(process.argv.slice(2))

package.json

@@ -25,6 +25,7 @@
     "css-compile-docs": "node-sass --output-style expanded --source-map true --source-map-contents true --precision 6 assets/scss/docs.scss assets/css/docs.min.css",
     "css-lint": "stylelint --config build/.stylelintrc --syntax scss \"scss/**/*.scss\"",
     "css-lint-docs": "stylelint --config build/.stylelintrc --syntax scss \"assets/scss/*.scss\" && stylelint --config docs/4.0/examples/.stylelintrc \"docs/**/*.css\"",
+    "css-lint-vars": "node build/lint-vars.js scss/ assets/scss/",
     "css-prefix": "postcss --config build/postcss.config.js --replace \"dist/css/*.css\" \"!dist/css/*.min.css\"",
     "css-prefix-docs": "postcss --config build/postcss.config.js --replace \"assets/css/docs.min.css\" \"docs/**/*.css\"",
     "css-minify": "cleancss --level 1 --source-map --source-map-inline-sources --output dist/css/bootstrap.min.css dist/css/bootstrap.css && cleancss --level 1 --source-map --source-map-inline-sources --output dist/css/bootstrap-grid.min.css dist/css/bootstrap-grid.css && cleancss --level 1 --source-map --source-map-inline-sources --output dist/css/bootstrap-reboot.min.css dist/css/bootstrap-reboot.css",
@@ -94,6 +95,7 @@
     "cross-env": "^5.1.1",
     "eslint": "^4.11.0",
     "eslint-plugin-compat": "^2.1.0",
+    "glob": "^7.1.2",
     "htmllint-cli": "^0.0.6",
     "jsunitsaucelabs": "^1.3.0",
     "karma": "^1.7.1",