Check ignore next warning comments in a warn() helper

lib/utils.js

@@ -1,5 +1,10 @@
 let { list } = require('postcss')
 
+let vendor = require('./vendor')
+
+const IGNORE_NEXT_WARNING = /(!\s*)?autoprefixer:\s*ignore\s+next\s+warning/i
+const PREFIXED_VALUE = /(^|[\s,(])-\w+-/
+
 /**
  * Throw special error, to tell beniary,
  * that this error is from Autoprefixer.
@@ -91,3 +96,30 @@ module.exports.isPureNumber = function (value) {
   }
   return false
 }
+
+/**
+ * Is the node right after an `ignore next warning` control comment?
+ * Prefixed copies inserted before the node are skipped on the way back.
+ */
+function hasIgnoreWarningComment(node) {
+  let prev = node.prev()
+  while (
+    prev &&
+    prev.type === 'decl' &&
+    (vendor.prefix(prev.prop) || PREFIXED_VALUE.test(prev.value))
+  ) {
+    prev = prev.prev()
+  }
+  return (
+    !!prev && prev.type === 'comment' && IGNORE_NEXT_WARNING.test(prev.text)
+  )
+}
+
+/**
+ * Add a warning, unless the node is hidden
+ * by an `ignore next warning` control comment.
+ */
+module.exports.warn = function (result, text, opts = {}) {
+  if (opts.node && hasIgnoreWarningComment(opts.node)) return
+  result.warn(text, opts)
+}