feat: implement validate addon

Author: streamich

addon/validate.js

@@ -0,0 +1,33 @@
+'use strict';
+
+var validateString = require('csstree-validator').validateString;
+
+exports.addon = function (renderer) {
+    if (process.env.NODE_ENV !== 'production') {
+        require('./__dev__/warnOnMissingDependencies')('validate', renderer, ['putRaw']);
+    }
+
+    if (process.env.NODE_ENV === 'production') {
+        console.warn(
+            'You are using nano-css "validate" in production. ' +
+            'This addon is suggested to be used only in development.'
+        );
+    }
+
+    var putRaw = renderer.putRaw;
+
+    renderer.putRaw = function (rawCssRule) {
+        var errors = validateString(rawCssRule)['<unknown>'];
+
+        if (errors.length) {
+            errors.forEach(function (error) {
+                console.error('Error in CSS: ' + error.message);
+                console.error(error);
+                // eslint-disable-next-line
+                console.log(rawCssRule);
+            });
+        }
+
+        putRaw(rawCssRule);
+    };
+};