Add mergeStyles plugin (#1381)

lib/css-tools.js

@@ -189,7 +189,10 @@ function csstreeToStyleDeclaration(declaration) {
  * @return {string} CSS string or empty array if no styles are set
  */
 function getCssStr(elem) {
-  if (elem.children[0].type === 'text' || elem.children[0].type === 'cdata') {
+  if (
+    elem.children.length > 0 &&
+    (elem.children[0].type === 'text' || elem.children[0].type === 'cdata')
+  ) {
     return elem.children[0].value;
   }
   return '';
@@ -203,10 +206,19 @@ function getCssStr(elem) {
  * @return {string} reference to field with CSS
  */
 function setCssStr(elem, css) {
-  if (elem.children[0].type === 'text' || elem.children[0].type === 'cdata') {
-    elem.children[0].value = css;
-    return elem.children[0].value;
+  if (elem.children.length === 0) {
+    elem.children.push({
+      type: 'text',
+      value: '',
+    });
   }
+
+  if (elem.children[0].type !== 'text' && elem.children[0].type !== 'cdata') {
+    return css;
+  }
+
+  elem.children[0].value = css;
+
   return css;
 }
 

lib/svgo/config.js

@@ -10,6 +10,7 @@ const pluginsOrder = [
   'removeXMLNS',
   'removeEditorsNSData',
   'cleanupAttrs',
+  'mergeStyles',
   'inlineStyles',
   'minifyStyles',
   'convertStyleToAttrs',