fix: collapseGroups does not move attributes atomically (#1930)

Author: johnkenny54

plugins/collapseGroups.js

@@ -1,6 +1,7 @@
 import { inheritableAttrs, elemsGroups } from './_collections.js';
 
 /**
+ * @typedef {import('../lib/types.js').XastElement} XastElement
  * @typedef {import('../lib/types.js').XastNode} XastNode
  */
 
@@ -80,26 +81,30 @@ export const fn = () => {
                 node.attributes.transform == null &&
                 firstChild.attributes.transform == null))
           ) {
+            const newChildElemAttrs = { ...firstChild.attributes };
+
             for (const [name, value] of Object.entries(node.attributes)) {
               // avoid copying to not conflict with animated attribute
               if (hasAnimatedAttr(firstChild, name)) {
                 return;
               }
-              if (firstChild.attributes[name] == null) {
-                firstChild.attributes[name] = value;
+
+              if (newChildElemAttrs[name] == null) {
+                newChildElemAttrs[name] = value;
               } else if (name === 'transform') {
-                firstChild.attributes[name] =
-                  value + ' ' + firstChild.attributes[name];
-              } else if (firstChild.attributes[name] === 'inherit') {
-                firstChild.attributes[name] = value;
+                newChildElemAttrs[name] = value + ' ' + newChildElemAttrs[name];
+              } else if (newChildElemAttrs[name] === 'inherit') {
+                newChildElemAttrs[name] = value;
               } else if (
-                inheritableAttrs.has(name) === false &&
-                firstChild.attributes[name] !== value
+                !inheritableAttrs.has(name) &&
+                newChildElemAttrs[name] !== value
               ) {
                 return;
               }
-              delete node.attributes[name];
             }
+
+            node.attributes = {};
+            firstChild.attributes = newChildElemAttrs;
           }
         }
 

test/plugins/collapseGroups.17.svg.txt

@@ -0,0 +1,24 @@
+Don't collapse group with a single child unless all attributes can be moved to the child.
+See issue #1928 for context.
+
+===
+
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 88 88">
+  <filter id="a">
+    <feGaussianBlur stdDeviation="1"/>
+  </filter>
+  <g transform="matrix(0.6875,0,0,0.6875,20.34375,66.34375)" style="filter:url(#a)">
+    <path d="M 33.346591,-83.471591 L -10.744318,-36.471591 L -10.49989,-32.5" style="fill-opacity:1"/>
+  </g>
+</svg>
+
+@@@
+
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 88 88">
+    <filter id="a">
+        <feGaussianBlur stdDeviation="1"/>
+    </filter>
+    <g transform="matrix(0.6875,0,0,0.6875,20.34375,66.34375)" style="filter:url(#a)">
+        <path d="M 33.346591,-83.471591 L -10.744318,-36.471591 L -10.49989,-32.5" style="fill-opacity:1"/>
+    </g>
+</svg>