fix(removeHiddenElems): dont remove node if children have referenced id (#1925)

plugins/removeHiddenElems.js

@@ -91,6 +91,23 @@ export const fn = (root, params) => {
    */
   let deoptimized = false;
 
+  /**
+   * Nodes can't be removed if they or any of their children have an id attribute that is referenced.
+   * @param {XastElement} node
+   * @returns boolean
+   */
+  function canRemoveNonRenderingNode(node) {
+    if (allReferences.has(node.attributes.id)) {
+      return false;
+    }
+    for (const child of node.children) {
+      if (child.type === 'element' && !canRemoveNonRenderingNode(child)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   /**
    * @param {XastChild} node
    * @param {XastParent} parentNode
@@ -113,11 +130,6 @@ export const fn = (root, params) => {
       enter: (node, parentNode) => {
         // transparent non-rendering elements still apply where referenced
         if (nonRendering.has(node.name)) {
-          if (node.attributes.id == null) {
-            detachNodeFromParent(node, parentNode);
-            return visitSkip;
-          }
-
           nonRenderedNodes.set(node, parentNode);
           return visitSkip;
         }
@@ -419,9 +431,7 @@ export const fn = (root, params) => {
             nonRenderedNode,
             nonRenderedParent,
           ] of nonRenderedNodes.entries()) {
-            const id = nonRenderedNode.attributes.id;
-
-            if (!allReferences.has(id)) {
+            if (canRemoveNonRenderingNode(nonRenderedNode)) {
               detachNodeFromParent(nonRenderedNode, nonRenderedParent);
             }
           }

test/plugins/removeHiddenElems.16.svg

@@ -0,0 +1,23 @@
+Don't remove non-rendering elements if children have IDs. 
+
+===
+
+<svg xmlns="http://www.w3.org/2000/svg">
+    <rect fill="url(#a)" width="64" height="64"/>
+    <symbol>
+        <linearGradient id="a">
+            <stop offset="5%" stop-color="gold" />
+        </linearGradient>
+    </symbol>
+</svg>
+
+@@@
+
+<svg xmlns="http://www.w3.org/2000/svg">
+    <rect fill="url(#a)" width="64" height="64"/>
+    <symbol>
+        <linearGradient id="a">
+            <stop offset="5%" stop-color="gold"/>
+        </linearGradient>
+    </symbol>
+</svg>

test/plugins/removeHiddenElems.17.svg

@@ -0,0 +1,23 @@
+Don't remove used symbols.
+
+===
+
+<svg xmlns="http://www.w3.org/2000/svg">
+    <rect fill="url(#a)" width="64" height="64"/>
+    <g>
+        <linearGradient id="a">
+            <stop offset="5%" stop-color="gold" />
+        </linearGradient>
+    </g>
+</svg>
+
+@@@
+
+<svg xmlns="http://www.w3.org/2000/svg">
+    <rect fill="url(#a)" width="64" height="64"/>
+    <g>
+        <linearGradient id="a">
+            <stop offset="5%" stop-color="gold"/>
+        </linearGradient>
+    </g>
+</svg>

test/plugins/removeHiddenElems.18.svg

@@ -0,0 +1,23 @@
+Preserve <defs> with referenced path.
+
+===
+
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+    <g id="test-body-content">
+        <defs>
+            <path id="reference" d="M240 1h239v358H240z"/>
+        </defs>
+        <use xlink:href="#reference" id="use" fill="gray" onclick="test(evt)"/>
+    </g>
+</svg>
+
+@@@
+
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+    <g id="test-body-content">
+        <defs>
+            <path id="reference" d="M240 1h239v358H240z"/>
+        </defs>
+        <use xlink:href="#reference" id="use" fill="gray" onclick="test(evt)"/>
+    </g>
+</svg>