From 0c6f7980ae237b82324c4536c206426020c910f3 Mon Sep 17 00:00:00 2001
From: Seth Falco <seth@falco.fun>
Date: Mon, 18 Sep 2023 20:31:04 +0100
Subject: [PATCH] fix(reusePaths): dont reuse id if referenced in href

---
 plugins/reusePaths.js          | 21 +++++++++++++++++-
 test/plugins/reusePaths.04.svg | 40 ++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 test/plugins/reusePaths.04.svg

diff --git a/plugins/reusePaths.js b/plugins/reusePaths.js
index 4d91d6f9d..3e8556dd4 100644
--- a/plugins/reusePaths.js
+++ b/plugins/reusePaths.js
@@ -26,6 +26,13 @@ exports.fn = () => {
    */
   const paths = new Map();
 
+  /**
+   * Set of hrefs that reference the id of another node.
+   *
+   * @type {Set<string>}
+   */
+  const hrefs = new Set();
+
   return {
     element: {
       enter: (node) => {
@@ -41,12 +48,23 @@ exports.fn = () => {
           }
           list.push(node);
         }
+
+        if (node.name === 'use') {
+          for (const name of ['href', 'xlink:href']) {
+            const href = node.attributes[name];
+
+            if (href != null && href.startsWith('#') && href.length > 1) {
+              hrefs.add(href.slice(1));
+            }
+          }
+        }
       },
 
       exit: (node, parentNode) => {
         if (node.name === 'svg' && parentNode.type === 'root') {
           /**
            * @type {XastElement}
+           * @see https://developer.mozilla.org/en-US/docs/Web/SVG/Element/defs
            */
           const defsTag = {
             type: 'element',
@@ -74,7 +92,8 @@ exports.fn = () => {
               };
               delete reusablePath.attributes.transform;
               let id;
-              if (reusablePath.attributes.id == null) {
+              const reusablePathId = reusablePath.attributes.id;
+              if (reusablePathId == null || hrefs.has(reusablePathId)) {
                 id = 'reuse-' + index;
                 index += 1;
                 reusablePath.attributes.id = id;
diff --git a/test/plugins/reusePaths.04.svg b/test/plugins/reusePaths.04.svg
new file mode 100644
index 000000000..a96d550c4
--- /dev/null
+++ b/test/plugins/reusePaths.04.svg
@@ -0,0 +1,40 @@
+Don't remove and reuse the ID of the duplicate path if it's already being linked
+in an href by another node.
+
+===
+
+<svg xmlns="http://www.w3.org/2000/svg"
+  xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="-29.947 60.987 69.975 102.505">
+  <g transform="translate(-59 64)">
+    <g id="b">
+      <path id="a" fill="#000" d="M0 0v1h.5Z" transform="rotate(18 3.157 -.5)"/>
+      <use xlink:href="#a" width="1" height="1" transform="scale(-1 1)"/>
+    </g>
+    <use xlink:href="#b" width="1" height="1" transform="rotate(72)"/>
+    <use xlink:href="#b" width="1" height="1" transform="rotate(-72)"/>
+    <use xlink:href="#b" width="1" height="1" transform="rotate(144)"/>
+    <use xlink:href="#b" width="1" height="1" transform="rotate(-144)"/>
+  </g>
+  <path id="c" fill="#000" d="M0 0v1h.5Z" transform="rotate(18 3.157 -.5)"/>
+  <use xlink:href="#c" width="1" height="1" transform="scale(-1 1)"/>
+</svg>
+
+@@@
+
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="-29.947 60.987 69.975 102.505">
+    <defs>
+        <path id="reuse-0" fill="#000" d="M0 0v1h.5Z"/>
+    </defs>
+    <g transform="translate(-59 64)">
+        <g id="b">
+            <use id="a" transform="rotate(18 3.157 -.5)" xlink:href="#reuse-0"/>
+            <use xlink:href="#a" width="1" height="1" transform="scale(-1 1)"/>
+        </g>
+        <use xlink:href="#b" width="1" height="1" transform="rotate(72)"/>
+        <use xlink:href="#b" width="1" height="1" transform="rotate(-72)"/>
+        <use xlink:href="#b" width="1" height="1" transform="rotate(144)"/>
+        <use xlink:href="#b" width="1" height="1" transform="rotate(-144)"/>
+    </g>
+    <use id="c" transform="rotate(18 3.157 -.5)" xlink:href="#reuse-0"/>
+    <use xlink:href="#c" width="1" height="1" transform="scale(-1 1)"/>
+</svg>