From 6eb4524aef02a7a59a2d2d26e3155a809d16a1ff Mon Sep 17 00:00:00 2001
From: Bogdan Chadkin <trysound@yandex.ru>
Date: Fri, 10 Sep 2021 20:30:34 +0300
Subject: [PATCH] Refactor removeUnusedNS plugin (#1559)

- covered with types
- migrated to visitor plugin api
- dropped traverse utility which is replaced by visitor
---
 lib/xast.js               |  20 -------
 plugins/removeUnusedNS.js | 109 +++++++++++++++-----------------------
 tsconfig.json             |   1 -
 3 files changed, 44 insertions(+), 86 deletions(-)

diff --git a/lib/xast.js b/lib/xast.js
index ffa5d4ecc..4b9d49603 100644
--- a/lib/xast.js
+++ b/lib/xast.js
@@ -55,26 +55,6 @@ const closestByName = (node, name) => {
 };
 exports.closestByName = closestByName;
 
-const traverseBreak = Symbol();
-exports.traverseBreak = traverseBreak;
-
-/**
- * @type {(node: any, fn: any) => any}
- */
-const traverse = (node, fn) => {
-  if (fn(node) === traverseBreak) {
-    return traverseBreak;
-  }
-  if (node.type === 'root' || node.type === 'element') {
-    for (const child of node.children) {
-      if (traverse(child, fn) === traverseBreak) {
-        return traverseBreak;
-      }
-    }
-  }
-};
-exports.traverse = traverse;
-
 const visitSkip = Symbol();
 exports.visitSkip = visitSkip;
 
diff --git a/plugins/removeUnusedNS.js b/plugins/removeUnusedNS.js
index 3e956b5f7..800a196a0 100644
--- a/plugins/removeUnusedNS.js
+++ b/plugins/removeUnusedNS.js
@@ -1,82 +1,61 @@
 'use strict';
 
-const { traverse } = require('../lib/xast.js');
-const { parseName } = require('../lib/svgo/tools.js');
-
+exports.type = 'visitor';
 exports.name = 'removeUnusedNS';
-
-exports.type = 'full';
-
 exports.active = true;
-
 exports.description = 'removes unused namespaces declaration';
 
 /**
- * Remove unused namespaces declaration.
- *
- * @param {Object} item current iteration item
- * @return {Boolean} if false, item will be filtered out
+ * Remove unused namespaces declaration from svg element
+ * which are not used in elements or attributes
  *
  * @author Kir Belevich
+ *
+ * @type {import('../lib/types').Plugin<void>}
  */
-exports.fn = function (root) {
-  let svgElem;
-  const xmlnsCollection = [];
-
+exports.fn = () => {
   /**
-   * Remove namespace from collection.
-   *
-   * @param {String} ns namescape name
+   * @type {Set<string>}
    */
-  function removeNSfromCollection(ns) {
-    const pos = xmlnsCollection.indexOf(ns);
-
-    // if found - remove ns from the namespaces collection
-    if (pos > -1) {
-      xmlnsCollection.splice(pos, 1);
-    }
-  }
-
-  traverse(root, (node) => {
-    if (node.type === 'element') {
-      if (node.name === 'svg') {
-        for (const name of Object.keys(node.attributes)) {
-          const { prefix, local } = parseName(name);
-          // collect namespaces
-          if (prefix === 'xmlns' && local) {
-            xmlnsCollection.push(local);
+  const unusedNamespaces = new Set();
+  return {
+    element: {
+      enter: (node, parentNode) => {
+        // collect all namespaces from svg element
+        // (such as xmlns:xlink="http://www.w3.org/1999/xlink")
+        if (node.name === 'svg' && parentNode.type === 'root') {
+          for (const name of Object.keys(node.attributes)) {
+            if (name.startsWith('xmlns:')) {
+              const local = name.slice('xmlns:'.length);
+              unusedNamespaces.add(local);
+            }
           }
         }
-
-        // if svg element has ns-attr
-        if (xmlnsCollection.length) {
-          // save svg element
-          svgElem = node;
-        }
-      }
-
-      if (xmlnsCollection.length) {
-        const { prefix } = parseName(node.name);
-        // check node for the ns-attrs
-        if (prefix) {
-          removeNSfromCollection(prefix);
+        if (unusedNamespaces.size !== 0) {
+          // preserve namespace used in nested elements names
+          if (node.name.includes(':')) {
+            const [ns] = node.name.split(':');
+            if (unusedNamespaces.has(ns)) {
+              unusedNamespaces.delete(ns);
+            }
+          }
+          // preserve namespace used in nested elements attributes
+          for (const name of Object.keys(node.attributes)) {
+            if (name.includes(':')) {
+              const [ns] = name.split(':');
+              unusedNamespaces.delete(ns);
+            }
+          }
         }
-
-        // check each attr for the ns-attrs
-        for (const name of Object.keys(node.attributes)) {
-          const { prefix } = parseName(name);
-          removeNSfromCollection(prefix);
+      },
+      exit: (node, parentNode) => {
+        // remove unused namespace attributes from svg element
+        if (node.name === 'svg' && parentNode.type === 'root') {
+          for (const name of unusedNamespaces) {
+            delete node.attributes[`xmlns:${name}`];
+          }
         }
-      }
-    }
-  });
-
-  // remove svg element ns-attributes if they are not used even once
-  if (xmlnsCollection.length) {
-    for (const name of xmlnsCollection) {
-      delete svgElem.attributes['xmlns:' + name];
-    }
-  }
-
-  return root;
+      },
+    },
+  };
 };
diff --git a/tsconfig.json b/tsconfig.json
index 046aacc8c..383037e8b 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -24,7 +24,6 @@
     "plugins/removeDimensions.js",
     "plugins/removeEmptyAttrs.js",
     "plugins/removeNonInheritableGroupAttrs.js",
-    "plugins/removeUnusedNS.js",
     "plugins/removeXMLNS.js",
     "plugins/sortAttrs.js",
     "plugins/removeEmptyContainers.js",