svg: fix nested use nodes

Previously, only single-level <use> references were supported.
If a <use> node pointed to another element that itself contained
a <use> node, the reference wasn’t resolved.
This has been fixed by replacing the array of postponed elements
with a list. The list is traversed, and nodes aren’t cloned while
they or any of their children remain unresolved. In such cases,
the target element also gets added to the list, enabling recursive
resolution of nested href references.

issue: https://github.com/thorvg/thorvg/issues/3615

src/loaders/svg/tvgSvgLoader.cpp

@@ -894,12 +894,6 @@ error:
     }
 
 
-static void _postpone(Array<SvgNodeIdPair>& nodes, SvgNode *node, char* id)
-{
-    nodes.push({node, id});
-}
-
-
 static bool _attrParseSvgNode(void* data, const char* key, const char* value)
 {
     SvgLoaderData* loader = (SvgLoaderData*)data;
@@ -1157,7 +1151,7 @@ static void _handleCssClassAttr(SvgLoaderData* loader, SvgNode* node, const char
         cssCopyStyleAttr(node, cssNode);
     }
 
-    if (!cssClassFound) _postpone(loader->nodesToStyle, node, *cssClass);
+    if (!cssClassFound) loader->nodesToStyle.push({node, *cssClass});
 }
 
 
@@ -2155,6 +2149,23 @@ static SvgNode* _findParentById(SvgNode* node, char* id, SvgNode* doc)
 }
 
 
+static bool _checkPostponed(SvgNode* node, SvgNode* cloneNode, int depth)
+{
+    if (node == cloneNode) return true;
+
+    if (depth == 512) {
+        TVGERR("SVG", "Infinite recursive call - stopped after %d calls! Svg file may be incorrectly formatted.", depth);
+        return false;
+    }
+
+    ARRAY_FOREACH(p, node->child) {
+        if (_checkPostponed(*p, cloneNode, depth + 1)) return true;
+    }
+
+    return false;
+}
+
+
 static constexpr struct
 {
     const char* tag;
@@ -2196,17 +2207,30 @@ static bool _attrParseUseNode(void* data, const char* key, const char* value)
         nodeFrom = _findNodeById(defs, id);
         if (nodeFrom) {
             if (!_findParentById(node, id, loader->doc)) {
-                _cloneNode(nodeFrom, node, 0);
+                //Check if none of nodeFrom's children are in the cloneNodes list
-                if (nodeFrom->type == SvgNodeType::Symbol) use->symbol = nodeFrom;
+                auto postpone = false;
+                INLIST_FOREACH(loader->cloneNodes, pair) {
+                    if (_checkPostponed(nodeFrom, pair->node, 1)) {
+                        postpone = true;
+                        loader->cloneNodes.back(new(tvg::malloc<SvgNodeIdPair*>(sizeof(SvgNodeIdPair))) SvgNodeIdPair(node, id));
+                        break;
+                    }
+                }
+                //None of the children of nodeFrom are on the cloneNodes list, so it can be cloned immediately
+                if (!postpone) {
+                    _cloneNode(nodeFrom, node, 0);
+                    if (nodeFrom->type == SvgNodeType::Symbol) use->symbol = nodeFrom;
+                    tvg::free(id);
+                }
             } else {
                 TVGLOG("SVG", "%s is ancestor element. This reference is invalid.", id);
+                tvg::free(id);
             }
-            tvg::free(id);
         } else {
             //some svg export software include <defs> element at the end of the file
             //if so the 'from' element won't be found now and we have to repeat finding
             //after the whole file is parsed
-            _postpone(loader->cloneNodes, node, id);
+            loader->cloneNodes.back(new(tvg::malloc<SvgNodeIdPair*>(sizeof(SvgNodeIdPair))) SvgNodeIdPair(node, id));
         }
     } else {
         return _attrParseGNode(data, key, value);
@@ -3356,22 +3380,39 @@ static void _cloneNode(SvgNode* from, SvgNode* parent, int depth)
 }
 
 
-static void _clonePostponedNodes(Array<SvgNodeIdPair>* cloneNodes, SvgNode* doc)
+static void _clonePostponedNodes(Inlist<SvgNodeIdPair>* cloneNodes, SvgNode* doc)
 {
-    ARRAY_FOREACH(p, *cloneNodes) {
+    auto nodeIdPair = cloneNodes->front();
-        auto nodeIdPair = *p;
+    while (nodeIdPair) {
-        auto defs = _getDefsNode(nodeIdPair.node);
+        if (!_findParentById(nodeIdPair->node, nodeIdPair->id, doc)) {
-        auto nodeFrom = _findNodeById(defs, nodeIdPair.id);
+            //Check if none of nodeFrom's children are in the cloneNodes list
-        if (!nodeFrom) nodeFrom = _findNodeById(doc, nodeIdPair.id);
+            auto postpone = false;
-        if (!_findParentById(nodeIdPair.node, nodeIdPair.id, doc)) {
+            auto nodeFrom = _findNodeById(_getDefsNode(nodeIdPair->node), nodeIdPair->id);
-            _cloneNode(nodeFrom, nodeIdPair.node, 0);
+            if (!nodeFrom) nodeFrom = _findNodeById(doc, nodeIdPair->id);
-            if (nodeFrom && nodeFrom->type == SvgNodeType::Symbol && nodeIdPair.node->type == SvgNodeType::Use) {
+            if (nodeFrom) {
-                nodeIdPair.node->node.use.symbol = nodeFrom;
+                INLIST_FOREACH((*cloneNodes), pair) {
+                    if (_checkPostponed(nodeFrom, pair->node, 1)) {
+                        postpone = true;
+                        cloneNodes->back(nodeIdPair);
+                        break;
+                    }
+                }
+            }
+            //Since none of the child nodes of nodeFrom are present in the cloneNodes list, it can be cloned immediately
+            if (!postpone) {
+                _cloneNode(nodeFrom, nodeIdPair->node, 0);
+                if (nodeFrom && nodeFrom->type == SvgNodeType::Symbol && nodeIdPair->node->type == SvgNodeType::Use) {
+                    nodeIdPair->node->node.use.symbol = nodeFrom;
+                }
+                tvg::free(nodeIdPair->id);
+                tvg::free(nodeIdPair);
             }
         } else {
-            TVGLOG("SVG", "%s is ancestor element. This reference is invalid.", nodeIdPair.id);
+            TVGLOG("SVG", "%s is ancestor element. This reference is invalid.", nodeIdPair->id);
+            tvg::free(nodeIdPair->id);
+            tvg::free(nodeIdPair);
         }
-        tvg::free(nodeIdPair.id);
+        nodeIdPair = cloneNodes->front();
     }
 }
 
@@ -3901,7 +3942,7 @@ void SvgLoader::run(unsigned tid)
         if (loaderData.nodesToStyle.count > 0) cssApplyStyleToPostponeds(loaderData.nodesToStyle, loaderData.cssStyle);
         if (loaderData.cssStyle) cssUpdateStyle(loaderData.doc, loaderData.cssStyle);
 
-        if (loaderData.cloneNodes.count > 0) _clonePostponedNodes(&loaderData.cloneNodes, loaderData.doc);
+        if (!loaderData.cloneNodes.empty()) _clonePostponedNodes(&loaderData.cloneNodes, loaderData.doc);
 
         _updateComposite(loaderData.doc, loaderData.doc);
         if (defs) _updateComposite(loaderData.doc, defs);

src/loaders/svg/tvgSvgLoaderCommon.h

@@ -25,6 +25,7 @@
 
 #include "tvgCommon.h"
 #include "tvgArray.h"
+#include "tvgInlist.h"
 
 struct Box
 {
@@ -564,6 +565,8 @@ struct SvgParser
 
 struct SvgNodeIdPair
 {
+    INLIST_ITEM(SvgNodeIdPair);
+    SvgNodeIdPair(SvgNode* n, char* i) : node{n}, id{i} {}
     SvgNode* node;
     char *id;
 };
@@ -592,7 +595,7 @@ struct SvgLoaderData
     Array<SvgStyleGradient*> gradients;
     Array<SvgStyleGradient*> gradientStack; //For stops
     SvgParser* svgParse = nullptr;
-    Array<SvgNodeIdPair> cloneNodes;
+    Inlist<SvgNodeIdPair> cloneNodes;
     Array<SvgNodeIdPair> nodesToStyle;
     Array<char*> images;        //embedded images
     Array<FontFace> fonts;