rcxml: convert dotted properties into nested nodes before processing

For example, the following node:

  <keybind name.action="ShowMenu" menu.action="root-menu"
            x.position.action="1" y.position.action="2" />

is converted to:

 <keybind>
   <action>
     <name>ShowMenu</name>
     <menu>root-menu</menu>
     <position>
       <x>1</x>
       <y>2</y>
     </position>
   </action>
 </keybind>

...before processing the entire xml tree. This is a preparation to prevent
breaking changes when we refactor rcxml.c to use recursion instead of
encoding nodes into dotted strings.

src/common/meson.build

@@ -23,4 +23,5 @@ labwc_sources += files(
   'surface-helpers.c',
   'spawn.c',
   'string-helpers.c',
+  'xml.c',
 )

src/common/xml.c

@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <assert.h>
+#include <glib.h>
+#include <stdbool.h>
+#include <strings.h>
+#include "common/xml.h"
+
+/*
+ * Converts an attribute A.B.C="X" into <C><B><A>X</A></B></C>
+ */
+static xmlNode *
+create_attribute_tree(const xmlAttr *attr)
+{
+	gchar **parts = g_strsplit((char *)attr->name, ".", -1);
+	int length = g_strv_length(parts);
+	xmlNode *root_node = NULL;
+	xmlNode *parent_node = NULL;
+	xmlNode *current_node = NULL;
+
+	for (int i = length - 1; i >= 0; i--) {
+		gchar *part = parts[i];
+		if (!*part) {
+			/* Ignore empty string */
+			continue;
+		}
+		current_node = xmlNewNode(NULL, (xmlChar *)part);
+		if (parent_node) {
+			xmlAddChild(parent_node, current_node);
+		} else {
+			root_node = current_node;
+		}
+		parent_node = current_node;
+	}
+
+	/*
+	 * Note: empty attributes or attributes with only dots are forbidden
+	 * and root_node becomes never NULL here.
+	 */
+	assert(root_node);
+
+	xmlChar *content = xmlNodeGetContent(attr->children);
+	xmlNodeSetContent(current_node, content);
+	xmlFree(content);
+
+	g_strfreev(parts);
+	return root_node;
+}
+
+/*
+ * Consider <keybind name.action="ShowMenu" x.position.action="1" y.position="2" />.
+ * These three attributes are represented by following trees.
+ *    action(dst)---name
+ *    action(src)---position---x
+ *    action--------position---y
+ * When we call merge_two_trees(dst, src) for the first 2 trees above, we walk
+ * over the trees from their roots towards leaves, and merge the identical
+ * node 'action' like:
+ *    action(dst)---name
+ *         \--------position---x
+ *    action(src)---position---y
+ * And when we call merge_two_trees(dst, src) again, we walk over the dst tree
+ * like 'action'->'position'->'x' and the src tree like 'action'->'position'->'y'.
+ * First, we merge the identical node 'action' again like:
+ *    action---name
+ *         \---position(dst)---x
+ *          \--position(src)---y
+ * Next, we merge the identical node 'position' like:
+ *    action---name
+ *         \---position---x
+ *                   \----y
+ */
+static bool
+merge_two_trees(xmlNode *dst, xmlNode *src)
+{
+	bool merged = false;
+
+	while (dst && src && src->children
+			&& !strcasecmp((char *)dst->name, (char *)src->name)) {
+		xmlNode *next_dst = dst->last;
+		xmlNode *next_src = src->children;
+		xmlAddChild(dst, src->children);
+		xmlUnlinkNode(src);
+		xmlFreeNode(src);
+		src = next_src;
+		dst = next_dst;
+		merged = true;
+	}
+
+	return merged;
+}
+
+void
+lab_xml_expand_dotted_attributes(xmlNode *parent)
+{
+	xmlNode *old_first_child = parent->children;
+	xmlNode *prev_tree = NULL;
+
+	if (parent->type != XML_ELEMENT_NODE) {
+		return;
+	}
+
+	for (xmlAttr *attr = parent->properties; attr;) {
+		/* Convert the attribute with dots into an xml tree */
+		xmlNode *tree = create_attribute_tree(attr);
+		if (!tree) {
+			/* The attribute doesn't contain dots */
+			prev_tree = NULL;
+			attr = attr->next;
+			continue;
+		}
+
+		/* Try to merge the tree with the previous one */
+		if (!merge_two_trees(prev_tree, tree)) {
+			/* If not merged, add the tree as a new child */
+			if (old_first_child) {
+				xmlAddPrevSibling(old_first_child, tree);
+			} else {
+				xmlAddChild(parent, tree);
+			}
+			prev_tree = tree;
+		}
+
+		xmlAttr *next_attr = attr->next;
+		xmlRemoveProp(attr);
+		attr = next_attr;
+	}
+
+	for (xmlNode *node = parent->children; node; node = node->next) {
+		lab_xml_expand_dotted_attributes(node);
+	}
+}

src/config/rcxml.c

@@ -25,6 +25,7 @@
 #include "common/parse-double.h"
 #include "common/string-helpers.h"
 #include "common/three-state.h"
+#include "common/xml.h"
 #include "config/default-bindings.h"
 #include "config/keybind.h"
 #include "config/libinput.h"
@@ -1509,7 +1510,9 @@ rcxml_parse_xml(struct buf *b)
 		return;
 	}
 	struct parser_state init_state = {0};
-	xml_tree_walk(xmlDocGetRootElement(d), &init_state);
+	xmlNode *root = xmlDocGetRootElement(d);
+	lab_xml_expand_dotted_attributes(root);
+	xml_tree_walk(root, &init_state);
 	xmlFreeDoc(d);
 	xmlCleanupParser();
 }