schema cmp UPDATE support for backwards-compatible ext

Author: michalvasko

CMakeLists.txt

@@ -160,6 +160,7 @@ set(libsrc
     src/plugins_exts/yangdata.c
     src/plugins_exts/schema_mount.c
     src/plugins_exts/structure.c
+    src/plugins_exts/schema_comparison.c
     src/xml.c
     src/xpath.c
     src/validation.c

src/plugins.c

@@ -98,6 +98,7 @@ extern struct lyplg_ext_record plugins_nacm[];
 extern struct lyplg_ext_record plugins_yangdata[];
 extern struct lyplg_ext_record plugins_schema_mount[];
 extern struct lyplg_ext_record plugins_structure[];
+extern struct lyplg_ext_record plugins_schema_cmp[];
 
 static pthread_mutex_t plugins_guard = PTHREAD_MUTEX_INITIALIZER;
 
@@ -619,6 +620,7 @@ lyplg_init(ly_bool builtin_type_plugins_only, ly_bool static_plugins_only)
     LY_CHECK_GOTO(ret = plugins_insert(NULL, LYPLG_EXTENSION, plugins_yangdata), error);
     LY_CHECK_GOTO(ret = plugins_insert(NULL, LYPLG_EXTENSION, plugins_schema_mount), error);
     LY_CHECK_GOTO(ret = plugins_insert(NULL, LYPLG_EXTENSION, plugins_structure), error);
+    LY_CHECK_GOTO(ret = plugins_insert(NULL, LYPLG_EXTENSION, plugins_schema_cmp), error);
 
     /* the global plugin sets contain only static plugins at this point, so assign to the counters here.
      * the counters are used to determine whether a plugin is static or not */

src/plugins_exts/schema_comparison.c

@@ -0,0 +1,73 @@
+/**
+ * @file schema_comparison.c
+ * @author Michal Vasko <[email protected]>
+ * @brief libyang extension plugin - backwards-compatible
+ *
+ * Copyright (c) 2025 CESNET, z.s.p.o.
+ *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "compat.h"
+#include "libyang.h"
+#include "ly_common.h"
+#include "plugins_exts.h"
+#include "plugins_internal.h"
+
+/**
+ * @brief Parse backwards-compatible extension instances.
+ *
+ * Implementation of ::lyplg_ext_parse_clb callback set as lyext_plugin::parse.
+ */
+static LY_ERR
+bc_parse(struct lysp_ctx *pctx, struct lysp_ext_instance *ext)
+{
+    /* check that the extension is instantiated at an allowed place */
+    if ((ext->parent_stmt != LY_STMT_PATTERN) && (ext->parent_stmt != LY_STMT_WHEN) &&
+            (ext->parent_stmt != LY_STMT_MUST) && (ext->parent_stmt != LY_STMT_DESCRIPTION) &&
+            (ext->parent_stmt != LY_STMT_EXTENSION_INSTANCE)) {
+        lyplg_ext_parse_log(pctx, ext, LY_LLWRN, 0, "Extension %s is not allowed in \"%s\" statement.", ext->name,
+                lyplg_ext_stmt2str(ext->parent_stmt));
+        return LY_ENOT;
+    }
+
+    return LY_SUCCESS;
+}
+
+/**
+ * @brief Plugin descriptions for the schema-comparison backwards-compatible extension
+ *
+ * Note that external plugins are supposed to use:
+ *
+ *   LYPLG_EXTENSIONS = {
+ */
+const struct lyplg_ext_record plugins_schema_cmp[] = {
+    {
+        .module = "ietf-schema-comparison",
+        .revision = "2025-09-03",
+        .name = "backwards-compatible",
+
+        .plugin.id = "ly2 schema-comparison",
+        .plugin.parse = bc_parse,
+        .plugin.compile = NULL,
+        .plugin.printer_info = NULL,
+        .plugin.printer_ctree = NULL,
+        .plugin.printer_ptree = NULL,
+        .plugin.node_xpath = NULL,
+        .plugin.snode = NULL,
+        .plugin.validate = NULL,
+        .plugin.pfree = NULL,
+        .plugin.cfree = NULL,
+        .plugin.compiled_size = NULL,
+        .plugin.compiled_print = NULL
+    },
+    {0} /* terminating zeroed item */
+};