parser FEATURE added collision check for grouping

Collision checking of names is similar to typedef checking.
diff --git a/src/parser_yang.c b/src/parser_yang.c
index 8147a7f..b62c54a 100644
--- a/src/parser_yang.c
+++ b/src/parser_yang.c
@@ -2977,7 +2977,7 @@
     grp->nodetype = LYS_GROUPING;
     grp->parent = parent;
 
-    YANG_READ_SUBSTMT_FOR(ctx, kw, word, word_len, ret, return LY_SUCCESS, return ret) {
+    YANG_READ_SUBSTMT_FOR(ctx, kw, word, word_len, ret, goto checks, return ret) {
         switch (kw) {
         case LY_STMT_DESCRIPTION:
             LY_CHECK_RET(parse_text_field(ctx, LY_STMT_DESCRIPTION, 0, &grp->dsc, Y_STR_ARG, &grp->exts));
@@ -3036,6 +3036,13 @@
             return LY_EVALID;
         }
     }
+    LY_CHECK_RET(ret);
+checks:
+    /* store data for collision check */
+    if (parent) {
+        assert(ctx->main_ctx);
+        LY_CHECK_RET(ly_set_add(&ctx->main_ctx->grps_nodes, parent, 0, NULL));
+    }
 
     return ret;
 }