yin parser FEATURE support usess forward references to groupings.

Sometimes, uses references grouping that was not yet defined (parsed).
RFC is not clear about this, but pyang allows it, so we are supporting
it also.
diff --git a/src/parser/yin.c b/src/parser/yin.c
index 21a2913..3265957 100644
--- a/src/parser/yin.c
+++ b/src/parser/yin.c
@@ -61,15 +61,22 @@
 #define OPT_INHERIT 0x08
 static int read_yin_common(struct ly_module *, struct ly_mnode *, struct ly_mnode *, struct lyxml_elem *, int);
 
-static struct ly_mnode *read_yin_choice(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
-static struct ly_mnode *read_yin_case(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
+struct mnode_list {
+	struct ly_mnode *mnode;
+	struct mnode_list *next;
+	unsigned int line;
+};
+
+static struct ly_mnode *read_yin_choice(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int, struct mnode_list **);
+static struct ly_mnode *read_yin_case(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int, struct mnode_list **);
 static struct ly_mnode *read_yin_anyxml(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
-static struct ly_mnode *read_yin_container(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
+static struct ly_mnode *read_yin_container(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int, struct mnode_list **);
 static struct ly_mnode *read_yin_leaf(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
 static struct ly_mnode *read_yin_leaflist(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
-static struct ly_mnode *read_yin_list(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
-static struct ly_mnode *read_yin_uses(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
-static struct ly_mnode *read_yin_grouping(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int);
+static struct ly_mnode *read_yin_list(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int, struct mnode_list **);
+static struct ly_mnode *read_yin_uses(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int, struct mnode_list **);
+static struct ly_mnode *read_yin_grouping(struct ly_module *, struct ly_mnode *, struct lyxml_elem *, int, struct mnode_list **);
+
 
 static int dup_typedef_check(const char* type, struct ly_tpdf *tpdf, int size)
 {
@@ -1133,7 +1140,7 @@
 static struct ly_mnode *read_yin_case(struct ly_module *module,
                                         struct ly_mnode *parent,
                                         struct lyxml_elem *yin,
-										int resolve)
+										int resolve, struct mnode_list **unres)
 {
 	struct lyxml_elem *sub, *next;
 	struct ly_mnode_case *mcase;
@@ -1151,17 +1158,17 @@
 	/* process choice's specific children */
 	LY_TREE_FOR_SAFE(yin->child, next, sub) {
 		if (!strcmp(sub->name, "container")) {
-			mnode = read_yin_container(module, retval, sub, resolve);
+			mnode = read_yin_container(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "leaf-list")) {
 			mnode = read_yin_leaflist(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "leaf")) {
 			mnode = read_yin_leaf(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "list")) {
-			mnode = read_yin_list(module, retval, sub, resolve);
+			mnode = read_yin_list(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "uses")) {
-			mnode = read_yin_uses(module, retval, sub, resolve);
+			mnode = read_yin_uses(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "choice")) {
-			mnode = read_yin_choice(module, retval, sub, resolve);
+			mnode = read_yin_choice(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "anyxml")) {
 			mnode = read_yin_anyxml(module, retval, sub, resolve);
 #if 0
@@ -1206,7 +1213,7 @@
 static struct ly_mnode *read_yin_choice(struct ly_module *module,
                                         struct ly_mnode *parent,
                                         struct lyxml_elem *yin,
-										int resolve)
+										int resolve, struct mnode_list **unres)
 {
 	struct lyxml_elem *sub, *next;
 	struct ly_ctx * const ctx = module->ctx;
@@ -1228,7 +1235,7 @@
 	/* process choice's specific children */
 	LY_TREE_FOR_SAFE(yin->child, next, sub) {
 		if (!strcmp(sub->name, "container")) {
-			if (!(mnode = read_yin_container(module, retval, sub, resolve))) {
+			if (!(mnode = read_yin_container(module, retval, sub, resolve, unres))) {
 				goto error;
 			}
 		} else if (!strcmp(sub->name, "leaf-list")) {
@@ -1240,11 +1247,11 @@
 				goto error;
 			}
 		} else if (!strcmp(sub->name, "list")) {
-			if (!(mnode = read_yin_list(module, retval, sub, resolve))) {
+			if (!(mnode = read_yin_list(module, retval, sub, resolve, unres))) {
 				goto error;
 			}
 		} else if (!strcmp(sub->name, "case")) {
-			if (!(mnode = read_yin_case(module, retval, sub, resolve))) {
+			if (!(mnode = read_yin_case(module, retval, sub, resolve, unres))) {
 				goto error;
 			}
 		} else if (!strcmp(sub->name, "anyxml")) {
@@ -1706,7 +1713,7 @@
 static struct ly_mnode *read_yin_list(struct ly_module *module,
                                       struct ly_mnode *parent,
                                       struct lyxml_elem *yin,
-									  int resolve)
+									  int resolve, struct mnode_list **unres)
 {
 	struct ly_mnode *retval, *mnode;
 	struct ly_mnode_list *list;
@@ -1875,19 +1882,19 @@
 	/* last part - process data nodes */
 	LY_TREE_FOR_SAFE(root.child, next, sub) {
 		if (!strcmp(sub->name, "container")) {
-			mnode = read_yin_container(module, retval, sub, resolve);
+			mnode = read_yin_container(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "leaf-list")) {
 			mnode = read_yin_leaflist(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "leaf")) {
 			mnode = read_yin_leaf(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "list")) {
-			mnode = read_yin_list(module, retval, sub, resolve);
+			mnode = read_yin_list(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "choice")) {
-			mnode = read_yin_choice(module, retval, sub, resolve);
+			mnode = read_yin_choice(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "uses")) {
-			mnode = read_yin_uses(module, retval, sub, resolve);
+			mnode = read_yin_uses(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "grouping")) {
-			mnode = read_yin_grouping(module, retval, sub, resolve);
+			mnode = read_yin_grouping(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "anyxml")) {
 			mnode = read_yin_anyxml(module, retval, sub, resolve);
 		} else {
@@ -1998,7 +2005,7 @@
 static struct ly_mnode *read_yin_container(struct ly_module *module,
                                            struct ly_mnode *parent,
                                            struct lyxml_elem *yin,
-										   int resolve)
+										   int resolve, struct mnode_list **unres)
 {
 	struct lyxml_elem *sub, *next, root = {0};
 	struct ly_mnode *mnode = NULL;
@@ -2088,19 +2095,19 @@
 	/* last part - process data nodes */
 	LY_TREE_FOR_SAFE(root.child, next, sub) {
 		if (!strcmp(sub->name, "container")) {
-			mnode = read_yin_container(module, retval, sub, resolve);
+			mnode = read_yin_container(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "leaf-list")) {
 			mnode = read_yin_leaflist(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "leaf")) {
 			mnode = read_yin_leaf(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "list")) {
-			mnode = read_yin_list(module, retval, sub, resolve);
+			mnode = read_yin_list(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "choice")) {
-			mnode = read_yin_choice(module, retval, sub, resolve);
+			mnode = read_yin_choice(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "uses")) {
-			mnode = read_yin_uses(module, retval, sub, resolve);
+			mnode = read_yin_uses(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "grouping")) {
-			mnode = read_yin_grouping(module, retval, sub, resolve);
+			mnode = read_yin_grouping(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "anyxml")) {
 			mnode = read_yin_anyxml(module, retval, sub, resolve);
 		}
@@ -2130,7 +2137,7 @@
 static struct ly_mnode *read_yin_grouping(struct ly_module *module,
                                           struct ly_mnode *parent,
                                           struct lyxml_elem *node,
-										  int resolve)
+										  int resolve, struct mnode_list **unres)
 {
 	struct lyxml_elem *sub, *next, root = {0};
 	struct ly_mnode *mnode = NULL;
@@ -2190,19 +2197,19 @@
 	/* last part - process data nodes */
 	LY_TREE_FOR_SAFE(root.child, next, sub) {
 		if (!strcmp(sub->name, "container")) {
-			mnode = read_yin_container(module, retval, sub, resolve);
+			mnode = read_yin_container(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "leaf-list")) {
 			mnode = read_yin_leaflist(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "leaf")) {
 			mnode = read_yin_leaf(module, retval, sub, resolve);
 		} else if (!strcmp(sub->name, "list")) {
-			mnode = read_yin_list(module, retval, sub, resolve);
+			mnode = read_yin_list(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "choice")) {
-			mnode = read_yin_choice(module, retval, sub, resolve);
+			mnode = read_yin_choice(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "uses")) {
-			mnode = read_yin_uses(module, retval, sub, resolve);
+			mnode = read_yin_uses(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "grouping")) {
-			mnode = read_yin_grouping(module, retval, sub, resolve);
+			mnode = read_yin_grouping(module, retval, sub, resolve, unres);
 		} else if (!strcmp(sub->name, "anyxml")) {
 			mnode = read_yin_anyxml(module, retval, sub, resolve);
 		}
@@ -2229,32 +2236,14 @@
 	return NULL;
 }
 
-/*
- * resolve - referenced grouping should be bounded to the namespace (resolved)
- * only when uses does not appear in grouping. In a case of grouping's uses,
- * we just get information but we do not apply augment or refine to it.
- */
-static struct ly_mnode *read_yin_uses(struct ly_module *module,
-                                      struct ly_mnode *parent,
-                                      struct lyxml_elem *node, int resolve)
+static int find_grouping(struct ly_mnode *parent, struct ly_mnode_uses *uses, int line)
 {
-	struct ly_mnode *retval;
-	struct ly_mnode *mnode = NULL, *mnode_aux;
-	struct ly_mnode_uses *uses;
-	struct ly_module *searchmod = NULL;
+	struct ly_module *searchmod = NULL, *module = uses->module;
+	struct ly_mnode *mnode, *mnode_aux;
 	const char *name;
 	int prefix_len = 0;
 	int i;
 
-	uses = calloc(1, sizeof *uses);
-	uses->nodetype = LY_NODE_USES;
-	uses->prev = (struct ly_mnode *)uses;
-	retval = (struct ly_mnode *)uses;
-
-	if (read_yin_common(module, parent, retval, node, OPT_MODULE | (resolve ? OPT_INHERIT : 0))) {
-		goto error;
-	}
-
 	/* get referenced grouping */
 	name = strchr(uses->name, ':');
 	if (!name) {
@@ -2285,14 +2274,14 @@
 		}
 		if (!searchmod) {
 			/* uses refers unknown data model */
-			LOGVAL(VE_INPREFIX, LOGLINE(node), name);
-			goto error;
+			LOGVAL(VE_INPREFIX, line, name);
+			return EXIT_FAILURE;
 		}
 
 		LY_TREE_FOR(searchmod->data, mnode) {
 			if (mnode->nodetype == LY_NODE_GROUPING && !strcmp(mnode->name, name)) {
 				uses->grp = (struct ly_mnode_grp *)mnode;
-				goto done;
+				return EXIT_SUCCESS;
 			}
 		}
 	} else {
@@ -2301,7 +2290,7 @@
 			LY_TREE_FOR(mnode_aux->child, mnode) {
 				if (mnode->nodetype == LY_NODE_GROUPING && !strcmp(mnode->name, name)) {
 					uses->grp = (struct ly_mnode_grp *)mnode;
-					break;
+					return EXIT_SUCCESS;
 				}
 			}
 		}
@@ -2310,7 +2299,7 @@
 		LY_TREE_FOR(module->data, mnode) {
 			if (mnode->nodetype == LY_NODE_GROUPING && !strcmp(mnode->name, name)) {
 				uses->grp = (struct ly_mnode_grp *)mnode;
-				goto done;
+				return EXIT_SUCCESS;
 			}
 		}
 
@@ -2319,18 +2308,56 @@
 			LY_TREE_FOR(module->inc[i].submodule->data, mnode) {
 				if (mnode->nodetype == LY_NODE_GROUPING && !strcmp(mnode->name, name)) {
 					uses->grp = (struct ly_mnode_grp *)mnode;
-					goto done;
+					return EXIT_SUCCESS;
 				}
 			}
 		}
 	}
 
-done:
-	if (!uses->grp) {
-		LOGVAL(VE_INARG, LOGLINE(node), uses->name, "uses");
+	/* not found, but no explicit error occured */
+	return EXIT_SUCCESS;
+}
+
+
+/*
+ * resolve - referenced grouping should be bounded to the namespace (resolved)
+ * only when uses does not appear in grouping. In a case of grouping's uses,
+ * we just get information but we do not apply augment or refine to it.
+ */
+static struct ly_mnode *read_yin_uses(struct ly_module *module,
+                                      struct ly_mnode *parent,
+                                      struct lyxml_elem *node, int resolve,
+									  struct mnode_list **unres)
+{
+	struct ly_mnode *retval;
+	struct ly_mnode_uses *uses;
+	struct mnode_list *unres_new;
+
+	uses = calloc(1, sizeof *uses);
+	uses->nodetype = LY_NODE_USES;
+	uses->prev = (struct ly_mnode *)uses;
+	retval = (struct ly_mnode *)uses;
+
+	if (read_yin_common(module, parent, retval, node, OPT_MODULE | (resolve ? OPT_INHERIT : 0))) {
 		goto error;
 	}
 
+	if (find_grouping(parent, uses, LOGLINE(node))) {
+		goto error;
+	}
+	if (!uses->grp) {
+		LOGVRB("Unresolved uses of \"%s\", trying to resolve it later", uses->name);
+		unres_new = calloc(1, sizeof *unres_new);
+		if (*unres) {
+			unres_new->next = *unres;
+		}
+		unres_new->mnode = retval;
+		unres_new->line = LOGLINE(node);
+
+		/* put it at the beginning of the unresolved list */
+		*unres = unres_new;
+	}
+
 	if (parent) {
 		ly_mnode_addchild(parent, retval);
 	}
@@ -2343,7 +2370,9 @@
 			/* default config is true */
 			retval->flags |= LY_NODE_CONFIG_W;
 		}
+	}
 
+	if (resolve && uses->grp) {
 		/* copy the data nodes from grouping into the uses context */
 		if (resolve_uses(uses)) {
 			goto error;
@@ -2364,8 +2393,9 @@
 {
 	struct ly_ctx *ctx = module->ctx;
 	struct ly_submodule *submodule = (struct ly_submodule *)module;
-	struct lyxml_elem *next, *node, *child, root = {0};
+	struct lyxml_elem *next, *node, *child, root = {0}, grps = {0};
 	struct ly_mnode *mnode = NULL;
+	struct mnode_list *unres = NULL, *unres_next; /* unresolved uses */
 	const char *value;
 	int c_imp = 0, c_rev = 0, c_tpdf = 0, c_ident = 0, c_inc = 0; /* counters */
 	int r;
@@ -2461,10 +2491,13 @@
 				!strcmp(node->name, "list") ||
 				!strcmp(node->name, "choice") ||
 				!strcmp(node->name, "uses") ||
-				!strcmp(node->name, "grouping") ||
 				!strcmp(node->name, "anyxml")) {
 			lyxml_unlink_elem(node);
 			lyxml_add_child(&root, node);
+		} else if (!strcmp(node->name, "grouping")) {
+			/* keep groupings separated and process them before other data statements */
+			lyxml_unlink_elem(node);
+			lyxml_add_child(&grps, node);
 
 		/* optional statements */
 		} else if (!strcmp(node->name, "description")) {
@@ -2670,28 +2703,55 @@
 		lyxml_free_elem(ctx, node);
 	}
 
-	/* last part - process data nodes */
+	/* last part - process data nodes. Start with groupings to allow uses
+	 * refer to them
+	 */
+	LY_TREE_FOR_SAFE(grps.child, next, node) {
+		mnode = read_yin_grouping(module, NULL, node, 0, &unres);
+		lyxml_free_elem(ctx, node);
+
+		if (!mnode) {
+			goto error;
+		}
+
+		/* include data element */
+		if (module->data) {
+			module->data->prev->next = mnode;
+			mnode->prev = module->data->prev;
+			module->data->prev = mnode;
+		} else {
+			module->data = mnode;
+		}
+	}
+	while (unres) {
+		if (find_grouping(unres->mnode->parent, (struct ly_mnode_uses *)unres->mnode, unres->line)) {
+			goto error;
+		}
+		if (!((struct ly_mnode_uses *)unres->mnode)->grp) {
+			LOGVAL(VE_INARG, unres->line, unres->mnode->name, "uses");
+			goto error;
+		}
+		unres_next = unres->next;
+		free(unres);
+		unres = unres_next;
+	}
+
 	LY_TREE_FOR_SAFE(root.child, next, node) {
 
 		if (!strcmp(node->name, "container")) {
-			mnode = read_yin_container(module, NULL, node, 1);
+			mnode = read_yin_container(module, NULL, node, 1, &unres);
 		} else if (!strcmp(node->name, "leaf-list")) {
 			mnode = read_yin_leaflist(module, NULL, node, 1);
 		} else if (!strcmp(node->name, "leaf")) {
 			mnode = read_yin_leaf(module, NULL, node, 1);
 		} else if (!strcmp(node->name, "list")) {
-			mnode = read_yin_list(module, NULL, node, 1);
+			mnode = read_yin_list(module, NULL, node, 1, &unres);
 		} else if (!strcmp(node->name, "choice")) {
-			mnode = read_yin_choice(module, NULL, node, 1);
-		} else if (!strcmp(node->name, "grouping")) {
-			mnode = read_yin_grouping(module, NULL, node, 0);
+			mnode = read_yin_choice(module, NULL, node, 1, &unres);
 		} else if (!strcmp(node->name, "uses")) {
-			mnode = read_yin_uses(module, NULL, node, 1);
+			mnode = read_yin_uses(module, NULL, node, 1, &unres);
 		} else if (!strcmp(node->name, "anyxml")) {
 			mnode = read_yin_anyxml(module, NULL, node, 1);
-		} else {
-			/* TODO error */
-			continue;
 		}
 		lyxml_free_elem(ctx, node);
 
@@ -2708,6 +2768,25 @@
 			module->data = mnode;
 		}
 	}
+	while (unres) {
+		/* find referenced grouping */
+		if (find_grouping(unres->mnode->parent, (struct ly_mnode_uses *)unres->mnode, unres->line)) {
+			goto error;
+		}
+		if (!((struct ly_mnode_uses *)unres->mnode)->grp) {
+			LOGVAL(VE_INARG, unres->line, unres->mnode->name, "uses");
+			goto error;
+		}
+
+		/* resolve uses by copying grouping content under the uses */
+		if (resolve_uses((struct ly_mnode_uses *)unres->mnode)) {
+			goto error;
+		}
+
+		unres_next = unres->next;
+		free(unres);
+		unres = unres_next;
+	}
 
 	return EXIT_SUCCESS;
 
@@ -2716,6 +2795,9 @@
 	while (root.child) {
 		lyxml_free_elem(module->ctx, root.child);
 	}
+	while (grps.child) {
+		lyxml_free_elem(module->ctx, grps.child);
+	}
 
 	return EXIT_FAILURE;
 }