Improve castNode notation by introducing list-extraction-specific variants.

This extends the castNode() notation introduced by commit 5bcab1114 to
provide, in one step, extraction of a list cell's pointer and coercion to
a concrete node type.  For example, "lfirst_node(Foo, lc)" is the same
as "castNode(Foo, lfirst(lc))".  Almost half of the uses of castNode
that have appeared so far include a list extraction call, so this is
pretty widely useful, and it saves a few more keystrokes compared to the
old way.

As with the previous patch, back-patch the addition of these macros to
pg_list.h, so that the notation will be available when back-patching.

Patch by me, after an idea of Andrew Gierth's.

Discussion: https://postgr.es/m/14197.1491841216@sss.pgh.pa.us

src/backend/commands/aggregatecmds.c

@@ -109,13 +109,13 @@ DefineAggregate(ParseState *pstate, List *name, List *args, bool oldstyle, List
 			aggKind = AGGKIND_ORDERED_SET;
 		else
 			numDirectArgs = 0;
-		args = castNode(List, linitial(args));
+		args = linitial_node(List, args);
 	}
 
 	/* Examine aggregate's definition clauses */
 	foreach(pl, parameters)
 	{
-		DefElem    *defel = castNode(DefElem, lfirst(pl));
+		DefElem    *defel = lfirst_node(DefElem, pl);
 
 		/*
 		 * sfunc1, stype1, and initcond1 are accepted as obsolete spellings

src/backend/commands/async.c

@@ -1636,7 +1636,7 @@ AtSubCommit_Notify(void)
 	List	   *parentPendingActions;
 	List	   *parentPendingNotifies;
 
-	parentPendingActions = castNode(List, linitial(upperPendingActions));
+	parentPendingActions = linitial_node(List, upperPendingActions);
 	upperPendingActions = list_delete_first(upperPendingActions);
 
 	Assert(list_length(upperPendingActions) ==
@@ -1647,7 +1647,7 @@ AtSubCommit_Notify(void)
 	 */
 	pendingActions = list_concat(parentPendingActions, pendingActions);
 
-	parentPendingNotifies = castNode(List, linitial(upperPendingNotifies));
+	parentPendingNotifies = linitial_node(List, upperPendingNotifies);
 	upperPendingNotifies = list_delete_first(upperPendingNotifies);
 
 	Assert(list_length(upperPendingNotifies) ==
@@ -1679,13 +1679,13 @@ AtSubAbort_Notify(void)
 	 */
 	while (list_length(upperPendingActions) > my_level - 2)
 	{
-		pendingActions = castNode(List, linitial(upperPendingActions));
+		pendingActions = linitial_node(List, upperPendingActions);
 		upperPendingActions = list_delete_first(upperPendingActions);
 	}
 
 	while (list_length(upperPendingNotifies) > my_level - 2)
 	{
-		pendingNotifies = castNode(List, linitial(upperPendingNotifies));
+		pendingNotifies = linitial_node(List, upperPendingNotifies);
 		upperPendingNotifies = list_delete_first(upperPendingNotifies);
 	}
 }

src/backend/commands/collationcmds.c

@@ -71,7 +71,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 
 	foreach(pl, parameters)
 	{
-		DefElem    *defel = castNode(DefElem, lfirst(pl));
+		DefElem    *defel = lfirst_node(DefElem, pl);
 		DefElem   **defelp;
 
 		if (pg_strcasecmp(defel->defname, "from") == 0)

src/backend/commands/copy.c

@@ -1034,7 +1034,7 @@ ProcessCopyOptions(ParseState *pstate,
 	/* Extract options from the statement node tree */
 	foreach(option, options)
 	{
-		DefElem    *defel = castNode(DefElem, lfirst(option));
+		DefElem    *defel = lfirst_node(DefElem, option);
 
 		if (strcmp(defel->defname, "format") == 0)
 		{
@@ -1488,7 +1488,7 @@ BeginCopy(ParseState *pstate,
 			/* examine queries to determine which error message to issue */
 			foreach(lc, rewritten)
 			{
-				Query	   *q = castNode(Query, lfirst(lc));
+				Query	   *q = lfirst_node(Query, lc);
 
 				if (q->querySource == QSRC_QUAL_INSTEAD_RULE)
 					ereport(ERROR,
@@ -1505,7 +1505,7 @@ BeginCopy(ParseState *pstate,
 					 errmsg("multi-statement DO INSTEAD rules are not supported for COPY")));
 		}
 
-		query = castNode(Query, linitial(rewritten));
+		query = linitial_node(Query, rewritten);
 
 		/* The grammar allows SELECT INTO, but we don't support that */
 		if (query->utilityStmt != NULL &&

src/backend/commands/createas.c

@@ -323,7 +323,7 @@ ExecCreateTableAs(CreateTableAsStmt *stmt, const char *queryString,
 			elog(ERROR, "unexpected rewrite result for %s",
 				 is_matview ? "CREATE MATERIALIZED VIEW" :
 				 "CREATE TABLE AS SELECT");
-		query = castNode(Query, linitial(rewritten));
+		query = linitial_node(Query, rewritten);
 		Assert(query->commandType == CMD_SELECT);
 
 		/* plan the query --- note we disallow parallelism */

src/backend/commands/dropcmds.c

@@ -214,7 +214,7 @@ type_in_list_does_not_exist_skipping(List *typenames, const char **msg,
 
 	foreach(l, typenames)
 	{
-		TypeName   *typeName = castNode(TypeName, lfirst(l));
+		TypeName   *typeName = lfirst_node(TypeName, l);
 
 		if (typeName != NULL)
 		{
@@ -371,8 +371,8 @@ does_not_exist_skipping(ObjectType objtype, Node *object)
 				{
 					/* XXX quote or no quote? */
 					msg = gettext_noop("cast from type %s to type %s does not exist, skipping");
-					name = TypeNameToString(castNode(TypeName, linitial(castNode(List, object))));
-					args = TypeNameToString(castNode(TypeName, lsecond(castNode(List, object))));
+					name = TypeNameToString(linitial_node(TypeName, castNode(List, object)));
+					args = TypeNameToString(lsecond_node(TypeName, castNode(List, object)));
 				}
 			}
 			break;
@@ -380,7 +380,7 @@ does_not_exist_skipping(ObjectType objtype, Node *object)
 			if (!type_in_list_does_not_exist_skipping(list_make1(linitial(castNode(List, object))), &msg, &name))
 			{
 				msg = gettext_noop("transform for type %s language \"%s\" does not exist, skipping");
-				name = TypeNameToString(castNode(TypeName, linitial(castNode(List, object))));
+				name = TypeNameToString(linitial_node(TypeName, castNode(List, object)));
 				args = strVal(lsecond(castNode(List, object)));
 			}
 			break;

src/backend/commands/explain.c

@@ -253,7 +253,7 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt, const char *queryString,
 		/* Explain every plan */
 		foreach(l, rewritten)
 		{
-			ExplainOneQuery(castNode(Query, lfirst(l)),
+			ExplainOneQuery(lfirst_node(Query, l),
 							CURSOR_OPT_PARALLEL_OK, NULL, es,
 							queryString, params, queryEnv);
 
@@ -408,7 +408,7 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 
 		rewritten = QueryRewrite(castNode(Query, copyObject(ctas->query)));
 		Assert(list_length(rewritten) == 1);
-		ExplainOneQuery(castNode(Query, linitial(rewritten)),
+		ExplainOneQuery(linitial_node(Query, rewritten),
 						0, ctas->into, es,
 						queryString, params, queryEnv);
 	}
@@ -427,7 +427,7 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 
 		rewritten = QueryRewrite(castNode(Query, copyObject(dcs->query)));
 		Assert(list_length(rewritten) == 1);
-		ExplainOneQuery(castNode(Query, linitial(rewritten)),
+		ExplainOneQuery(linitial_node(Query, rewritten),
 						dcs->options, NULL, es,
 						queryString, params, queryEnv);
 	}

src/backend/commands/extension.c

@@ -714,7 +714,7 @@ execute_sql_string(const char *sql, const char *filename)
 	 */
 	foreach(lc1, raw_parsetree_list)
 	{
-		RawStmt    *parsetree = castNode(RawStmt, lfirst(lc1));
+		RawStmt    *parsetree = lfirst_node(RawStmt, lc1);
 		List	   *stmt_list;
 		ListCell   *lc2;
 
@@ -727,7 +727,7 @@ execute_sql_string(const char *sql, const char *filename)
 
 		foreach(lc2, stmt_list)
 		{
-			PlannedStmt *stmt = castNode(PlannedStmt, lfirst(lc2));
+			PlannedStmt *stmt = lfirst_node(PlannedStmt, lc2);
 
 			CommandCounterIncrement();
 

src/backend/commands/foreigncmds.c

@@ -1589,7 +1589,7 @@ ImportForeignSchema(ImportForeignSchemaStmt *stmt)
 		 */
 		foreach(lc2, raw_parsetree_list)
 		{
-			RawStmt    *rs = castNode(RawStmt, lfirst(lc2));
+			RawStmt    *rs = lfirst_node(RawStmt, lc2);
 			CreateForeignTableStmt *cstmt = (CreateForeignTableStmt *) rs->stmt;
 			PlannedStmt *pstmt;
 

src/backend/commands/functioncmds.c

@@ -578,7 +578,7 @@ update_proconfig_value(ArrayType *a, List *set_items)
 
 	foreach(l, set_items)
 	{
-		VariableSetStmt *sstmt = castNode(VariableSetStmt, lfirst(l));
+		VariableSetStmt *sstmt = lfirst_node(VariableSetStmt, l);
 
 		if (sstmt->kind == VAR_RESET_ALL)
 			a = NULL;
@@ -972,7 +972,8 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 
 		foreach(lc, castNode(List, transformDefElem))
 		{
-			Oid			typeid = typenameTypeId(NULL, lfirst(lc));
+			Oid			typeid = typenameTypeId(NULL,
+												lfirst_node(TypeName, lc));
 			Oid			elt = get_base_element_type(typeid);
 
 			typeid = elt ? elt : typeid;

src/backend/commands/matview.c

@@ -264,7 +264,7 @@ ExecRefreshMatView(RefreshMatViewStmt *stmt, const char *queryString,
 	 * The stored query was rewritten at the time of the MV definition, but
 	 * has not been scribbled on by the planner.
 	 */
-	dataQuery = castNode(Query, linitial(actions));
+	dataQuery = linitial_node(Query, actions);
 
 	/*
 	 * Check for active uses of the relation in the current transaction, such

src/backend/commands/opclasscmds.c

@@ -460,7 +460,7 @@ DefineOpClass(CreateOpClassStmt *stmt)
 	 */
 	foreach(l, stmt->items)
 	{
-		CreateOpClassItem *item = castNode(CreateOpClassItem, lfirst(l));
+		CreateOpClassItem *item = lfirst_node(CreateOpClassItem, l);
 		Oid			operOid;
 		Oid			funcOid;
 		Oid			sortfamilyOid;
@@ -834,7 +834,7 @@ AlterOpFamilyAdd(AlterOpFamilyStmt *stmt, Oid amoid, Oid opfamilyoid,
 	 */
 	foreach(l, items)
 	{
-		CreateOpClassItem *item = castNode(CreateOpClassItem, lfirst(l));
+		CreateOpClassItem *item = lfirst_node(CreateOpClassItem, l);
 		Oid			operOid;
 		Oid			funcOid;
 		Oid			sortfamilyOid;
@@ -959,7 +959,7 @@ AlterOpFamilyDrop(AlterOpFamilyStmt *stmt, Oid amoid, Oid opfamilyoid,
 	 */
 	foreach(l, items)
 	{
-		CreateOpClassItem *item = castNode(CreateOpClassItem, lfirst(l));
+		CreateOpClassItem *item = lfirst_node(CreateOpClassItem, l);
 		Oid			lefttype,
 					righttype;
 		OpFamilyMember *member;

src/backend/commands/portalcmds.c

@@ -83,7 +83,7 @@ PerformCursorOpen(DeclareCursorStmt *cstmt, ParamListInfo params,
 	if (list_length(rewritten) != 1)
 		elog(ERROR, "non-SELECT statement in DECLARE CURSOR");
 
-	query = castNode(Query, linitial(rewritten));
+	query = linitial_node(Query, rewritten);
 
 	if (query->commandType != CMD_SELECT)
 		elog(ERROR, "non-SELECT statement in DECLARE CURSOR");

src/backend/commands/prepare.c

@@ -267,7 +267,7 @@ ExecuteQuery(ExecuteStmt *stmt, IntoClause *intoClause,
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 					 errmsg("prepared statement is not a SELECT")));
-		pstmt = castNode(PlannedStmt, linitial(plan_list));
+		pstmt = linitial_node(PlannedStmt, plan_list);
 		if (pstmt->commandType != CMD_SELECT)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
@@ -679,7 +679,7 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 	/* Explain each query */
 	foreach(p, plan_list)
 	{
-		PlannedStmt *pstmt = castNode(PlannedStmt, lfirst(p));
+		PlannedStmt *pstmt = lfirst_node(PlannedStmt, p);
 
 		if (pstmt->commandType != CMD_UTILITY)
 			ExplainOnePlan(pstmt, into, es, query_string, paramLI, queryEnv,

src/backend/commands/tablecmds.c

@@ -5942,7 +5942,7 @@ ATExecSetIdentity(Relation rel, const char *colName, Node *def, LOCKMODE lockmod
 
 	foreach(option, castNode(List, def))
 	{
-		DefElem	   *defel = castNode(DefElem, lfirst(option));
+		DefElem	   *defel = lfirst_node(DefElem, option);
 
 		if (strcmp(defel->defname, "generated") == 0)
 		{
@@ -9547,7 +9547,7 @@ ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId, char *cmd,
 	querytree_list = NIL;
 	foreach(list_item, raw_parsetree_list)
 	{
-		RawStmt    *rs = castNode(RawStmt, lfirst(list_item));
+		RawStmt    *rs = lfirst_node(RawStmt, list_item);
 		Node	   *stmt = rs->stmt;
 
 		if (IsA(stmt, IndexStmt))

src/backend/commands/trigger.c

@@ -340,7 +340,7 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 
 		foreach(lc, varList)
 		{
-			TriggerTransition   *tt = castNode(TriggerTransition, lfirst(lc));
+			TriggerTransition   *tt = lfirst_node(TriggerTransition, lc);
 
 			if (!(tt->isTable))
 				ereport(ERROR,

src/backend/commands/user.c

@@ -1388,7 +1388,7 @@ roleSpecsToIds(List *memberNames)
 
 	foreach(l, memberNames)
 	{
-		RoleSpec   *rolespec = castNode(RoleSpec, lfirst(l));
+		RoleSpec   *rolespec = lfirst_node(RoleSpec, l);
 		Oid			roleid;
 
 		roleid = get_rolespec_oid(rolespec, false);

src/backend/commands/view.c

@@ -516,7 +516,7 @@ DefineView(ViewStmt *stmt, const char *queryString,
 
 		foreach(targetList, viewParse->targetList)
 		{
-			TargetEntry *te = castNode(TargetEntry, lfirst(targetList));
+			TargetEntry *te = lfirst_node(TargetEntry, targetList);
 
 			/* junk columns don't get aliases */
 			if (te->resjunk)