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

8 files changed, 23 insertions, 23 deletions

diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index c4140a65d2..567dd54c6c 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -829,7 +829,7 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 		AttrNumber	attr_num;
 		TargetEntry *tle;
 
-		col = castNode(ResTarget, lfirst(icols));
+		col = lfirst_node(ResTarget, icols);
 		attr_num = (AttrNumber) lfirst_int(attnos);
 
 		tle = makeTargetEntry(expr,
@@ -954,7 +954,7 @@ transformInsertRow(ParseState *pstate, List *exprlist,
 		Expr	   *expr = (Expr *) lfirst(lc);
 		ResTarget  *col;
 
-		col = castNode(ResTarget, lfirst(icols));
+		col = lfirst_node(ResTarget, icols);
 
 		expr = transformAssignedExpr(pstate, expr,
 									 EXPR_KIND_INSERT_TARGET,
@@ -2300,7 +2300,7 @@ transformUpdateTargetList(ParseState *pstate, List *origTlist)
 		}
 		if (orig_tl == NULL)
 			elog(ERROR, "UPDATE target count mismatch --- internal error");
-		origTarget = castNode(ResTarget, lfirst(orig_tl));
+		origTarget = lfirst_node(ResTarget, orig_tl);
 
 		attrno = attnameAttNum(pstate->p_target_relation,
 							   origTarget->name, true);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 29ca5f13ea..89d2836c49 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -798,7 +798,7 @@ stmtmulti:	stmtmulti ';' stmt
 					if ($1 != NIL)
 					{
 						/* update length of previous stmt */
-						updateRawStmtEnd(castNode(RawStmt, llast($1)), @2);
+						updateRawStmtEnd(llast_node(RawStmt, $1), @2);
 					}
 					if ($3 != NULL)
 						$$ = lappend($1, makeRawStmt($3, @2 + 1));
diff --git a/src/backend/parser/parse_collate.c b/src/backend/parser/parse_collate.c
index cc235d422f..aa443f23ad 100644
--- a/src/backend/parser/parse_collate.c
+++ b/src/backend/parser/parse_collate.c
@@ -514,7 +514,7 @@ assign_collations_walker(Node *node, assign_collations_context *context)
 
 				if (qtree->targetList == NIL)
 					return false;
-				tent = castNode(TargetEntry, linitial(qtree->targetList));
+				tent = linitial_node(TargetEntry, qtree->targetList);
 				if (tent->resjunk)
 					return false;
 
@@ -649,7 +649,7 @@ assign_collations_walker(Node *node, assign_collations_context *context)
 
 							foreach(lc, expr->args)
 							{
-								CaseWhen   *when = castNode(CaseWhen, lfirst(lc));
+								CaseWhen   *when = lfirst_node(CaseWhen, lc);
 
 								/*
 								 * The condition expressions mustn't affect
@@ -865,7 +865,7 @@ assign_aggregate_collations(Aggref *aggref,
 	/* Process aggregated args, holding resjunk ones at arm's length */
 	foreach(lc, aggref->args)
 	{
-		TargetEntry *tle = castNode(TargetEntry, lfirst(lc));
+		TargetEntry *tle = lfirst_node(TargetEntry, lc);
 
 		if (tle->resjunk)
 			assign_expr_collations(loccontext->pstate, (Node *) tle);
@@ -909,7 +909,7 @@ assign_ordered_set_collations(Aggref *aggref,
 	/* Process aggregated args appropriately */
 	foreach(lc, aggref->args)
 	{
-		TargetEntry *tle = castNode(TargetEntry, lfirst(lc));
+		TargetEntry *tle = lfirst_node(TargetEntry, lc);
 
 		if (merge_sort_collations)
 			(void) assign_collations_walker((Node *) tle, loccontext);
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 323be23bca..4f9b1a76b0 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -1669,7 +1669,7 @@ transformCaseExpr(ParseState *pstate, CaseExpr *c)
 	resultexprs = NIL;
 	foreach(l, c->args)
 	{
-		CaseWhen   *w = castNode(CaseWhen, lfirst(l));
+		CaseWhen   *w = lfirst_node(CaseWhen, l);
 		CaseWhen   *neww = makeNode(CaseWhen);
 		Node	   *warg;
 
@@ -2334,7 +2334,7 @@ transformXmlExpr(ParseState *pstate, XmlExpr *x)
 
 	foreach(lc, x->named_args)
 	{
-		ResTarget  *r = castNode(ResTarget, lfirst(lc));
+		ResTarget  *r = lfirst_node(ResTarget, lc);
 		Node	   *expr;
 		char	   *argname;
 
diff --git a/src/backend/parser/parse_node.c b/src/backend/parser/parse_node.c
index 34006c70cd..fb3d117a7d 100644
--- a/src/backend/parser/parse_node.c
+++ b/src/backend/parser/parse_node.c
@@ -337,7 +337,7 @@ transformArraySubscripts(ParseState *pstate,
 	 */
 	foreach(idx, indirection)
 	{
-		A_Indices  *ai = castNode(A_Indices, lfirst(idx));
+		A_Indices  *ai = lfirst_node(A_Indices, idx);
 		Node	   *subexpr;
 
 		if (isSlice)
diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
index 062b8a1d22..f960f3844c 100644
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -931,7 +931,7 @@ markRTEForSelectPriv(ParseState *pstate, RangeTblEntry *rte,
 			JoinExpr   *j;
 
 			if (rtindex > 0 && rtindex <= list_length(pstate->p_joinexprs))
-				j = castNode(JoinExpr, list_nth(pstate->p_joinexprs, rtindex - 1));
+				j = list_nth_node(JoinExpr, pstate->p_joinexprs, rtindex - 1);
 			else
 				j = NULL;
 			if (j == NULL)
diff --git a/src/backend/parser/parse_type.c b/src/backend/parser/parse_type.c
index 0d7a2b1e1b..b71b17bd2a 100644
--- a/src/backend/parser/parse_type.c
+++ b/src/backend/parser/parse_type.c
@@ -478,7 +478,7 @@ TypeNameListToString(List *typenames)
 	initStringInfo(&string);
 	foreach(l, typenames)
 	{
-		TypeName   *typeName = castNode(TypeName, lfirst(l));
+		TypeName   *typeName = lfirst_node(TypeName, l);
 
 		if (l != list_head(typenames))
 			appendStringInfoChar(&string, ',');
@@ -719,7 +719,7 @@ typeStringToTypeName(const char *str)
 	 */
 	if (list_length(raw_parsetree_list) != 1)
 		goto fail;
-	stmt = (SelectStmt *) castNode(RawStmt, linitial(raw_parsetree_list))->stmt;
+	stmt = (SelectStmt *) linitial_node(RawStmt, raw_parsetree_list)->stmt;
 	if (stmt == NULL ||
 		!IsA(stmt, SelectStmt) ||
 		stmt->distinctClause != NIL ||
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 926699608b..e5461944e2 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -388,7 +388,7 @@ generateSerialExtraStmts(CreateStmtContext *cxt, ColumnDef *column,
 
 	foreach(option, seqoptions)
 	{
-		DefElem    *defel = castNode(DefElem, lfirst(option));
+		DefElem    *defel = lfirst_node(DefElem, option);
 
 		if (strcmp(defel->defname, "sequence_name") == 0)
 		{
@@ -605,7 +605,7 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
 
 	foreach(clist, column->constraints)
 	{
-		Constraint *constraint = castNode(Constraint, lfirst(clist));
+		Constraint *constraint = lfirst_node(Constraint, clist);
 
 		switch (constraint->contype)
 		{
@@ -1635,7 +1635,7 @@ transformIndexConstraints(CreateStmtContext *cxt)
 	 */
 	foreach(lc, cxt->ixconstraints)
 	{
-		Constraint *constraint = castNode(Constraint, lfirst(lc));
+		Constraint *constraint = lfirst_node(Constraint, lc);
 
 		Assert(constraint->contype == CONSTR_PRIMARY ||
 			   constraint->contype == CONSTR_UNIQUE ||
@@ -1956,8 +1956,8 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 			List	   *opname;
 
 			Assert(list_length(pair) == 2);
-			elem = castNode(IndexElem, linitial(pair));
-			opname = castNode(List, lsecond(pair));
+			elem = linitial_node(IndexElem, pair);
+			opname = lsecond_node(List, pair);
 
 			index->indexParams = lappend(index->indexParams, elem);
 			index->excludeOpNames = lappend(index->excludeOpNames, opname);
@@ -1984,7 +1984,7 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 
 		foreach(columns, cxt->columns)
 		{
-			column = castNode(ColumnDef, lfirst(columns));
+			column = lfirst_node(ColumnDef, columns);
 			if (strcmp(column->colname, key) == 0)
 			{
 				found = true;
@@ -2013,7 +2013,7 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 
 			foreach(inher, cxt->inhRelations)
 			{
-				RangeVar   *inh = castNode(RangeVar, lfirst(inher));
+				RangeVar   *inh = lfirst_node(RangeVar, inher);
 				Relation	rel;
 				int			count;
 
@@ -2823,7 +2823,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 					 */
 					foreach(lc, castNode(List, cmd->def))
 					{
-						DefElem	   *def = castNode(DefElem, lfirst(lc));
+						DefElem	   *def = lfirst_node(DefElem, lc);
 
 						if (strcmp(def->defname, "generated") == 0)
 							newdef = lappend(newdef, def);
@@ -2900,7 +2900,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 	 */
 	foreach(l, cxt.alist)
 	{
-		IndexStmt  *idxstmt = castNode(IndexStmt, lfirst(l));
+		IndexStmt  *idxstmt = lfirst_node(IndexStmt, l);
 
 		idxstmt = transformIndexStmt(relid, idxstmt, queryString);
 		newcmd = makeNode(AlterTableCmd);