Standardize some more loops that chase down parallel lists.

We have forboth() and forthree() macros that simplify iterating
through several parallel lists, but not everyplace that could
reasonably use those was doing so.  Also invent forfour() and
forfive() macros to do the same for four or five parallel lists,
and use those where applicable.

The immediate motivation for doing this is to reduce the number
of ad-hoc lnext() calls, to reduce the footprint of a WIP patch.
However, it seems like good cleanup and error-proofing anyway;
the places that were combining forthree() with a manually iterated
loop seem particularly illegible and bug-prone.

There was some speculation about restructuring related parsetree
representations to reduce the need for parallel list chasing of
this sort.  Perhaps that's a win, or perhaps not, but in any case
it would be considerably more invasive than this patch; and it's
not particularly related to my immediate goal of improving the
List infrastructure.  So I'll leave that question for another day.

Patch by me; thanks to David Rowley for review.

Discussion: https://postgr.es/m/11587.1550975080@sss.pgh.pa.us

1 files changed, 11 insertions, 26 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 1258092dc8c..85055bbb95a 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -9811,31 +9811,18 @@ get_tablefunc(TableFunc *tf, deparse_context *context, bool showimplicit)
 		ListCell   *l5;
 		int			colnum = 0;
 
-		l2 = list_head(tf->coltypes);
-		l3 = list_head(tf->coltypmods);
-		l4 = list_head(tf->colexprs);
-		l5 = list_head(tf->coldefexprs);
-
 		appendStringInfoString(buf, " COLUMNS ");
-		foreach(l1, tf->colnames)
+		forfive(l1, tf->colnames, l2, tf->coltypes, l3, tf->coltypmods,
+				l4, tf->colexprs, l5, tf->coldefexprs)
 		{
 			char	   *colname = strVal(lfirst(l1));
-			Oid			typid;
-			int32		typmod;
-			Node	   *colexpr;
-			Node	   *coldefexpr;
-			bool		ordinality = tf->ordinalitycol == colnum;
+			Oid			typid = lfirst_oid(l2);
+			int32		typmod = lfirst_int(l3);
+			Node	   *colexpr = (Node *) lfirst(l4);
+			Node	   *coldefexpr = (Node *) lfirst(l5);
+			bool		ordinality = (tf->ordinalitycol == colnum);
 			bool		notnull = bms_is_member(colnum, tf->notnulls);
 
-			typid = lfirst_oid(l2);
-			l2 = lnext(l2);
-			typmod = lfirst_int(l3);
-			l3 = lnext(l3);
-			colexpr = (Node *) lfirst(l4);
-			l4 = lnext(l4);
-			coldefexpr = (Node *) lfirst(l5);
-			l5 = lnext(l5);
-
 			if (colnum > 0)
 				appendStringInfoString(buf, ", ");
 			colnum++;
@@ -10349,12 +10336,11 @@ get_from_clause_coldeflist(RangeTblFunction *rtfunc,
 
 	appendStringInfoChar(buf, '(');
 
-	/* there's no forfour(), so must chase one list the hard way */
 	i = 0;
-	l4 = list_head(rtfunc->funccolnames);
-	forthree(l1, rtfunc->funccoltypes,
-			 l2, rtfunc->funccoltypmods,
-			 l3, rtfunc->funccolcollations)
+	forfour(l1, rtfunc->funccoltypes,
+			l2, rtfunc->funccoltypmods,
+			l3, rtfunc->funccolcollations,
+			l4, rtfunc->funccolnames)
 	{
 		Oid			atttypid = lfirst_oid(l1);
 		int32		atttypmod = lfirst_int(l2);
@@ -10378,7 +10364,6 @@ get_from_clause_coldeflist(RangeTblFunction *rtfunc,
 			appendStringInfo(buf, " COLLATE %s",
 							 generate_collation_name(attcollation));
 
-		l4 = lnext(l4);
 		i++;
 	}