Fix core dump in transformValuesClause when there are no columns.

The parser code that transformed VALUES from row-oriented to
column-oriented lists failed if there were zero columns.
You can't write that straightforwardly (though probably you
should be able to), but the case can be reached by expanding
a "tab.*" reference to a zero-column table.

Per bug #17477 from Wang Ke.  Back-patch to all supported branches.

Discussion: https://postgr.es/m/17477-0af3c6ac6b0a6ae0@postgresql.org

Author: tglsfdc

src/backend/parser/analyze.c

@@ -1346,7 +1346,7 @@ static Query *
 transformValuesClause(ParseState *pstate, SelectStmt *stmt)
 {
 	Query	   *qry = makeNode(Query);
-	List	   *exprsLists;
+	List	   *exprsLists = NIL;
 	List	   *coltypes = NIL;
 	List	   *coltypmods = NIL;
 	List	   *colcollations = NIL;
@@ -1431,6 +1431,9 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
 
 		/* Release sub-list's cells to save memory */
 		list_free(sublist);
+
+		/* Prepare an exprsLists element for this row */
+		exprsLists = lappend(exprsLists, NIL);
 	}
 
 	/*
@@ -1485,25 +1488,15 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
 	/*
 	 * Finally, rearrange the coerced expressions into row-organized lists.
 	 */
-	exprsLists = NIL;
-	foreach(lc, colexprs[0])
-	{
-		Node	   *col = (Node *) lfirst(lc);
-		List	   *sublist;
-
-		sublist = list_make1(col);
-		exprsLists = lappend(exprsLists, sublist);
-	}
-	list_free(colexprs[0]);
-	for (i = 1; i < sublist_length; i++)
+	for (i = 0; i < sublist_length; i++)
 	{
 		forboth(lc, colexprs[i], lc2, exprsLists)
 		{
 			Node	   *col = (Node *) lfirst(lc);
 			List	   *sublist = lfirst(lc2);
 
-			/* sublist pointer in exprsLists won't need adjustment */
-			(void) lappend(sublist, col);
+			sublist = lappend(sublist, col);
+			lfirst(lc2) = sublist;
 		}
 		list_free(colexprs[i]);
 	}

src/test/regress/expected/select.out

@@ -517,6 +517,13 @@ TABLE int8_tbl;
  4567890123456789 | -4567890123456789
 (9 rows)
 
+-- corner case: VALUES with no columns
+CREATE TEMP TABLE nocols();
+INSERT INTO nocols DEFAULT VALUES;
+SELECT * FROM nocols n, LATERAL (VALUES(n.*)) v;
+--
+(1 row)
+
 --
 -- Test ORDER BY options
 --

src/test/regress/sql/select.sql

@@ -148,6 +148,11 @@ SELECT 2+2, 57
 UNION ALL
 TABLE int8_tbl;
 
+-- corner case: VALUES with no columns
+CREATE TEMP TABLE nocols();
+INSERT INTO nocols DEFAULT VALUES;
+SELECT * FROM nocols n, LATERAL (VALUES(n.*)) v;
+
 --
 -- Test ORDER BY options
 --