Fix broken jsonb_set() logic for replacing array elements.

Commit 0b62fd03 did a fairly sloppy job of refactoring setPath()
to support jsonb_insert() along with jsonb_set().  In its defense,
though, there was no regression test case exercising the case of
replacing an existing element in a jsonb array.

Per bug #14366 from Peng Sun.  Back-patch to 9.6 where bug was introduced.

Report: <20161012065349.1412.47858@wrigleys.postgresql.org>

src/backend/utils/adt/jsonfuncs.c

@@ -34,11 +34,11 @@
 #include "utils/typcache.h"
 
 /* Operations available for setPath */
-#define JB_PATH_NOOP					0x0000
 #define JB_PATH_CREATE					0x0001
 #define JB_PATH_DELETE					0x0002
-#define JB_PATH_INSERT_BEFORE			0x0004
-#define JB_PATH_INSERT_AFTER			0x0008
+#define JB_PATH_REPLACE					0x0004
+#define JB_PATH_INSERT_BEFORE			0x0008
+#define JB_PATH_INSERT_AFTER			0x0010
 #define JB_PATH_CREATE_OR_INSERT \
 	(JB_PATH_INSERT_BEFORE | JB_PATH_INSERT_AFTER | JB_PATH_CREATE)
 
@@ -3545,7 +3545,7 @@ jsonb_set(PG_FUNCTION_ARGS)
 	it = JsonbIteratorInit(&in->root);
 
 	res = setPath(&it, path_elems, path_nulls, path_len, &st,
-				  0, newval, create ? JB_PATH_CREATE : JB_PATH_NOOP);
+				  0, newval, create ? JB_PATH_CREATE : JB_PATH_REPLACE);
 
 	Assert(res != NULL);
 
@@ -4003,7 +4003,7 @@ setPathArray(JsonbIterator **it, Datum *path_elems, bool *path_nulls,
 				if (op_type & (JB_PATH_INSERT_AFTER | JB_PATH_INSERT_BEFORE))
 					(void) pushJsonbValue(st, r, &v);
 
-				if (op_type & JB_PATH_INSERT_AFTER)
+				if (op_type & (JB_PATH_INSERT_AFTER | JB_PATH_REPLACE))
 					addJsonbToParseState(st, newval);
 
 				done = true;
@@ -4035,7 +4035,7 @@ setPathArray(JsonbIterator **it, Datum *path_elems, bool *path_nulls,
 				}
 			}
 
-			if (op_type & JB_PATH_CREATE_OR_INSERT && !done &&
+			if ((op_type & JB_PATH_CREATE_OR_INSERT) && !done &&
 				level == path_len - 1 && i == nelems - 1)
 			{
 				addJsonbToParseState(st, newval);

src/test/regress/expected/jsonb.out

@@ -3238,6 +3238,12 @@ select jsonb_set('[]','{1}','"b"', false);
  []
 (1 row)
 
+select jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0}','[2,3,4]', false);
+        jsonb_set        
+-------------------------
+ [[2, 3, 4], 2, null, 3]
+(1 row)
+
 -- jsonb_set adding instead of replacing
 -- prepend to array
 select jsonb_set('{"a":1,"b":[0,1,2],"c":{"d":4}}','{b,-33}','{"foo":123}');

src/test/regress/sql/jsonb.sql

@@ -814,6 +814,7 @@ select '[]'::jsonb #- '{a}';
 select jsonb_set('"a"','{a}','"b"'); --error
 select jsonb_set('{}','{a}','"b"', false);
 select jsonb_set('[]','{1}','"b"', false);
+select jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0}','[2,3,4]', false);
 
 -- jsonb_set adding instead of replacing