Preserve tz when converting to jsonb timestamptz

This removes an inconsistency in the treatment of different datatypes by
the jsonpath timestamp_tz() function. Conversions from data types that
are not timestamp-aware, such as date and timestamp, are now treated
consistently with conversion from those that are such as timestamptz.

Author: David Wheeler
Reviewed-by: Junwang Zhao and Jeevan Chalke

Discussion: https://postgr.es/m/7DE080CE-6D8C-4794-9BD1-7D9699172FAB%40justatheory.com

Backpatch to release 17.

src/backend/utils/adt/jsonpath_exec.c

@@ -2707,12 +2707,27 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 			break;
 		case jpiTimestampTz:
 			{
+				struct pg_tm tm;
+				fsec_t		fsec;
+
 				/* Convert result type to timestamp with time zone */
 				switch (typid)
 				{
 					case DATEOID:
 						checkTimezoneIsUsedForCast(cxt->useTz,
 												   "date", "timestamptz");
+
+						/*
+						 * Get the timezone value explicitly since JsonbValue
+						 * keeps that separate.
+						 */
+						j2date(DatumGetDateADT(value) + POSTGRES_EPOCH_JDATE,
+							   &(tm.tm_year), &(tm.tm_mon), &(tm.tm_mday));
+						tm.tm_hour = 0;
+						tm.tm_min = 0;
+						tm.tm_sec = 0;
+						tz = DetermineTimeZoneOffset(&tm, session_timezone);
+
 						value = DirectFunctionCall1(date_timestamptz,
 													value);
 						break;
@@ -2726,6 +2741,16 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 					case TIMESTAMPOID:
 						checkTimezoneIsUsedForCast(cxt->useTz,
 												   "timestamp", "timestamptz");
+
+						/*
+						 * Get the timezone value explicitly since JsonbValue
+						 * keeps that separate.
+						 */
+						if (timestamp2tm(DatumGetTimestamp(value), NULL, &tm,
+										 &fsec, NULL, NULL) == 0)
+							tz = DetermineTimeZoneOffset(&tm,
+														 session_timezone);
+
 						value = DirectFunctionCall1(timestamp_timestamptz,
 													value);
 						break;

src/test/regress/expected/jsonb_jsonpath.out

@@ -2964,7 +2964,7 @@ HINT:  Use *_tz() function for time zone support.
 select jsonb_path_query_tz('"2023-08-15"', '$.timestamp_tz()'); -- should work
      jsonb_path_query_tz     
 -----------------------------
- "2023-08-15T07:00:00+00:00"
+ "2023-08-15T00:00:00-07:00"
 (1 row)
 
 select jsonb_path_query('"12:34:56"', '$.timestamp_tz()');
@@ -3151,7 +3151,7 @@ HINT:  Use *_tz() function for time zone support.
 select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz()'); -- should work
      jsonb_path_query_tz     
 -----------------------------
- "2023-08-15T02:34:56+00:00"
+ "2023-08-15T12:34:56+10:00"
 (1 row)
 
 select jsonb_path_query('"2023-08-15 12:34:56 +05:30"', '$.timestamp_tz()');