Disallow jsonpath methods involving TZ in immutable functions

Timezones are not immutable and so neither is any function that relies on
them. In commit 66ea94e, we introduced a few methods which do casting
from one time to another and thus may involve the current timezone.  To
preserve the immutability of jsonpath functions currently marked
immutable, disallow these methods from being called from non-TZ aware
functions.

Jeevan Chalke, per a report from Jian He.

Author: adunstan

doc/src/sgml/func.sgml

@@ -18240,7 +18240,12 @@ ERROR:  jsonpath member accessor can only be applied to an object
       <type>timestamptz</type>, and <type>time</type> to <type>timetz</type>.
       However, all but the first of these conversions depend on the current
       <xref linkend="guc-timezone"/> setting, and thus can only be performed
-      within timezone-aware <type>jsonpath</type> functions.
+      within timezone-aware <type>jsonpath</type> functions.  Similarly, other
+      date/time-related methods that convert strings to date/time types
+      also do this casting, which may involve the current
+      <xref linkend="guc-timezone"/> setting. Therefore, these conversions can
+      also only be performed within timezone-aware <type>jsonpath</type>
+      functions.
      </para>
     </note>
 

src/backend/utils/adt/jsonpath_exec.c

@@ -268,6 +268,8 @@ static JsonbValue *getScalar(JsonbValue *scalar, enum jbvType type);
 static JsonbValue *wrapItemsInArray(const JsonValueList *items);
 static int	compareDatetime(Datum val1, Oid typid1, Datum val2, Oid typid2,
 							bool useTz, bool *cast_error);
+static void checkTimezoneIsUsedForCast(bool useTz, const char *type1,
+									   const char *type2);
 
 /****************** User interface to JsonPath executor ********************/
 
@@ -2409,6 +2411,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 													value);
 						break;
 					case TIMESTAMPTZOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "timestamptz", "date");
 						value = DirectFunctionCall1(timestamptz_date,
 													value);
 						break;
@@ -2433,6 +2437,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 					case TIMEOID:	/* Nothing to do for TIME */
 						break;
 					case TIMETZOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "timetz", "time");
 						value = DirectFunctionCall1(timetz_time,
 													value);
 						break;
@@ -2441,6 +2447,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 													value);
 						break;
 					case TIMESTAMPTZOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "timestamptz", "time");
 						value = DirectFunctionCall1(timestamptz_time,
 													value);
 						break;
@@ -2480,6 +2488,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 													 text_to_cstring(datetime)))));
 						break;
 					case TIMEOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "time", "timetz");
 						value = DirectFunctionCall1(time_timetz,
 													value);
 						break;
@@ -2531,6 +2541,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 					case TIMESTAMPOID:	/* Nothing to do for TIMESTAMP */
 						break;
 					case TIMESTAMPTZOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "timestamptz", "timestamp");
 						value = DirectFunctionCall1(timestamptz_timestamp,
 													value);
 						break;
@@ -2570,6 +2582,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 				switch (typid)
 				{
 					case DATEOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "date", "timestamptz");
 						value = DirectFunctionCall1(date_timestamptz,
 													value);
 						break;
@@ -2581,6 +2595,8 @@ executeDateTimeMethod(JsonPathExecContext *cxt, JsonPathItem *jsp,
 													 text_to_cstring(datetime)))));
 						break;
 					case TIMESTAMPOID:
+						checkTimezoneIsUsedForCast(cxt->useTz,
+												   "timestamp", "timestamptz");
 						value = DirectFunctionCall1(timestamp_timestamptz,
 													value);
 						break;