Make jsonpath .string() be immutable for datetimes.

Discussion of commit ed055d249 revealed that we don't actually
want jsonpath's .string() method to depend on DateStyle, nor
TimeZone either, because the non-"_tz" jsonpath functions are
supposed to be immutable.  Potentially we could allow a TimeZone
dependency in the "_tz" variants, but it seems better to just
uniformly define this method as returning the same string that
jsonb text output would do.  That's easier to implement too,
saving a couple dozen lines.

Patch by me, per complaint from Peter Eisentraut.  Back-patch
to v17 where this feature came in (in 66ea94e8e).  Also
back-patch ed055d249 to provide test cases.

Discussion: https://postgr.es/m/5e8879d0-a3c8-4be2-950f-d83aa2af953a@eisentraut.org

3 files changed, 36 insertions, 83 deletions

diff --git a/src/backend/utils/adt/jsonpath_exec.c b/src/backend/utils/adt/jsonpath_exec.c
index e569c7efb83..1184cba983a 100644
--- a/src/backend/utils/adt/jsonpath_exec.c
+++ b/src/backend/utils/adt/jsonpath_exec.c
@@ -72,6 +72,7 @@
 #include "utils/datetime.h"
 #include "utils/float.h"
 #include "utils/formatting.h"
+#include "utils/json.h"
 #include "utils/jsonpath.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
@@ -1629,32 +1630,13 @@ executeItemOptUnwrapTarget(JsonPathExecContext *cxt, JsonPathItem *jsp,
 						break;
 					case jbvDatetime:
 						{
-							switch (jb->val.datetime.typid)
-							{
-								case DATEOID:
-									tmp = DatumGetCString(DirectFunctionCall1(date_out,
-																			  jb->val.datetime.value));
-									break;
-								case TIMEOID:
-									tmp = DatumGetCString(DirectFunctionCall1(time_out,
-																			  jb->val.datetime.value));
-									break;
-								case TIMETZOID:
-									tmp = DatumGetCString(DirectFunctionCall1(timetz_out,
-																			  jb->val.datetime.value));
-									break;
-								case TIMESTAMPOID:
-									tmp = DatumGetCString(DirectFunctionCall1(timestamp_out,
-																			  jb->val.datetime.value));
-									break;
-								case TIMESTAMPTZOID:
-									tmp = DatumGetCString(DirectFunctionCall1(timestamptz_out,
-																			  jb->val.datetime.value));
-									break;
-								default:
-									elog(ERROR, "unrecognized SQL/JSON datetime type oid: %u",
-										 jb->val.datetime.typid);
-							}
+							char		buf[MAXDATELEN + 1];
+
+							JsonEncodeDateTime(buf,
+											   jb->val.datetime.value,
+											   jb->val.datetime.typid,
+											   &jb->val.datetime.tz);
+							tmp = pstrdup(buf);
 						}
 						break;
 					case jbvNull:
diff --git a/src/test/regress/expected/jsonb_jsonpath.out b/src/test/regress/expected/jsonb_jsonpath.out
index 70eeb655a2a..acdf7e436f9 100644
--- a/src/test/regress/expected/jsonb_jsonpath.out
+++ b/src/test/regress/expected/jsonb_jsonpath.out
@@ -2652,30 +2652,30 @@ select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()')
 ERROR:  cannot convert value from timestamptz to timestamp without time zone usage
 HINT:  Use *_tz() function for time zone support.
 select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
-    jsonb_path_query_tz     
-----------------------------
- "Tue Aug 15 00:04:56 2023"
+  jsonb_path_query_tz  
+-----------------------
+ "2023-08-15T00:04:56"
 (1 row)
 
 select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
 ERROR:  cannot convert value from timestamp to timestamptz without time zone usage
 HINT:  Use *_tz() function for time zone support.
 select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()'); -- should work
-      jsonb_path_query_tz       
---------------------------------
- "Tue Aug 15 12:34:56 2023 PDT"
+     jsonb_path_query_tz     
+-----------------------------
+ "2023-08-15T12:34:56-07:00"
 (1 row)
 
 select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
-        jsonb_path_query        
---------------------------------
- "Tue Aug 15 00:04:56 2023 PDT"
+      jsonb_path_query       
+-----------------------------
+ "2023-08-15T12:34:56+05:30"
 (1 row)
 
 select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
-      jsonb_path_query      
-----------------------------
- "Tue Aug 15 12:34:56 2023"
+   jsonb_path_query    
+-----------------------
+ "2023-08-15T12:34:56"
 (1 row)
 
 select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
@@ -2687,7 +2687,7 @@ select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
 select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
  jsonb_path_query_tz 
 ---------------------
- "12:34:56-07"
+ "12:34:56-07:00"
 (1 row)
 
 select jsonb_path_query('"12:34:56"', '$.time().string()');
@@ -2699,53 +2699,26 @@ select jsonb_path_query('"12:34:56"', '$.time().string()');
 select jsonb_path_query('"2023-08-15"', '$.date().string()');
  jsonb_path_query 
 ------------------
- "08-15-2023"
-(1 row)
-
-set datestyle = 'ISO';
-select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
-   jsonb_path_query_tz    
---------------------------
- "2023-08-15 12:34:56-07"
+ "2023-08-15"
 (1 row)
 
+-- .string() does not react to timezone or datestyle
+begin;
+set local timezone = 'UTC';
+set local datestyle = 'German';
 select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
-     jsonb_path_query     
---------------------------
- "2023-08-15 00:04:56-07"
+      jsonb_path_query       
+-----------------------------
+ "2023-08-15T12:34:56+05:30"
 (1 row)
 
 select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
    jsonb_path_query    
 -----------------------
- "2023-08-15 12:34:56"
-(1 row)
-
-select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
- jsonb_path_query 
-------------------
- "12:34:56+05:30"
-(1 row)
-
-select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
- jsonb_path_query_tz 
----------------------
- "12:34:56-07"
-(1 row)
-
-select jsonb_path_query('"12:34:56"', '$.time().string()');
- jsonb_path_query 
-------------------
- "12:34:56"
-(1 row)
-
-select jsonb_path_query('"2023-08-15"', '$.date().string()');
- jsonb_path_query 
-------------------
- "2023-08-15"
+ "2023-08-15T12:34:56"
 (1 row)
 
-reset datestyle;
+rollback;
 -- Test .time()
 select jsonb_path_query('null', '$.time()');
 ERROR:  jsonpath item method .time() can only be applied to a string
diff --git a/src/test/regress/sql/jsonb_jsonpath.sql b/src/test/regress/sql/jsonb_jsonpath.sql
index 4d57e13eda0..da3f7969ca2 100644
--- a/src/test/regress/sql/jsonb_jsonpath.sql
+++ b/src/test/regress/sql/jsonb_jsonpath.sql
@@ -611,15 +611,13 @@ select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
 select jsonb_path_query('"12:34:56"', '$.time().string()');
 select jsonb_path_query('"2023-08-15"', '$.date().string()');
 
-set datestyle = 'ISO';
-select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
+-- .string() does not react to timezone or datestyle
+begin;
+set local timezone = 'UTC';
+set local datestyle = 'German';
 select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
 select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
-select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
-select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
-select jsonb_path_query('"12:34:56"', '$.time().string()');
-select jsonb_path_query('"2023-08-15"', '$.date().string()');
-reset datestyle;
+rollback;
 
 -- Test .time()
 select jsonb_path_query('null', '$.time()');