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

4 files changed, 98 insertions, 15 deletions

diff --git a/src/test/regress/expected/horology.out b/src/test/regress/expected/horology.out
index 241713cc51e..58da26ab0e1 100644
--- a/src/test/regress/expected/horology.out
+++ b/src/test/regress/expected/horology.out
@@ -1,13 +1,18 @@
 --
 -- HOROLOGY
 --
-SET DateStyle = 'Postgres, MDY';
-SHOW TimeZone;  -- Many of these tests depend on the prevailing setting
+SHOW TimeZone;  -- Many of these tests depend on the prevailing settings
  TimeZone 
 ----------
  PST8PDT
 (1 row)
 
+SHOW DateStyle;
+   DateStyle   
+---------------
+ Postgres, MDY
+(1 row)
+
 --
 -- Test various input formats
 --
diff --git a/src/test/regress/expected/jsonb_jsonpath.out b/src/test/regress/expected/jsonb_jsonpath.out
index b5bcece94e3..57c117ea580 100644
--- a/src/test/regress/expected/jsonb_jsonpath.out
+++ b/src/test/regress/expected/jsonb_jsonpath.out
@@ -2586,15 +2586,6 @@ select jsonb_path_query('[2, true]', '$.string()');
  "true"
 (2 rows)
 
-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"
-(1 row)
-
 select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string()');
   jsonb_path_query_array  
 --------------------------
@@ -2607,6 +2598,77 @@ select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string().type()');
  ["string", "string", "string"]
 (1 row)
 
+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  
+-----------------------
+ "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     
+-----------------------------
+ "2023-08-15T12:34:56-07:00"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
+      jsonb_path_query       
+-----------------------------
+ "2023-08-15T12:34:56+05:30"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
+   jsonb_path_query    
+-----------------------
+ "2023-08-15T12:34:56"
+(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 
+---------------------
+ "12:34:56-07:00"
+(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"
+(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"', '$.timestamp_tz().string()');
+      jsonb_path_query       
+-----------------------------
+ "2023-08-15T12:34:56+05:30"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
+   jsonb_path_query    
+-----------------------
+ "2023-08-15T12:34:56"
+(1 row)
+
+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/horology.sql b/src/test/regress/sql/horology.sql
index e5cf12ff63d..0fe3c783e61 100644
--- a/src/test/regress/sql/horology.sql
+++ b/src/test/regress/sql/horology.sql
@@ -1,9 +1,9 @@
 --
 -- HOROLOGY
 --
-SET DateStyle = 'Postgres, MDY';
 
-SHOW TimeZone;  -- Many of these tests depend on the prevailing setting
+SHOW TimeZone;  -- Many of these tests depend on the prevailing settings
+SHOW DateStyle;
 
 --
 -- Test various input formats
diff --git a/src/test/regress/sql/jsonb_jsonpath.sql b/src/test/regress/sql/jsonb_jsonpath.sql
index 5e14f7759bb..c647af55e94 100644
--- a/src/test/regress/sql/jsonb_jsonpath.sql
+++ b/src/test/regress/sql/jsonb_jsonpath.sql
@@ -587,10 +587,26 @@ select jsonb_path_query('1234', '$.string()');
 select jsonb_path_query('true', '$.string()');
 select jsonb_path_query('1234', '$.string().type()');
 select jsonb_path_query('[2, true]', '$.string()');
-select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()');
-select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
 select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string()');
 select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string().type()');
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()');
+select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
+select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()'); -- should work
+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()');
+
+-- .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()');
+rollback;
 
 -- Test .time()
 select jsonb_path_query('null', '$.time()');