Add support for AT LOCAL

When converting a timestamp to/from with/without time zone, the SQL
Standard specifies an AT LOCAL variant of AT TIME ZONE which uses the
session's time zone.  This includes three system functions able to do
the work in the same way as the existing flavors for AT TIME ZONE,
except that these need to be marked as stable as they depend on the
session's TimeZone GUC.

Bump catalog version.

Author: Vik Fearing
Reviewed-by: Laurenz Albe, Cary Huang, Michael Paquier
Discussion: https://postgr.es/m/8e25dec4-5667-c1a5-6581-167d710c2182@postgresfriends.org

Author: michaelpq

doc/src/sgml/func.sgml

@@ -10611,7 +10611,7 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
   </sect2>
 
   <sect2 id="functions-datetime-zoneconvert">
-   <title><literal>AT TIME ZONE</literal></title>
+   <title><literal>AT TIME ZONE and AT LOCAL</literal></title>
 
    <indexterm>
     <primary>time zone</primary>
@@ -10622,6 +10622,10 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
     <primary>AT TIME ZONE</primary>
    </indexterm>
 
+   <indexterm>
+    <primary>AT LOCAL</primary>
+   </indexterm>
+
    <para>
     The <literal>AT TIME ZONE</literal> operator converts time
     stamp <emphasis>without</emphasis> time zone to/from
@@ -10632,7 +10636,7 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
    </para>
 
     <table id="functions-datetime-zoneconvert-table">
-     <title><literal>AT TIME ZONE</literal> Variants</title>
+     <title><literal>AT TIME ZONE</literal> and <literal>AT LOCAL</literal> Variants</title>
      <tgroup cols="1">
       <thead>
        <row>
@@ -10665,6 +10669,22 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
         </para></entry>
        </row>
 
+       <row>
+        <entry role="func_table_entry"><para role="func_signature">
+         <type>timestamp without time zone</type> <literal>AT LOCAL</literal>
+         <returnvalue>timestamp with time zone</returnvalue>
+        </para>
+        <para>
+         Converts given time stamp <emphasis>without</emphasis> time zone to
+         time stamp <emphasis>with</emphasis> the session's
+         <varname>TimeZone</varname> value as time zone.
+        </para>
+        <para>
+         <literal>timestamp '2001-02-16 20:38:40' at local</literal>
+         <returnvalue>2001-02-17 03:38:40+00</returnvalue>
+        </para></entry>
+       </row>
+
        <row>
         <entry role="func_table_entry"><para role="func_signature">
          <type>timestamp with time zone</type> <literal>AT TIME ZONE</literal> <replaceable>zone</replaceable>
@@ -10681,6 +10701,22 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
         </para></entry>
        </row>
 
+       <row>
+        <entry role="func_table_entry"><para role="func_signature">
+         <type>timestamp with time zone</type> <literal>AT LOCAL</literal>
+         <returnvalue>timestamp without time zone</returnvalue>
+        </para>
+        <para>
+         Converts given time stamp <emphasis>with</emphasis> time zone to
+         time stamp <emphasis>without</emphasis> time zone, as the time would
+         appear with the session's <varname>TimeZone</varname> value as time zone.
+        </para>
+        <para>
+         <literal>timestamp with time zone '2001-02-16 20:38:40-05' at local</literal>
+         <returnvalue>2001-02-16 18:38:40</returnvalue>
+        </para></entry>
+       </row>
+
        <row>
         <entry role="func_table_entry"><para role="func_signature">
          <type>time with time zone</type> <literal>AT TIME ZONE</literal> <replaceable>zone</replaceable>
@@ -10696,6 +10732,25 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
          <returnvalue>10:34:17+00</returnvalue>
         </para></entry>
        </row>
+
+       <row>
+        <entry role="func_table_entry"><para role="func_signature">
+         <type>time with time zone</type> <literal>AT LOCAL</literal>
+         <returnvalue>time with time zone</returnvalue>
+        </para>
+        <para>
+         Converts given time <emphasis>with</emphasis> time zone to a new time
+         zone.  Since no date is supplied, this uses the currently active UTC
+         offset for the session's <varname>TimeZone</varname> value.
+        </para>
+        <para>
+         Assuming the session's <varname>TimeZone</varname> is set to <literal>UTC</literal>:
+        </para>
+        <para>
+         <literal>time with time zone '05:34:17-05' at local</literal>
+         <returnvalue>10:34:17+00</returnvalue>
+        </para></entry>
+       </row>
       </tbody>
      </tgroup>
     </table>
@@ -10710,6 +10765,13 @@ SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-0
     UTC, so it is not very common in practice.
    </para>
 
+   <para>
+    The syntax <literal>AT LOCAL</literal> may be used as shorthand for
+    <literal>AT TIME ZONE <replaceable>local</replaceable></literal>, where
+    <replaceable>local</replaceable> is the session's
+    <varname>TimeZone</varname> value.
+   </para>
+
    <para>
     Examples (assuming the current <xref linkend="guc-timezone"/> setting
     is <literal>America/Los_Angeles</literal>):
@@ -10722,14 +10784,31 @@ SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'America/D
 
 SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago';
 <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 05:38:40</computeroutput>
+
+SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT LOCAL;
+<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 17:38:40</computeroutput>
+
+SELECT TIME WITH TIME ZONE '20:38:40-05' AT LOCAL;
+<lineannotation>Result: </lineannotation><computeroutput>17:38:40</computeroutput>
 </screen>
     The first example adds a time zone to a value that lacks it, and
     displays the value using the current <varname>TimeZone</varname>
     setting.  The second example shifts the time stamp with time zone value
     to the specified time zone, and returns the value without a time zone.
     This allows storage and display of values different from the current
     <varname>TimeZone</varname> setting.  The third example converts
-    Tokyo time to Chicago time.
+    Tokyo time to Chicago time.  The fourth example shifts the time stamp
+    with time zone value to the time zone currently specified by the
+    <varname>TimeZone</varname> setting and returns the value without a
+    time zone.
+   </para>
+
+   <para>
+    The fifth example is a cautionary tale. Due to the fact that there is no
+    date associated with the input value, the conversion is made using the
+    current date of the session. Therefore, this static example may show a wrong
+    result depending on the time of the year it is viewed because
+    <literal>'America/Los_Angeles'</literal> observes Daylight Savings Time.
    </para>
 
    <para>
@@ -10745,6 +10824,18 @@ SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'A
     <literal><replaceable>time</replaceable> AT TIME ZONE
     <replaceable>zone</replaceable></literal>.
    </para>
+
+   <para>
+    The function <literal><function>timezone</function>(<replaceable>timestamp</replaceable>)</literal>
+    is equivalent to the SQL-conforming construct <literal><replaceable>timestamp</replaceable>
+    AT LOCAL</literal>.
+   </para>
+
+   <para>
+    The function <literal><function>timezone</function>(<replaceable>time</replaceable>)</literal>
+    is equivalent to the SQL-conforming construct <literal><replaceable>time</replaceable>
+    AT LOCAL</literal>.
+   </para>
   </sect2>
 
   <sect2 id="functions-datetime-current">

src/backend/parser/gram.y

@@ -14508,6 +14508,13 @@ a_expr:		c_expr									{ $$ = $1; }
 											   COERCE_SQL_SYNTAX,
 											   @2);
 				}
+			| a_expr AT LOCAL						%prec AT
+				{
+					$$ = (Node *) makeFuncCall(SystemFuncName("timezone"),
+											   list_make1($1),
+											   COERCE_SQL_SYNTAX,
+											   -1);
+				}
 		/*
 		 * These operators must be called out explicitly in order to make use
 		 * of bison's automatic operator-precedence handling.  All other

src/backend/utils/adt/date.c

@@ -3125,3 +3125,18 @@ timetz_izone(PG_FUNCTION_ARGS)
 
 	PG_RETURN_TIMETZADT_P(result);
 }
+
+/* timetz_at_local()
+ *
+ * Unlike for timestamp[tz]_at_local, the type for timetz does not flip between
+ * time with/without time zone, so we cannot just call the conversion function.
+ */
+Datum
+timetz_at_local(PG_FUNCTION_ARGS)
+{
+	Datum		time = PG_GETARG_DATUM(0);
+	const char *tzn = pg_get_timezone_name(session_timezone);
+	Datum		zone = PointerGetDatum(cstring_to_text(tzn));
+
+	return DirectFunctionCall2(timetz_zone, zone, time);
+}

src/backend/utils/adt/ruleutils.c

@@ -10347,6 +10347,16 @@ get_func_sql_syntax(FuncExpr *expr, deparse_context *context)
 			appendStringInfoChar(buf, ')');
 			return true;
 
+		case F_TIMEZONE_TIMESTAMP:
+		case F_TIMEZONE_TIMESTAMPTZ:
+		case F_TIMEZONE_TIMETZ:
+			/* AT LOCAL */
+			appendStringInfoChar(buf, '(');
+			get_rule_expr_paren((Node *) linitial(expr->args), context, false,
+								(Node *) expr);
+			appendStringInfoString(buf, " AT LOCAL)");
+			return true;
+
 		case F_OVERLAPS_TIMESTAMPTZ_INTERVAL_TIMESTAMPTZ_INTERVAL:
 		case F_OVERLAPS_TIMESTAMPTZ_INTERVAL_TIMESTAMPTZ_TIMESTAMPTZ:
 		case F_OVERLAPS_TIMESTAMPTZ_TIMESTAMPTZ_TIMESTAMPTZ_INTERVAL:

src/backend/utils/adt/timestamp.c

@@ -5921,3 +5921,23 @@ generate_series_timestamptz_at_zone(PG_FUNCTION_ARGS)
 {
 	return generate_series_timestamptz_internal(fcinfo);
 }
+
+/* timestamp_at_local()
+ * timestamptz_at_local()
+ *
+ * The regression tests do not like two functions with the same proargs and
+ * prosrc but different proname, but the grammar for AT LOCAL needs an
+ * overloaded name to handle both types of timestamp, so we make simple
+ * wrappers for it.
+ */
+Datum
+timestamp_at_local(PG_FUNCTION_ARGS)
+{
+	return timestamp_timestamptz(fcinfo);
+}
+
+Datum
+timestamptz_at_local(PG_FUNCTION_ARGS)
+{
+	return timestamptz_timestamp(fcinfo);
+}

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202309251
+#define CATALOG_VERSION_NO	202310131
 
 #endif

src/include/catalog/pg_proc.dat

@@ -2319,6 +2319,9 @@
 { oid => '1159', descr => 'adjust timestamp to new time zone',
   proname => 'timezone', prorettype => 'timestamp',
   proargtypes => 'text timestamptz', prosrc => 'timestamptz_zone' },
+{ oid => '9159', descr => 'adjust timestamp to local time zone',
+  proname => 'timezone', provolatile => 's', prorettype => 'timestamp',
+  proargtypes => 'timestamptz', prosrc => 'timestamptz_at_local' },
 
 { oid => '1160', descr => 'I/O',
   proname => 'interval_in', provolatile => 's', prorettype => 'interval',
@@ -6095,6 +6098,9 @@
 { oid => '2038', descr => 'adjust time with time zone to new zone',
   proname => 'timezone', prorettype => 'timetz',
   proargtypes => 'interval timetz', prosrc => 'timetz_izone' },
+{ oid => '9161', descr => 'adjust time to local time zone',
+  proname => 'timezone', provolatile => 's', prorettype => 'timetz',
+  proargtypes => 'timetz', prosrc => 'timetz_at_local' },
 { oid => '2039', descr => 'hash',
   proname => 'timestamp_hash', prorettype => 'int4', proargtypes => 'timestamp',
   prosrc => 'timestamp_hash' },
@@ -6190,6 +6196,9 @@
 { oid => '2070', descr => 'adjust timestamp to new time zone',
   proname => 'timezone', prorettype => 'timestamptz',
   proargtypes => 'interval timestamp', prosrc => 'timestamp_izone' },
+{ oid => '9160', descr => 'adjust timestamp to local time zone',
+  proname => 'timezone', provolatile => 's', prorettype => 'timestamptz',
+  proargtypes => 'timestamp', prosrc => 'timestamp_at_local' },
 { oid => '2071',
   proname => 'date_pl_interval', prorettype => 'timestamp',
   proargtypes => 'date interval', prosrc => 'date_pl_interval' },

src/test/regress/expected/timestamptz.out

@@ -3135,6 +3135,62 @@ SELECT '2014-10-25 23:00:00 UTC'::timestamptz AT TIME ZONE 'MSK';
  Sun Oct 26 02:00:00 2014
 (1 row)
 
+--
+-- Test LOCAL time zone
+--
+BEGIN;
+SET LOCAL TIME ZONE 'Europe/Paris';
+VALUES (CAST('1978-07-07 19:38 America/New_York' AS TIMESTAMP WITH TIME ZONE) AT LOCAL);
+         column1          
+--------------------------
+ Sat Jul 08 01:38:00 1978
+(1 row)
+
+VALUES (TIMESTAMP '1978-07-07 19:38' AT LOCAL);
+            column1            
+-------------------------------
+ Fri Jul 07 19:38:00 1978 CEST
+(1 row)
+
+SET LOCAL TIME ZONE 'Australia/Sydney';
+VALUES (CAST('1978-07-07 19:38 America/New_York' AS TIMESTAMP WITH TIME ZONE) AT LOCAL);
+         column1          
+--------------------------
+ Sat Jul 08 09:38:00 1978
+(1 row)
+
+VALUES (TIMESTAMP '1978-07-07 19:38' AT LOCAL);
+            column1            
+-------------------------------
+ Fri Jul 07 19:38:00 1978 AEST
+(1 row)
+
+SET LOCAL TimeZone TO 'UTC';
+CREATE VIEW timestamp_local_view AS
+  SELECT CAST('1978-07-07 19:38 America/New_York' AS TIMESTAMP WITH TIME ZONE) AT LOCAL AS ttz_at_local,
+         timezone(CAST('1978-07-07 19:38 America/New_York' AS TIMESTAMP WITH TIME ZONE)) AS ttz_func,
+         TIMESTAMP '1978-07-07 19:38' AT LOCAL AS t_at_local,
+         timezone(TIMESTAMP '1978-07-07 19:38') AS t_func;
+SELECT pg_get_viewdef('timestamp_local_view', true);
+                                        pg_get_viewdef                                        
+----------------------------------------------------------------------------------------------
+  SELECT ('Fri Jul 07 23:38:00 1978 UTC'::timestamp with time zone AT LOCAL) AS ttz_at_local,+
+     timezone('Fri Jul 07 23:38:00 1978 UTC'::timestamp with time zone) AS ttz_func,         +
+     ('Fri Jul 07 19:38:00 1978'::timestamp without time zone AT LOCAL) AS t_at_local,       +
+     timezone('Fri Jul 07 19:38:00 1978'::timestamp without time zone) AS t_func;
+(1 row)
+
+\x
+TABLE timestamp_local_view;
+-[ RECORD 1 ]+-----------------------------
+ttz_at_local | Fri Jul 07 23:38:00 1978
+ttz_func     | Fri Jul 07 23:38:00 1978
+t_at_local   | Fri Jul 07 19:38:00 1978 UTC
+t_func       | Fri Jul 07 19:38:00 1978 UTC
+
+\x
+DROP VIEW timestamp_local_view;
+COMMIT;
 --
 -- Test that AT TIME ZONE isn't misoptimized when using an index (bug #14504)
 --

src/test/regress/expected/timetz.out

@@ -262,3 +262,45 @@ SELECT date_part('epoch',       TIME WITH TIME ZONE '2020-05-26 13:30:25.575401-
  63025.575401
 (1 row)
 
+--
+-- AT LOCAL with timetz
+--
+BEGIN;
+SET LOCAL TimeZone TO 'UTC';
+CREATE VIEW timetz_local_view AS
+  SELECT f1 AS dat,
+       timezone(f1) AS dat_func,
+       f1 AT LOCAL AS dat_at_local,
+       f1 AT TIME ZONE current_setting('TimeZone') AS dat_at_time
+  FROM TIMETZ_TBL
+  ORDER BY f1;
+SELECT pg_get_viewdef('timetz_local_view', true);
+                             pg_get_viewdef                             
+------------------------------------------------------------------------
+  SELECT f1 AS dat,                                                    +
+     timezone(f1) AS dat_func,                                         +
+     (f1 AT LOCAL) AS dat_at_local,                                    +
+     (f1 AT TIME ZONE current_setting('TimeZone'::text)) AS dat_at_time+
+    FROM timetz_tbl                                                    +
+   ORDER BY f1;
+(1 row)
+
+TABLE timetz_local_view;
+      dat       |    dat_func    |  dat_at_local  |  dat_at_time   
+----------------+----------------+----------------+----------------
+ 00:01:00-07    | 07:01:00+00    | 07:01:00+00    | 07:01:00+00
+ 01:00:00-07    | 08:00:00+00    | 08:00:00+00    | 08:00:00+00
+ 02:03:00-07    | 09:03:00+00    | 09:03:00+00    | 09:03:00+00
+ 08:08:00-04    | 12:08:00+00    | 12:08:00+00    | 12:08:00+00
+ 07:07:00-08    | 15:07:00+00    | 15:07:00+00    | 15:07:00+00
+ 11:59:00-07    | 18:59:00+00    | 18:59:00+00    | 18:59:00+00
+ 12:00:00-07    | 19:00:00+00    | 19:00:00+00    | 19:00:00+00
+ 12:01:00-07    | 19:01:00+00    | 19:01:00+00    | 19:01:00+00
+ 15:36:39-04    | 19:36:39+00    | 19:36:39+00    | 19:36:39+00
+ 15:36:39-05    | 20:36:39+00    | 20:36:39+00    | 20:36:39+00
+ 23:59:00-07    | 06:59:00+00    | 06:59:00+00    | 06:59:00+00
+ 23:59:59.99-07 | 06:59:59.99+00 | 06:59:59.99+00 | 06:59:59.99+00
+(12 rows)
+
+DROP VIEW timetz_local_view;
+COMMIT;