Revert "Disallow infinite endpoints in generate_series() for timestamps."

This reverts commit eafdf9de06e9b60168f5e47cedcfceecdc6d4b5f
and its back-branch counterparts.  Corey Huinker pointed out that
we'd discussed this exact change back in 2016 and rejected it,
on the grounds that there's at least one usage pattern with LIMIT
where an infinite endpoint can usefully be used.  Perhaps that
argument needs to be re-litigated, but there's no time left before
our back-branch releases.  To keep our options open, restore the
status quo ante; if we do end up deciding to change things, waiting
one more quarter won't hurt anything.

Rather than just doing a straight revert, I added a new test case
demonstrating the usage with LIMIT.  That'll at least remind us of
the issue if we forget again.

Discussion: https://postgr.es/m/3603504.1652068977@sss.pgh.pa.us
Discussion: https://postgr.es/m/CADkLM=dzw0Pvdqp5yWKxMd+VmNkAMhG=4ku7GnCZxebWnzmz3Q@mail.gmail.com

src/backend/utils/adt/timestamp.c

@@ -5757,20 +5757,6 @@ generate_series_timestamp(PG_FUNCTION_ARGS)
 		MemoryContext oldcontext;
 		Interval	interval_zero;
 
-		/* Reject infinities in start and stop values */
-		if (TIMESTAMP_IS_NOBEGIN(start) ||
-			TIMESTAMP_IS_NOEND(start))
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("start value cannot be infinity")));
-		if (TIMESTAMP_IS_NOBEGIN(finish) ||
-			TIMESTAMP_IS_NOEND(finish))
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("stop value cannot be infinity")));
-
-		/* Interval doesn't (currently) have infinity, so nothing to check */
-
 		/* create a function context for cross-call persistence */
 		funcctx = SRF_FIRSTCALL_INIT();
 
@@ -5851,20 +5837,6 @@ generate_series_timestamptz(PG_FUNCTION_ARGS)
 		MemoryContext oldcontext;
 		Interval	interval_zero;
 
-		/* Reject infinities in start and stop values */
-		if (TIMESTAMP_IS_NOBEGIN(start) ||
-			TIMESTAMP_IS_NOEND(start))
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("start value cannot be infinity")));
-		if (TIMESTAMP_IS_NOBEGIN(finish) ||
-			TIMESTAMP_IS_NOEND(finish))
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("stop value cannot be infinity")));
-
-		/* Interval doesn't (currently) have infinity, so nothing to check */
-
 		/* create a function context for cross-call persistence */
 		funcctx = SRF_FIRSTCALL_INIT();
 

src/test/regress/expected/timestamp.out

@@ -2055,15 +2055,26 @@ select * from generate_series('2020-01-01 00:00'::timestamp,
  Thu Jan 02 03:00:00 2020
 (28 rows)
 
+-- the LIMIT should allow this to terminate in a reasonable amount of time
+-- (but that unfortunately doesn't work yet for SELECT * FROM ...)
+select generate_series('2022-01-01 00:00'::timestamp,
+                       'infinity'::timestamp,
+                       '1 month'::interval) limit 10;
+     generate_series      
+--------------------------
+ Sat Jan 01 00:00:00 2022
+ Tue Feb 01 00:00:00 2022
+ Tue Mar 01 00:00:00 2022
+ Fri Apr 01 00:00:00 2022
+ Sun May 01 00:00:00 2022
+ Wed Jun 01 00:00:00 2022
+ Fri Jul 01 00:00:00 2022
+ Mon Aug 01 00:00:00 2022
+ Thu Sep 01 00:00:00 2022
+ Sat Oct 01 00:00:00 2022
+(10 rows)
+
 -- errors
-select * from generate_series('-infinity'::timestamp,
-                              '2020-01-02 03:00'::timestamp,
-                              '1 hour'::interval);
-ERROR:  start value cannot be infinity
-select * from generate_series('2020-01-01 00:00'::timestamp,
-                              'infinity'::timestamp,
-                              '1 hour'::interval);
-ERROR:  stop value cannot be infinity
 select * from generate_series('2020-01-01 00:00'::timestamp,
                               '2020-01-02 03:00'::timestamp,
                               '0 hour'::interval);

src/test/regress/expected/timestamptz.out

@@ -2333,15 +2333,26 @@ select * from generate_series('2020-01-01 00:00'::timestamptz,
  Thu Jan 02 03:00:00 2020 PST
 (28 rows)
 
+-- the LIMIT should allow this to terminate in a reasonable amount of time
+-- (but that unfortunately doesn't work yet for SELECT * FROM ...)
+select generate_series('2022-01-01 00:00'::timestamptz,
+                       'infinity'::timestamptz,
+                       '1 month'::interval) limit 10;
+       generate_series        
+------------------------------
+ Sat Jan 01 00:00:00 2022 PST
+ Tue Feb 01 00:00:00 2022 PST
+ Tue Mar 01 00:00:00 2022 PST
+ Fri Apr 01 00:00:00 2022 PDT
+ Sun May 01 00:00:00 2022 PDT
+ Wed Jun 01 00:00:00 2022 PDT
+ Fri Jul 01 00:00:00 2022 PDT
+ Mon Aug 01 00:00:00 2022 PDT
+ Thu Sep 01 00:00:00 2022 PDT
+ Sat Oct 01 00:00:00 2022 PDT
+(10 rows)
+
 -- errors
-select * from generate_series('-infinity'::timestamptz,
-                              '2020-01-02 03:00'::timestamptz,
-                              '1 hour'::interval);
-ERROR:  start value cannot be infinity
-select * from generate_series('2020-01-01 00:00'::timestamptz,
-                              'infinity'::timestamptz,
-                              '1 hour'::interval);
-ERROR:  stop value cannot be infinity
 select * from generate_series('2020-01-01 00:00'::timestamptz,
                               '2020-01-02 03:00'::timestamptz,
                               '0 hour'::interval);

src/test/regress/sql/timestamp.sql

@@ -375,13 +375,12 @@ select make_timestamp(0, 7, 15, 12, 30, 15);
 select * from generate_series('2020-01-01 00:00'::timestamp,
                               '2020-01-02 03:00'::timestamp,
                               '1 hour'::interval);
+-- the LIMIT should allow this to terminate in a reasonable amount of time
+-- (but that unfortunately doesn't work yet for SELECT * FROM ...)
+select generate_series('2022-01-01 00:00'::timestamp,
+                       'infinity'::timestamp,
+                       '1 month'::interval) limit 10;
 -- errors
-select * from generate_series('-infinity'::timestamp,
-                              '2020-01-02 03:00'::timestamp,
-                              '1 hour'::interval);
-select * from generate_series('2020-01-01 00:00'::timestamp,
-                              'infinity'::timestamp,
-                              '1 hour'::interval);
 select * from generate_series('2020-01-01 00:00'::timestamp,
                               '2020-01-02 03:00'::timestamp,
                               '0 hour'::interval);

src/test/regress/sql/timestamptz.sql

@@ -414,13 +414,12 @@ RESET TimeZone;
 select * from generate_series('2020-01-01 00:00'::timestamptz,
                               '2020-01-02 03:00'::timestamptz,
                               '1 hour'::interval);
+-- the LIMIT should allow this to terminate in a reasonable amount of time
+-- (but that unfortunately doesn't work yet for SELECT * FROM ...)
+select generate_series('2022-01-01 00:00'::timestamptz,
+                       'infinity'::timestamptz,
+                       '1 month'::interval) limit 10;
 -- errors
-select * from generate_series('-infinity'::timestamptz,
-                              '2020-01-02 03:00'::timestamptz,
-                              '1 hour'::interval);
-select * from generate_series('2020-01-01 00:00'::timestamptz,
-                              'infinity'::timestamptz,
-                              '1 hour'::interval);
 select * from generate_series('2020-01-01 00:00'::timestamptz,
                               '2020-01-02 03:00'::timestamptz,
                               '0 hour'::interval);