Improve handling of date_trunc() units for infinite input values

Previously, if an infinite value was passed to date_trunc(), then the
same infinite value would always be returned regardless of the field
unit given by the caller.  This commit updates the function so that an
error is returned when an invalid unit is passed to date_trunc() with an
infinite value.

This matches the behavior of date_trunc() with a finite value and
date_part() with an infinite value, making the handling of interval,
timestamp and timestamptz more consistent across the board for these two
functions.

Some tests are added to cover all these new failure cases, with an
unsupported unit and infinite values for the three data types.  There
were no test cases in core that checked all these patterns up to now.

Author: Joseph Koshakow
Discussion: https://postgr.es/m/CAAvxfHc4084dGzEJR0_pBZkDuqbPGc5wn7gK_M0XR_kRiCdUJQ@mail.gmail.com

src/backend/utils/adt/timestamp.c

@@ -4620,9 +4620,6 @@ timestamp_trunc(PG_FUNCTION_ARGS)
 	struct pg_tm tt,
 			   *tm = &tt;
 
-	if (TIMESTAMP_NOT_FINITE(timestamp))
-		PG_RETURN_TIMESTAMP(timestamp);
-
 	lowunits = downcase_truncate_identifier(VARDATA_ANY(units),
 											VARSIZE_ANY_EXHDR(units),
 											false);
@@ -4631,6 +4628,39 @@ timestamp_trunc(PG_FUNCTION_ARGS)
 
 	if (type == UNITS)
 	{
+		if (TIMESTAMP_NOT_FINITE(timestamp))
+		{
+			/*
+			 * Errors thrown here for invalid units should exactly match those
+			 * below, else there will be unexpected discrepancies between
+			 * finite- and infinite-input cases.
+			 */
+			switch (val)
+			{
+				case DTK_WEEK:
+				case DTK_MILLENNIUM:
+				case DTK_CENTURY:
+				case DTK_DECADE:
+				case DTK_YEAR:
+				case DTK_QUARTER:
+				case DTK_MONTH:
+				case DTK_DAY:
+				case DTK_HOUR:
+				case DTK_MINUTE:
+				case DTK_SECOND:
+				case DTK_MILLISEC:
+				case DTK_MICROSEC:
+					PG_RETURN_TIMESTAMP(timestamp);
+					break;
+				default:
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("unit \"%s\" not supported for type %s",
+									lowunits, format_type_be(TIMESTAMPOID))));
+					result = 0;
+			}
+		}
+
 		if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
 			ereport(ERROR,
 					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
@@ -4836,6 +4866,40 @@ timestamptz_trunc_internal(text *units, TimestampTz timestamp, pg_tz *tzp)
 
 	if (type == UNITS)
 	{
+		if (TIMESTAMP_NOT_FINITE(timestamp))
+		{
+			/*
+			 * Errors thrown here for invalid units should exactly match those
+			 * below, else there will be unexpected discrepancies between
+			 * finite- and infinite-input cases.
+			 */
+			switch (val)
+			{
+				case DTK_WEEK:
+				case DTK_MILLENNIUM:
+				case DTK_CENTURY:
+				case DTK_DECADE:
+				case DTK_YEAR:
+				case DTK_QUARTER:
+				case DTK_MONTH:
+				case DTK_DAY:
+				case DTK_HOUR:
+				case DTK_MINUTE:
+				case DTK_SECOND:
+				case DTK_MILLISEC:
+				case DTK_MICROSEC:
+					PG_RETURN_TIMESTAMPTZ(timestamp);
+					break;
+
+				default:
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("unit \"%s\" not supported for type %s",
+									lowunits, format_type_be(TIMESTAMPTZOID))));
+					result = 0;
+			}
+		}
+
 		if (timestamp2tm(timestamp, &tz, tm, &fsec, NULL, tzp) != 0)
 			ereport(ERROR,
 					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
@@ -4966,9 +5030,6 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
 	TimestampTz timestamp = PG_GETARG_TIMESTAMPTZ(1);
 	TimestampTz result;
 
-	if (TIMESTAMP_NOT_FINITE(timestamp))
-		PG_RETURN_TIMESTAMPTZ(timestamp);
-
 	result = timestamptz_trunc_internal(units, timestamp, session_timezone);
 
 	PG_RETURN_TIMESTAMPTZ(result);
@@ -4986,13 +5047,6 @@ timestamptz_trunc_zone(PG_FUNCTION_ARGS)
 	TimestampTz result;
 	pg_tz	   *tzp;
 
-	/*
-	 * timestamptz_zone() doesn't look up the zone for infinite inputs, so we
-	 * don't do so here either.
-	 */
-	if (TIMESTAMP_NOT_FINITE(timestamp))
-		PG_RETURN_TIMESTAMP(timestamp);
-
 	/*
 	 * Look up the requested timezone.
 	 */
@@ -5020,12 +5074,6 @@ interval_trunc(PG_FUNCTION_ARGS)
 
 	result = (Interval *) palloc(sizeof(Interval));
 
-	if (INTERVAL_NOT_FINITE(interval))
-	{
-		memcpy(result, interval, sizeof(Interval));
-		PG_RETURN_INTERVAL_P(result);
-	}
-
 	lowunits = downcase_truncate_identifier(VARDATA_ANY(units),
 											VARSIZE_ANY_EXHDR(units),
 											false);
@@ -5034,6 +5082,41 @@ interval_trunc(PG_FUNCTION_ARGS)
 
 	if (type == UNITS)
 	{
+		if (INTERVAL_NOT_FINITE(interval))
+		{
+			/*
+			 * Errors thrown here for invalid units should exactly match those
+			 * below, else there will be unexpected discrepancies between
+			 * finite- and infinite-input cases.
+			 */
+			switch (val)
+			{
+				case DTK_MILLENNIUM:
+				case DTK_CENTURY:
+				case DTK_DECADE:
+				case DTK_YEAR:
+				case DTK_QUARTER:
+				case DTK_MONTH:
+				case DTK_DAY:
+				case DTK_HOUR:
+				case DTK_MINUTE:
+				case DTK_SECOND:
+				case DTK_MILLISEC:
+				case DTK_MICROSEC:
+					memcpy(result, interval, sizeof(Interval));
+					PG_RETURN_INTERVAL_P(result);
+					break;
+
+				default:
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("unit \"%s\" not supported for type %s",
+									lowunits, format_type_be(INTERVALOID)),
+							 (val == DTK_WEEK) ? errdetail("Months usually have fractional weeks.") : 0));
+					result = 0;
+			}
+		}
+
 		interval2itm(*interval, tm);
 		switch (val)
 		{

src/test/regress/expected/interval.out

@@ -2219,6 +2219,15 @@ SELECT i AS interval, date_trunc('hour', i)
  -infinity | -infinity
 (2 rows)
 
+SELECT i AS interval, date_trunc('week', i)
+    FROM INFINITE_INTERVAL_TBL
+    WHERE NOT isfinite(i);
+ERROR:  unit "week" not supported for type interval
+DETAIL:  Months usually have fractional weeks.
+SELECT i AS interval, date_trunc('ago', i)
+    FROM INFINITE_INTERVAL_TBL
+    WHERE NOT isfinite(i);
+ERROR:  unit "ago" not recognized for type interval
 SELECT i AS interval, justify_days(i), justify_hours(i), justify_interval(i)
     FROM INFINITE_INTERVAL_TBL
     WHERE NOT isfinite(i);

src/test/regress/expected/timestamp.out

@@ -591,6 +591,8 @@ SELECT date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc
  Mon Feb 23 00:00:00 2004
 (1 row)
 
+SELECT date_trunc( 'ago', timestamp 'infinity' ) AS invalid_trunc;
+ERROR:  unit "ago" not recognized for type timestamp without time zone
 -- verify date_bin behaves the same as date_trunc for relevant intervals
 -- case 1: AD dates, origin < input
 SELECT

src/test/regress/expected/timestamptz.out

@@ -701,6 +701,8 @@ SELECT date_trunc( 'week', timestamp with time zone '2004-02-29 15:44:17.71393'
  Mon Feb 23 00:00:00 2004 PST
 (1 row)
 
+SELECT date_trunc( 'ago', timestamp with time zone 'infinity' ) AS invalid_trunc;
+ERROR:  unit "ago" not recognized for type timestamp with time zone
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'Australia/Sydney') as sydney_trunc;  -- zone name
          sydney_trunc         
 ------------------------------
@@ -719,6 +721,8 @@ SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'VET
  Thu Feb 15 20:00:00 2001 PST
 (1 row)
 
+SELECT date_trunc('ago', timestamp with time zone 'infinity', 'GMT') AS invalid_zone_trunc;
+ERROR:  unit "ago" not recognized for type timestamp with time zone
 -- verify date_bin behaves the same as date_trunc for relevant intervals
 SELECT
   str,

src/test/regress/sql/interval.sql

@@ -776,6 +776,14 @@ SELECT i AS interval, date_trunc('hour', i)
     FROM INFINITE_INTERVAL_TBL
     WHERE NOT isfinite(i);
 
+SELECT i AS interval, date_trunc('week', i)
+    FROM INFINITE_INTERVAL_TBL
+    WHERE NOT isfinite(i);
+
+SELECT i AS interval, date_trunc('ago', i)
+    FROM INFINITE_INTERVAL_TBL
+    WHERE NOT isfinite(i);
+
 SELECT i AS interval, justify_days(i), justify_hours(i), justify_interval(i)
     FROM INFINITE_INTERVAL_TBL
     WHERE NOT isfinite(i);

src/test/regress/sql/timestamp.sql

@@ -176,6 +176,8 @@ SELECT d1 - timestamp without time zone '1997-01-02' AS diff
 
 SELECT date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc;
 
+SELECT date_trunc( 'ago', timestamp 'infinity' ) AS invalid_trunc;
+
 -- verify date_bin behaves the same as date_trunc for relevant intervals
 
 -- case 1: AD dates, origin < input

src/test/regress/sql/timestamptz.sql

@@ -200,10 +200,14 @@ SELECT d1 - timestamp with time zone '1997-01-02' AS diff
    FROM TIMESTAMPTZ_TBL WHERE d1 BETWEEN '1902-01-01' AND '2038-01-01';
 
 SELECT date_trunc( 'week', timestamp with time zone '2004-02-29 15:44:17.71393' ) AS week_trunc;
+SELECT date_trunc( 'ago', timestamp with time zone 'infinity' ) AS invalid_trunc;
 
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'Australia/Sydney') as sydney_trunc;  -- zone name
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'GMT') as gmt_trunc;  -- fixed-offset abbreviation
 SELECT date_trunc('day', timestamp with time zone '2001-02-16 20:38:40+00', 'VET') as vet_trunc;  -- variable-offset abbreviation
+SELECT date_trunc('ago', timestamp with time zone 'infinity', 'GMT') AS invalid_zone_trunc;
+
+
 
 -- verify date_bin behaves the same as date_trunc for relevant intervals
 SELECT