Refactor datetime functions' timezone lookup code to reduce duplication.

We already had five copies of essentially the same logic, and an
upcoming patch introduces yet another use-case.  That's past my
threshold of pain, so introduce a common subroutine.  There's not
that much net code savings, but the chance of typos should go down.

Inspired by a patch from Przemysław Sztoch, but different in detail.

Discussion: https://postgr.es/m/01a84551-48dd-1359-bf7e-f6b0203a6bd0@sztoch.pl

4 files changed, 142 insertions, 180 deletions

diff --git a/src/backend/utils/adt/date.c b/src/backend/utils/adt/date.c
index 99171d9c928..a163fbb4ab5 100644
--- a/src/backend/utils/adt/date.c
+++ b/src/backend/utils/adt/date.c
@@ -3052,38 +3052,23 @@ timetz_zone(PG_FUNCTION_ARGS)
 	TimeTzADT  *result;
 	int			tz;
 	char		tzname[TZ_STRLEN_MAX + 1];
-	char	   *lowzone;
-	int			dterr,
-				type,
+	int			type,
 				val;
 	pg_tz	   *tzp;
-	DateTimeErrorExtra extra;
 
 	/*
-	 * Look up the requested timezone.  First we look in the timezone
-	 * abbreviation table (to handle cases like "EST"), and if that fails, we
-	 * look in the timezone database (to handle cases like
-	 * "America/New_York").  (This matches the order in which timestamp input
-	 * checks the cases; it's important because the timezone database unwisely
-	 * uses a few zone names that are identical to offset abbreviations.)
+	 * Look up the requested timezone.
 	 */
 	text_to_cstring_buffer(zone, tzname, sizeof(tzname));
 
-	/* DecodeTimezoneAbbrev requires lowercase input */
-	lowzone = downcase_truncate_identifier(tzname,
-										   strlen(tzname),
-										   false);
+	type = DecodeTimezoneName(tzname, &val, &tzp);
 
-	dterr = DecodeTimezoneAbbrev(0, lowzone, &type, &val, &tzp, &extra);
-	if (dterr)
-		DateTimeParseError(dterr, &extra, NULL, NULL, NULL);
-
-	if (type == TZ || type == DTZ)
+	if (type == TZNAME_FIXED_OFFSET)
 	{
 		/* fixed-offset abbreviation */
 		tz = -val;
 	}
-	else if (type == DYNTZ)
+	else if (type == TZNAME_DYNTZ)
 	{
 		/* dynamic-offset abbreviation, resolve using transaction start time */
 		TimestampTz now = GetCurrentTransactionStartTimestamp();
@@ -3093,27 +3078,15 @@ timetz_zone(PG_FUNCTION_ARGS)
 	}
 	else
 	{
-		/* try it as a full zone name */
-		tzp = pg_tzset(tzname);
-		if (tzp)
-		{
-			/* Get the offset-from-GMT that is valid now for the zone */
-			TimestampTz now = GetCurrentTransactionStartTimestamp();
-			struct pg_tm tm;
-			fsec_t		fsec;
+		/* Get the offset-from-GMT that is valid now for the zone name */
+		TimestampTz now = GetCurrentTransactionStartTimestamp();
+		struct pg_tm tm;
+		fsec_t		fsec;
 
-			if (timestamp2tm(now, &tz, &tm, &fsec, NULL, tzp) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-						 errmsg("timestamp out of range")));
-		}
-		else
-		{
+		if (timestamp2tm(now, &tz, &tm, &fsec, NULL, tzp) != 0)
 			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("time zone \"%s\" not recognized", tzname)));
-			tz = 0;				/* keep compiler quiet */
-		}
+					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+					 errmsg("timestamp out of range")));
 	}
 
 	result = (TimeTzADT *) palloc(sizeof(TimeTzADT));
diff --git a/src/backend/utils/adt/datetime.c b/src/backend/utils/adt/datetime.c
index 516ee9c154b..be2e55bb29f 100644
--- a/src/backend/utils/adt/datetime.c
+++ b/src/backend/utils/adt/datetime.c
@@ -26,6 +26,7 @@
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
+#include "parser/scansup.h"
 #include "utils/builtins.h"
 #include "utils/date.h"
 #include "utils/datetime.h"
@@ -3162,6 +3163,90 @@ DecodeSpecial(int field, const char *lowtoken, int *val)
 }
 
 
+/* DecodeTimezoneName()
+ * Interpret string as a timezone abbreviation or name.
+ * Throw error if the name is not recognized.
+ *
+ * The return value indicates what kind of zone identifier it is:
+ *	TZNAME_FIXED_OFFSET: fixed offset from UTC
+ *	TZNAME_DYNTZ: dynamic timezone abbreviation
+ *	TZNAME_ZONE: full tzdb zone name
+ *
+ * For TZNAME_FIXED_OFFSET, *offset receives the UTC offset (in seconds,
+ * with ISO sign convention: positive is east of Greenwich).
+ * For the other two cases, *tz receives the timezone struct representing
+ * the zone name or the abbreviation's underlying zone.
+ */
+int
+DecodeTimezoneName(const char *tzname, int *offset, pg_tz **tz)
+{
+	char	   *lowzone;
+	int			dterr,
+				type;
+	DateTimeErrorExtra extra;
+
+	/*
+	 * First we look in the timezone abbreviation table (to handle cases like
+	 * "EST"), and if that fails, we look in the timezone database (to handle
+	 * cases like "America/New_York").  This matches the order in which
+	 * timestamp input checks the cases; it's important because the timezone
+	 * database unwisely uses a few zone names that are identical to offset
+	 * abbreviations.
+	 */
+
+	/* DecodeTimezoneAbbrev requires lowercase input */
+	lowzone = downcase_truncate_identifier(tzname,
+										   strlen(tzname),
+										   false);
+
+	dterr = DecodeTimezoneAbbrev(0, lowzone, &type, offset, tz, &extra);
+	if (dterr)
+		DateTimeParseError(dterr, &extra, NULL, NULL, NULL);
+
+	if (type == TZ || type == DTZ)
+	{
+		/* fixed-offset abbreviation, return the offset */
+		return TZNAME_FIXED_OFFSET;
+	}
+	else if (type == DYNTZ)
+	{
+		/* dynamic-offset abbreviation, return its referenced timezone */
+		return TZNAME_DYNTZ;
+	}
+	else
+	{
+		/* try it as a full zone name */
+		*tz = pg_tzset(tzname);
+		if (*tz == NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("time zone \"%s\" not recognized", tzname)));
+		return TZNAME_ZONE;
+	}
+}
+
+/* DecodeTimezoneNameToTz()
+ * Interpret string as a timezone abbreviation or name.
+ * Throw error if the name is not recognized.
+ *
+ * This is a simple wrapper for DecodeTimezoneName that produces a pg_tz *
+ * result in all cases.
+ */
+pg_tz *
+DecodeTimezoneNameToTz(const char *tzname)
+{
+	pg_tz	   *result;
+	int			offset;
+
+	if (DecodeTimezoneName(tzname, &offset, &result) == TZNAME_FIXED_OFFSET)
+	{
+		/* fixed-offset abbreviation, get a pg_tz descriptor for that */
+		result = pg_tzset_offset(-offset);	/* flip to POSIX sign convention */
+	}
+	return result;
+}
+
+
 /* ClearPgItmIn
  *
  * Zero out a pg_itm_in
diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index de93db89d48..c266d0d02ed 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -479,12 +479,7 @@ parse_sane_timezone(struct pg_tm *tm, text *zone)
 	/*
 	 * Look up the requested timezone.  First we try to interpret it as a
 	 * numeric timezone specification; if DecodeTimezone decides it doesn't
-	 * like the format, we look in the timezone abbreviation table (to handle
-	 * cases like "EST"), and if that also fails, we look in the timezone
-	 * database (to handle cases like "America/New_York").  (This matches the
-	 * order in which timestamp input checks the cases; it's important because
-	 * the timezone database unwisely uses a few zone names that are identical
-	 * to offset abbreviations.)
+	 * like the format, we try timezone abbreviations and names.
 	 *
 	 * Note pg_tzset happily parses numeric input that DecodeTimezone would
 	 * reject.  To avoid having it accept input that would otherwise be seen
@@ -501,11 +496,9 @@ parse_sane_timezone(struct pg_tm *tm, text *zone)
 	dterr = DecodeTimezone(tzname, &tz);
 	if (dterr != 0)
 	{
-		char	   *lowzone;
 		int			type,
 					val;
 		pg_tz	   *tzp;
-		DateTimeErrorExtra extra;
 
 		if (dterr == DTERR_TZDISP_OVERFLOW)
 			ereport(ERROR,
@@ -516,34 +509,22 @@ parse_sane_timezone(struct pg_tm *tm, text *zone)
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("time zone \"%s\" not recognized", tzname)));
 
-		/* DecodeTimezoneAbbrev requires lowercase input */
-		lowzone = downcase_truncate_identifier(tzname,
-											   strlen(tzname),
-											   false);
-		dterr = DecodeTimezoneAbbrev(0, lowzone, &type, &val, &tzp, &extra);
-		if (dterr)
-			DateTimeParseError(dterr, &extra, NULL, NULL, NULL);
+		type = DecodeTimezoneName(tzname, &val, &tzp);
 
-		if (type == TZ || type == DTZ)
+		if (type == TZNAME_FIXED_OFFSET)
 		{
 			/* fixed-offset abbreviation */
 			tz = -val;
 		}
-		else if (type == DYNTZ)
+		else if (type == TZNAME_DYNTZ)
 		{
 			/* dynamic-offset abbreviation, resolve using specified time */
 			tz = DetermineTimeZoneAbbrevOffset(tm, tzname, tzp);
 		}
 		else
 		{
-			/* try it as a full zone name */
-			tzp = pg_tzset(tzname);
-			if (tzp)
-				tz = DetermineTimeZoneOffset(tm, tzp);
-			else
-				ereport(ERROR,
-						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-						 errmsg("time zone \"%s\" not recognized", tzname)));
+			/* full zone name */
+			tz = DetermineTimeZoneOffset(tm, tzp);
 		}
 	}
 
@@ -4304,12 +4285,7 @@ timestamptz_trunc_zone(PG_FUNCTION_ARGS)
 	text	   *zone = PG_GETARG_TEXT_PP(2);
 	TimestampTz result;
 	char		tzname[TZ_STRLEN_MAX + 1];
-	char	   *lowzone;
-	int			dterr,
-				type,
-				val;
 	pg_tz	   *tzp;
-	DateTimeErrorExtra extra;
 
 	/*
 	 * timestamptz_zone() doesn't look up the zone for infinite inputs, so we
@@ -4319,37 +4295,11 @@ timestamptz_trunc_zone(PG_FUNCTION_ARGS)
 		PG_RETURN_TIMESTAMP(timestamp);
 
 	/*
-	 * Look up the requested timezone (see notes in timestamptz_zone()).
+	 * Look up the requested timezone.
 	 */
 	text_to_cstring_buffer(zone, tzname, sizeof(tzname));
 
-	/* DecodeTimezoneAbbrev requires lowercase input */
-	lowzone = downcase_truncate_identifier(tzname,
-										   strlen(tzname),
-										   false);
-
-	dterr = DecodeTimezoneAbbrev(0, lowzone, &type, &val, &tzp, &extra);
-	if (dterr)
-		DateTimeParseError(dterr, &extra, NULL, NULL, NULL);
-
-	if (type == TZ || type == DTZ)
-	{
-		/* fixed-offset abbreviation, get a pg_tz descriptor for that */
-		tzp = pg_tzset_offset(-val);
-	}
-	else if (type == DYNTZ)
-	{
-		/* dynamic-offset abbreviation, use its referenced timezone */
-	}
-	else
-	{
-		/* try it as a full zone name */
-		tzp = pg_tzset(tzname);
-		if (!tzp)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("time zone \"%s\" not recognized", tzname)));
-	}
+	tzp = DecodeTimezoneNameToTz(tzname);
 
 	result = timestamptz_trunc_internal(units, timestamp, tzp);
 
@@ -5429,12 +5379,9 @@ timestamp_zone(PG_FUNCTION_ARGS)
 	TimestampTz result;
 	int			tz;
 	char		tzname[TZ_STRLEN_MAX + 1];
-	char	   *lowzone;
-	int			dterr,
-				type,
+	int			type,
 				val;
 	pg_tz	   *tzp;
-	DateTimeErrorExtra extra;
 	struct pg_tm tm;
 	fsec_t		fsec;
 
@@ -5442,31 +5389,19 @@ timestamp_zone(PG_FUNCTION_ARGS)
 		PG_RETURN_TIMESTAMPTZ(timestamp);
 
 	/*
-	 * Look up the requested timezone.  First we look in the timezone
-	 * abbreviation table (to handle cases like "EST"), and if that fails, we
-	 * look in the timezone database (to handle cases like
-	 * "America/New_York").  (This matches the order in which timestamp input
-	 * checks the cases; it's important because the timezone database unwisely
-	 * uses a few zone names that are identical to offset abbreviations.)
+	 * Look up the requested timezone.
 	 */
 	text_to_cstring_buffer(zone, tzname, sizeof(tzname));
 
-	/* DecodeTimezoneAbbrev requires lowercase input */
-	lowzone = downcase_truncate_identifier(tzname,
-										   strlen(tzname),
-										   false);
+	type = DecodeTimezoneName(tzname, &val, &tzp);
 
-	dterr = DecodeTimezoneAbbrev(0, lowzone, &type, &val, &tzp, &extra);
-	if (dterr)
-		DateTimeParseError(dterr, &extra, NULL, NULL, NULL);
-
-	if (type == TZ || type == DTZ)
+	if (type == TZNAME_FIXED_OFFSET)
 	{
 		/* fixed-offset abbreviation */
 		tz = val;
 		result = dt2local(timestamp, tz);
 	}
-	else if (type == DYNTZ)
+	else if (type == TZNAME_DYNTZ)
 	{
 		/* dynamic-offset abbreviation, resolve using specified time */
 		if (timestamp2tm(timestamp, NULL, &tm, &fsec, NULL, tzp) != 0)
@@ -5478,28 +5413,16 @@ timestamp_zone(PG_FUNCTION_ARGS)
 	}
 	else
 	{
-		/* try it as a full zone name */
-		tzp = pg_tzset(tzname);
-		if (tzp)
-		{
-			/* Apply the timezone change */
-			if (timestamp2tm(timestamp, NULL, &tm, &fsec, NULL, tzp) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-						 errmsg("timestamp out of range")));
-			tz = DetermineTimeZoneOffset(&tm, tzp);
-			if (tm2timestamp(&tm, fsec, &tz, &result) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-						 errmsg("timestamp out of range")));
-		}
-		else
-		{
+		/* full zone name, rotate to that zone */
+		if (timestamp2tm(timestamp, NULL, &tm, &fsec, NULL, tzp) != 0)
 			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("time zone \"%s\" not recognized", tzname)));
-			result = 0;			/* keep compiler quiet */
-		}
+					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+					 errmsg("timestamp out of range")));
+		tz = DetermineTimeZoneOffset(&tm, tzp);
+		if (tm2timestamp(&tm, fsec, &tz, &result) != 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+					 errmsg("timestamp out of range")));
 	}
 
 	if (!IS_VALID_TIMESTAMP(result))
@@ -5687,42 +5610,27 @@ timestamptz_zone(PG_FUNCTION_ARGS)
 	Timestamp	result;
 	int			tz;
 	char		tzname[TZ_STRLEN_MAX + 1];
-	char	   *lowzone;
-	int			dterr,
-				type,
+	int			type,
 				val;
 	pg_tz	   *tzp;
-	DateTimeErrorExtra extra;
 
 	if (TIMESTAMP_NOT_FINITE(timestamp))
 		PG_RETURN_TIMESTAMP(timestamp);
 
 	/*
-	 * Look up the requested timezone.  First we look in the timezone
-	 * abbreviation table (to handle cases like "EST"), and if that fails, we
-	 * look in the timezone database (to handle cases like
-	 * "America/New_York").  (This matches the order in which timestamp input
-	 * checks the cases; it's important because the timezone database unwisely
-	 * uses a few zone names that are identical to offset abbreviations.)
+	 * Look up the requested timezone.
 	 */
 	text_to_cstring_buffer(zone, tzname, sizeof(tzname));
 
-	/* DecodeTimezoneAbbrev requires lowercase input */
-	lowzone = downcase_truncate_identifier(tzname,
-										   strlen(tzname),
-										   false);
-
-	dterr = DecodeTimezoneAbbrev(0, lowzone, &type, &val, &tzp, &extra);
-	if (dterr)
-		DateTimeParseError(dterr, &extra, NULL, NULL, NULL);
+	type = DecodeTimezoneName(tzname, &val, &tzp);
 
-	if (type == TZ || type == DTZ)
+	if (type == TZNAME_FIXED_OFFSET)
 	{
 		/* fixed-offset abbreviation */
 		tz = -val;
 		result = dt2local(timestamp, tz);
 	}
-	else if (type == DYNTZ)
+	else if (type == TZNAME_DYNTZ)
 	{
 		/* dynamic-offset abbreviation, resolve using specified time */
 		int			isdst;
@@ -5732,30 +5640,18 @@ timestamptz_zone(PG_FUNCTION_ARGS)
 	}
 	else
 	{
-		/* try it as a full zone name */
-		tzp = pg_tzset(tzname);
-		if (tzp)
-		{
-			/* Apply the timezone change */
-			struct pg_tm tm;
-			fsec_t		fsec;
+		/* full zone name, rotate from that zone */
+		struct pg_tm tm;
+		fsec_t		fsec;
 
-			if (timestamp2tm(timestamp, &tz, &tm, &fsec, NULL, tzp) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-						 errmsg("timestamp out of range")));
-			if (tm2timestamp(&tm, fsec, NULL, &result) != 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-						 errmsg("timestamp out of range")));
-		}
-		else
-		{
+		if (timestamp2tm(timestamp, &tz, &tm, &fsec, NULL, tzp) != 0)
 			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("time zone \"%s\" not recognized", tzname)));
-			result = 0;			/* keep compiler quiet */
-		}
+					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+					 errmsg("timestamp out of range")));
+		if (tm2timestamp(&tm, fsec, NULL, &result) != 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+					 errmsg("timestamp out of range")));
 	}
 
 	if (!IS_VALID_TIMESTAMP(result))
diff --git a/src/include/utils/datetime.h b/src/include/utils/datetime.h
index c8f78a9f1ec..a871e3223de 100644
--- a/src/include/utils/datetime.h
+++ b/src/include/utils/datetime.h
@@ -295,6 +295,11 @@ typedef struct DateTimeErrorExtra
 	const char *dtee_abbrev;	/* relevant time zone abbreviation */
 } DateTimeErrorExtra;
 
+/* Result codes for DecodeTimezoneName() */
+#define TZNAME_FIXED_OFFSET	0
+#define TZNAME_DYNTZ		1
+#define TZNAME_ZONE			2
+
 
 extern void GetCurrentDateTime(struct pg_tm *tm);
 extern void GetCurrentTimeUsec(struct pg_tm *tm, fsec_t *fsec, int *tzp);
@@ -340,6 +345,9 @@ extern int	DecodeTimezoneAbbrev(int field, const char *lowtoken,
 extern int	DecodeSpecial(int field, const char *lowtoken, int *val);
 extern int	DecodeUnits(int field, const char *lowtoken, int *val);
 
+extern int	DecodeTimezoneName(const char *tzname, int *offset, pg_tz **tz);
+extern pg_tz *DecodeTimezoneNameToTz(const char *tzname);
+
 extern int	j2day(int date);
 
 extern struct Node *TemporalSimplify(int32 max_precis, struct Node *node);