Support timezone abbreviations that sometimes change.

Up to now, PG has assumed that any given timezone abbreviation (such as
"EDT") represents a constant GMT offset in the usage of any particular
region; we had a way to configure what that offset was, but not for it
to be changeable over time.  But, as with most things horological, this
view of the world is too simplistic: there are numerous regions that have
at one time or another switched to a different GMT offset but kept using
the same timezone abbreviation.  Almost the entire Russian Federation did
that a few years ago, and later this month they're going to do it again.
And there are similar examples all over the world.

To cope with this, invent the notion of a "dynamic timezone abbreviation",
which is one that is referenced to a particular underlying timezone
(as defined in the IANA timezone database) and means whatever it currently
means in that zone.  For zones that use or have used daylight-savings time,
the standard and DST abbreviations continue to have the property that you
can specify standard or DST time and get that time offset whether or not
DST was theoretically in effect at the time.  However, the abbreviations
mean what they meant at the time in question (or most recently before that
time) rather than being absolutely fixed.

The standard abbreviation-list files have been changed to use this behavior
for abbreviations that have actually varied in meaning since 1970.  The
old simple-numeric definitions are kept for abbreviations that have not
changed, since they are a bit faster to resolve.

While this is clearly a new feature, it seems necessary to back-patch it
into all active branches, because otherwise use of Russian zone
abbreviations is going to become even more problematic than it already was.
This change supersedes the changes in commit 513d06ded et al to modify the
fixed meanings of the Russian abbreviations; since we've not shipped that
yet, this will avoid an undesirably incompatible (not to mention incorrect)
change in behavior for timestamps between 2011 and 2014.

This patch makes some cosmetic changes in ecpglib to keep its usage of
datetime lookup tables as similar as possible to the backend code, but
doesn't do anything about the increasingly obsolete set of timezone
abbreviation definitions that are hard-wired into ecpglib.  Whatever we
do about that will likely not be appropriate material for back-patching.
Also, a potential free() of a garbage pointer after an out-of-memory
failure in ecpglib has been fixed.

This patch also fixes pre-existing bugs in DetermineTimeZoneOffset() that
caused it to produce unexpected results near a timezone transition, if
both the "before" and "after" states are marked as standard time.  We'd
only ever thought about or tested transitions between standard and DST
time, but that's not what's happening when a zone simply redefines their
base GMT offset.

In passing, update the SGML documentation to refer to the Olson/zoneinfo/
zic timezone database as the "IANA" database, since it's now being
maintained under the auspices of IANA.

3 files changed, 50 insertions, 21 deletions

diff --git a/src/include/pgtime.h b/src/include/pgtime.h
index b3c867a4cf8..a85bc2781b5 100644
--- a/src/include/pgtime.h
+++ b/src/include/pgtime.h
@@ -54,13 +54,20 @@ extern int pg_next_dst_boundary(const pg_time_t *timep,
 					 long int *after_gmtoff,
 					 int *after_isdst,
 					 const pg_tz *tz);
-extern size_t pg_strftime(char *s, size_t max, const char *format,
-			const struct pg_tm * tm);
-
+extern bool pg_interpret_timezone_abbrev(const char *abbrev,
+							 const pg_time_t *timep,
+							 long int *gmtoff,
+							 int *isdst,
+							 const pg_tz *tz);
 extern bool pg_get_timezone_offset(const pg_tz *tz, long int *gmtoff);
 extern const char *pg_get_timezone_name(pg_tz *tz);
 extern bool pg_tz_acceptable(pg_tz *tz);
 
+/* these functions are in strftime.c */
+
+extern size_t pg_strftime(char *s, size_t max, const char *format,
+			const struct pg_tm * tm);
+
 /* these functions and variables are in pgtz.c */
 
 extern pg_tz *session_timezone;
diff --git a/src/include/utils/datetime.h b/src/include/utils/datetime.h
index 2e69503f96d..9b53ee38ccf 100644
--- a/src/include/utils/datetime.h
+++ b/src/include/utils/datetime.h
@@ -77,7 +77,7 @@ struct tzEntry;
 #define BC		1
 
 /*
- * Fields for time decoding.
+ * Field types for time decoding.
  *
  * Can't have more of these than there are bits in an unsigned int
  * since these are turned into bit masks during parsing and decoding.
@@ -93,9 +93,9 @@ struct tzEntry;
 #define YEAR	2
 #define DAY		3
 #define JULIAN	4
-#define TZ		5
-#define DTZ		6
-#define DTZMOD	7
+#define TZ		5				/* fixed-offset timezone abbreviation */
+#define DTZ		6				/* fixed-offset timezone abbrev, DST */
+#define DYNTZ	7				/* dynamic timezone abbreviation */
 #define IGNORE_DTF	8
 #define AMPM	9
 #define HOUR	10
@@ -119,18 +119,24 @@ struct tzEntry;
 #define DECADE		25
 #define CENTURY		26
 #define MILLENNIUM	27
+/* hack for parsing two-word timezone specs "MET DST" etc */
+#define DTZMOD	28				/* "DST" as a separate word */
 /* reserved for unrecognized string values */
 #define UNKNOWN_FIELD	31
 
 /*
  * Token field definitions for time parsing and decoding.
- * These need to fit into the datetkn table type.
- * At the moment, that means keep them within [-127,127].
- * These are also used for bit masks in DecodeDateDelta()
+ *
+ * Some field type codes (see above) use these as the "value" in datetktbl[].
+ * These are also used for bit masks in DecodeDateTime and friends
  *	so actually restrict them to within [0,31] for now.
  * - thomas 97/06/19
- * Not all of these fields are used for masks in DecodeDateDelta
+ * Not all of these fields are used for masks in DecodeDateTime
  *	so allow some larger than 31. - thomas 1997-11-17
+ *
+ * Caution: there are undocumented assumptions in the code that most of these
+ * values are not equal to IGNORE_DTF nor RESERV.  Be very careful when
+ * renumbering values in either of these apparently-independent lists :-(
  */
 
 #define DTK_NUMBER		0
@@ -203,18 +209,27 @@ struct tzEntry;
 /* keep this struct small; it gets used a lot */
 typedef struct
 {
-	char		token[TOKMAXLEN];
-	char		type;
-	char		value;			/* this may be unsigned, alas */
+	char		token[TOKMAXLEN + 1];	/* always NUL-terminated */
+	char		type;			/* see field type codes above */
+	int32		value;			/* meaning depends on type */
 } datetkn;
 
 /* one of its uses is in tables of time zone abbreviations */
 typedef struct TimeZoneAbbrevTable
 {
-	int			numabbrevs;
+	Size		tblsize;		/* size in bytes of TimeZoneAbbrevTable */
+	int			numabbrevs;		/* number of entries in abbrevs[] array */
 	datetkn		abbrevs[1];		/* VARIABLE LENGTH ARRAY */
+	/* DynamicZoneAbbrev(s) may follow the abbrevs[] array */
 } TimeZoneAbbrevTable;
 
+/* auxiliary data for a dynamic time zone abbreviation (non-fixed-offset) */
+typedef struct DynamicZoneAbbrev
+{
+	pg_tz	   *tz;				/* NULL if not yet looked up */
+	char		zone[1];		/* zone name (var length, NUL-terminated) */
+} DynamicZoneAbbrev;
+
 
 /* FMODULO()
  * Macro to replace modf(), which is broken on some platforms.
@@ -296,6 +311,9 @@ extern void DateTimeParseError(int dterr, const char *str,
 				   const char *datatype) __attribute__((noreturn));
 
 extern int	DetermineTimeZoneOffset(struct pg_tm * tm, pg_tz *tzp);
+extern int	DetermineTimeZoneAbbrevOffset(struct pg_tm * tm, const char *abbr, pg_tz *tzp);
+extern int DetermineTimeZoneAbbrevOffsetTS(TimestampTz ts, const char *abbr,
+								pg_tz *tzp, int *isdst);
 
 extern void EncodeDateOnly(struct pg_tm * tm, int style, char *str);
 extern void EncodeTimeOnly(struct pg_tm * tm, fsec_t fsec, bool print_tz, int tz, int style, char *str);
@@ -305,6 +323,8 @@ extern void EncodeInterval(struct pg_tm * tm, fsec_t fsec, int style, char *str)
 extern int ValidateDate(int fmask, bool isjulian, bool is2digits, bool bc,
 			 struct pg_tm * tm);
 
+extern int DecodeTimezoneAbbrev(int field, char *lowtoken,
+					 int *offset, pg_tz **tz);
 extern int	DecodeSpecial(int field, char *lowtoken, int *val);
 extern int	DecodeUnits(int field, char *lowtoken, int *val);
 
@@ -314,8 +334,8 @@ extern Node *TemporalTransform(int32 max_precis, Node *node);
 
 extern bool CheckDateTokenTables(void);
 
-extern void ConvertTimeZoneAbbrevs(TimeZoneAbbrevTable *tbl,
-					   struct tzEntry *abbrevs, int n);
+extern TimeZoneAbbrevTable *ConvertTimeZoneAbbrevs(struct tzEntry *abbrevs,
+					   int n);
 extern void InstallTimeZoneAbbrevs(TimeZoneAbbrevTable *tbl);
 
 extern Datum pg_timezone_abbrevs(PG_FUNCTION_ARGS);
diff --git a/src/include/utils/tzparser.h b/src/include/utils/tzparser.h
index 82728a67dd0..637f449e36c 100644
--- a/src/include/utils/tzparser.h
+++ b/src/include/utils/tzparser.h
@@ -22,10 +22,12 @@
  */
 typedef struct tzEntry
 {
-	/* the actual data: TZ abbrev (downcased), offset, DST flag */
-	char	   *abbrev;
-	int			offset;			/* in seconds from UTC */
-	bool		is_dst;
+	/* the actual data */
+	char	   *abbrev;			/* TZ abbreviation (downcased) */
+	char	   *zone;			/* zone name if dynamic abbrev, else NULL */
+	/* for a dynamic abbreviation, offset/is_dst are not used */
+	int			offset;			/* offset in seconds from UTC */
+	bool		is_dst;			/* true if a DST abbreviation */
 	/* source information (for error messages) */
 	int			lineno;
 	const char *filename;