Arrange to install a "posixrules" entry in our timezone database, so that

POSIX-style timezone specs that don't exactly match any database entry will
be treated as having correct USA DST rules.  Also, document that this can
be changed if you want to use some other DST rules with a POSIX zone spec.

We could consider changing localtime.c's TZDEFRULESTRING, but since that
facility can only deal with one DST transition rule, it seems fairly useless
now; might as well just plan to override it using a "posixrules" entry.

Backpatch as far as 8.0.  There isn't much we can do in 7.x ... either your
libc gets it right, or it doesn't.

doc/src/sgml/datetime.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/datetime.sgml,v 2.47 2005/09/09 02:31:48 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/datetime.sgml,v 2.47.2.1 2007/03/14 17:38:21 tgl Exp $
 -->
 
  <appendix id="datetime-appendix">
@@ -2230,24 +2230,33 @@ $PostgreSQL: pgsql/doc/src/sgml/datetime.sgml,v 2.47 2005/09/09 02:31:48 tgl Exp
 
    <para>
     In addition to the names listed in the table,
-    <productname>PostgreSQL</productname> will accept time zone names of the
-    form <replaceable>STD</><replaceable>offset</> or
+    <productname>PostgreSQL</productname> will accept POSIX-style time zone
+    specifications of the form <replaceable>STD</><replaceable>offset</> or
     <replaceable>STD</><replaceable>offset</><replaceable>DST</>, where
     <replaceable>STD</> is a zone abbreviation, <replaceable>offset</> is a
     numeric offset in hours west from UTC, and <replaceable>DST</> is an
-    optional daylight-savings zone abbreviation, assumed to stand for one hour
-    ahead of the given offset.  For example, if <literal>EST5EDT</> were not
-    already a recognized zone name, it would be accepted and would be
-    functionally equivalent to USA East Coast time.  When a daylight-savings
-    zone name is present, it is assumed to be used according to USA time zone
-    rules, so this feature is of limited use outside North America.
-    One should also be wary that this provision can lead to
-    silently accepting bogus input, since there is no check on the
-    reasonableness of the zone abbreviations.  For example,
-    <literal>SET TIMEZONE TO FOOBAR0</> will work, leaving the system
-    effectively using a rather peculiar abbreviation for GMT.
+    optional daylight-savings zone abbreviation, assumed to stand for one
+    hour ahead of the given offset. For example, if <literal>EST5EDT</>
+    were not already a recognized zone name, it would be accepted and would
+    be functionally equivalent to USA East Coast time.  When a
+    daylight-savings zone name is present, it is assumed to be used
+    according to the same daylight-savings transition rules used in the
+    <literal>zic</> time zone database's <filename>posixrules</> entry.
+    In a standard <productname>PostgreSQL</productname> installation,
+    <filename>posixrules</> is the same as <literal>US/Eastern</>, so
+    that POSIX-style time zone specifications follow USA daylight-savings
+    rules.  If needed, you can adjust this behavior by replacing the
+    <filename>posixrules</> file.
    </para>
 
+    <para>
+     One should be wary that the POSIX-style time zone feature can
+     lead to silently accepting bogus input, since there is no check on the
+     reasonableness of the zone abbreviations.  For example, <literal>SET
+     TIMEZONE TO FOOBAR0</> will work, leaving the system effectively using
+     a rather peculiar abbreviation for UTC.
+    </para>
+
   </sect1>
 
   <sect1 id="datetime-units-history">

src/timezone/Makefile

@@ -4,7 +4,7 @@
 #    Makefile for the timezone library
 
 # IDENTIFICATION
-#    $PostgreSQL: pgsql/src/timezone/Makefile,v 1.22 2005/07/06 21:40:09 momjian Exp $
+#    $PostgreSQL: pgsql/src/timezone/Makefile,v 1.22.2.1 2007/03/14 17:38:22 tgl Exp $
 #
 #-------------------------------------------------------------------------
 
@@ -25,6 +25,10 @@ TZDATA := africa antarctica asia australasia europe northamerica southamerica \
 	pacificnew etcetera factory backward systemv solar87 solar88 solar89
 TZDATAFILES := $(TZDATA:%=$(srcdir)/data/%)
 
+# which zone should determine the DST rules (not the specific UTC offset!)
+# for POSIX-style timezone specs
+POSIXRULES = US/Eastern
+
 all: SUBSYS.o submake-libpgport zic
 
 SUBSYS.o: $(OBJS)
@@ -34,7 +38,7 @@ zic: $(ZICOBJS)
 	$(CC) $(CFLAGS) $(ZICOBJS) $(LDFLAGS) $(LIBS) -o $@$(X)
 
 install: all installdirs
-	./zic -d $(DESTDIR)$(datadir)/timezone $(TZDATAFILES)
+	./zic -d $(DESTDIR)$(datadir)/timezone -p $(POSIXRULES) $(TZDATAFILES)
 
 installdirs:
 	$(mkinstalldirs) $(DESTDIR)$(datadir)