Future-proof regression tests against possibly-missing posixrules file.

The IANA time zone folk have deprecated use of a "posixrules" file in
the tz database.  While for now it's our choice whether to keep
supplying one in our own builds, installations built with
--with-system-tzdata will soon be needing to cope with that file not
being present, at least on some platforms.

This causes a problem for the horology test, which expected the
nonstandard POSIX zone spec "CST7CDT" to apply pre-2007 US daylight
savings rules.  That does happen if the posixrules file supplies such
information, but otherwise the test produces undesired results.
To fix, add an explicit transition date rule that matches 2005 practice.
(We could alternatively have switched the test to use some real time
zone, but it seems useful to have coverage of this type of zone spec.)

While at it, update a documentation example that also relied on
"CST7CDT"; use a real-world zone name instead.  Also, document why
the zone names EST5EDT, CST6CDT, MST7MDT, PST8PDT aren't subject to
similar failures when "posixrules" is missing.

Back-patch to all supported branches, since the hazard is the same
for all.

Discussion: https://postgr.es/m/1665379.1592581287@sss.pgh.pa.us

diff --git a/doc/src/sgml/datetime.sgml b/doc/src/sgml/datetime.sgml
index a0cf4bab5231217c78a814911ec59645e0365d0d..c35dee7e13d33a1d23da7f9b9bfe1304f701df00 100644 (file)
--- a/doc/src/sgml/datetime.sgml
+++ b/doc/src/sgml/datetime.sgml
@@ -757,6 +757,18 @@
    CET and ends on the last Sunday in October at 3AM CEST.
   </para>
 
+  <para>
+   The four timezone names <literal>EST5EDT</literal>,
+   <literal>CST6CDT</literal>, <literal>MST7MDT</literal>,
+   and <literal>PST8PDT</literal> look like they are POSIX zone
+   specifications.  However, they actually are treated as named time zones
+   because (for historical reasons) there are files by those names in the
+   IANA time zone database.  The practical implication of this is that
+   these zone names will produce valid historical USA daylight-savings
+   transitions, even when a plain POSIX specification would not due to
+   lack of a suitable <filename>posixrules</filename> file.
+  </para>
+
   <para>
    One should be wary that it is easy to misspell a POSIX-style time zone
    specification, since there is no check on the reasonableness of the

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 96f1ee9bc26d4ebf128d96c6d85c4de74643e197..538f30c59dda9fb2c41dbfbb77903d596b29dc54 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -7517,18 +7517,22 @@ SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS
    When adding an <type>interval</type> value to (or subtracting an
    <type>interval</type> value from) a <type>timestamp with time zone</type>
    value, the days component advances or decrements the date of the
-   <type>timestamp with time zone</type> by the indicated number of days.
+   <type>timestamp with time zone</type> by the indicated number of days,
+   keeping the time of day the same.
    Across daylight saving time changes (when the session time zone is set to a
    time zone that recognizes DST), this means <literal>interval '1 day'</literal>
    does not necessarily equal <literal>interval '24 hours'</literal>.
-   For example, with the session time zone set to <literal>CST7CDT</literal>,
-   <literal>timestamp with time zone '2005-04-02 12:00-07' + interval '1 day'</literal>
-   will produce <literal>timestamp with time zone '2005-04-03 12:00-06'</literal>,
-   while adding <literal>interval '24 hours'</literal> to the same initial
-   <type>timestamp with time zone</type> produces
-   <literal>timestamp with time zone '2005-04-03 13:00-06'</literal>, as there is
-   a change in daylight saving time at <literal>2005-04-03 02:00</literal> in time zone
-   <literal>CST7CDT</literal>.
+   For example, with the session time zone set
+   to <literal>America/Denver</literal>:
+<screen>
+SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '1 day';
+<lineannotation>Result: </lineannotation><computeroutput>2005-04-03 12:00:00-06</computeroutput>
+SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '24 hours';
+<lineannotation>Result: </lineannotation><computeroutput>2005-04-03 13:00:00-06</computeroutput>
+</screen>
+   This happens because an hour was skipped due to a change in daylight saving
+   time at <literal>2005-04-03 02:00:00</literal> in time zone
+   <literal>America/Denver</literal>.
   </para>
 
   <para>

diff --git a/src/test/regress/expected/horology.out b/src/test/regress/expected/horology.out
index 3064749cc4e4559d93baeee4ea99985b0fae58c6..5c4e2a6fcf6c21dddb9e53dec21a06ac281bde35 100644 (file)
--- a/src/test/regress/expected/horology.out
+++ b/src/test/regress/expected/horology.out
@@ -652,7 +652,8 @@ SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
 (1 row)
 
 -- timestamp with time zone, interval arithmetic around DST change
-SET TIME ZONE 'CST7CDT';
+-- (just for fun, let's use an intentionally nonstandard POSIX zone spec)
+SET TIME ZONE 'CST7CDT,M4.1.0,M10.5.0';
 SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' as "Apr 3, 12:00";
          Apr 3, 12:00         
 ------------------------------

diff --git a/src/test/regress/sql/horology.sql b/src/test/regress/sql/horology.sql
index 87fdcdcf297d561f76d37e3c05d7f3bb9e64b689..9ac3f2344844ddf10c8cf69619316b3f419b77d6 100644 (file)
--- a/src/test/regress/sql/horology.sql
+++ b/src/test/regress/sql/horology.sql
@@ -122,7 +122,8 @@ SELECT (timestamp with time zone 'tomorrow' = (timestamp with time zone 'yesterd
 SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
 
 -- timestamp with time zone, interval arithmetic around DST change
-SET TIME ZONE 'CST7CDT';
+-- (just for fun, let's use an intentionally nonstandard POSIX zone spec)
+SET TIME ZONE 'CST7CDT,M4.1.0,M10.5.0';
 SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' as "Apr 3, 12:00";
 SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '24 hours' as "Apr 3, 13:00";
 SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '1 day' as "Apr 2, 12:00";