That script is incorrect in that it sets the combine function for
max(citext) twice instead of setting the combine function for
max(citext) once and the combine functon for min(citext) once.  The
consequence is that if you install 1.0 or 1.1 and then update to 1.2,
you end up with min(citext) not having a combine function, contrary to
what was intended.  If you install 1.2 directly, you're OK.

Fix things up by defining a new 1.3 version.  Upgrading from 1.2 to
1.3 won't change anything for people who first installed the 1.2
version, but people upgrading from 1.0 or 1.1 will get the right
catalog contents once they reach 1.3.

Report and patch by David Rowley, reviewed by Andreas Karlsson.

All citext functions are PARALLEL SAFE, and a couple of them can
benefit from having aggregate combine functions.

Andreas Karlsson

These functions should return SETOF TEXT[], like the core functions they
are wrappers for; but they were incorrectly declared as returning just
TEXT[].  This mistake had two results: first, if there was no match you got
a scalar null result, whereas what you should get is an empty set (zero
rows).  Second, the 'g' flag was effectively ignored, since you would get
only one result array even if there were multiple matches, as reported by
Jeff Certain.

While ignoring 'g' is a clear bug, the behavior for no matches might well
have been thought to be the intended behavior by people who hadn't compared
it carefully to the core regexp_matches() functions.  So we should tread
carefully about introducing this change in the back branches.  Still, it
clearly is a bug and so providing some fix is desirable.

After discussion, the conclusion was to introduce the change in a 1.1
version of the citext extension (as we would need to do anyway); 1.0 still
contains the incorrect behavior.  1.1 is the default and only available
version in HEAD, but it is optional in the back branches, where 1.0 remains
the default version.  People wishing to adopt the fix in back branches will
need to explicitly do ALTER EXTENSION citext UPDATE TO '1.1'.  (I also
provided a downgrade script in the back branches, so people could go back
to 1.0 if necessary.)

This should be called out as an incompatible change in the 9.5 release
notes, although we'll also document it in the next set of back-branch
release notes.  The notes should mention that any views or rules that use
citext's regexp_matches() functions will need to be dropped before
upgrading to 1.1, and then recreated again afterwards.

Back-patch to 9.1.  The bug goes all the way back to citext's introduction
in 8.4, but pre-9.1 there is no extension mechanism with which to manage
the change.  Given the lack of previous complaints it seems unnecessary to
change this behavior in 9.0, anyway.

It's been deprecated for ages according to Tom, and it breaks now given
the previous patch anyway.

Per buildfarm

We have seen one too many reports of people trying to use 9.1 extension
files in the old-fashioned way of sourcing them in psql.  Not only does
that usually not work (due to failure to substitute for MODULE_PATHNAME
and/or @extschema@), but if it did work they'd get a collection of loose
objects not an extension.  To prevent this, insert an \echo ... \quit
line that prints a suitable error message into each extension script file,
and teach commands/extension.c to ignore lines starting with \echo.
That should not only prevent any adverse consequences of loading a script
file the wrong way, but make it crystal clear to users that they need to
do it differently now.

Tom Lane, following an idea of Andrew Dunstan's.  Back-patch into 9.1
... there is not going to be much value in this if we wait till 9.2.

It was never terribly consistent to use OR REPLACE (because of the lack of
comparable functionality for data types, operators, etc), and
experimentation shows that it's now positively pernicious in the extension
world.  We really want a failure to occur if there are any conflicts, else
it's unclear what the extension-ownership state of the conflicted object
ought to be.  Most of the time, CREATE EXTENSION will fail anyway because
of conflicts on other object types, but an extension defining only
functions can succeed, with bad results.

This isn't fully tested as yet, in particular I'm not sure that the
"foo--unpackaged--1.0.sql" scripts are OK.  But it's time to get some
buildfarm cycles on it.

sepgsql is not converted to an extension, mainly because it seems to
require a very nonstandard installation process.

Dimitri Fontaine and Tom Lane

This adds collation support for columns and domains, a COLLATE clause
to override it per expression, and B-tree index support.

Peter Eisentraut
reviewed by Pavel Stehule, Itagaki Takahiro, Robert Haas, Noah Misch

David Wheeler

by putting it into the standard string category, we cause casts from citext
to text to be recognized as "preferred" casts.  This eliminates the need
for creation of alias functions and operators that only serve to prevent
ambiguous-function errors; get rid of the ones that were in the original
commit.

David E. Wheeler