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From: Thomas Munro <thomas.munro@gmail.com>
Date: Thu, 24 Nov 2022 15:57:57 +1300
Message-ID: 
 <CA+hUKG+4_14qF5Ah36rgg+Kn6nOEPXW9aJD6EXUTOFULJkMBug@mail.gmail.com>
Subject: Re: Collation version tracking for macOS
To: Jeff Davis <pgsql@j-davis.com>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	Jeremy Schneider <schneider@ardentperf.com>, Peter Geoghegan <pg@bowt.ie>,
 "Nasby, Jim" <nasbyj@amazon.com>,
	Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>
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On Thu, Nov 24, 2022 at 3:07 PM Jeff Davis <pgsql@j-davis.com> wrote:
> I'm sure this has been discussed, but which distros even support
> multiple major versions of ICU?

For Debian and friends, you can install any number of libicuNN
packages (if you can find them eg from previous release repos), but
there's only one libicu-dev.  That means that one specific major
version is blessed by each Debian release and has its headers and
static libraries for you to use as a developer, but you can still
install the dynamic libraries from older releases at the same time to
satisfy the dependencies of packages or programs that were built on an
earlier OS release.  They don't declare conflicts on each other and
they contain non-conflicting filenames.  That's similar to the way
standard libraries and various other things are treated, for backward
compatibility.

For RHEL and friends, I'm pretty sure it's the same concept, but I
don't use those and haven't seen it with my own eyes.

I don't know for other Linux distros/families, but I expect the above
two cover a huge percentage of our users and I expect others to have
made similar choices.

For the BSDs, which tend to have a single binary package with both
headers and libraries owing to their origins as source-based
distributions (ports), the above way of thinking doesn't work; I
couldn't develop this on my usual FreeBSD battlestation without
building ICU myself (problem being that there's only one "pkg install
icu") and I hope to talk to someone who knows what to do about that
eventually.  I want this to work there easily for end users.

macOS and Windows have so many different ways of installing things
that there isn't a single answer there; supposedly open source is like
a bazaar and closed source like a cathedral, but as far as package
management goes, it looks more like rubble to me.