Re: Meson far from ready on Windows

> I don't think requiring or expecting vcpkg or conan is reasonable at all,
> for a number of reasons:
>
> - Neither supports all the dependencies at present.
> - There are real supply chain verification concerns for vendors.
> - That would be a huge change from what we've required in the last 19
> years, with no deprecation notices or warnings for packagers etc.

I don't think we should hard-require one specifically. I do think it'd be good
if we provided an easy recipe for dependencies to be installed though.

I think such flexibility acually means it becomes *more* important to abstract
away some of the concrete ways of using the various dependencies. It doesn't
make sense for postgres to understand the internals of each dependency on all
platforms to a detail that it can cope with all the different ways of linking
against them.

E.g. libxml can be built with icu, lzma, zlib support. If libxml is built
statically, postgres needs to link to all those libraries as well.  How can we
know which of those dependencies are enabled?

Even if we can make that somehow work, it's not reasonable for postgres
developers adding a dependency to have to figure out how to probe all of this,
when literally no other platform works that way anymore.

If you look around at recipes for building postgres on windows, they all have
to patch src/tools/msvc (see links at the bottom), because the builtin paths
and flags just don't work outside of a single way of acquiring the dependency.

The fact that this thread started only now is actually a good example for how
broken the approach to internalize all knowledge about building against
libraries into postgres is. This could all have been figured out 1+ years ago
- but wasn't.

Unless you want to require postgres devs to get constantly in the muck on
windows, we'll never get that right until just before the release.

I don't particularly care how we abstract away the low level linking details
on windows. We can use pkgconf, we can use cmake, we can invent our own thing.
But it has to be something other than hardcoding windows library paths and
compiler flags into our buildsystem.


And yes, that might make it a bit harder for a packager on windows, but
windows is already a *massive* drag on PG developers, it has to be somewhat
manageable.

I do think we can make the effort of windows dependency management a lot more
reasonable than it is now though, by providing a recipe for acquiring the
dependency in some form. It's a lot easier to for packagers and developers to
customize ontop of something like that.

Err, that was a copy-paste mistake on my end and doesn't even use the vcpkg
generated stuff.

Here's an example build with most dependencies enabled (see below for more
details):

https://cirrus-ci.com/task/6497321108635648?logs=configure#L323

I started hacking a bit further on testing all dependencies, which led me down
a few rabbitholes:


- kerberos: When built linking against a debug runtime, it spews *ginormous*
  amounts of information onto stderr. Unfortunately its buildsystem doesn't
  seperate out debugging output and linking against a debug runtime. Argh.

  The tests fail even with a non-debug runtime though, due to debugging output
  in some cases, not sure why:
  https://cirrus-ci.com/task/5872684519653376?logs=check_world#L502

  Separately, the kerberos tests don't seem to be prepared to work on windows
  :(.

  So I disabled using it in CI for now.

- Linking the backend dynamically against lz4, icu, ssl, xml, xslt, zstd, zlib
  slows down the tests noticeably (~20%).  So I ended up building those
  statically.

  I ran into some issue with using a static libintl. I made it work, but for
  now reverted to a dynamic one.


- Enabling nls slows down the tests by about 15%, somewhat painful. This is
  when statically linking, it's a bit worse when linked dynamically :(.

- readline: Instead of the old issue with a compiler error, now we get a
  compiler crash:
  https://developercommunity.visualstudio.com/t/tab-completec4023:-fatal-error-C1001:/10685868

  The issue is fairly trivial to work around, we just need to break the the
  if/else chain into two. Probably deserves a bigger refactoring, but that's
  for another day.

I haven't yet looked into a) uuid b) tcl.  I think those are the only other
missing dependencies.

> > Many of them do include at least cmake files on windows if you build them
> > though?

> The only one that does is libxml2 as far as I can see. And that doesn't
> seem to work even if I use --cmake-prefix-path= as you suggested:

Ugh, that's because they used a different name for their cmake dependency than
for pkg-config. We can add the alternative spelling to meson.build.



>
> > > And that's why we really need to be able to locate headers and libraries
> > > easily by passing paths to meson, as we can't rely on pkgconfig, cmake,
> > or
> > > things being in some standard directory on Windows.
> >
> > Except that that often causes hard to diagnose breakages, because that
> > doesn't allow including the necessary compiler/linker flags [2].  It's a
> > bad model, we shouldn't perpetuate it.  If we want to forever make windows
> > a complicated annoying stepchild, that's the way to go.
>
> That is a good point, though I suspect it wouldn't solve your second
> example of the Kerberos libraries, as you'll get both 32 and 64 bit libs if
> you follow their standard process for building on Windows so you still need
> to have code to pick the right ones.

vcpkg for one does provide .pc files for kerberos.

> We've either got to be extremely prescriptive in our docs, telling people
> precisely what they need to download for each dependency, or how to build it
> themselves in the way that will work with PostgreSQL, or the build system
> needs to be flexible enough to handle different dependency variations, as
> the old VC++ build system was.

I'm confused - the old build system wasn't flexible around this stuff *at
all*. Everyone had to patch it to get dependencies to work, unless you chose
exactly the right source to download from - which was often not documented or
outdated.

For example:
- https://github.com/microsoft/vcpkg/blob/master/ports/libpq/windows/msbuild.patch

- https://github.com/conan-io/conan-center-index/blob/1b24f7c74994ec6573e322b7ae4111c10f620ffa/recipes/libpq/all/conanfile.py#L116-L160

- https://github.com/conda-forge/postgresql-feedstock/tree/main/recipe/patches