Feedback-ID: id4a34324:Fastmail
Date: Mon, 11 Jul 2022 13:17:55 -0700
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	David Rowley <dgrowleyml@gmail.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: automatically generating node support functions
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Hi,

On 2022-07-11 15:54:22 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > On Mon, Jul 11, 2022 at 1:57 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> More generally, I'm having second thoughts about the wisdom of
> >> auto-generating the NodeTag enum at all.  With the current setup,
> >> I am absolutely petrified about the risk of silent ABI breakage
> >> thanks to the enum order changing.
> 
> > I think this is a valid concern, but having it be automatically
> > generated is awfully handy, so I think it would be nice to find some
> > way of preserving that.
> 
> Agreed.  The fundamental problem seems to be that each build toolchain
> has its own source of truth about the file processing order, but we now
> see that there had better be only one.  We could make the sole source
> of truth about that be gen_node_support.pl itself, I think.
> 
> We can't simply move the file list into gen_node_support.pl, because

> (a) the build system has to know about the dependencies involved

Meson has builtin support for tools like gen_node_support.pl reporting which
files they've read and then to use those as dependencies. It'd not be a lot of
effort to open-code that with make either.

Doesn't look like we have dependency handling in Solution.pm?


> (b) gen_node_support.pl wouldn't know what to do in VPATH situations.

We could easily add a --include-path argument or such. That'd be trivial to
set for all of the build solutions.

FWIW, for meson I already needed to add an option to specify the location of
output files (since scripts are called from the root of the build directory).

Greetings,

Andres Freund