From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
cc: Andres Freund <andres@anarazel.de>, David Rowley <dgrowleyml@gmail.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: automatically generating node support functions
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Comments: In-reply-to Peter Eisentraut <peter.eisentraut@enterprisedb.com>
	message dated "Mon, 11 Jul 2022 16:09:24 +0200"
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Date: Mon, 11 Jul 2022 11:37:39 -0400
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Peter Eisentraut <peter.eisentraut@enterprisedb.com> writes:
> On 11.07.22 01:09, Tom Lane wrote:
>> Andres Freund <andres@anarazel.de> writes:
> I was just rebasing meson ontop of this and was wondering whether the input
> filenames were in a particular order:

> First, things used by later files need to be found in earlier files.  So 
> that constrains the order a bit.

Yeah, the script needs to see supertype nodes before subtype nodes,
else it will not realize that the subtypes are nodes at all.  However,
there is not very much cross-header-file subtyping.  I experimented with
rearranging the input-file order, and found that the *only* thing that
breaks it is to put primnodes.h after pathnodes.h (which fails because
PlaceHolderVar is a subtype of Expr).  You don't even need nodes.h to be
first, which astonished me initially, but then I realized that both
NodeTag and struct Node are special-cased in gen_node_support.pl,
so we know enough to get by even before reading nodes.h.

More generally, the main *nodes.h files themselves are arranged in
pipeline order, eg parsenodes.h #includes primnodes.h.  So that seems
to be a pretty safe thing to rely on even if we grow more cross-header
subtyping cases later.  But I'd vote for putting the incidental files
in alphabetical order.

> Second, the order of the files determines the ordering of the output. 
> The current order of the files reflects approximately the order how the 
> manual code was arranged.  That could be changed.  We could also just 
> sort the node types in the script and dump out everything alphabetically.

+1 for sorting alphabetically.  I experimented with that and it's a
really trivial change.

			regards, tom lane