BUG #18760: ../doc/src/sgml/postgres.sgml:24: element book: validity error : No declaration for attribute id of

The following bug has been logged on the website:

Bug reference: 18760
Logged by: Thomas Petazzoni
Email address: thomas(dot)petazzoni(at)bootlin(dot)com
PostgreSQL version: 17.2
Operating system: Linux
Description:

When building PostgreSQL 17.2 on a Linux host machine (within a Debian
Bullseye container), the build fails with:

../doc/src/sgml/postgres.sgml:24: element book: validity error : No
declaration for attribute id of element book
<book id="postgres">
^
../doc/src/sgml/postgres.sgml:25: element title: validity error : No
declaration for element title
<title>PostgreSQL &version; Documentation</title>

and many other similar failures. Complete build log available at
http://autobuild.buildroot.net/results/378/378027db50fdcb311b420ad6886795dd8c2888f6/build-end.log.

Passing -Ddocs=disabled -Ddocs_pdf=disabled does not fix the issue: indeed
despite those options, the PostgreSQL build system detects that xmllint and
xsltproc are available, and uses them nevertheless. Passing bogus
-DXMLLINT=/nowhere -DXSLTPROC=/nowhere options prevents PostgreSQL from
finding xmllint and xsltproc, which makes it skip build the documentation,
and gets a successful build, but that's really more a hack than a correct
solution.

It looks like doc/src/sgml/meson.build would need some changes to properly
obey to the "docs" and "docs_pdf" meson options.