bug#62485: Improve build system and make "real" defaults

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 27 Mar 2023 13:44:19 +0000
> From: c.buhtz@posteo.jp
> 
> Hello,
> 
> I was told that sqlite3 support is enabled by default when building 
> Emacs29. Is it or is it not?

Emacs builds with sqlite support if you have the sqlite3 library
installed.

> Based on my own experience it seems to me that it depends on the fact if 
> lib-sqlite3-dev is installed or not.

Yes.

> When the lib is not installed and I don't set an explicite sqlite3 
> switch in the make-configure-build-system it build runs successfully 
> without any warning or error. You see?! Sqlite is not default.

Who told you it was the default?  The file NEWS says:

  +++
  ** Emacs can be built with built-in support for accessing SQLite databases.
  This uses the popular sqlite3 library, and can be disabled by using
  the '--without-sqlite3' option to the 'configure' script.

> If you want to make it default then inform the user about missing 
> sqlite-lib in all cases and not only if the --with-sqlite switch is set 
> by the user.

That is not how we define the optional dependencies.  We only do that
for dependencies without which Emacs will be much less powerful or
performant.  Most optional dependencies are not of this kind: Emacs
can be entirely functional without SQLite support.

This is not a bug.

Closing.