Re: moving $(mkdir_p) from automake to autoconf

[Ralf Wildenhues]

Hello,

I'm still undecided with this.  I see the benefit, but I see quite a few
subtle issues with it as well.  I'd like to see a more evolved patch
before judging.

* Bruno Haible wrote on Tue, Apr 18, 2006 at 02:43:42PM CEST:
>   
> + @defmac AC_PROG_MKDIR_P
> + @acindex{AC_PROG_MKDIR_P}
> + @ovindex mkdir_p
> + Set output variable @code{mkdir_p} to a command that ensures that for
> + each argument, a directory named by this argument exists, creating it
> + and its parent directories if needed.
> + 
> + This macro uses the @samp{mkdir} command if possible.  It may also fall
> + back to the @samp{install-sh -d} command.
> + 
> + Autoconf comes with a copy of @file{install-sh} that you can use.  If
> + you use @code{AC_PROG_MKDIR_P}, you must include @file{install-sh} in
> + your distribution.
> + @end defmac
> + 

First, this description does not document that `install_sh' will be set
and AC_SUBSTed.

This description does not make it clear that @mkdir_p@ may only be used
in files later used as input to `make'.  The naive user may choose to
use $mkdir_p in, say, shell scripts, maybe in configure.ac even: on his
GNU/Linux system, that will work fine, and not expose the limitations.

For the internal, undocumented Automake macro this may have been ok, but
for a generic, documented Autoconf macro this is definitely not ok.

This also opens up the question of whether we could actually make
$mkdir_p work in shell scripts as well, and if, how.  Surely it'd have
to be
  mkdir_p='${install_sh} -d'

then, and track down further issues with how $install_sh may have been
set.  Unfortunately, this setting changed over past Automake versions:
now there may be a $(SHELL) prepending it (automake/m4/install-sh.m4):
  install_sh=${install_sh-"\$(SHELL) $am_aux_dir/install-sh"}

Probably best to link to the documentation of AS_MKDIR_P for use in
configure.ac itself, and forbid use in other, non-M4sh shell scripts.


The next issue that comes with this macro is that, because both Automake
and Autoconf race for setting $install_sh and $mkdir_p currently, it
depends on the order in which the user invokes AC_PROG_MKDIR_P and
AM_INIT_AUTOMAKE, which will win.  This certainly needs to be
documented, or better even, a preferred order be enforced by AC_BEFORE
et al.

The proposed macro for Autoconf disallows user overrides for both
$install_sh and $mkdir_p, whereas Automake would override the latter
only.

Cheers,
Ralf