limited install locations for scripts

[Bruno Haible]

Hi,

The Automake manual, node "Scripts", says:

       Scripts can be installed in `bindir', `sbindir', `libexecdir',
    `pkglibexecdir', or `pkgdatadir'.

Also http://lists.gnu.org/archive/html/automake/2012-01/msg00004.html
confirms this.

But why is this set of install locations limited? Why can't I use a
subdirectory of pkgdatadir, for example?

How to reproduce:
======================== configure.ac ==================
AC_INIT([configure.ac])
AM_INIT_AUTOMAKE([test], [0])

pkgdatadir='${datadir}/test'
AC_SUBST([pkgdatadir])

AC_OUTPUT([Makefile])
======================== Makefile.am ===================
AUTOMAKE_OPTIONS = 1.11 foreign no-dependencies color-tests

pkglibdir = ${pkgdatadir}/lib

TESTS = main.sh

EXTRA_DIST = main.in.sh

pkgdata_SCRIPTS = main.sh
pkglib_SCRIPTS = functions.sh

========================================================
$ aclocal
$ automake -a -c
configure.ac:2: installing './install-sh'
configure.ac:2: installing './missing'
Makefile.am:10: error: 'pkglibdir' is not a legitimate directory for 'SCRIPTS'

Bruno