[m-dev.] Proposal: Improve specifying Mercury install paths

[Keri Harris]

Hi,

I've run into a couple of issues with install paths in Mercury:

1. Mercury installed with --prefix=/usr may not respect any 32 bit vs
64 bit library separation on some hosts. For example on RedHat Linux or
Gentoo Linux, 32 bit libraries are installed into /lib, /usr/lib while
64 bit libraries are installed into /lib64, /usr/lib64. There doesn't
appear to be any way to install Mercury into the following directory
structure:

   /usr/bin/mmc
   /usr/lib64/mercury/lib/$grade/...
                     /ints/...
                     /...

2. Running "mmc libmyproject.install" always adds lib/mercury into the
install path, even if --install-prefix is specified. This prevents some
custom install paths from being used. e.g. it's not possible to install
Mercury 'extras' projects into the following directory structure:

   /usr/lib/mercury/extras/lib/$grade/...
                          /ints/...
                          /...

I was wondering if it would make sense to extend both the Mercury
install scripts and the Mercury compiler to support some type of
"mercury-prefix" setting. Configuring Mercury with --mercury-
prefix=$dir would set INSTALL_LIBDIR=$dir. mmc would look up a global
mercury-prefix setting:

  - if --mercury-prefix=$dir is specified then install libraries into
$dir/lib/$grade
  - else if --install-prefix=$dir is specified then install libraries
into $dir/lib/mercury/lib/$grade
  - else use default "mercury-prefix" setting and install into
$mercury_prefix/lib/$grade

Admittedly, --mercury-prefix would make --install-prefix somewhat
redundant but keeping it at least maintains backwards compatibility,
and I'm not sure what appetite there would be for changing/removing
such a setting.

Examples of using such a "mercury-prefix" parameter follow:

Installing Mercury
------------------

* no prefix specified (current install behaviour is maintained)

  => infer prefix=/usr/local/mercury-x.y
  => infer mercury-prefix=$prefix/lib/mercury

   /usr/local/mercury-x.y/bin/mmc
   /usr/local/mercury-x.y/lib/mercury/lib/$grade/...
                                     /ints/...
                                     /...

* prefix=/usr (current install behaviour is maintained)

  => infer mercury-prefix=$prefix/lib/mercury

   /usr/bin/mmc
   /usr/lib/mercury/lib/$grade/...
                   /ints/...
                   /...

* prefix=/usr, mercury-prefix=/usr/lib64/mercury

   /usr/bin/mmc
   /usr/lib64/mercury/lib/$grade/...
                     /ints/...
                     /...

* prefix=/opt/mercury, mercury-prefix=/opt/mercury

   /opt/mercury/bin/mmc
   /opt/mercury/lib/$grade/...
               /ints/...
               /...

Installing libraries (assuming Mercury installed with prefix=/usr)
--------------------

* mmc libmyproject.install

   /usr/lib/mercury/lib/$grade/libmyproject.so
                   /ints/...
                   /...

* mmc --mercury-prefix=/usr/lib64/myproject libmyproject.install

   /usr/lib64/myproject/lib/$grade/libmyproject.so
                       /ints/...
                       /...

* mmc --mercury-prefix=/opt/myproject libmyproject.install

   /opt/myproject/lib/$grade/libmyproject.so
                 /ints/...
                 /...


I can look at putting together a patch for this if it is something that
would benefit Mercury.


Thanks

Keri