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

[Keri Harris]

On 29/03/2020 01:41, Julien Fischer wrote:
> Hi Keri,
> 
> On Sat, 28 Mar 2020, Keri Harris wrote:
> 
> 
> 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/...
>                     /...
> 
> I assume that what you are doing there is essentially:
> 
>     ./configure --prefix=/usr
> 
> ?

That's correct


> Allowing that may have been the original intent when the library
> installation directory was designed, however that was well before
> Linux
> distributions started using /usr/lib64 etc.
> 
> At this point, I think it may be simpler to achieve something close
> to
> what you want by making it possible to specify alternative
> installation
> directories for the executables ({prefix}/bin) and documentation
> ({prefix}/share) instead.  (Autoconf already provides --bindir etc,
> we
> just don't use them.)
> 
> In that case I would suggest setting the installation prefix for the
> rest of the system to /usr/lib64/mercury or /usr/lib/mercury and
> living
> with the fact that there will be a few extra layers of subdirectories
> (i.e. lib/mercury) beneath that.
> 
> The library files being installed under $prefix/lib/mercury is hard
> coded throughout a good part of the system and changing that would be
> a
> reasonable chunk of work.  (For not much benefit IMO.)
> 

I've attached a patch that modifies the Mercury scripts to respect --
bindir. Note that any time @bindir@ is occurs both @prefix@ and
@exec_prefix@ need to also be present in the script. e.g:

    prefix=@prefix@
    exec_prefix=@exec_prefix@
    MERCURY_COMPILER=${MERCURY_COMPILER-"@bindir@/mercury_compile"}

Running configure without a --bindir arg will set the following default
values:

    $ ./configure

    prefix = ...
    exec_prefix=${prefix}
    MERCURY_COMPILER=${MERCURY_COMPILER-
"${exec_prefix}/bin/mercury_compile"}

Running with a --bindir arg bypasses $prefix and $exec_prefix as we
would expect:

    $ ./configure --bindir=/usr/bin

    prefix = ...
    exec_prefix=${prefix}
    MERCURY_COMPILER=${MERCURY_COMPILER-"/usr/bin/mercury_compile"}

Other Mercury install directories already support various autoconf
directories like @docdir@, @infodir etc. While having extra layers of
subdirectories is not a prefect solution, it's probably satisfactory
for most installations.


Changing the meaning of mmc --install-prefix within the mercury
compiler is another possible solution. It also isn't too complicated -
just compiler/file_util.m & compiler/make.program_target.m would need
to change. To date on Gentoo Linux I've been patching those files to
replace the hard coded lib/mercury paths with multilib-aware paths. The
obvious drawback to patching compiler .m files is that you can only do
that after having an instance of mercury_compile already built.


Thanks

Keri

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