Shipments in Cabal

[Isaac Jones]

Krasimir Angelov <kr.angelov at gmail.com> writes:

> Hello Guys,
>
> I have started developing Shipments in Cabal. 

Awesome!  FWIW, you should probably take a look at the package
dependency code in cabal-get, and you also might want to look at the
new cabal-install tool, as I expect that when we ship a cabal w/
cabal-install, people will use it a lot.  Although having shipments
makes cabal-install less important.

The smarts in cabal-get is that it checks to see what's already
installed, and this might not really be desirable for a shipment
(unless we want to have a flag for only installing the necessary
stuff).

BTW, could you open a new ticket or wiki page at the cabal wiki /
ticket tracker:
http://hackage.haskell.org/cgi-bin/trac/trac.cgi/report/3

> It is working like it was discussed previously. When there are
> multiple *.cabal files, in the directory where the Setup.lhs lies,
> then they all will be build in dependency order.

Are you using a temporary package-conf file?

> Packages that contain both executables and libraries are deprecated.

Sounds good.

> In order to keep the backward compatibility the package description
> parser returns a list of PackageDescription. In the list there is
> one element for the library and one element for each executable. The
> package name for the executables is equal to the "executable" field
> in the corresponding stanza in the package description file.

I see.  You didn't want to break backward compatibility w/ the
PackageDescription type?

> The trouble that I see is with the bindir, libdir, etc directory
> names. They all may depend on $pkgid value which is different for each
> package in the shipment. The consequence is that by default all
> binaries will be installed in their own directories.
> I think it is better to install them in common directory instead. It
> might be better if we were able to use $shipment variable instead of
> $pkgid. Another possible usage of is in "sdist" command. By default
> the "sdist" command is building the ${pkgid}.tar.gz archive. In
> presence of multiple packages I think it should build one common
> package: ${shipment}.tar.gz.
>
> The problem is how to guess the $shipment value. There are some ideas:
>
> a> The shipment name might be kept in some special file.

I kinda like this, package.cabalship (or whatever) might look like:

shipment: shipmentname
version: 1.1 -- inherited by the packages if they have no version num
copyright -- ditto

The only down side I see to this is that if version can be in the
shipment, and need not be in the .cabal files, then the .cabal files
are no longer stand-alone (they need the shipment file).

OTOH, if you have a scheme where you want to have version numbers the
same across all packages in your shipment, well then it would be very
nice to not have to specify it in each .cabal file.

What are the advantages of having standalone .cabal files within a
shipment?  I don't see anything too big unless someone wants to be
able to grab just part of the shipment, but in that case, they could
just get the .cabalship file anyway.

The other advantage is that .cabal files would not be backward
compatible w/ older cabals but I guess that older cabals will already
break in the presence of multiple .cabal files in a directory, so
maybe it doesn't matter.  Opinions.

> b> In HSQL I am using package names like: hsql, hsql-odbc, hsql-mysql, .....
> One solution is to use the common prefix in the package names as
> shipment name. When there is only one package, then the shipment name
> will be equal to the package name. The advantage is that, when the
> shipment name is encoded in the package name, then for the user it
> will be easier to find the package sources.
> The drawback is that we have to force some restriction on the package names.

I don't really like the idea of forcing them to name their packages in
a particular way.  For instance, you might have a package cabal but
want an executable install-cabal.  We don't want to force people to
use particular names for their binaries.

> c> Another solution is to use the name of the top level directory. The
> drawback is that the user can't rename the top level directory.

Another simple idea is that we could add a shipment: field to the
.cabal file.  This would cause some redundancy between .cabal files,
but that's nicer than b> or c>.

Of course, shipment: wouldn't have to be in each file; it would just
be required that one of the files has that field in it, but that's not
very neat / symmetric.

Also, have you thought about how one might specify that they only want
to operate on one part of the package (a single .cabal file?).  Maybe
defaultSetup could take optional command-line option which is the
.cabal file(s) to operate on, and if none are specified, then use
*.cabal.

This is where the cabal-get dependency code could come in handy.
Let's say I have a shipment with A.cabal, B.cabal, and C.cabal where A
depends on B and B depends on C.  I already have C installed for some
strange reason, it would be nice to say:

./setup configure  A.cabal B.cabal
./setup build
./setup install

and that should work just fine, because C is already installed.  OTOH,
if you said:

./setup configure  A.cabal
./setup build
./setup install

then setup should complain that you don't have B.

This is something like how cabal-install works.  I can say:
cabal-install foo/foo.cabal bar/bar.cabal --user --prefix=/home/ijones/usr



peace,

  isaac