Re: packaging system

[David Bateman]

Søren,

I think a bit more complete dependency checking code might be good idea 
to get into place early to save us some pain later. At the moment you 
have a line "Depends:" in the DESCRIPTION file, that contains a list of 
all packages that the current package depends on. May I suggest that 
each package dependency has a seperate "Depends:" line of the form

Depends: PACKAGE [<|=|>] VERSION

to take into account the possible need for a particular version of a 
package or newer than, or range of versions.. For example you might have

Depends: Signal >= 1.0.0
Depends: Signal < 2.0.0

To say that the current package needs version 1.x for the package 
"Signal" and not any previous or newer versions, or

Depends: StupidPackage = 1.0.1

to say that version 1.0.1 of StupidPackage is the only one that is known 
to work with the new package.

There are also issues of upgrading packages and circular dependencies 
that might prevent installation. The way around this is to allow the 
install/uninstall scripts to accept cell-arrays that have a list of the 
packages to install/uninstall. The first thing to do in that case would 
be to gather all of the existing, upgraded and new DESCRIPTION files and 
check that the dependencies after the install will be met, and only then 
start the install/uninstall of all of the packaging in the cell array. 
So a typical call might be "install ({'Comm', 'Signal'});" to allow the 
installation of Comm and Signal is each depends on the other. I don't 
think we want to get fancy and automatically install dependent packages 
as this means that we'd need a mechanism to automatically download 
packages from within octave itself, which would just add another thing 
octave depends on.

As for dependency check on uninstall, I see no issues in traversing the 
package tree reading all of the DESCRIPTION files. I don't believe it 
will be that slow. Getting the dependency stuff right will save us a lot 
of pain in the future so I see this as time well spent (though I 
understand its your time and not mine).

One further point, your install scription introduces a new dependency of 
octave on the external application "tar". Are there any other new 
dependencies? How will this dependency be handled in a cygwin build? 
What about a mingw build? This might cause issues..... However, its a 
secondary point...

In any case great job, as this is something that has been needed for a 
long time...

Cheers
David

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David Bateman                                address@hidden
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