[Python-Dev] PEP 376 - Open questions

[Paul Moore]

2009/7/8 Nick Coghlan <ncoghlan at gmail.com>:
> Antoine Pitrou wrote:
>> Nick Coghlan <ncoghlan <at> gmail.com> writes:
>>> For example, I quite like the concept behind the various ideas for
>>> "location" or "prefix" definitions either in the RECORD file itself or
>>> in a separate PREFIXES file, since such approaches feeds directly in to
>>> part b) above.
>>
>> I don't understand the point. Since RECORD is specific to a particular machine
>> and installation (it is generated at install time), what would you gain by
>> adding a fake genericity to its entries?
>
> My understanding is that RECORD isn't generated at install time for the
> bdist_* commands -it's generated at the time the binary distribution is
> created. Hence the problems raised with the idea of having absolute
> paths in RECORD - if they were written directly into RECORD they would
> reflect where the files were when the distribution was created, not
> where they end up when it is installed.

This is a key open question, IMHO. No-one has done any work on
updating the core bdist_xxx commands to the new structure, and the PEP
is silent on the matter, so it's still all speculation.

The current "best guess" assumption is that, given that bdist_xxx uses
a "setup.py install --root=xxx" incantation to generate the structure
to package, the RECORD can be picked up from this. There are a number
of issues with this assumption, though - it doesn't handle absolute
locations well (there are existing bugs), paths may be affected by the
environment at the time the installer is built, and it requires RECORD
to be relocatable.

An alternative solution would be for the bdist_xxx commands to ignore
the RECORD file generated in the temp area, and build its own on the
target machine when the installer is run. This is conceptuially far
cleaner, it's in line with the implicit assumptions in the PEP, and it
avoids a lot of the problems with path formats (the filenames in
RECORD could be absolute local pathnames, and that's the end of the
story). But - and it's a big but - this dumps RECORD file handling on
the bdist_xxx command, and they all need to implement the same code,
resulting in a lot of duplication and opportunity for inconsistency.

I have no answer here. But I think we need feedback from the people
who will ultimately be building bdist_xxx formats - Debian packagers,
people wrting alternate RPM builders, etc. There's also Phillip
commenting from the setuptools POV and MAL who has mentioned his build
process.

Bottom line - Is RECORD to be created on the target machine at install
time, or must it be relocatable?
Subsequent question - if it's to be relocatable, how will that work?

Paul.