You make some good points.

I'd be inclined to add a feature that causes the location of the eggs  
directory  to depend on the index and find-links option -- possibly by  
using a hash of these.

Jim

On Feb 18, 2009, at 8:54 AM, Martijn Faassen wrote:

> Public bug reported:
>
> grokproject, a tool to create projects using the Grok web framework,
> currently inspects .buildout and if there is no default.cfg, creates a
> line which says:
>
> [buildout]
> eggs-directory = /path/to/home/.buildout/eggs
>
> This so that users are set up with a shared eggs directory which  
> greatly
> cuts down on download times when people create new projects or add a
> dependency to an existing project that they had used elsewhere. We  
> don't
> do this in grokproject-generated buildouts directly as that would set
> hard paths in buildout.cfg, and that would make them not
> interchangeable. It also introduces a single convention on where to  
> look
> for shared eggs.
>
> For Grok, which restricts which versions of eggs to download from pypi
> using the 'versions' construct in buildout, this approach works pretty
> well. Some other projects however rely on a custom index to restrict
> which versions of packages are installed. If a shared eggs directory  
> is
> in use, the wrong eggs will be pulled in from this shared directory  
> and
> the installation procedure fails. This is a problem whenever someone
> adds a line like this to their .buildout/default.cfg, not just in the
> case of Grok.
>
> Globally sharing eggs can be useful. It also breaks the isolation
> assumption that some buildouts have. It would be nice if we could have
> another level of isolation: isolation per "framework" (or perhaps per
> index). eggs-directory (and perhaps the download cache as well) could
> then be different for each framework. Grok could then happily share  
> eggs
> in ~buildout/.eggs-grok, and nobody else would be bothered by it.
>
> One solution to do this with existing buildout technology would be  
> to create a default.cfg which has something
> like this:
>
> [grok-dir]
> path = /home/faassen/.buildout/eggs-grok
>
> and then in a specific grokproject-generated buildout.cfg we'd do
> something like this:
>
> [buildout]
> eggs-directory = ${grok-dir:path}
>
> (not sure whether the grok-dir part needs to be on the parts line  
> here)
>
> This would fail however if there were *no* default.cfg that defined
> grok-dir. We cannot move the [grok-dir] section into the project's
> buildout either as this would create a hardcoded path inside
> buildout.cfg.
>
> We could resolve this by adding something like 'shared-eggs- 
> directory-base' and 'shared-eggs-directory'.
> In default.cfg, we'd have:
>
> [buildout]
> shared-eggs-directory-base = /path/to/.buildout/eggs
>
> In our own buildout.cfg we'd have:
>
> [buildout]
> ...
> shared-eggs-directory = grok
>
> this would cause the system to look for /path/to/.buildout/eggs-grok
> (shared-eggs-directory-base + '-' + shared-eggs-directory) and assign
> this to eggs-directory. If no shared-eggs-directory-base can be found
> it'll ignore shared-eggs-directory and just use the default for eggs-
> directory (eggs local to the buildout), so that the buildout will  
> still
> work without a default.cfg in place. If an explicit eggs-directory is
> found this will always trump shared-eggs-directory.
>
> This way, Grok will put all its eggs in a shared eggs directory shared
> by all other grok installations on the system, but other buildouts  
> won't
> be bothered by it, as there'd be no reason to place an egg-directory  
> in
> buildout.cfg anymore.
>
> ** Affects: grok
>     Importance: Undecided
>         Status: New
>
> ** Affects: zc.buildout
>     Importance: Undecided
>         Status: New
>
> ** Also affects: grok
>   Importance: Undecided
>       Status: New
>
> -- 
> a per-framework shared eggs directory
> https://bugs.launchpad.net/bugs/331022
> You received this bug notification because you are subscribed to
> Buildout.

--
Jim Fulton
Zope Corporation