[compiz] solving plugin dependency issues

[Guillaume]

Hello,

We already done something similar in beryl to fix these conflicting
plugins issues. What we did was to introduce two new rules,
CompPluginRuleConflicts and CompPluginRuleAfterAlt. The first one
prevents two incompatible plugin from being loaded at once, and the
later one allows a plugin to require only one plugin in a list of
alternatives.

Anyway, I really like your Feature idea, it's probably the best way to
handle such problems, and it'd be much more flexible than my silly
alternatives rule (since with Features one plugin may need several
Features).

About the implementation, I just wonder if it'd be better to extend
the current Dependencies system with two new rules
(CompPluginRuleProvideFeature and CompPluginRuleNeedFeature) or extend
the plugin API as you suggested. Both approachs sound acceptable.

If you're ok with that, I'll write a first draft tomorrow.

Regards,
Guillaume Seguin

2006/10/7, David Reveman <davidr at novell.com>:
> The dependency checking currently provided is clearly not good enough.
> There's currently two issues with the plugins that exist in the compiz
> repository.
>
> plane plugin conflicts with cube and rotate plugin, zoom plugin should
> probably work with either cube or plane but currently only loads when
> cube plugin is used.
>
> Adding a
> { CompPluginRuleBefore, "cube" }
> to the plane plugin and a
> { CompPluginRuleBefore, "plane" }
> to the cube plugin will solve the conflict but it's not perfect as it
> means that all plugins sort of needs to be aware of all other plugins.
>
> Having the zoom plugin load if either the cube plugin or the plane
> plugin is loaded is currently not possible.
>
> I'm suggesting that we add some way to register and depend on features.
> E.g. the cube and plane plugins would both register a "largedesktop"
> feature. zoom plugin could depend on the "largedesktop" feature instead
> of the cube plugin and it wouldn't be possible to load two plugins that
> provide the same feature.
>
> Adding a feature list to the plugin vTable and a
> CompPluginRuleNeedFeature rule that can be used to depend on specific
> features should do it.
>
> -David
>
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