Add a has_fixed_supported_configs plugin property

[mgorny]

Add a has_fixed_supported_configs that indicates whether get_supported_configs() always returns a fixed list that does not depend on the system state. Only plugins featuring this flag can be used with plugin-use = "build".

[mgorny]

I think it ended up simpler than I expected it to be.

[konstin]

What about calling this plugin-use instead, and plugins can declare what modes they are compatible with, with the default (when you don't set the attribute) being that the plugin reads system state and needs to run on installation?

[mgorny]

I'm not sure if we can express it "right". The two have quite a different model:

• plugin-use = "none" doesn't use plugin at all, so depending on how you look at it, it's "never" or "always" supported by a plugin
• plugin-use = "build" is valid only for specific subsets of plugins that are guaranteed to return fixed get_supported_configs(), so we can safely call it in the build system, and expect to return the same thing as on the final install system
• plugin-use = "all" is always valid, since all plugins provide both functions

I mean, you could technically say "I want my plugin used only at a build time", but that's an arbitrary "political" restriction, not a technical limitation, and I'm not convinced we should go this way.

So basically a "supported plugin-use" would always be either:

• {"build", "all"}
• {"all"}

[konstin]

Make sense!