The dependencies between themes should be invisible to the user

[fingon]

I spent probably couple of hours wondering about source of this error when customizing my own minimal import:

ERROR: Error loading lua config: /osm2pgsql-themepark/lua/themepark.lua:136: attempt to index a nil value.

when the input flex Lua code was this:

local themepark = require('themepark')
themepark:add_topic('shortbread_v1/water')

It turns out it was fixed by adding:

themepark:add_topic('core/name-all')

but it was not really obvious either from the error, or from the documentation I had found.

Improvement ideas

• Perhaps the topics should ensure the themes/topics they refer to are defined on their own?

• Perhaps the error message could be better? (in this case, core/name column was not defined)

[joto]

The underlying problem is that the dependency needs configration by the user. That's why we can't just hide it.

Currently dependencies are implicit which is a) simple and b) gives us a lot of flexibility. But, I agree, the error message is useless and the whole thing is not understandable for the user. I am not sure yet whether we just need better error messages, or whether the Themepark framework needs to support some kind of dependency tracking.