Support simple dependencies or ordering between plugins

[pombredanne]

I have faced this problem: I have several post scan plugins, and some need to run first some later.
There is no way to ensure this for now.
Ideally we would want to have a proper, sat-like dependency resolution mechanism. But a cruder, static way based on a relative ordering (for instance using the sort_order plugin class attribute) would be plenty good enough.
@yashdsaraf what do you think?

[yashdsaraf]

Hi @pombredanne
From what I remember the goal was for the plugin architecture to eventually allow third party plugins as well. In that case sort_order would be rather confusing for the plugin developers, don't you think?

[pombredanne]

@yashdsaraf it could be indeed: what do you suggest instead?

[yashdsaraf]

Maybe some hooks like before or after using which a certain plugin can decide its approximate execution order by specifying which plugin should executed before or after this one?
Then for even more fine tuning they could have a sort_order.

[pombredanne]

the simple order works ok in the short term.... but I am keeping this open to implment @yash-nisar suggestion of before/after

[adityaviki]

@pombredanne I am thinking of working on this. Can you provide me with a little more detail on where I could implement these hooks?

[pombredanne]

@adityaviki sorry for missing your comment. There has been some attempt to support this in https://github.com/nexB/plugincode/blob/c6bd7c6cb3b505b9c24558c32a7e94f9a494ef90/src/plugincode/__init__.py
and used https://github.com/nexB/scancode-toolkit/blob/9ed2cb4e78a8b1b138bcb201f50203b43098febb/src/packagedcode/plugin_package.py#L59

But this is not enforced at all.

We have however enforcing a "surface" CLI options dependency as in https://github.com/nexB/scancode-toolkit/blob/bebbcf7daed62a609271251158114457e99aaa9c/src/summarycode/summarizer.py#L278

Moving this to plugincode repo.