[POC] - Support dependencies in modules

[karimMourra]

This is a POC to allow modules to share code by specifying module dependencies in the webpack.conf.js
The POC includes a testVideoProvider which is only meant to be used for demo purposes, as it imports some of the constant strings and code that is intended to be shared across video providers.

This POC adds a .dependencies.json file which is meant to be a lookup for each module's dependencies.
THe dependencies then get added to the entry at build time.

Note that when the dist is built, the constant strings are no longer duplicated.

[karimMourra]

@dgirardi please let me know what you think of this approach to use dependencies

[dgirardi]

In general I like this approach, but I have several reservations:

• running "gulp bundle" (& build, etc) should work with this, the task definitions need to be updated.
• I think this should be considered a breaking change, because it no longer allows people to concatenate output files in the way they can now.
• I don't think the intermediaries should be called "modules", to avoid confusion. (likewise I don't think they should live under the modules folder). They look and act differently from what Prebid calls modules. "libraries" / lib would be a better choice IMO.

Adding @snapwich for more input.

[dgirardi]

I'd prefer if there was only one configuration file for this, to make it harder for them to get out of sync, my vote would be for something like

"libraries": {
  "video": {
    "files": [...],
    "dependants": [
       "jwPlayerVideoProvider",
        ....
    }
  }
},

IMO it could be put in the same ".submodules.json" file we already have with some refactoring / renaming.

[karimMourra]

Hi @dgirardi the comments make sense thank you for the feedback. What do you mean by "it no longer allows people to concatenate output files in the way they can now." ; I am not familiar with output file concatenation

[dgirardi]

At the moment the build generates "prebid-core.js" and one additional js file for each module; third party vendors can take those and concatenate them to make custom Prebid bundles. I am worried that changing this system will be breaking because of that - but I suggest submitting this PR for more visibility from other reviewers, maybe we decide that's not an issue. (We don't have a better way to gauge impact other than asking).

[karimMourra]

@dgirardi I fixed the bundling. Please let me know if you believe this is ready to be merged in the main videoLibrary branch

[dgirardi]

I think this is ready, but my suggestion is to post this separately - it will be smaller and more likely to get through a second review quickly. (Your choice though)

If you want to separate it out, there are some cases in prebid#7936 that are much smaller (compared to the video module) where this would be useful, if you want to use one as a proof-of-concept. For example, there's a utils.getOrigin function that is only used in a couple of modules.

[dgirardi]

I don't think this is the right logic to use for libraries - because the dependencies on them will not work unless they are explicitly declared in .submodules.json, I think this should just return the list of libraries as it's defined in there.
Otherwise this allows inconsistencies when the library does not use index.js in the way we expect here, or the compilation of files that are not used by anyone.