Make `:examples` be separate projects and use the compiler plugin

[Jolanrensen]

Because :examples are include()'d in from the main settings.gradle.kts, they are built using the "raw" dataframe sources. This is great for making sure changing our API does not break our tests, but it comes with some limits:

• we need to inherit versions of libraries, like the Kotlin version
• Enabling the compiler plugin in modules inside :dataframe is not that easy and requires a lot of boilerplate build-code that I don't think our users would appreciate to find in our examples.

Some other examples, like :examples/android-example and :examples/kotlin-dataframe-plugin-example use includeBuild() to avoid these issues. However, they come with the downside of using their own versions (which are easily forgotten to be bumped after releases), and as they use their own version of dataframe, they will not fail when we break our API until it's too late.

Maybe we can find a middle ground in Gradle where we dó use includeBuild but can still substitute or override dependencies, or we make a generic "enable the compiler plugin for local modules" function we can call from all local modules in such a way that users can identify and omit them for themselves.

[Jolanrensen]

We could also reuse the idea we have with our notebook examples:

• We build examples in a /dev folder with our actual modules.
• Upon a new version published, we move them out of the /dev folder and give them a fixed DF version that users can easily copy. Possibly combined with Add GH Action to produce direct links to download example subprojects #1616

[koperagen]

Maintaining two versions seems to be the only option. If we publish zip, it should depend on stable release. At the same time another copy will depend on master (using substitute) and help track changes

[koperagen]

61c06c4
Please take this into account

[Jolanrensen]

I've been experimenting with gradle convention plugins and composite builds: https://github.com/Jolanrensen/GradleConventionsExperiment

I believe this sample project can be used as a good base for the DataFrame project itself:

• (type safe) convention plugins allow us to remove duplicate build code and avoid using allProjects {}
  • (It's also the recommended way to structure builds according to Gradle and Kotlin)
• It provides a template for how we can:
  • keep our examples as standalone projects (so, zippable)
  • but up to date (61c06c4) by overwriting their actual gradle config files programmatically
  • and testable, by building them along with our main build using a call to the Gradle Tooling API
  • both the release version of the example, and the /dev version, which will have DataFrame substituted automatically by the actual root sources so we can catch API changes immediately.

[Jolanrensen]

Maybe convert one of the examples to "implied columns" by string api: #1678