As the person who literally implemented the Rails Application Templates in the incarnation still used today, they have many pitfalls that may not be obvious unless you maintain them and/or write anything mildly complex with them. For example:
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Brittle. Whenever you change the generated code, which is often common, there is a chance template code will break or it will generate the wrong application
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They don’t compose. As application templates get more and more complex, it is unlikely you can run multiple of them
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Untested. Back then I don’t remember seeing a single application generator which comes with a comprehensive test suite (which would help addressing previous points)
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Hard to maintain. It is really hard to maintain an application template as you extend it because they lack structure
But most importantly, I think application templates most often miss the point: what are the odds that you need to execute something exactly when the application is being generated? For example, take mix phx.gen.auth, it could be designed as an --auth flag to phx.new but it is just so much better as its own standalone project.
So what about Tailwind support on Phoenix if it is not part of Phoenix? How would someone approach that? Easy:
$ mix archive.install hex phx_new
$ mix archive.install hex phx_new_tailwind
$ mix phx.new foo
$ cd foo
$ mix phx.new.tailwind # change everything required for tailwind support
While this approach doesn’t necessarily address point 1, because this type of code will always be brittle, it pretty much does better in all other points mentioned above. The beauty of phx_new_tailwind is:
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Is its own project, with proper structure, and hopefully tests
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Has its own command, which means it has a proper place to document all of its options and behaviour (something you don’t get with application templates iirc)
I am sure this process is nowhere as fleshed out as Rails Application Templates, but I would rather use this approach as a starting point and improve it based on feedback than pick a solution that has many known pitfalls. In any case, it is 100% possible today.
This is not even specific to Phoenix… as the same can be achieved with Rails generators and it is pretty much the approach I preferred back then: devise and simple_form used rails devise:install and rails simple_form:install commands instead of templates. I remember maintaining some front-end based installers way back then too.
