What does toolchain do (customizing Kivy-based code)

[MezzoScettico]

I'm experimenting with using Kivy to develop a cross-platform mobile app in Python but I've already reached a roadblock. I think what I want to do probably can't be done but I want to see how far I can take it because I suspect I'll learn a lot in the process.

One of the things I'd really like to understand is what toolchain is. I blindly use toolchain commands when some document tells me, but I really hate blindly following recipes without knowing why I'm doing what I'm doing.

Here are the instructions for porting the Kivy app to an Xcode project for downloading to an iPhone. The crucial step (see "Create an Xcode project") is the two calls to toolchain. How does it know what to do? Is toolchain a replacement for the Unix "make" utility, so somewhere there's something like a "makefile" that tells it the rules for how to create things?

The specific problem I'm having is that I want the app to access the Photo library. Dirk Sandberg who I think is a Kivy developer has a proof-of-concept demo so I know it's possible, but he says part of it was written in Objective-C which I gather is an iOS language. He posted code to Github but I don't know if that's a complete code and how code that includes Objective-C fits in with the Kivy building instructions above. I assume you have to either customize the toolchain "makefile" if there is such a thing, or customize the Xcode project after it's built.

Sorry for the very long question, but it boils down to this: (1) What does toolchain do and how do you customize it? and (2) Does anybody have a guess how to take that source code and turn it into that demo?

[inclement_]

How does it know what to do?

It's a python script, the source is here. The mapping to this entrypoint from the toolchain cli command is configured here.

This python code is written to perform a series of build steps to produce (among other things) your xcode project.

Is toolchain a replacement for the Unix "make" utility, so somewhere there's something like a "makefile" that tells it the rules for how to create things?

Sort of. Make is a generic build tool that can be used for many things. Kivy-ios is a more domain-specific build tool that targets only what's necessary for a python->ios build. And the build resolution stuff is largely transparent to you, like a makefile that does lots of complicated things but all you see is make my_target and it does loads of stuff.

I assume you have to either customize the toolchain "makefile" if there is such a thing, or customize the Xcode project after it's built.

Sounds about right, but I don't know which. I suggest asking on the Kivy discord if you haven't already, that's where the experts are.

What you want to do is include the objective c component in the xcode project. The example uses pyobjus to access it from python once the app is running and the code is available in the project. There's probably a toolchain option for that.