WIP: Add ability to modify platform.txt via mkArduinoPackageOverlay

[simojo]

This PR adds a way to include an attribute set that modifies platform.txt located at packages/${name}/hardware/${architecture}/${version}/platform.txt. I created this feature as a way to sidestep some issues I encountered when compiling for the Digispark.

Overview

The functionality allows you to provide the attrset argument called buildProperties to mkArduinoPackageOverlay in the same manner you would call:

arduino-cli --build-property KEY=VALUE

Example

Calling mkArduinoPackageOverlay while specifying custom buildProperties looks like the following:

      (arduino-nix.mkArduinoPackageOverlay {
        packageIndexFile = (arduino-index + "/index/package_digistump_index.json");
        buildProperties = {
          "KEY1" = "VALUE1";
          "KEY2" = "VALUE2";
        };
      })

which corresponds to platform.txt looking like the following:

...
KEY1=VALUE1
KEY2=VALUE2
...

Note that, if the key did not already exist in platform.txt, it would be appended on a new line. Otherwise, it is appended to the same line with a space.

The caveat (suggestions, anyone?)

Calling mkArduinoPackageOverlay without specifying any extra buildProperties would need to look like this now:

-(arduino-nix.mkArduinoPackageOverlay (arduino-index + "/index/package_index.json"))
+(arduino-nix.mkArduinoPackageOverlay { packageIndexFile = (arduino-index + "/index/package_index.json"); })

which is obviously non-optimal. I'm open to suggestions for how to make this better, as I'm still learning the nix lang.

[simojo]

@bouk would you mind weighing in on this feature?

[bouk]

Hi @simojo, thanks for taking the time to create this PR.

I don't think this is needed however, if you want to modify a platform you can do something like:

`platforms.rp2040.rp2040."version".overrideAttrs (self: super: {
  fixupPhase = "...";
})

Which is what we do for something similar. I would accept a PR that updates the README to include this information 😄

[simojo]

Sounds good, I'll make a mental note to update the docs README so others who need something similar can see it :)