fauno warned us of it: https://lists.parabola.nu/pipermail/dev/2016-November/004602.html

Packages must be compared to check whether the new arduino in [community] should be preferred or blacklisted (in which case the one in [pcr] should be updated and moved to [libre]).

Also, what was the one in [java] doing? I forgot

So I found that neither the [community] nor the [pcr] packages are being built from sources. Both descend from the same AUR package. The "source" archive contains many binary files that look like Arduino firmware, and more importantly, bytecode libraries in the form of .jars. Most of these libraries are accompanied by license files. I didn't check thoroughly, but even if all of them were free, we would still need to take arduino to [java] until someone sets out to package the libraries from source.

Speaking of [java], after updating some broken URLs I imitated what the old arduino in there was doing during prepare(): getting rid of the .jars, .hex files and other stuff. As one would expect, neither build could proceed without the libraries. So I guess the [java] PKGBUILD was merely serving a symbolic act in showing what's the problematic stuff that needs to be deleted.

At least we now know we can't keep that package in [community]. It's either [java] or blacklist. [pcr] must also go.

[community]: https://git.archlinux.org/svntogit/community.git/tree/trunk/PKGBUILD?h=packages/arduino
[pcr]: https://git.parabola.nu/abslibre.git/tree/pcr/arduino/PKGBUILD
[java]: https://git.parabola.nu/abslibre.git/tree/java/arduino/PKGBUILD

It turns out that [java]'s arduino does actually build (it just needed minor adjustments), because it uses Parabola packages for libraries. The next step is to produce an updated package.

The arduino package has since been removed from the [pcr] and only the [community] package exists now.