Adds a rule that can be used out of the box to use Periphery in bazel…

[maxwellE]

… projects

Using the example provided here you are able to generate periphery reports for any collection of swift based targets. To run the example run

bazel build //periphery/example:periphery_xcode_report

It is important to note the flags specified in the .bazelrc file, they are critical to periphery working via bazel

[ileitch]

Thanks so much for adding this, I'm really excited about native Bazel support!

I recently began work on Periphery v3 that aims to make Periphery a simpler to use by removing the need to specify the list of targets to scan. Instead, by default, Periphery will scan all Swift sources in the index store. The --index-exclude, --exclude-targets and --exclude-tests options can then be used to refine the output.

The format of the generic project config file has changed to reflect this: https://github.com/peripheryapp/periphery/blob/v3/Sources/PeripheryKit/Generic/GenericProjectDriver.swift#L8-L10. This should simplify the aspect a bit, since we no longer need to collect the source files. If you're willing, I think it would be great to include this Bazel support in v3.

[ileitch]

Closing this now that #786 is merged. This PR was a huge help to me, especially the aspect implementation, thank you!

One difference between this PR and the implementation in master is the generation of the report as an output. I think perhaps we could wrap the scan rule with another that executes the scan and uses tee to pipe the output to a file. That way we get the benefit of the Bazel output while also seeing the output printed to stdout.