I am using Carthage dependency manager in my iOS project.
I have the Carthage/build folder in my repository to always have ready to go built frameworks when checking out the repo.
I am wondering what the bcsymbolmap files in the build folder are for. Quite a few of them are created with every carthage update.
Do I need to keep these files? Should I have them in my repository?
No, you don't need those files. If you set up Carthage properly, binary, .dsym and .bcsymbolmap files will be copied on build phase. When you archive the build for distributing using App Store, all needed files will be included in archive and after you upload the build to App Store you will be able to upload dsyms files anytime (to be able to decode your crash reports). If fact you don't need to store .dsyms and .bcsymbolmap files in your repository.
There is a good article explaining what is happening when the framework is being build (and what in fact Carthage scripts do) https://instabug.com/blog/ios-binary-framework/. Also it explains what for .bcsymbolmaps files used for - so Apple servers can rebuild your code using Bitcode and then you can desymbolicate your crash reports.
So, you don't need to keep those files. No need to store them in repository. The other reason not to store content of Build folder is that anyway your project can fail build with it on another machine with different environment. If you want to build your project with the same versions of dependencies - use Carthage bootstrap command instead of update.
P.S.
Also you can investigate what copy-frameworks command do:
https://github.com/Carthage/Carthage/blob/fc0166b4827736bac2c804fc928797f1a742c455/Source/carthage/CopyFrameworks.swift