Merge pull request #165 from hmrc/PLATUI-1736_adr_scala_cross_compila…

…tion

PLATUI-1736: Add adr with decision not to allow scala cross compilation

docs/maintainers/adr/0001-scala-cross-compilation.md

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+# play-ui scala 2.13 cross compilation 
+
+* Status: accepted
+* Date: 2022-05-19
+
+## Context and Problem Statement
+
+The need to allow scala cross compilation for scala version 2.13
+
+## Decision Drivers
+
+* as new scala versions are released we are in the process of allowing cross compilation between these new scala versions, 
+for all our libraries and services so when service teams that use our libraries/services update their scala versions our libraries/services will support it.
+* we don't want new services to start using play-ui
+* we want to be able to easily change our mind if we need to
+
+## Considered Options
+
+* Do not allow scala cross compilation for scala version 2.13
+* Add scala cross compilation for scala version 2.13
+
+## Decision Outcome
+
+Chosen option "Do not allow scala cross compilation" because play-ui is a deprecated library, and we do not actively support development for it anymore.
+
+### Positive Consequences
+
+* As adding scala cross compilation for version 2.13 would be implicitly supporting this deprecated library, we would not want to give service teams that are still using this library the wrong impression that we are still actively supporting it.
+* By adding scala cross compilation for version 2.13, we could be creating more work for ourselves as there could be issues when service teams still actively using this library upgrade there scala version to 2.13. We would end up supporting those queries which we shouldn't do as we do not actively support this deprecated library anymore.
+* There wouldn't be risk of needing to add cross compilation and not being able to- we've checked if we could if we wanted to
+
+### Negative Consequences
+
+* As there are service teams that are actively using this library and cannot for some reason move away from using this library, there might be a time when we would need to support scala version 2.13 for those service teams.