Stack Docker Bug

Stack has functionality to build Haskell software in a Docker image running Alpine Linux, which makes it very easy to create static executables. Unless an image is specified in the configuration, a default image is used. In the past, the default image was pulled from the fpco/stack-build repository, tagged with the full LTS version (example: lts-18.3). At some point, however, new images were no longer pushed to that repository. Instead, new images are being pushed to the commercialhaskell/stackage repository, tagged with the LTS major version (example: lts18).

I noticed this bug while developing lsupg, but I figured that it would be fixed in the next release of Stack. Stack 2.7.3 was released yesterday, however, and the bug still exists. I went ahead and created an issue this evening.

Investigating the implementation, I found that the addDefaultTag function is used to determine the tag for both the default repository as well as user-specified repositories (that do not already include a tag or digest). I am not sure what behavior is desired in this case, so I submitted an example diff of an implementation that formats tags depending on the LTS version in both cases. I hope to receive some feedback.