Is it possible to disable publish without disabling publishLocal in sbt? - sbt

Question

I have an sbt project where docker:publishLocal will create a docker image on my machine for testing, and docker:publish will publish the image to a repository and also publish jar files from the build to a repository.
If my project is a snapshot, I would like to disable publishing to the repositories, while still being able to build the local image.
ThisBuild / publishArtifact := ! isSnapshot.value
does the right thing for the publish command, but it also disables publishLocal.
I want to write something like
if (isSnapshot.value) {
publish := { }
}
but that gives me an error that I do not understand at all:
[info] Loading project definition from /Users/dev/project
/Users/dev/build.sbt:1: error: type mismatch;
found : Unit
required: sbt.internal.DslEntry
if (isSnapshot.value) {
^
Past experience dictates that redefining publish to conditionally call the original version won't work, as
publish := {
if (!isSnapshot.value) publish.value
}
gives warnings that the task is always evaluated.
Is there a way to do this?

Answer 1

The problem with this code is that it evaluates publish.value regardless of the if structure. I recommend reading the documentation on task dependencies. If you want to "delay" the evaluation of a task in one of the if branches, you need to use dynamic task definition:
publish := Def.taskDyn {
if (isSnapshot.value)
Def.task {} // doing nothing
else
Def.task { publish.value } // could be written as just publish
}.value
But apart from fixing your code, you should be aware that there is a special setting for the functionality you want, it's called skip:
publish/skip := isSnapshot.value
Another thing to notice, is the scoping. If you want to override docker:publish, which is the same as Docker/publish in the new syntax, you should add this Docker/ scope prefix to every mention of publish in the code above.