This flips the default := operation to the cached task. For example, the following task would be cached:

val someKey = taskKey[String]("something")

someKey := {
  name.value + version.value + "!"
}

Per-task-key opt-out

To opt out of the cache at the key level, use @cacheLevel(include = Array.empty).

@cacheLevel(include = Array.empty)
val someKey = taskKey[String]("something")

// someKey will not be cached
someKey := {
  name.value + somethingUncachable.value + "!"
}

Per-task opt-out

To opt out of the cache individually, use Def.uncached(...).

val someKey = taskKey[String]("something")

someKey := Def.uncached {
  name.value + somethingUncachable.value + "!"
}

Build-wide opt-out

Add the following to project/plugins.sbt:

Compile / scalacOptions += "-Xmacro-settings:sbt:no-default-task-cache"

Note about side effects

Any tasks involving files require careful consideration to capture the side effects.
See https://www.scala-sbt.org/2.x/docs/en/concepts/caching.html#caching-files for details.