sbt - 将设置提取到顶级 val

Question

给定:

resourceGenerators in Compile += Def.task {
  val jar = (update in Compile).value
    .matching((_: ModuleID) == nemesisProto)
    .head
  IO.unzip(jar, (resourceManaged in Compile).value / "protobuf").toSeq
}.taskValue

PB.protoSources in Compile := Seq((resourceManaged in Compile).value / "protobuf")

是否可以将 (resourceManaged in Compile).value/"protobuf" 重构到一个公共(public)位置？

我尝试将它分配给一个 val:

val protobufResourceFile = (resourceManaged in Compile).value / "protobuf"

resourceGenerators in Compile += Def.task {
  val jar = (update in Compile).value
    .matching((_: ModuleID) == nemesisProto)
    .head
  IO.unzip(jar, protobufResourceFile).toSeq
}.taskValue

PB.protoSources in Compile := Seq(protobufResourceFile)

只得到如下错误:

 error: `value` can only be used within a task or setting macro, such as :=, +=, ++=, Def.task, or Def.setting.
val protobufResourceFolder = (resourceManaged in Compile).value / "protobuf"
                                                          ^

Answer 1

差不多。正如错误消息所述，您根本无法解包 sbt dsl 之外的值。所以，像这样的事情通常使用 SettingKey 来完成:

val protobufResourceFile = settingKey[File]("Protobuf resource file ...")

protobufResourceFile := (resourceManaged in Compile).value / "protobuf"

resourceGenerators in Compile += Def.task {
  val jar = (update in Compile).value
    .matching((_: ModuleID) == nemesisProto)
    .head
  IO.unzip(jar, protobufResourceFile.value).toSeq
}.taskValue

PB.protoSources in Compile := Seq(protobufResourceFile.value)

不过，在这种特定情况下，它可能有点矫枉过正。