better support of custom configurations in SemanticdbPlugin

Second take at https://github.com/sbt/sbt/issues/5886, which fixed the
problem for Test specifically but not for custom configurations.

* Any child of Compile (like Custom in the scripted) had to use
  testSettings, whether they were related to testing or not
* Custom configurations with grand parents (like SystemTest in the
  scripted) would get duplicated scalacOptions no matter what they used

main/src/main/scala/sbt/plugins/SemanticdbPlugin.scala

@@ -13,10 +13,10 @@ import java.io.File
 import Keys._
 import sbt.internal.SysProp
 import sbt.librarymanagement.syntax._
-import sbt.librarymanagement.CrossVersion
+import sbt.librarymanagement.{ Configuration, CrossVersion }
 import Project.inConfig
 import sbt.internal.inc.ScalaInstance
-import sbt.SlashSyntax0._
+import sbt.ScopeFilter.Make._
 
 object SemanticdbPlugin extends AutoPlugin {
   override def requires = JvmPlugin
@@ -50,7 +50,7 @@ object SemanticdbPlugin extends AutoPlugin {
     }
   ) ++
     inConfig(Compile)(configurationSettings) ++
-    inConfig(Test)(configurationSettings ++ testSettings)
+    inConfig(Test)(configurationSettings)
 
   lazy val configurationSettings: Seq[Def.Setting[_]] = List(
     semanticdbTargetRoot := {
@@ -58,8 +58,22 @@ object SemanticdbPlugin extends AutoPlugin {
       if (in) classDirectory.value
       else semanticdbTargetRoot.value
     },
+    semanticdbOptions --= Def.settingDyn {
+      val scalaV = scalaVersion.value
+      val config = configuration.value
+      Def.setting {
+        semanticdbTargetRoot.?.all(ancestorConfigs(config)).value.flatten
+          .flatMap(targetRootOptions(scalaV, _))
+      }
+    }.value,
     semanticdbOptions ++=
       targetRootOptions(scalaVersion.value, semanticdbTargetRoot.value),
+    scalacOptions --= Def.settingDyn {
+      val config = configuration.value
+      Def.setting {
+        semanticdbOptions.?.all(ancestorConfigs(config)).value.flatten.flatten
+      }
+    }.value,
     scalacOptions ++= {
       if (semanticdbEnabled.value)
         semanticdbOptions.value
@@ -67,15 +81,8 @@ object SemanticdbPlugin extends AutoPlugin {
     }
   )
 
-  lazy val testSettings: Seq[Def.Setting[_]] = List(
-    // remove Compile targetRoot from Test config
-    semanticdbOptions --= targetRootOptions(
-      (Compile / scalaVersion).value,
-      (Compile / semanticdbTargetRoot).value
-    ),
-    // remove duplicated semanticdbOptions
-    scalacOptions --= (Compile / semanticdbOptions).value
-  )
+  @deprecated("use configurationSettings only", "1.5.0")
+  lazy val testSettings: Seq[Def.Setting[_]] = List()
 
   def targetRootOptions(scalaVersion: String, targetRoot: File): Seq[String] = {
     if (ScalaInstance.isDotty(scalaVersion)) {
@@ -84,4 +91,11 @@ object SemanticdbPlugin extends AutoPlugin {
       Seq(s"-P:semanticdb:targetroot:$targetRoot")
     }
   }
+
+  private def ancestorConfigs(config: Configuration) = {
+    def ancestors(configs: Vector[Configuration]): Vector[Configuration] =
+      configs ++ configs.flatMap(conf => ancestors(conf.extendsConfigs))
+
+    ScopeFilter(configurations = inConfigurations(ancestors(config.extendsConfigs): _*))
+  }
 }

sbt/src/sbt-test/project/semanticdb/build.sbt

@@ -2,4 +2,29 @@ ThisBuild / scalaVersion := "2.12.12"
 ThisBuild / semanticdbEnabled := true
 ThisBuild / semanticdbIncludeInJar := true
 
+// see https://github.com/sbt/sbt/issues/5886
+lazy val check = taskKey[Unit]("Checks that scalacOptions have the same number of parameters across configurations")
+lazy val anyConfigInThisProject = ScopeFilter(configurations = inAnyConfiguration)
+
+lazy val Custom = config("custom").extend(Compile)
+lazy val SystemTest = config("st").extend(IntegrationTest)
+
 lazy val root = (project in file("."))
+  .configs(IntegrationTest, Custom, SystemTest)
+  .settings(
+    inConfig(IntegrationTest)(Defaults.testSettings ++ sbt.plugins.SemanticdbPlugin.configurationSettings),
+    inConfig(Custom)(Defaults.configSettings ++ sbt.plugins.SemanticdbPlugin.configurationSettings),
+    inConfig(SystemTest)(Defaults.testSettings ++ sbt.plugins.SemanticdbPlugin.configurationSettings),
+    check := {
+      val scalacOptionsCountsAcrossConfigs = scalacOptions.?.all(anyConfigInThisProject)
+        .value
+        .map(_.toSeq.flatten.size)
+        .filterNot(_ == 0)
+        .distinct
+      assert(
+        scalacOptionsCountsAcrossConfigs.size == 1,
+        s"Configurations expected to have the same number of scalacOptions but found different numbers: $scalacOptionsCountsAcrossConfigs"
+      )
+    }
+
+  )

sbt/src/sbt-test/project/semanticdb/src/custom/scala/foo/Custom.scala

@@ -0,0 +1,3 @@
+package foo
+
+object Custom

sbt/src/sbt-test/project/semanticdb/src/it/scala/foo/IntegrationTest.scala

@@ -0,0 +1,3 @@
+package foo
+
+object IntegrationTest

sbt/src/sbt-test/project/semanticdb/src/main/scala/foo/Compile.scala

@@ -1,6 +1,6 @@
 package foo
 
-object Test {
+object Compile {
   def main(args: Array[String]): Unit = {
     println("hello world")
   }

sbt/src/sbt-test/project/semanticdb/src/st/scala/foo/SystemTest.scala

@@ -0,0 +1,3 @@
+package foo
+
+object SystemTest

sbt/src/sbt-test/project/semanticdb/src/test/scala/foo/Test.scala

@@ -0,0 +1,3 @@
+package foo
+
+object Test

sbt/src/sbt-test/project/semanticdb/test

@@ -1,2 +1,16 @@
 > compile
-$ exists target/scala-2.12/classes/META-INF/semanticdb/src/main/scala/foo/Test.scala.semanticdb
+$ exists target/scala-2.12/classes/META-INF/semanticdb/src/main/scala/foo/Compile.scala.semanticdb
+
+> test:compile
+$ exists target/scala-2.12/test-classes/META-INF/semanticdb/src/test/scala/foo/Test.scala.semanticdb
+
+> it:compile
+$ exists target/scala-2.12/it-classes/META-INF/semanticdb/src/it/scala/foo/IntegrationTest.scala.semanticdb
+
+> custom:compile
+$ exists target/scala-2.12/custom-classes/META-INF/semanticdb/src/custom/scala/foo/Custom.scala.semanticdb
+
+> st:compile
+$ exists target/scala-2.12/st-classes/META-INF/semanticdb/src/st/scala/foo/SystemTest.scala.semanticdb
+
+> check