Fix aggregation

main/src/main/scala/sbt/internal/Aggregation.scala

@@ -251,12 +251,12 @@ object Aggregation {
       proj: Option[Reference],
       extra: BuildUtil[Proj],
       reverse: Boolean
-  ): Seq[ProjectRef] = {
+  ): Seq[ProjectRef] =
     val resRef = proj.map(p => extra.projectRefFor(extra.resolveRef(p)))
-    resRef.toList.flatMap(ref =>
+    resRef.toList.flatMap { ref =>
-      if (reverse) extra.aggregates.reverse(ref) else extra.aggregates.forward(ref)
+      if reverse then extra.aggregates.reverse(ref)
-    )
+      else extra.aggregates.forward(ref)
-  }
+    }
 
   def aggregate[T, Proj](
       key: ScopedKey[T],

main/src/main/scala/sbt/internal/BuildUtil.scala

@@ -114,7 +114,7 @@ object BuildUtil {
     val depPairs =
       for {
         (uri, unit) <-
-          units.toIterable // don't lose this toIterable, doing so breaks actions/cross-multiproject & actions/update-state-fail
+          units.toSeq // don't lose this toSeq, doing so breaks actions/cross-multiproject & actions/update-state-fail
         project <- unit.projects
         ref = ProjectRef(uri, project.id)
         agg <- project.aggregate

sbt-app/src/sbt-test/actions/cross-strict-aggregation-scala-3/core/src/main/B.scala

@@ -0,0 +1,4 @@
+package foo
+
+object B
+

sbt-app/src/sbt-test/actions/cross-strict-aggregation-scala-3/test

@@ -6,6 +6,11 @@ $ exists core/target/scala-3.0.2
 -$ exists subproj/target/scala-3.1.2
 
 > clean
+-$ exists core/target/scala-3.0.2
+-$ exists core/target/scala-3.1.2
+-$ exists subproj/target/scala-3.0.2
+-$ exists subproj/target/scala-3.1.2
+
 > ++3.1.2 compile
 
 -$ exists core/target/scala-3.0.2