Try using the val alias

Author: allanrenucci

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -405,8 +405,21 @@ class Definitions {
     // We load SeqType from the alias in scala package object
     //  - in 2.12: scala.collection.Seq
     //  - in 2.13: scala.collection.immutable.Seq
-    val alias = ctx.base.staticRef("scala.Seq".toTypeName).requiredSymbol(_.isAliasType)
-    alias.info.classSymbol.typeRef
+
+    // force to avoid cycles
+    // ctx.requiredClassRef("scala.collection.Seq").symbol.ensureCompleted()
+    // ctx.requiredClassRef("scala.collection.immutable.Seq").symbol.ensureCompleted()
+
+    // // Using type Seq[+A] = ...
+    // val alias = ctx.base.staticRef("scala.Seq".toTypeName).requiredSymbol(_.isAliasType)
+    // alias.info.classSymbol.typeRef
+
+    // Using val Seq = ...
+    val scalaSeq = ctx.base.staticRef("scala.Seq".toTermName)
+    val seqName = scalaSeq.info.resultType.termSymbol.fullName
+    ctx.requiredClassRef(seqName.toTypeName)
+
+    // ctx.requiredClassRef("scala.collection.Seq")
   }
 
   def SeqClass(implicit ctx: Context) = SeqType.symbol.asClass

tests/pos/seqtype-cycle/Test2.scala

@@ -1,5 +1,6 @@
 package object scala {
   type Throwable = java.lang.Throwable // needed for some reasons
 
-  type Seq[+A] = scala.Seq[A]
+  type Seq[+A] = scala.collection.Seq[A]
+  val Seq = scala.collection.Seq
 }

tests/pos/seqtype-cycle/Test3.scala

@@ -1,5 +1,12 @@
 package scala
 
-trait Seq[@specialized(1, 2) A]
-
 class specialized(types: Int*) extends scala.annotation.StaticAnnotation
+
+package collection {
+  class Foo[@specialized(1, 2) A]
+
+  trait Seq[A] extends Foo[A]
+  object Seq extends SeqFactory[Seq]
+
+  trait SeqFactory[CC[X] <: Seq[X]]
+}