title: Exception java.lang.NoClassDefFoundError: scala/collection/SeqLike in Scala project that does not refer to SeqLike class - why?
body: <p>I am using Java 12 / Scala 12.3 project <a href="https://github.com/dominique-unruh/scala-isabelle/" rel="nofollow noreferrer">https://github.com/dominique-unruh/scala-isabelle/</a> for the digesting of Isabelle-HOL source code. This is not easy stuff. But project compiles and tests executes correctly.</p>
  <p>Then I imported Sext library <a href="https://github.com/nikita-volkov/sext/" rel="nofollow noreferrer">https://github.com/nikita-volkov/sext/</a> for pretty-printing Scala object tree (as there is not inner pretty-printing or toJson tree methods in Scala) via addition in build.sbt</p>
  <pre><code>libraryDependencies += &quot;com.github.nikita-volkov&quot; % &quot;sext&quot; % &quot;0.2.4&quot;
  </code></pre>
  <p>The project compiles but</p>
  <pre><code>val ctxt = Context(&quot;Main&quot;)
  println(ctxt.treeString)
  </code></pre>
  <p>gives error message:</p>
  <pre><code>Exception in thread &quot;main&quot; java.lang.NoClassDefFoundError: scala/collection/SeqLike
      at sext.package$.SextAnyTreeString(package.scala:109)
      at de.unruh.isabelle.Example2theory$.main(Example2theory.scala:151)
      at de.unruh.isabelle.Example2theory.main(Example2theory.scala)
  Caused by: java.lang.ClassNotFoundException: scala.collection.SeqLike
      at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
      at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
      at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
      ... 3 more
  </code></pre>
  <p>When I check Scala 2.13 documentation <a href="https://www.scala-lang.org/files/archive/api/2.13.5/scala/collection/" rel="nofollow noreferrer">https://www.scala-lang.org/files/archive/api/2.13.5/scala/collection/</a> then there is no SeqLike indeed, 2.12 has it <a href="https://www.scala-lang.org/api/2.12.5/scala/collection/SeqLike.html" rel="nofollow noreferrer">https://www.scala-lang.org/api/2.12.5/scala/collection/SeqLike.html</a></p>
  <p>But from where this SeqLike comes in my Scala code that compiles under 2.13? Sext library does not refer to SeqLike as well. How it is possible that such class is required?</p>