String multiplication + mkString causes OutOfMemoryError in Scala 2.13.0-M4

[xerial]

This simple code causes OutOfMemoryError in Scala 2.13.0-M4:

("?" * 10).mkString(",")

[error] (run-main-0) java.lang.OutOfMemoryError: Java heap space
[error] java.lang.OutOfMemoryError: Java heap space
[error] 	at java.util.Arrays.copyOf(Arrays.java:3332)
[error] 	at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
[error] 	at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:649)
[error] 	at java.lang.StringBuilder.append(StringBuilder.java:202)
[error] 	at scala.collection.mutable.StringBuilder.append(Builder.scala:209)
[error] 	at scala.collection.StringOps$.addString$extension2(StringOps.scala:524)
[error] 	at scala.collection.StringOps$.mkString$extension0(StringOps.scala:496)
[error] 	at scala.collection.StringOps$.mkString$extension1(StringOps.scala:504)
[error] 	at Sample2$.main(Sample2.scala:3)
[error] 	at Sample2.main(Sample2.scala)
[error] 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error] 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[error] 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error] 	at java.lang.reflect.Method.invoke(Method.java:498)
[error] 	at sbt.Run.invokeMain(Run.scala:93)
[error] 	at sbt.Run.run0(Run.scala:87)
[error] 	at sbt.Run.execute$1(Run.scala:65)
[error] 	at sbt.Run.$anonfun$run$4(Run.scala:77)
[error] 	at sbt.Run$$Lambda$4891/1073245253.apply$mcV$sp(Unknown Source)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] 	at sbt.util.InterfaceUtil$$anon$1.get(InterfaceUtil.scala:10)
[error] 	at sbt.TrapExit$App.run(TrapExit.scala:252)
[error] 	at java.lang.Thread.run(Thread.java:748)
[error] java.lang.RuntimeException: Nonzero exit code: 1
[error] 	at sbt.Run$.executeTrapExit(Run.scala:124)
[error] 	at sbt.Run.run(Run.scala:77)
[error] 	at sbt.Defaults$.$anonfun$bgRunTask$5(Defaults.scala:1168)
[error] 	at sbt.Defaults$.$anonfun$bgRunTask$5$adapted(Defaults.scala:1163)
[error] 	at sbt.internal.BackgroundThreadPool.$anonfun$run$1(DefaultBackgroundJobService.scala:366)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] 	at scala.util.Try$.apply(Try.scala:209)
[error] 	at sbt.internal.BackgroundThreadPool$BackgroundRunnable.run(DefaultBackgroundJobService.scala:289)
[error] 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
[error] 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
[error] 	at java.lang.Thread.run(Thread.java:748)

A workaround is adding toSeq:

("?" * 10).toSeq.mkString(",")

[xerial]

Duplicate of #10951?

[SethTisue]

Duplicate of #10951