mutable.Map.getOrElseUpdate issue

[igreenfield]

If you use recursive getOrElseUpdate you can easily end up with a map that contains the same key twice with different values:

val map = mutable.Map[String, String]()

map.getOrElseUpdate("key", {
  map.getOrElseUpdate("key", "value1")
  "value2"
})

map

The second call could come from another place in the application this is just a sample.

[yairogen]

👍

[hrhino]

This issue also seems to exist in the 2.13 collections library; perhaps consider reporting it there, as well.

hhoughton:tmp hhoughton$ scala-launch 2.12.4 -cp `coursier fetch -q -p ch.epfl.scala:collection-strawman_2.12:0.8.0`
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_121).
Type in expressions for evaluation. Or try :help.

scala> import strawman._, collection._
import strawman._
import collection._

scala> :pa
// Entering paste mode (ctrl-D to finish)

val map = mutable.Map[String, String]()

map.getOrElseUpdate("key", {
  map.getOrElseUpdate("key", "value1")
  "value2"
})

// Exiting paste mode, now interpreting.

map: strawman.collection.mutable.Map[String,String] = HashMap(key -> value2, key -> value1)
res0: String = value2

[retronym]

Seems like a duplicate of #10187, although the fix in 2.13.x is different from that in 2.12.x.

I'll investigate further.

[retronym]

Ah, I see that this was reported after the attempted fix in 2.12.x, but shows a case where the behaviour is still wrong.

[retronym]

We should backport the fix to 2.12.7