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REPL silently hides the fact that rendering of large structures are elided (no ... is shown as in Scala2 REPL)

See original GitHub issue

Compiler version

3.0.0-M4-bin-20210209-a66eaf3-NIGHTLY

Minimized code + Output

scala> val xs = collection.immutable.ArraySeq.fill(100)(0)

scala> val ys = xs :+ 11111  // works as expected, last elem is 11111
val ys: scala.collection.immutable.ArraySeq[Int] = ArraySeq(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11111)

scala> val xs = collection.immutable.ArraySeq.fill(1000)(0)  

scala> val ys = xs :+ 11111  // HERE THE LAST printed elem by the REPL echo is 0 (sic!) 
val ys: scala.collection.immutable.ArraySeq[Int] = ArraySeq(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
[... many zeros and commas elided by me, the reporter]
0, 0, 0, 0, 0, 0, 0)

scala> ys.toString  // but this works, last line of output is as expeced: 
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11111)

This is happening because of this: https://github.com/lampepfl/dotty/blob/a7cb965fc9b106c9c85965afed96bda34e9063f5/compiler/src/dotty/tools/repl/Rendering.scala#L32

Expectation

When large structures are elided the REPL printout should end with ... as in Scala2 REPL to indicate that not everything is shown.

It is especially confusing that it ends with ,0) instead of , ... as this made me think that all elements where in the output.

Issue Analytics

State:
Created 3 years ago
Comments:17 (9 by maintainers)

Top GitHub Comments

1reaction

bjornregnellcommented, Feb 10, 2021

So this is a deeper collection rendering issue to take in Scala 2. But I think making the REPL not creating surprise as my fix fixes, is good, even if it does not fix the deeper issue…

0reactions

som-snyttcommented, Feb 10, 2021

Thanks. That is more how than why. Maybe anything less than a show typeclass will be a limited solution.

https://github.com/scala/bug/issues/11785#issuecomment-755003346

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