Prevent nesting properties

[NthPortal]

Prevent nesting properties or otherwise adding properties
during execution.

[NthPortal]

an alternative would be to add a private[scalacheck] def freeze(): Unit and call it from the task when it gets the properties or right before execution

[SethTisue]

elsewhere you said "the scalacheck folks said this is not something you're supposed to do", was on that on Twitter?

[NthPortal]

@SethTisue https://gitter.im/scalacheck/Lobby?at=5f3f12ce07c30d132a9ecaa3

[NthPortal]

for reference, what currently happens when you nest properties is not particularly sensible in the first place. they do run, but their name/path does not include the property they were nested inside of, and they get executed at the end, rather than in order.

[SethTisue]

does anyone object to this? if not, let's merge it (in a week or so, say)

[NthPortal]

I don't see any objections

[SethTisue]

okay, if you squash it, I'll merge it

[NthPortal]

squashed

[ashawley]

What was the motivation for this change? I recall discussing in Gitter that there was an effort to optimize the Scala collections library that revealed a defect in this code in ScalaCheck. Is there an upstream issue to read more about this?

[NthPortal]

There were two motivations for this change:

• nesting properties was never supported, and it is better to explicitly disallow things you don't support rather than have them partially or mostly work and then have behaviour accidentally change underneath people if you end up changing the internal implementation
• what happens if you nest properties is that it creates a new property while executing the rest of the properties, and adds it to the ListBuffer that's being iterated over in order to execute all of the properties. as of 2.13.4, it is very likely that ListBuffer iterators (and soon other types as well) will throw an exception if you modify the underlying collection while using them

[ashawley]

Thanks, for the explanation. Had you run across a test suite that had nested properties and an exception was thrown with the ListBuffer change?

[NthPortal]

yes. scala/scala's 😬

[ashawley]

Ok, I wonder if I was wrong about nested properties not being supported. I know nesting properties isn't documented, but I suppose it may be possible for people to use it. I recall that cats and discipline projects could be doing something like this with law checking.

[SethTisue]

@ashawley would you like me to run this through the Scala community build?

[ashawley]

Yes, that would be useful. I was planning to ask. I'll open an issue there.

[SethTisue]

We're good over at scala/community-build#1226, so it looks like this change will stand.

[ashawley]

Yes, thanks for doing that for us, Seth!