Create chunks in Stream.fromIterator (#2010)

[susuro]

Improves performance of Stream.fromIterator and Stream.fromBlockingIterator by creating chunks of requested size, as described in #2010.

[mpilquist]

Looks like mima configuration is messed up: [info] fs2-core: mimaPreviousArtifacts is empty, not analyzing binary compatibility.

If we fix that so it correctly checks binary compatibility, the build will fail on this change. Can you try making it an overload instead?

[mpilquist]

Mima check is failing with:

[error] fs2-core: Failed binary compatibility check against co.fs2:fs2-core_2.12:2.0.0! Found 2 potential problems (filtered 662)
[error]  * extension method apply$extension(Boolean,scala.concurrent.ExecutionContext,scala.collection.Iterator,cats.effect.Sync,cats.effect.ContextShift)fs2.internal.FreeC in object fs2.Stream#PartiallyAppliedFromBlockingIterator does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("fs2.Stream#PartiallyAppliedFromBlockingIterator.apply$extension")
[error]  * extension method apply$extension(Boolean,scala.collection.Iterator,cats.effect.Sync)fs2.internal.FreeC in object fs2.Stream#PartiallyAppliedFromIterator does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("fs2.Stream#PartiallyAppliedFromIterator.apply$extension")
[error] stack trace is suppressed; run last mimaReportBinaryIssues for the full output

[susuro]

I have no clue why this has broken the binary compatibility and how to cope with it. Any idea?

[susuro]

I don't see how this can really break the compatibility. I would suggest excluding it from compatibility checks:

ProblemFilters.exclude[DirectMissingMethodProblem]("fs2.Stream#PartiallyAppliedFromIterator.apply$extension"),
ProblemFilters.exclude[DirectMissingMethodProblem]("fs2.Stream#PartiallyAppliedFromBlockingIterator.apply$extension")

[mpilquist]

Can you try compiling some code against 2.4.4 that uses fromIterator and then running that compiled code against the current head?

[susuro]

I did two tests on Scala 2.13, calling fromIterator directly and through a library. Both, the application and the library were built against 2.4.4 and first run with this version on classpath, then with the version from head. Each execution was correct. The head version was built with publishLocal after slight modification of build.sbt to get the library for Scala 2.13 (only 0.26 was published originally).
To check if the methodology is correct, I built also a modified head version with default chunk size parameter instead of an overload. This time I got indeed an error Exception in thread "main" java.lang.NoSuchMethodError: 'fs2.internal.FreeC fs2.Stream$PartiallyAppliedFromIterator$.apply$extension(boolean, scala.collection.Iterator, cats.effect.Sync)'.
I am not sure if this proves the compatibility enough, though.

[mpilquist]

OK cool, I guess it's a false report by mima. Let's add the exclusions.

[susuro]

I see you have already added it. Thanks.