How to deal with "changed semantics" warning?

Question
1

We use Scala 2.12.13 and SBT 1.4.7.

I’m getting the warning that "method values in trait MapLike has changed semantics in version 2.8.0:
values returns Iterable[V] rather than Iterator[V]".

So I thought I’d spell it out:

val things: scala.collection.immutable.IndexedSeq[SomeThing] = ...
val x: Iterable[scala.collection.immutable.IndexedSeq[SomeThing]] =
        things.groupBy(thing => thing.id_thing).values

but I still get the warning (on “values” in the third line).

What (more) should I do to silence this warning?

2

I found a way to solve my immediate problem by using “valuesIterator” instead of “values” but I’d still like to understand why the warning remains in the above code.

3

The warning is issued as soon as you use the .values method, since it is annotated with a @migration note.

See scala/src/library/scala/annotation/migration.scala at 60b503bcfdd61e086fa6b978c38009f2604dd365 · scala/scala · GitHub

You could suppress all migration warnings when using the -Xmigration compiler flag; just give it a version number >= 2.8.0.

4

I have been using

scalacOptions ++= Seq(
    <snip/>
    "-Xmigration", "2.12.13",
    <snip/>
)

but I have now tried ">=2.8.0", ">2.8.0", and ">=2.12.13" but I get the same result everywhere.

Am I misunderstanding you?

5

The synopsis is:

$ scalac -X
...
-Xmigration:<version>            Warn about constructs whose behavior may have changed since version.

So, it should work with -Xmigration:2.8 for example. And you can also give the special value none to see no migration warnings at all.

6

I see. That contradicts what I see at https://docs.scala-lang.org/overviews/compiler-options/index.html there it says:

-Xmigration VERSION
Warn about constructs whose behavior may have changed since version.

Default: none

No colon. It’s unfortunate that we are (or at least appear to be) so inconsistent; some flags need a colon others don’t.

Any idea why SBT/scalac did not die with an error or at least showed a warning? That would have saved me quite a bit of time.

In any case, thank you very much. You’ve saved what’s left of my hair. :wink: