remove "-Xmigration" from main scalacOptions. add explicit type

[xuwei-k]

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• Have you added tests for any changed functionality?

Helpful things

Fixes

Purpose

remove "-Xmigration" from main code and add explicit types. for avoid different return types Scala 2 and 3.

Background Context

"-Xmigration" suppress some warnings. But I think this is not good idea.

please see following example and scala/scala pull request.

• Emit migration warnings under -Xsource:3 as fatal warnings, not errors; -Xmigration turns off erroring scala/scala#10439

Scala 3

Welcome to Scala 3.3.1 (11.0.20.1, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                             
scala> trait A { def x: Any } ; class B extends A { def x = "x" }
// defined trait A
// defined class B
                                                                                                                                             
scala> new B().x // not String !. different type with Scala 2.13
val res0: Any = x

no option

Welcome to Scala 2.13.12 (OpenJDK 64-Bit Server VM, Java 11.0.20.1).
Type in expressions for evaluation. Or try :help.

scala> trait A { def x: Any } ; class B extends A { def x = "x" }
trait A
class B

scala> new B().x
val res0: String = x

-Xsource:3

$ scala -Xsource:3
Welcome to Scala 2.13.12 (OpenJDK 64-Bit Server VM, Java 11.0.20.1).
Type in expressions for evaluation. Or try :help.

scala> trait A { def x: Any } ; class B extends A { def x = "x" }
                                                        ^
       error: under -Xsource:3, inferred Any instead of String [quickfixable]
       Scala 3 migration messages are errors under -Xsource:3. Use -Wconf / @nowarn to filter them or add -Xmigration to demote them to warnings.
       Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=scala3-migration, site=B.x

scala> trait A { def x: Any } ; class B extends A { def x: String = "x" }
trait A
class B

-Xsource:3 and -Xmigration

$ scala -Xsource:3 -Xmigration
Welcome to Scala 2.13.12 (OpenJDK 64-Bit Server VM, Java 11.0.20.1).
Type in expressions for evaluation. Or try :help.

scala> trait A { def x: Any } ; class B extends A { def x = "x" }
                                                        ^
       warning: under -Xsource:3, inferred Any instead of String [quickfixable]
trait A
class B

scala> def f: Seq[Int] = Nil // unnecessary migration message!!!
              ^
       warning: type Seq in package scala has changed semantics in version 2.13.0:
       scala.Seq is now scala.collection.immutable.Seq instead of scala.collection.Seq
def f: Seq[Int]

References

[mkurz]

@xuwei-k can you please rebase? Thanks!

[mkurz]

Thanks LGTM!

However, I pushed two commits:

• First I removed the MiMa filter you added because it is not necessary (anymore?)
• I also removed the -Wconf... flags you added, because also they are not necessary anymore because Scala 2.13.13 fixed the errors, see
  • Drop package objects with inheritance scala/scala-dev#441 (comment)
  • Package object extends deprecated under -Xsource:3 not dotty scala/bug#12886
  • Allow either -Xsource:3 (for preparing to switch to 3) or -Xsource:3-cross (for crossbuilding on 2 and 3) scala/scala#10573 <-- This PR removes the package object inheritance is deprecated errors/warnings

[mkurz]

The -Xmigration flag for the test scope eventually got removed in

• Scala 2.13.14 / Add explicit types and remove -Xmigration flag in tests #12577

I adjusted all the test finally (necessary for upgrading to Scala 2.13.14 without adding any Wconf filters, see #12576 (comment))

[mkurz]

Backported this changes (together with removing -Xmigration from tests) to 2.9.x and 3.0.x:

• [3.0.x] Scala 2.13.14 / Add explicit types and remove -Xmigration flag #12576
• [2.9.x] Scala 2.13.14 / Add explicit types and remove -Xmigration flag #12575