SI-8576 Minimal changes for `-Xcheckinit` compatibility

As explained in https://issues.scala-lang.org/browse/SI-8576, I expect
serialization compatibility between builds with and without
`-Xcheckinit` to be unattainable. This commit contains some minor fixes
for issues discovered while running builds with `-Xcheckinit`:

- Add `@SerialVersionUID` to `scala.collection.immutable.Vector`, as
  requested in SI-8576. Note that this does not make `Vector`
  serialization compatible.

- Use lazy initialization for `global` in `PresentationCompilation`. It
  used to access the uninitialized `self` variable (which seems to be
  inconsequential in practice and only fails under `-Xcheckinit`).

We should consider using `Externalizable` instead of `Serializable` for
collections in 2.13 to make collection classes serialization compatible.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/repl/scala/tools/nsc/interpreter/PresentationCompilation.scala b/src/repl/scala/tools/nsc/interpreter/PresentationCompilation.scala
index b9a4054ffc..d675563bc9 100644
--- a/src/repl/scala/tools/nsc/interpreter/PresentationCompilation.scala
+++ b/src/repl/scala/tools/nsc/interpreter/PresentationCompilation.scala
@@ -69,7 +69,7 @@ trait PresentationCompilation {
     val interactiveGlobal = new interactive.Global(copySettings, storeReporter) { self =>
       override lazy val platform: ThisPlatform = {
         new JavaPlatform {
-          val global: self.type = self
+          lazy val global: self.type = self
           override private[nsc] lazy val classPath: ClassPath = mergedFlatClasspath
         }
       }