SI-8871 Fix specialization under REPL / FSC

The transformation of applications to specialized methods
relies on the owner of said method having had the specialization
info transform run which stashes a bunch of related data into
per-run caches such as `SpecializeTypes#{typeEnv}`.

Recently, we found that per-run caches didn't quite live up
to there name, and in fact weren't being cleaned up before
a new run. This was remedied in 00e11ff.

However, no good deed goes unpunished, and this led to a
regression in specialization in the REPL and FSC.

This commit makes two changes:

  - change the specialization info tranformer to no longer
    directly enter specialized methods into the `info` of whatever
    the current phase happens to be. This stops them showing up
    `enteringTyper` of the following run.
  - change `adaptInfos` to simply discard all but the oldest
    entry in the type history when bringing a symbol from one
    run into the next. This generalizes the approach taken to
    fix SI-7801. The specialization info transformer will now
    execute in each run, and repopulate `typeEnv` and friends.

I see that we have a seemingly related bandaid for this sort
of problem since 08505bd4ec. In a followup, I'll try to revert
that.

4 files changed, 18 insertions, 0 deletions

diff --git a/test/files/res/t8871.check b/test/files/res/t8871.check
new file mode 100644
index 0000000000..bbd9331b16
--- /dev/null
+++ b/test/files/res/t8871.check
@@ -0,0 +1,5 @@
+
+nsc> 
+nsc> 
+nsc> 
+nsc> 
diff --git a/test/files/res/t8871.res b/test/files/res/t8871.res
new file mode 100644
index 0000000000..9b1a5fb57f
--- /dev/null
+++ b/test/files/res/t8871.res
@@ -0,0 +1,4 @@
+t8871/tag.scala
+t8871/usetag.scala
+t8871/usetag.scala
+
diff --git a/test/files/res/t8871/tag.scala b/test/files/res/t8871/tag.scala
new file mode 100644
index 0000000000..1a1803b77d
--- /dev/null
+++ b/test/files/res/t8871/tag.scala
@@ -0,0 +1,3 @@
+class Tag {
+  @inline def apply[@specialized A, T](a: A): A = a
+}
diff --git a/test/files/res/t8871/usetag.scala b/test/files/res/t8871/usetag.scala
new file mode 100644
index 0000000000..139d768552
--- /dev/null
+++ b/test/files/res/t8871/usetag.scala
@@ -0,0 +1,6 @@
+trait Foo
+
+object Test {
+  val y = new Tag().apply[Double, Foo](3.3)
+  // under FSC, this gave t8871/usetag.scala:4: error: wrong number of type parameters for method apply$mDc$sp: [T](a: Double)Double
+}