Adding some Sets/Maps to perRunCaches, and elim...

Adding some Sets/Maps to perRunCaches, and eliminating ambiguously named
imports.

Did a tour of the compiler adding a few longer-lived mutable structures
to the per-run cache clearing mechanism. Some of these were not a big
threat, but there is (almost) literally no cost to tracking them and the
fewer mutable structures which are created "lone wolf style" the easier
it is to spot the one playing by his own rules.

While I was at it I followed through on long held ambition to eliminate
the importing of highly ambiguous names like "Map" and "HashSet" from
the mutable and immutable packages. I didn't quite manage elimination
but it's pretty close. Something potentially as pernicious which I
didn't do much about is this import:

  import scala.collection._

Imagine coming across that one on lines 407 and 474 of a 1271 file.
That's not cool. Some poor future programmer will be on line 1100 and
use "Map[A, B]" in some function and only after the product has shipped
will it be discovered that the signature is wrong and the rocket will
now be crashing into the mountainside straightaway. No review.

1 files changed, 0 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/settings/Warnings.scala b/src/compiler/scala/tools/nsc/settings/Warnings.scala
index b11c6f00ee..0d42fa503d 100644
--- a/src/compiler/scala/tools/nsc/settings/Warnings.scala
+++ b/src/compiler/scala/tools/nsc/settings/Warnings.scala
@@ -7,10 +7,6 @@ package scala.tools
 package nsc
 package settings
 
-import annotation.elidable
-import scala.tools.util.PathResolver.Defaults
-import scala.collection.mutable.HashSet
-
 /** Settings influencing the printing of warnings.
  */
 trait Warnings {