Fix Platform type in Global to be JavaPlatform.

At the moment we have just one Platform: JavaPlatform in the
compiler. The whole Platform abstraction feels dubious and
Java backends need to downcast to JavaPlatform to implement some
optimizations. It seems like for now it's just better to fix platform
declared in Global to be JavaPlatform and get rid of downcasting.

I checked that even JavaScript backend declares itself as a subtype
of JavaPlatform so it seems like our abstraction is not that useful.

If we have an alternative platform with specific requirements we
might want to refactor our Platform abstraction again but for now
it seems dubious to pay a price for abstraction nobody uses.

Author: gkossakowski

src/compiler/scala/tools/nsc/Global.scala

@@ -85,7 +85,7 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
     val settings: Settings = Global.this.settings
   } with JavaPlatform
 
-  type ThisPlatform = Platform { val symbolTable: Global.this.type }
+  type ThisPlatform = JavaPlatform { val global: Global.this.type }
   lazy val platform: ThisPlatform  = new GlobalPlatform
 
   type PlatformClassPath = ClassPath[AbstractFile]

src/compiler/scala/tools/nsc/backend/icode/GenICode.scala

@@ -1479,30 +1479,18 @@ abstract class GenICode extends SubComponent  {
 
       if (mustUseAnyComparator) {
         // when -optimise is on we call the @inline-version of equals, found in ScalaRunTime
-        val equalsMethod: Symbol =
+        val equalsMethod: Symbol = {
           if (!settings.optimise) {
-            def default = platform.externalEquals
-            platform match {
-              // TODO: define `externalEqualsNumNum`, `externalEqualsNumChar` and `externalEqualsNumObject` in Platform
-              // so we don't need special casing here
-              case x: JavaPlatform =>
-                // We need this cast because pattern matcher doesn't narrow type properly
-                val javaPlatformRefined = x.asInstanceOf[JavaPlatform { val global: GenICode.this.global.type }]
-                import javaPlatformRefined._
-                  if (l.tpe <:< BoxedNumberClass.tpe) {
-                    if (r.tpe <:< BoxedNumberClass.tpe) externalEqualsNumNum
-                    else if (r.tpe <:< BoxedCharacterClass.tpe) externalEqualsNumChar
-                    else externalEqualsNumObject
-                  }
-                  else default
-
-              case _ => default
-            }
-          }
-          else {
+            if (l.tpe <:< BoxedNumberClass.tpe) {
+              if (r.tpe <:< BoxedNumberClass.tpe) platform.externalEqualsNumNum
+              else if (r.tpe <:< BoxedCharacterClass.tpe) platform.externalEqualsNumChar
+              else platform.externalEqualsNumObject
+            } else platform.externalEquals
+          } else {
             ctx.bb.emit(LOAD_MODULE(ScalaRunTimeModule))
             getMember(ScalaRunTimeModule, nme.inlinedEquals)
           }
+        }
 
         val ctx1 = genLoad(l, ctx, ObjectReference)
         val ctx2 = genLoad(r, ctx1, ObjectReference)

src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala

@@ -1188,25 +1188,11 @@ abstract class BCodeBodyBuilder extends BCodeSkelBuilder {
 
       if (mustUseAnyComparator) {
         val equalsMethod: Symbol = {
-
-          def default: Symbol = platform.externalEquals
-
-          platform match {
-            // TODO: define `externalEqualsNumNum`, `externalEqualsNumChar` and `externalEqualsNumObject` in Platform
-            // so we don't need special casing here
-            case x: JavaPlatform =>
-              // We need this cast because pattern matcher doesn't narrow type properly
-              val javaPlatformRefined = x.asInstanceOf[JavaPlatform { val global: BCodeBodyBuilder.this.global.type }]
-              import javaPlatformRefined._
-                if (l.tpe <:< BoxedNumberClass.tpe) {
-                  if (r.tpe <:< BoxedNumberClass.tpe) externalEqualsNumNum
-                  else if (r.tpe <:< BoxedCharacterClass.tpe) externalEqualsNumChar
-                  else externalEqualsNumObject
-                }
-                else default
-
-            case _ => default
-          }
+          if (l.tpe <:< BoxedNumberClass.tpe) {
+            if (r.tpe <:< BoxedNumberClass.tpe) platform.externalEqualsNumNum
+            else if (r.tpe <:< BoxedCharacterClass.tpe) platform.externalEqualsNumChar
+            else platform.externalEqualsNumObject
+          } else platform.externalEquals
         }
         genLoad(l, ObjectReference)
         genLoad(r, ObjectReference)