Remove the hard-coded InteractiveCompilationUnit from ScalaHover

The associated compilation unit may change (see #1002251) when the editor
is reused. On top of that, the structured editor in the Play plugin needs
a no-arg constructor (it’s instantiated through an extension point).

This change allows the Play plugin to use plain Scala hovers, including
all the goodies (configured font and CSS, scaladoc, etc).

org.scala-ide.sdt.core/src/org/scalaide/ui/internal/editor/ScalaSourceViewerConfiguration.scala

@@ -188,7 +188,7 @@ class ScalaSourceViewerConfiguration(
 
   override def getInformationPresenter(sourceViewer: ISourceViewer) = {
     val p = new InformationPresenter(getInformationControlCreator(sourceViewer))
-    val ip = new HoverInformationProvider(compilationUnit map (new ScalaHover(_)))
+    val ip = new HoverInformationProvider(Some(new ScalaHover()))
 
     p.setDocumentPartitioning(getConfiguredDocumentPartitioning(sourceViewer))
     getConfiguredContentTypes(sourceViewer) foreach (p.setInformationProvider(ip, _))
@@ -236,7 +236,7 @@ class ScalaSourceViewerConfiguration(
 
   override def getTextHover(sv: ISourceViewer, contentType: String, stateMask: Int): ITextHover =
     compilationUnit.map(scu =>
-      ScalaHoverDebugOverrideExtensionPoint.hoverFor(scu).getOrElse(new ScalaHover(scu))
+      ScalaHoverDebugOverrideExtensionPoint.hoverFor(scu).getOrElse(new ScalaHover())
     ).getOrElse(new DefaultTextHover(sv))
 
   override def getHyperlinkDetectors(sv: ISourceViewer): Array[IHyperlinkDetector] = {

org.scala-ide.sdt.core/src/org/scalaide/ui/internal/editor/hover/ScalaHover.scala

@@ -27,6 +27,9 @@ import scala.tools.nsc.interactive.CompilerControl
 import scala.tools.nsc.symtab.Flags
 import org.scalaide.core.internal.compiler.ScalaPresentationCompiler
 import org.eclipse.jdt.internal.ui.text.java.hover.JavadocHover
+import org.scalaide.ui.internal.editor.InteractiveCompilationUnitEditor
+import org.eclipse.core.filebuffers.FileBuffers
+import org.scalaide.core.extensions.SourceFileProviderRegistry
 
 object ScalaHover extends HasLogger {
   /** could return null, but prefer to return empty (see API of ITextHover). */
@@ -90,9 +93,21 @@ object ScalaHover extends HasLogger {
   }
 }
 
-class ScalaHover(val icu: InteractiveCompilationUnit) extends ITextHover with ITextHoverExtension with ITextHoverExtension2 with HtmlHover {
+class ScalaHover extends ITextHover with ITextHoverExtension with ITextHoverExtension2 with HtmlHover {
   import ScalaHover._
 
+  protected def getCompilationUnit(textViewer: ITextViewer): InteractiveCompilationUnit = {
+    val doc = textViewer.getDocument
+    val icu = for {
+      buffer <- Option(FileBuffers.getTextFileBufferManager.getTextFileBuffer(doc))
+      location = buffer.getLocation
+      provider <- Option(SourceFileProviderRegistry.getProvider(location))
+      icu <- provider.createFrom(location)
+    } yield icu
+    icu.getOrElse(null)
+  }
+
+
   /**
    * Returns the focused control creator, which is known as the presenter
    * control creator in the Eclipse API.
@@ -105,6 +120,7 @@ class ScalaHover(val icu: InteractiveCompilationUnit) extends ITextHover with IT
     new FocusedControlCreator(HoverFontId)
 
   override def getHoverInfo2(viewer: ITextViewer, region: IRegion): AnyRef = {
+    val icu = getCompilationUnit(viewer)
     icu.withSourceFile({ (src, compiler) =>
       import compiler.{ stringToTermName => _, stringToTypeName => _, _ }
       import RegionUtils.RichRegion

org.scala-ide.sdt.debug/src/org/scalaide/debug/internal/editor/TextHoverFactory.scala

@@ -24,10 +24,11 @@ import org.scalaide.core.compiler.IScalaPresentationCompiler.Implicits._
 class TextHoverFactory extends TextHoverFactoryInterface {
   import IScalaPresentationCompiler.Implicits._
 
-  def createFor(scu: ScalaCompilationUnit): ITextHover = new ScalaHover(scu) with ITextHoverExtension with ITextHoverExtension2 {
+  def createFor(scu: ScalaCompilationUnit): ITextHover = new ScalaHover with ITextHoverExtension with ITextHoverExtension2 {
     var stringWasReturnedAtGetHoverInfo2 = false
 
     override def getHoverInfo2(viewer: ITextViewer, region: IRegion): AnyRef = {
+      val icu = getCompilationUnit(viewer)
       icu.withSourceFile{(src, compiler) =>
         import compiler._
         import org.scalaide.util.eclipse.RegionUtils.RichRegion