Support for -from-tasty in Dottydoc

Dottydoc can now be used in one of two ways:

 - By receiving a list of source files that will be parsed, typed, and
   for which the documentation will be generated
 - When `-from-tasty` is set, by receiving a list of fully qualified
   class names. The trees will be unpickled and the documentation will
   be generated.

compiler/src/dotty/tools/dotc/fromtasty/ReadTastyTreesFromClasses.scala

@@ -33,7 +33,7 @@ class ReadTastyTreesFromClasses extends FrontEnd {
       }
 
       def alreadyLoaded(): None.type = {
-        ctx.warning(s"sclass $className cannot be unpickled because it is already loaded")
+        ctx.warning(s"class $className cannot be unpickled because it is already loaded")
         None
       }
 

doc-tool/src/dotty/tools/dottydoc/DocCompiler.scala

@@ -3,8 +3,12 @@ package dottydoc
 
 import core._
 import core.transform._
+import dotc.core.Contexts.Context
 import dotc.core.Phases.Phase
-import dotc.Compiler
+import dotc.core.Mode
+import dotc.{Compiler, Run}
+
+import dotty.tools.dotc.fromtasty.{ReadTastyTreesFromClasses, TASTYRun}
 
 /** Custom Compiler with phases for the documentation tool
  *
@@ -20,6 +24,15 @@ import dotc.Compiler
  */
 class DocCompiler extends Compiler {
 
+  override def newRun(implicit ctx: Context): Run = {
+    if (ctx.settings.fromTasty.value) {
+      reset()
+      new TASTYRun(this, ctx.addMode(Mode.ReadPositions).addMode(Mode.ReadComments))
+    } else {
+      super.newRun
+    }
+  }
+
   override protected def frontendPhases: List[List[Phase]] =
     List(new DocFrontEnd) :: Nil
 

doc-tool/src/dotty/tools/dottydoc/DocFrontEnd.scala

@@ -1,6 +1,7 @@
 package dotty.tools
 package dottydoc
 
+import dotc.fromtasty.ReadTastyTreesFromClasses
 import dotc.typer.FrontEnd
 import dotc.core.Contexts.Context
 import dotc.CompilationUnit
@@ -12,6 +13,16 @@ import dotc.CompilationUnit
  *  `discardAfterTyper`.
  */
 class DocFrontEnd extends FrontEnd {
+
+  override def runOn(units: List[CompilationUnit])(implicit ctx: Context): List[CompilationUnit] = {
+    if (ctx.settings.fromTasty.value) {
+      val fromTastyFrontend = new ReadTastyTreesFromClasses
+      fromTastyFrontend.runOn(units)
+    } else {
+      super.runOn(units)
+    }
+  }
+
   override protected def discardAfterTyper(unit: CompilationUnit)(implicit ctx: Context) =
     unit.isJava
 }