require explicit enabling of reading outline TASTy with -from-tasty

Author: bishabosha

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -437,4 +437,5 @@ private sealed trait YSettings:
   // Pipeline compilation options
   val YjavaTasty: Setting[Boolean] = BooleanSetting("-Yjava-tasty", "Pickler phase should compute pickles for .java defined symbols for use by build tools")
   val YjavaTastyOutput: Setting[AbstractFile] = OutputSetting("-Yjava-tasty-output", "directory|jar", "(Internal use only!) destination for generated .tasty files containing Java type signatures.", NoAbstractFile)
+  val YallowOutlineFromTasty: Setting[Boolean] = BooleanSetting("-Yallow-outline-from-tasty", "Allow outline TASTy to be loaded with the -from-tasty option.")
 end YSettings

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -46,7 +46,6 @@ import dotty.tools.tasty.TastyFormat.*
 import scala.annotation.constructorOnly
 import scala.annotation.internal.sharable
 import scala.compiletime.uninitialized
-import dotty.tools.tasty.UnpickleException
 
 /** Unpickler for typed trees
  *  @param reader              the reader from which to unpickle
@@ -120,9 +119,6 @@ class TreeUnpickler(reader: TastyReader,
    */
   def enter(roots: Set[SymDenotation])(using Context): Unit = {
     this.roots = roots
-    if isOutline && !unpicklingJava then
-      // TODO: overly cautious here, eventually we could enable this with 2-pass compilation.
-      throw UnpickleException("Outline TASTy is not supported for Scala sources.")
     val rdr = new TreeReader(reader).fork
     ownerTree = new OwnerTree(NoAddr, 0, rdr.fork, reader.endAddr)
     if (rdr.isTopLevel)

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

@@ -50,6 +50,8 @@ class ReadTasty extends Phase {
                 if attributes.isJava && !ctx.settings.YjavaTasty.value then
                   // filter out Java compilation units if -Yjava-tasty is not set
                   None
+                else if attributes.isOutline && !ctx.settings.YallowOutlineFromTasty.value then
+                  cannotUnpickle("it contains outline signatures and -Yallow-outline-from-tasty is not set.")
                 else
                   val unit = CompilationUnit(cls, cls.rootTree, forceTrees = true)
                   unit.pickled += (cls -> (() => unpickler.unpickler.bytes))

sbt-test/pipelining/Yjava-tasty-from-tasty/build.sbt

@@ -16,6 +16,7 @@ lazy val a_from_tasty = project.in(file("a_from_tasty"))
     Compile / unmanagedClasspath := Seq(Attributed.blank((ThisBuild / baseDirectory).value / "a-pre-java-tasty.jar")),
     scalacOptions += "-from-tasty", // read the jar file tasties as the source files
     scalacOptions += "-Yjava-tasty",
+    scalacOptions += "-Yallow-outline-from-tasty", // allow outline signatures to be read with -from-tasty
     scalacOptions ++= Seq("-Yjava-tasty-output", ((ThisBuild / baseDirectory).value / "a_from_tasty-java-tasty.jar").toString),
     scalacOptions += "-Ycheck:all",
     classDirectory := ((ThisBuild / baseDirectory).value / "a_from_tasty-classes"), // send classfiles to a different directory