Merge pull request #399 from sjrd/fix-scalaz-unpickling

Fix #397: Use a fake owner for orphan symbols in Scala 2 pickles.
scalacenter · Nov 27, 2023 · d6adb02 · d6adb02
2 parents 9f94cad + 3df9336
commit d6adb02
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Showing 3 changed files with 19 additions and 13 deletions.
diff --git a/tasty-query/shared/src/main/scala/tastyquery/Definitions.scala b/tasty-query/shared/src/main/scala/tastyquery/Definitions.scala
@@ -134,6 +134,16 @@ final class Definitions private[tastyquery] (ctx: Context, rootPackage: PackageS
 
   val NothingAnyBounds = AbstractTypeBounds(SyntacticNothingType, AnyClass.topLevelRef)
 
+  // See `case noRef: NoExternalSymbolRef` in PickleReader
+  private[tastyquery] val scala2FakeOwner: TermSymbol =
+    TermSymbol
+      .createNotDeclaration(termName("<nosymbol>"), scalaPackage)
+      .withFlags(Synthetic, None)
+      .withDeclaredType(AnyType)
+      .setAnnotations(Nil)
+      .checkCompleted()
+  end scala2FakeOwner
+
   private def createSpecialTypeAlias(
     name: TypeName,
     owner: DeclaringSymbol,

diff --git a/tasty-query/shared/src/main/scala/tastyquery/reader/ReaderContext.scala b/tasty-query/shared/src/main/scala/tastyquery/reader/ReaderContext.scala
@@ -43,6 +43,8 @@ private[reader] final class ReaderContext(underlying: Context):
 
   def uninitializedMethodTermRef: TermRef = underlying.defn.uninitializedMethodTermRef
 
+  def scala2FakeOwner: TermSymbol = underlying.defn.scala2FakeOwner
+
   def findPackageFromRootOrCreate(fullyQualifiedName: PackageFullName): PackageSymbol =
     underlying.findPackageFromRootOrCreate(fullyQualifiedName)
 

diff --git a/tasty-query/shared/src/main/scala/tastyquery/reader/pickles/PickleReader.scala b/tasty-query/shared/src/main/scala/tastyquery/reader/pickles/PickleReader.scala
@@ -203,17 +203,13 @@ private[pickles] class PickleReader {
       case sym: Symbol =>
         sym
       case noRef: NoExternalSymbolRef if tag == TYPEsym || tag == VALsym =>
-        /* For some reason, Scala 2 pickles `TYPEsym` and `VALsym` symbols whose owner references `NONEsym`.
-         * However, they do not appear to be referenced *themselves* from anywhere. They
-         * only appear in the table, and hence get read from the loop in `Unpickler.run`.
-         * We ignore these entries here by replacing them with `NONEsym`. If they end up
-         * being actually referenced somewhere, then that somewhere will then crash with
-         * an unexpected reference to `NONEsym`, which would provide us with more context
-         * to perhaps solve this at a deeper level.
-         * If someone wants to investigate, there is a case of `TYPEsym` in `scala.collection.Iterator`.
-         * There is a case of `VALsym` somewhere in sbt, triggered when tasty-mima-checking sbt-tasty-mima itself.
+        /* Sometimes, Scala 2 pickles `TYPEsym` and `VALsym` symbols whose owner references `NONEsym`.
+         * This seems to happen in METHODtpe and POLYtpe that are not for declared methods
+         * (but for type lambdas, or in annotations), for their parameter symbols.
+         * Our system does not have a notion of "no symbol". Instead, we use one fake
+         * owner to host these "orphan" symbols.
          */
-        return NoExternalSymbolRef.instance
+        rctx.scala2FakeOwner
       case external =>
         errorBadSignature(
           s"expected local symbol reference but found $external for owner of ${name1.toDebugString} with tag $tag"
@@ -727,9 +723,7 @@ private[pickles] class PickleReader {
         // create PolyType
         //   - PT => register at index
         val restpe = readTypeMappableRef()
-        val typeParams = pkl.until(end, () => readMaybeExternalSymbolRef()).collect { case typeParam: TypeParamSymbol =>
-          typeParam
-        }
+        val typeParams = pkl.until(end, () => readLocalSymbolRef().asInstanceOf[TypeParamSymbol])
         if typeParams.nonEmpty then TempPolyType(typeParams, restpe)
         else restpe
       case EXISTENTIALtpe =>