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Actively remove Scala 2 pickles and emit synthetic TASTy attribute for copied stdlib .class files #24846

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Merged
WojciechMazur merged 10 commits into from
Jan 7, 2026
Merged

Actively remove Scala 2 pickles and emit synthetic TASTy attribute for copied stdlib .class files #24846

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6499b0d
fix bytecode attributes for patched files
hamzaremmal Oct 14, 2025
57dac79
Add validation to ensure Scala 2 pickles are not stored
WojciechMazur Dec 28, 2025
a7e214e
Rename unpickler to removeScala2Pickles
WojciechMazur Dec 28, 2025
ac420c3
Add validation for existance of TASTy attribute. Add synthetic TASTY …
WojciechMazur Dec 29, 2025
d673395
Fix sjs builds - use fixed scala-library-nonboostrapped source directory
WojciechMazur Dec 29, 2025
c2d9e9e
Remove dependency on scala-library-nonbootstraped project - detect .c…
WojciechMazur Dec 30, 2025
e831daa
Ensure that Scala 2 pickle attributes are also removed
WojciechMazur Dec 30, 2025
596a5fe
Remove `TastyAttributeReader` replace with inline reader using protot…
WojciechMazur Dec 30, 2025
9178964
Add assertion to ensure that no new TASTy attributes are generated or…
WojciechMazur Dec 30, 2025
47e2dd3
Validate existance of 'Scala' attribute in all .scala outputputs. Pat…
WojciechMazur Jan 6, 2026
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Ensure that Scala 2 pickle attributes are also removed
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@WojciechMazur
WojciechMazur committed Dec 30, 2025
commit e831daadc6a1915a76886b285faf1b3ee224703c
25 changes: 17 additions & 8 deletions project/ScalaLibraryPlugin.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,9 @@ object ScalaLibraryPlugin extends AutoPlugin {
"Lscala/reflect/ScalaLongSignature;"
)

/** Scala 2 attribute names that should be stripped from class files */
private val Scala2PickleAttributes = Set("ScalaSig", "ScalaInlineInfo")

/** Check if an annotation descriptor is a Scala 2 pickle annotation */
private def isScala2PickleAnnotation(descriptor: String): Boolean =
Scala2PickleAnnotations.contains(descriptor)
Expand Down Expand Up @@ -142,9 +145,9 @@ object ScalaLibraryPlugin extends AutoPlugin {
val writer = new ClassWriter(0)
// Remove Scala 2 pickles and Scala signatures
val visitor = new ClassVisitor(Opcodes.ASM9, writer) {
override def visitAttribute(attr: Attribute): Unit = attr.`type` match {
case "ScalaSig" | "ScalaInlineInfo" => ()
case _ => super.visitAttribute(attr)
override def visitAttribute(attr: Attribute): Unit = {
val shouldRemove = Scala2PickleAttributes.contains(attr.`type`)
if (!shouldRemove) super.visitAttribute(attr)
}

override def visitAnnotation(desc: String, visible: Boolean): AnnotationVisitor =
Expand Down Expand Up @@ -204,20 +207,27 @@ object ScalaLibraryPlugin extends AutoPlugin {
output
}

/** Check if class file bytecode contains Scala 2 pickle annotations */
/** Check if class file bytecode contains Scala 2 pickle annotations or attributes */
private def hasScala2Pickles(bytes: Array[Byte]): Boolean = {
var found = false
var hasPickleAnnotation = false
var hasScalaSigAttr = false
var hasScalaInlineInfoAttr = false
val visitor = new ClassVisitor(Opcodes.ASM9) {
override def visitAnnotation(desc: String, visible: Boolean): AnnotationVisitor = {
if (isScala2PickleAnnotation(desc)) found = true
if (isScala2PickleAnnotation(desc)) hasPickleAnnotation = true
null
}
override def visitAttribute(attr: Attribute): Unit =
if (Scala2PickleAttributes.contains(attr.`type`)) attr.`type` match {
case "ScalaSig" => hasScalaSigAttr = true
case "ScalaInlineInfo" => hasScalaInlineInfoAttr = true
}
}
new ClassReader(bytes).accept(
visitor,
ClassReader.SKIP_CODE | ClassReader.SKIP_DEBUG | ClassReader.SKIP_FRAMES
)
found
hasPickleAnnotation || hasScalaSigAttr || hasScalaInlineInfoAttr
}

def validateNoScala2Pickles(jar: File): Unit = {
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@hamzaremmal hamzaremmal Dec 30, 2025

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It doesn't validate that ScalaSig and ScalaInlineInfo attributes were removed.

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@WojciechMazur WojciechMazur Dec 30, 2025

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I've adjusted it so that both of these are now validated

Expand Down Expand Up @@ -388,7 +398,6 @@ object ScalaLibraryPlugin extends AutoPlugin {
}
}


/** Custom ASM Attribute for TASTY that can be written to class files */
private class TastyAttribute(val uuid: Array[Byte]) extends Attribute("TASTY") {
override def write(classWriter: ClassWriter, code: Array[Byte], codeLength: Int, maxStack: Int, maxLocals: Int): ByteVector = {
Expand Down