Improve error message for mismatched tasty versions, allow configurat…

…ion of header unpickler (#18828)

fixes #18427

Adds configuration ability to `TastyHeaderUnpickler`, why? `tasty-core`
is intended to be a generic library, so for its error messages to
suddenly assume the consumer is a scala compiler would be a breaking
change, so we instead by default use a generic configuration (the old
"tooling" style) and allow to plug-in a "scala compiler" configuration

Also the configuration allows us to easily test the content of error
messages.

compiler/src/dotty/tools/backend/jvm/CodeGen.scala

@@ -25,6 +25,7 @@ import java.io.DataOutputStream
 import java.nio.channels.ClosedByInterruptException
 
 import dotty.tools.tasty.{ TastyBuffer, TastyHeaderUnpickler }
+import dotty.tools.dotc.core.tasty.TastyUnpickler
 
 import scala.tools.asm
 import scala.tools.asm.tree._
@@ -94,7 +95,7 @@ class CodeGen(val int: DottyBackendInterface, val primitives: DottyPrimitives)(
       for (binary <- unit.pickled.get(claszSymbol.asClass)) {
         generatedTasty += GeneratedTasty(store, binary)
         val tasty =
-          val uuid = new TastyHeaderUnpickler(binary()).readHeader()
+          val uuid = new TastyHeaderUnpickler(TastyUnpickler.scala3CompilerConfig, binary()).readHeader()
           val lo = uuid.getMostSignificantBits
           val hi = uuid.getLeastSignificantBits
 

compiler/src/dotty/tools/dotc/core/SymbolLoaders.scala

@@ -24,7 +24,8 @@ import ast.desugar
 
 import parsing.JavaParsers.OutlineJavaParser
 import parsing.Parsers.OutlineParser
-import dotty.tools.tasty.TastyHeaderUnpickler
+import dotty.tools.tasty.{TastyHeaderUnpickler, UnpickleException, UnpicklerConfig}
+import dotty.tools.dotc.core.tasty.TastyUnpickler
 
 
 object SymbolLoaders {
@@ -421,22 +422,33 @@ class TastyLoader(val tastyFile: AbstractFile) extends SymbolLoader {
   def description(using Context): String = "TASTy file " + tastyFile.toString
 
   override def doComplete(root: SymDenotation)(using Context): Unit =
-    val (classRoot, moduleRoot) = rootDenots(root.asClass)
-    val tastyBytes = tastyFile.toByteArray
-    val unpickler = new tasty.DottyUnpickler(tastyBytes)
-    unpickler.enter(roots = Set(classRoot, moduleRoot, moduleRoot.sourceModule))(using ctx.withSource(util.NoSource))
-    if mayLoadTreesFromTasty then
-      classRoot.classSymbol.rootTreeOrProvider = unpickler
-      moduleRoot.classSymbol.rootTreeOrProvider = unpickler
-    checkTastyUUID(tastyFile, tastyBytes)
+    try
+      val (classRoot, moduleRoot) = rootDenots(root.asClass)
+      val tastyBytes = tastyFile.toByteArray
+      val unpickler = new tasty.DottyUnpickler(tastyBytes)
+      unpickler.enter(roots = Set(classRoot, moduleRoot, moduleRoot.sourceModule))(using ctx.withSource(util.NoSource))
+      if mayLoadTreesFromTasty then
+        classRoot.classSymbol.rootTreeOrProvider = unpickler
+        moduleRoot.classSymbol.rootTreeOrProvider = unpickler
+      checkTastyUUID(tastyFile, tastyBytes)
+    catch case e: RuntimeException =>
+      val message = e match
+        case e: UnpickleException =>
+          i"""TASTy file ${tastyFile.canonicalPath} could not be read, failing with:
+            |  ${Option(e.getMessage).getOrElse("")}"""
+        case _ =>
+          i"""TASTy file ${tastyFile.canonicalPath} is broken, reading aborted with ${e.getClass}
+            |  ${Option(e.getMessage).getOrElse("")}"""
+      if (ctx.debug) e.printStackTrace()
+      throw IOException(message)
 
 
   private def checkTastyUUID(tastyFile: AbstractFile, tastyBytes: Array[Byte])(using Context): Unit =
     val classfile =
       val className = tastyFile.name.stripSuffix(".tasty")
       tastyFile.resolveSibling(className + ".class")
     if classfile != null then
-      val tastyUUID = new TastyHeaderUnpickler(tastyBytes).readHeader()
+      val tastyUUID = new TastyHeaderUnpickler(TastyUnpickler.scala3CompilerConfig, tastyBytes).readHeader()
       new ClassfileTastyUUIDParser(classfile)(ctx).checkTastyUUID(tastyUUID)
     else
       // This will be the case in any of our tests that compile with `-Youtput-only-tasty`

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

@@ -4,7 +4,8 @@ package tasty
 
 import scala.language.unsafeNulls
 
-import dotty.tools.tasty.{TastyFormat, TastyBuffer, TastyReader, TastyHeaderUnpickler}
+import dotty.tools.tasty.{TastyFormat, TastyBuffer, TastyReader, TastyHeaderUnpickler, UnpicklerConfig}
+import TastyHeaderUnpickler.TastyVersion
 import TastyFormat.NameTags._, TastyFormat.nameTagToString
 import TastyBuffer.NameRef
 
@@ -24,6 +25,39 @@ object TastyUnpickler {
     def apply(ref: NameRef): TermName = names(ref.index)
     def contents: Iterable[TermName] = names
   }
+
+  trait Scala3CompilerConfig extends UnpicklerConfig:
+    private def asScala3Compiler(version: TastyVersion): String =
+      if (version.major == 28) {
+        // scala 3.x.y series
+        if (version.experimental > 0)
+          // scenario here is someone using 3.4.0 to read 3.4.1-RC1-NIGHTLY, in this case, we should show 3.4 nightly.
+          s"the same nightly or snapshot Scala 3.${version.minor - 1} compiler"
+        else s"a Scala 3.${version.minor}.0 compiler or newer"
+      }
+      else if (version.experimental > 0) "the same Scala compiler" // unknown major version, just say same
+      else "a more recent Scala compiler" // unknown major version, just say later
+
+    /** The description of the upgraded scala compiler that can read the given TASTy version */
+    final def upgradedReaderTool(version: TastyVersion): String = asScala3Compiler(version)
+
+    /** The description of the upgraded scala compiler that can produce the given TASTy version */
+    final def upgradedProducerTool(version: TastyVersion): String = asScala3Compiler(version)
+
+    final def recompileAdditionalInfo: String = """
+      |  Usually this means that the library dependency containing this file should be updated.""".stripMargin
+
+    final def upgradeAdditionalInfo(fileVersion: TastyVersion): String =
+      if (fileVersion.isExperimental && experimentalVersion == 0) {
+        """
+          |  Note that you are using a stable compiler, which can not read experimental TASTy.""".stripMargin
+      }
+      else ""
+  end Scala3CompilerConfig
+
+  /** A config for the TASTy reader of a scala 3 compiler */
+  val scala3CompilerConfig: UnpicklerConfig = new Scala3CompilerConfig with UnpicklerConfig.DefaultTastyVersion {}
+
 }
 
 import TastyUnpickler._
@@ -88,7 +122,7 @@ class TastyUnpickler(reader: TastyReader) {
     result
   }
 
-  new TastyHeaderUnpickler(reader).readHeader()
+  new TastyHeaderUnpickler(scala3CompilerConfig, reader).readHeader()
 
   locally {
     until(readEnd()) { nameAtRef.add(readNameContents()) }