Tighten allowance for serialization methods

Author: som-snytt

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -716,7 +716,7 @@ object CheckUnused:
         peekScopeType == ScopeType.Template
         && !memDef.symbol.isConstructor
         && memDef.symbol.is(Private, butNot = SelfName | Synthetic | CaseAccessor)
-        && !ignoredNames(memDef.symbol.name.toTermName)
+        && !ignoredSignature(memDef.symbol)
 
       private def isUnsetVarDef(using Context): Boolean =
         val sym = memDef.symbol
@@ -747,7 +747,12 @@ object CheckUnused:
         case _: Block => Local
         case _ => Other
 
-    val ignoredNames: Set[TermName] = Set("readResolve", "readObject", "writeObject", "writeReplace").map(termName(_))
+    val ignoredNames: Set[TermName] =
+      Set("readResolve", "readObject", "readObjectNoData", "writeObject", "writeReplace").map(termName(_))
+
+    def ignoredSignature(m: Symbol)(using Context): Boolean =
+      m.is(Method) && ignoredNames(m.name.toTermName) && m.owner.isClass
+      && m.owner.asClass.classDenot.parentSyms.contains(defn.JavaSerializableClass)
 
     final case class ImportSelectorData(val qualTpe: Type, val selector: ImportSelector):
       private var myUsed: Boolean = false

tests/warn/unused-privates.scala

@@ -187,7 +187,7 @@ trait Forever {
 }
 
 trait Ignorance {
-  private val readResolve = 42      // no warn special members
+  private val readResolve = 42      // warn wrong signatured for special members
 }
 
 trait CaseyKasem {
@@ -257,3 +257,31 @@ class `recursive reference is not a usage` {
     def f() = new P()
   }
 }
+
+class `absolve serial framework` extends Serializable:
+  import java.io.{IOException, ObjectInputStream, ObjectOutputStream, ObjectStreamException}
+  @throws(classOf[IOException])
+  private def writeObject(stream: ObjectOutputStream): Unit = ()
+  @throws(classOf[ObjectStreamException])
+  private def writeReplace(): Object = ???
+  @throws(classOf[ClassNotFoundException])
+  @throws(classOf[IOException])
+  private def readObject(stream: ObjectInputStream): Unit = ()
+  @throws(classOf[ObjectStreamException])
+  private def readObjectNoData(): Unit = ()
+  @throws(classOf[ObjectStreamException])
+  private def readResolve(): Object = ???
+
+class `absolve ONLY serial framework`:
+  import java.io.{IOException, ObjectInputStream, ObjectOutputStream, ObjectStreamException}
+  @throws(classOf[IOException])
+  private def writeObject(stream: ObjectOutputStream): Unit = () // warn
+  @throws(classOf[ObjectStreamException])
+  private def writeReplace(): Object = ??? // warn
+  @throws(classOf[ClassNotFoundException])
+  @throws(classOf[IOException])
+  private def readObject(stream: ObjectInputStream): Unit = () // warn
+  @throws(classOf[ObjectStreamException])
+  private def readObjectNoData(): Unit = () // warn
+  @throws(classOf[ObjectStreamException])
+  private def readResolve(): Object = ??? // warn