Require seeing ScalaSig before scanning for Scala pickling annotations

An alternative fix for #15166, which aligns with the behavior of the
Scala 2 classfile parser.

Before this commit, all classfiles, including those produced by the Java
compiler and compilers of other JVM languages, were scanned for Scala
pickling annotations. In certain situations (as in tests/pos/i15166),
this is problematic, as the denotation of an annotation symbol defined as
a Java inner class may be forced before the inner class table is populated
and setClassInfo is called on the class root.

We avoid this situation by only performing the pickling annotation scan for
those classfiles having the `ScalaSig` attribute, i.e. those produced by
the Scala 2 compiler.

We also drop support for pickling TASTy using the classfile annotations
  `scala.annotation.internal.TASTYSignature` and
  `scala.annotation.internal.TASTYLongSignature`.
These were never used by the compiler, there are no plans for future use,
and preserving support would complicate this fix.

Author: griggt

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

@@ -920,8 +920,6 @@ class Definitions {
   @tu lazy val ScalaStrictFPAnnot: ClassSymbol = requiredClass("scala.annotation.strictfp")
   @tu lazy val ScalaStaticAnnot: ClassSymbol = requiredClass("scala.annotation.static")
   @tu lazy val SerialVersionUIDAnnot: ClassSymbol = requiredClass("scala.SerialVersionUID")
-  @tu lazy val TASTYSignatureAnnot: ClassSymbol = requiredClass("scala.annotation.internal.TASTYSignature")
-  @tu lazy val TASTYLongSignatureAnnot: ClassSymbol = requiredClass("scala.annotation.internal.TASTYLongSignature")
   @tu lazy val TailrecAnnot: ClassSymbol = requiredClass("scala.annotation.tailrec")
   @tu lazy val ThreadUnsafeAnnot: ClassSymbol = requiredClass("scala.annotation.threadUnsafe")
   @tu lazy val ConstructorOnlyAnnot: ClassSymbol = requiredClass("scala.annotation.constructorOnly")

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -871,7 +871,7 @@ class ClassfileParser(
 
   /** Parse inner classes. Expects `in.bp` to point to the superclass entry.
    *  Restores the old `bp`.
-   *  @return true iff classfile is from Scala, so no Java info needs to be read.
+   *  @return Some(unpickler) iff classfile is from Scala, so no Java info needs to be read.
    */
   def unpickleOrParseInnerClasses()(using ctx: Context, in: DataReader): Option[Embedded] = {
     val oldbp = in.bp
@@ -1028,7 +1028,7 @@ class ClassfileParser(
         // attribute isn't, this classfile is a compilation artifact.
         return Some(NoEmbedded)
 
-      if (scan(tpnme.RuntimeVisibleAnnotationATTR) || scan(tpnme.RuntimeInvisibleAnnotationATTR)) {
+      if (scan(tpnme.ScalaSignatureATTR) && scan(tpnme.RuntimeVisibleAnnotationATTR)) {
         val attrLen = in.nextInt
         val nAnnots = in.nextChar
         var i = 0
@@ -1039,14 +1039,10 @@ class ClassfileParser(
           while (j < nArgs) {
             val argName = pool.getName(in.nextChar)
             if (argName.name == nme.bytes) {
-              if (attrClass == defn.ScalaSignatureAnnot)
+              if attrClass == defn.ScalaSignatureAnnot then
                 return unpickleScala(parseScalaSigBytes)
-              else if (attrClass == defn.ScalaLongSignatureAnnot)
+              else if attrClass == defn.ScalaLongSignatureAnnot then
                 return unpickleScala(parseScalaLongSigBytes)
-              else if (attrClass == defn.TASTYSignatureAnnot)
-                return unpickleTASTY(parseScalaSigBytes)
-              else if (attrClass == defn.TASTYLongSignatureAnnot)
-                return unpickleTASTY(parseScalaLongSigBytes)
             }
             parseAnnotArg(skip = true)
             j += 1

library/src/scala/annotation/internal/TASTYLongSignature.java

@@ -7,6 +7,7 @@
 
 @Retention(RetentionPolicy.RUNTIME)
 @Target(ElementType.TYPE)
+@Deprecated
 public @interface TASTYLongSignature {
     public String[] bytes();
 }

library/src/scala/annotation/internal/TASTYSignature.java

@@ -7,6 +7,7 @@
 
 @Retention(RetentionPolicy.RUNTIME)
 @Target(ElementType.TYPE)
+@Deprecated
 public @interface TASTYSignature {
     public String bytes();
 }

tests/pos/i15166/InterfaceAudience_JAVA_ONLY_1.java

@@ -0,0 +1,8 @@
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@InterfaceStability_JAVA_ONLY_1.Evolving(bytes="no")
+public class InterfaceAudience_JAVA_ONLY_1 {
+    @Retention(RetentionPolicy.RUNTIME)
+    public @interface Public { String bytes(); }
+}

tests/pos/i15166/InterfaceStability_JAVA_ONLY_1.java

@@ -0,0 +1,8 @@
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@InterfaceAudience_JAVA_ONLY_1.Public(bytes="yes")
+public class InterfaceStability_JAVA_ONLY_1 {
+    @Retention(RetentionPolicy.RUNTIME)
+    public @interface Evolving { String bytes(); }
+}

tests/pos/i15166/Test_2.scala

@@ -0,0 +1,4 @@
+// scalac: -Xfatal-warnings
+object Test {
+  val x: InterfaceAudience_JAVA_ONLY_1.Public = ???
+}