SI-9393 fix modifiers of ClassBTypes for Java annotations

The Scala classfile and java source parsers make Java annotation
classes (which are actually interfaces at the classfile level) look
like Scala annotation classes:
  - the INTERFACE / ABSTRACT flags are not added
  - scala.annotation.Annotation is added as superclass
  - scala.annotation.ClassfileAnnotation is added as interface

This makes type-checking @Annot uniform, whether it is defined in Java
or Scala.

This is a hack that leads to various bugs (SI-9393, SI-9400). Instead
the type-checking should be special-cased for Java annotations.

This commit fixes SI-9393 and a part of SI-9400, but it's still easy
to generate invalid classfiles. Restores the assertions that were
disabled in #4621. I'd like to leave these assertions in: they
are valuable and helped uncovering the issue being fixed here.

A new flag JAVA_ANNOTATION is introduced for Java annotation
ClassSymbols, similar to the existing ENUM flag. When building
ClassBTypes for Java annotations, the flags, superclass and interfaces
are recovered to represent the situation in the classfile.

Cleans up and documents the flags space in the area of "late" and
"anti" flags.

The test for SI-9393 is extended to test both the classfile and the
java source parser.

1 files changed, 25 insertions, 8 deletions

diff --git a/src/reflect/scala/reflect/internal/Flags.scala b/src/reflect/scala/reflect/internal/Flags.scala
index 1707061817..ab56020713 100644
--- a/src/reflect/scala/reflect/internal/Flags.scala
+++ b/src/reflect/scala/reflect/internal/Flags.scala
@@ -64,7 +64,7 @@ import scala.collection.{ mutable, immutable }
 // 46:        ARTIFACT
 // 47: DEFAULTMETHOD/M
 // 48:            ENUM
-// 49:
+// 49:      JAVA_ANNOTATION
 // 50:
 // 51:    lateDEFERRED
 // 52:       lateFINAL
@@ -120,7 +120,8 @@ class ModifierFlags {
   final val ARTIFACT      = 1L << 46      // symbol should be ignored when typechecking; will be marked ACC_SYNTHETIC in bytecode
                                           // to see which symbols are marked as ARTIFACT, see scaladocs for FlagValues.ARTIFACT
   final val DEFAULTMETHOD = 1L << 47      // symbol is a java default method
-  final val ENUM          = 1L << 48      // symbol is an enum
+  final val ENUM          = 1L << 48      // symbol is a java enum
+  final val JAVA_ANNOTATION    = 1L << 49      // symbol is a java annotation
 
   // Overridden.
   def flagToString(flag: Long): String = ""
@@ -172,12 +173,28 @@ class Flags extends ModifierFlags {
   final val SYNCHRONIZED  = 1L << 45      // symbol is a method which should be marked ACC_SYNCHRONIZED
 
   // ------- shift definitions -------------------------------------------------------
+  //
+  // Flags from 1L to (1L << 50) are normal flags.
+  //
+  // The flags DEFERRED (1L << 4) to MODULE (1L << 8) have a `late` counterpart. Late flags change
+  // their counterpart from 0 to 1 after a specific phase (see below). The first late flag
+  // (lateDEFERRED) is at (1L << 51), i.e., late flags are shifted by 47. The last one is (1L << 55).
+  //
+  // The flags PROTECTED (1L) to PRIVATE (1L << 2) have a `not` counterpart. Negated flags change
+  // their counterpart from 1 to 0 after a specific phase (see below). They are shifted by 56, i.e.,
+  // the first negated flag (notPROTECTED) is at (1L << 56), the last at (1L << 58).
+  //
+  // Late and negative flags are only enabled after certain phases, implemented by the phaseNewFlags
+  // method of the SubComponent, so they implement a bit of a flag history.
+  //
+  // The flags (1L << 59) to (1L << 63) are currently unused. If added to the InitialFlags mask,
+  // they could be used as normal flags.
 
-  final val InitialFlags  = 0x0001FFFFFFFFFFFFL // flags that are enabled from phase 1.
-  final val LateFlags     = 0x00FE000000000000L // flags that override flags in 0x1FC.
-  final val AntiFlags     = 0x7F00000000000000L // flags that cancel flags in 0x07F
-  final val LateShift     = 47L
-  final val AntiShift     = 56L
+  final val InitialFlags  = 0x0007FFFFFFFFFFFFL // normal flags, enabled from the first phase: 1L to (1L << 50)
+  final val LateFlags     = 0x00F8000000000000L // flags that override flags in (1L << 4) to (1L << 8): DEFERRED, FINAL, INTERFACE, METHOD, MODULE
+  final val AntiFlags     = 0x0700000000000000L // flags that cancel flags in 1L to (1L << 2): PROTECTED, OVERRIDE, PRIVATE
+  final val LateShift     = 47
+  final val AntiShift     = 56
 
   // Flags which sketchily share the same slot
   // 16:   BYNAMEPARAM/M      CAPTURED COVARIANT/M
@@ -436,7 +453,7 @@ class Flags extends ModifierFlags {
     case            ARTIFACT => "<artifact>"                          // (1L << 46)
     case       DEFAULTMETHOD => "<defaultmethod>"                     // (1L << 47)
     case                ENUM => "<enum>"                              // (1L << 48)
-    case    0x2000000000000L => ""                                    // (1L << 49)
+    case     JAVA_ANNOTATION => "<annotation>"                        // (1L << 49)
     case    0x4000000000000L => ""                                    // (1L << 50)
     case      `lateDEFERRED` => "<latedeferred>"                      // (1L << 51)
     case         `lateFINAL` => "<latefinal>"                         // (1L << 52)