Properly pickle implicit/erased method types

Previously, the implicit/erased flags were lost.

The tag used for METHODtype was changed to make the encoding of the
implicit/erased flags more convenient, this requires a major TASTY bump.

Author: smarter

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

@@ -163,7 +163,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   BYNAMEtype            underlying_Type
                   PARAMtype      Length binder_ASTref paramNum_Nat
                   POLYtype       Length result_Type NamesTypes
-                  METHODtype     Length result_Type NamesTypes      // needed for refinements
+                  methodType(_, _) Length result_Type NamesTypes    // needed for refinements
                   TYPELAMBDAtype Length result_Type NamesTypes      // variance encoded in front of name: +/-/(nothing)
                   SHAREDtype            type_ASTRef
   NamesTypes    = NameType*
@@ -226,7 +226,7 @@ Standard Section: "Positions" Assoc*
 object TastyFormat {
 
   final val header = Array(0x5C, 0xA1, 0xAB, 0x1F)
-  val MajorVersion = 4
+  val MajorVersion = 5
   val MinorVersion = 0
 
   /** Tags used to serialize names */
@@ -392,14 +392,28 @@ object TastyFormat {
   final val ANDtpt = 165
   final val ORtype = 166
   final val ORtpt = 167
-  final val METHODtype = 168
-  final val POLYtype = 169
-  final val TYPELAMBDAtype = 170
-  final val LAMBDAtpt = 171
-  final val PARAMtype = 172
-  final val ANNOTATION = 173
-  final val TERMREFin = 174
-  final val TYPEREFin = 175
+  final val POLYtype = 168
+  final val TYPELAMBDAtype = 169
+  final val LAMBDAtpt = 170
+  final val PARAMtype = 171
+  final val ANNOTATION = 172
+  final val TERMREFin = 173
+  final val TYPEREFin = 174
+
+  // In binary: 101100EI
+  // I = implicit method type
+  // E = erased method type
+  final val METHODtype = 176
+  final val IMPLICITMETHODtype = 177
+  final val ERASEDMETHODtype = 178
+  final val ERASEDIMPLICITMETHODtype = 179
+
+  def methodType(isImplicit: Boolean = false, isErased: Boolean = false) = {
+    val implicitOffset = if (isImplicit) 1 else 0
+    val erasedOffset = if (isErased) 2 else 0
+    METHODtype + implicitOffset + erasedOffset
+  }
+
   final val HOLE = 255
 
   final val firstSimpleTreeTag = UNITconst
@@ -588,6 +602,9 @@ object TastyFormat {
     case BYNAMEtpt => "BYNAMEtpt"
     case POLYtype => "POLYtype"
     case METHODtype => "METHODtype"
+    case IMPLICITMETHODtype => "IMPLICITMETHODtype"
+    case ERASEDMETHODtype => "ERASEDMETHODtype"
+    case ERASEDIMPLICITMETHODtype => "ERASEDIMPLICITMETHODtype"
     case TYPELAMBDAtype => "TYPELAMBDAtype"
     case LAMBDAtpt => "LAMBDAtpt"
     case PARAMtype => "PARAMtype"

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

@@ -251,7 +251,7 @@ class TreePickler(pickler: TastyPickler) {
     case tpe: PolyType if richTypes =>
       pickleMethodic(POLYtype, tpe)
     case tpe: MethodType if richTypes =>
-      pickleMethodic(METHODtype, tpe)
+      pickleMethodic(methodType(isImplicit = tpe.isImplicitMethod, isErased = tpe.isErasedMethod), tpe)
     case tpe: ParamRef =>
       assert(pickleParamRef(tpe), s"orphan parameter reference: $tpe")
     case tpe: LazyRef =>

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

@@ -287,6 +287,12 @@ class TreeUnpickler(reader: TastyReader,
               readMethodic(PolyType, _.toTypeName)
             case METHODtype =>
               readMethodic(MethodType, _.toTermName)
+            case IMPLICITMETHODtype =>
+              readMethodic(ImplicitMethodType, _.toTermName)
+            case ERASEDMETHODtype =>
+              readMethodic(ErasedMethodType, _.toTermName)
+            case ERASEDIMPLICITMETHODtype =>
+              readMethodic(ErasedImplicitMethodType, _.toTermName)
             case TYPELAMBDAtype =>
               readMethodic(HKTypeLambda, _.toTypeName)
             case PARAMtype =>

tests/pos/implicit-dep.scala

@@ -0,0 +1,9 @@
+trait HasT {
+  type T
+}
+
+object Test {
+
+
+  def foo: implicit Int => implicit (g: HasT) => g.T = ???
+}