Replace pickling of sub matches to use an annotation

s.t. the TastyFormat is unchanged

Co-authored-by: Hamza Remmal <[email protected]>

Author: EugeneFlesselle

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

@@ -1061,6 +1061,7 @@ class Definitions {
   @tu lazy val ScalaStaticAnnot: ClassSymbol = requiredClass("scala.annotation.static")
   @tu lazy val SerialVersionUIDAnnot: ClassSymbol = requiredClass("scala.SerialVersionUID")
   @tu lazy val SilentIntoAnnot: ClassSymbol = requiredClass("scala.annotation.internal.$into")
+  @tu lazy val SilentSubMatchAnnot: ClassSymbol = requiredClass("scala.annotation.internal.$subMatch")
   @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/tasty/TreePickler.scala

@@ -590,7 +590,10 @@ class TreePickler(pickler: TastyPickler, attributes: Attributes) {
             if (tree.isInline)
               if (selector.isEmpty) writeByte(IMPLICIT)
               else { writeByte(INLINE); pickleTree(selector) }
-            else if tree.isSubMatch then { writeByte(LAZY); pickleTree(selector) }
+            else if tree.isSubMatch then
+              // Temporary measure until we can change TastyFormat
+              val annot = New(defn.SilentSubMatchAnnot.typeRef, Nil)
+              pickleTree(selector.annotated(annot))
             else pickleTree(selector)
             tree.cases.foreach(pickleTree)
           }

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

@@ -1542,7 +1542,7 @@ class TreeUnpickler(reader: TastyReader,
               val tpt = ifBefore(end)(readTpt(), EmptyTree)
               Closure(Nil, meth, tpt)
             case MATCH =>
-              simplifyLub(
+              simplifyLub:
                 if (nextByte == IMPLICIT) {
                   readByte()
                   InlineMatch(EmptyTree, readCases(end))
@@ -1551,10 +1551,9 @@ class TreeUnpickler(reader: TastyReader,
                   readByte()
                   InlineMatch(readTree(), readCases(end))
                 }
-                else if nextByte == LAZY then // similarly to InlineMatch we use an arbitrary Cat.1 tag
-                  readByte()
-                  SubMatch(readTree(), readCases(end))
-                else Match(readTree(), readCases(end)))
+                else readTree() match
+                  case Typed(sel, tpt) if tpt.tpe.hasAnnotation(defn.SilentSubMatchAnnot) => SubMatch(sel, readCases(end))
+                  case sel => Match(sel, readCases(end))
             case RETURN =>
               val from = readSymRef()
               val expr = ifBefore(end)(readTree(), EmptyTree)

library/src/scala/annotation/internal/$subMatch.scala

@@ -0,0 +1,7 @@
+package scala.annotation.internal
+
+import scala.annotation.experimental
+
+/** An internal annotation on (part of) that serves as a marker for sub matches. */
+@experimental
+class $subMatch extends annotation.StaticAnnotation

project/Build.scala

@@ -1201,6 +1201,7 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/annotation/internal/SourceFile.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/reachCapability.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/$$into.scala"),
+        file(s"${baseDirectory.value}/src/scala/annotation/internal/$$subMatch.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/TASTYLongSignature.java"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/readOnlyCapability.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/unshared.scala"),
@@ -1339,6 +1340,7 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/annotation/internal/SourceFile.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/reachCapability.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/$$into.scala"),
+        file(s"${baseDirectory.value}/src/scala/annotation/internal/$$subMatch.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/TASTYLongSignature.java"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/readOnlyCapability.scala"),
         file(s"${baseDirectory.value}/src/scala/annotation/internal/unshared.scala"),