Define Predef.{summon,nn} overwrites directly in Scala 2 library TASTy

project/TastyMiMaFilters.scala

@@ -3,6 +3,16 @@ import tastymima.intf._
 
 object TastyMiMaFilters {
   val StdlibBootstrapped: java.util.List[ProblemMatcher] = asList(
+
+    // FIXME: method overwritten in scala2-library-bootstrapped/src/scala/Predef.scala
+    ProblemMatcher.make(ProblemKind.IncompatibleTypeChange, "scala.Predef.nn"), // The symbol scala.Predef.nn has an incompatible type in current version: before: [T](x: T)(x.type & T); after: [T](x: scala.|[T, scala.Null])scala.&[x.type, T]
+    // FIXME: method NOT overwritten yet in scala2-library-bootstrapped/src/scala/Predef.scala
+    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.valueOf"), // The member scala.Predef.valueOf with signature (1):java.lang.Object does not have a correspondant in current version
+    // FIXME: method NOT overwritten yet in scala2-library-bootstrapped/src/scala/Predef.scala
+    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.ne"), // The member scala.Predef.ne with signature (java.lang.Object,java.lang.Object):scala.Boolean does not have a correspondant in current version
+    // FIXME: method NOT overwritten yet in scala2-library-bootstrapped/src/scala/Predef.scala
+    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.eq"), // The member scala.Predef.eq with signature (java.lang.Object,java.lang.Object):scala.Boolean does not have a correspondant in current version
+
     // Probably OK
     ProblemMatcher.make(ProblemKind.IncompatibleSelfTypeChange, "scala.*"),
 
@@ -54,11 +64,6 @@ object TastyMiMaFilters {
     ProblemMatcher.make(ProblemKind.NewAbstractMember, "scala.collection.convert.impl.TableStepperBase.i0_="),
     ProblemMatcher.make(ProblemKind.NewAbstractMember, "scala.collection.convert.impl.TableStepperBase.maxLength_="),
 
-    // Problem: ???
-    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.nn"), // The member scala.Predef.nn with signature (1,java.lang.Object):java.lang.Object does not have a correspondant in current version
-    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.ne"), // The member scala.Predef.ne with signature (java.lang.Object,java.lang.Object):scala.Boolean does not have a correspondant in current version
-    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.eq"), // The member scala.Predef.eq with signature (java.lang.Object,java.lang.Object):scala.Boolean does not have a correspondant in current version
-
     // Probably OK: protected lazy val (processThread, (futureThread, futureValue), destroyer) = { ... }
     // None of these can be accessed from user code.
     // https://github.com/scala/scala/blob/cff8a9af4da67658d8e1e32f929e1aff03ffa384/src/library/scala/sys/process/ProcessImpl.scala#L99C5-L99C83
@@ -75,10 +80,6 @@ object TastyMiMaFilters {
     //   https://github.com/scala/scala/blob/2.13.x/src/library/scala/collection/mutable/ArrayBuilder.scala#L504C1-L504C87
     ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.collection.mutable.ArrayBuilder.ofUnit.addAll"), // The member scala.collection.mutable.ArrayBuilder.ofUnit.addAll with signature (java.lang.Object,scala.Int,scala.Int):scala.collection.mutable.ArrayBuilder$.ofUnit does not have a correspondant in current version
 
-    // Probably OK (TASTy MiMa bug): Patched Predef members
-    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.valueOf"), // The member scala.Predef.valueOf with signature (1):java.lang.Object does not have a correspondant in current version
-    ProblemMatcher.make(ProblemKind.MissingTermMember, "scala.Predef.summon"), // The member scala.Predef.summon with signature (1,java.lang.Object):java.lang.Object does not have a correspondant in current version
-
     // TASTy-MiMa bugs
     ProblemMatcher.make(ProblemKind.InternalError, "scala.collection.SeqView.appendedAll"),
     ProblemMatcher.make(ProblemKind.InternalError, "scala.collection.SeqView.concat"),

scala2-library-bootstrapped/src/scala/Predef.scala

@@ -508,6 +508,64 @@ object Predef extends LowPriorityImplicits {
    */
   // $ to avoid accidental shadowing (e.g. scala/bug#7788)
   implicit def $conforms[A]: A => A = <:<.refl
+
+  // TODO Add `valueOf`:
+  //      Issue is that this introduces a cyclic dependency between
+  //      the Scala 2 and 3 library due to the reference to `summonFrom`.
+  // /**
+  //  * Retrieve the single value of a type with a unique inhabitant.
+  //  *
+  //  * @example {{{
+  //  * object Foo
+  //  * val foo = valueOf[Foo.type]
+  //  * // foo is Foo.type = Foo
+  //  *
+  //  * val bar = valueOf[23]
+  //  * // bar is 23.type = 23
+  //  * }}}
+  //  * @group utilities
+  //  */
+  // inline def valueOf[T]: T = summonFrom {
+  //   case ev: ValueOf[T] => ev.value
+  // }
+
+  /** Summon a given value of type `T`. Usually, the argument is not passed explicitly.
+   *
+   *  @tparam T the type of the value to be summoned
+   *  @return the given value typed: the provided type parameter
+   */
+  transparent inline def summon[T](using x: T): x.type = x
+
+  // Extension methods for working with explicit nulls
+
+  /** Strips away the nullability from a value. Note that `.nn` performs a checked cast,
+   *  so if invoked on a `null` value it will throw an `NullPointerException`.
+   *  @example {{{
+   *  val s1: String | Null = "hello"
+   *  val s2: String = s1.nn
+   *
+   *  val s3: String | Null = null
+   *  val s4: String = s3.nn // throw NullPointerException
+   *  }}}
+   */
+  extension [T](x: T | Null) inline def nn: x.type & T =
+    if x.asInstanceOf[Any] == null then scala.runtime.Scala3RunTime.nnFail()
+    x.asInstanceOf[x.type & T]
+
+  // FIXME
+  //   tests/explicit-nulls/pos/eq-ne.scala failed
+  //   tests/explicit-nulls/pos/flow-predef-eq.scala failed
+  // extension (inline x: AnyRef | Null)
+  //   /** Enables an expression of type `T|Null`, where `T` is a subtype of `AnyRef`, to be checked for `null`
+  //    *  using `eq` rather than only `==`. This is needed because `Null` no longer has
+  //    *  `eq` or `ne` methods, only `==` and `!=` inherited from `Any`. */
+  //   inline def eq(inline y: AnyRef | Null): Boolean =
+  //     x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+  //   /** Enables an expression of type `T|Null`, where `T` is a subtype of `AnyRef`, to be checked for `null`
+  //    *  using `ne` rather than only `!=`. This is needed because `Null` no longer has
+  //    *  `eq` or `ne` methods, only `==` and `!=` inherited from `Any`. */
+  //   inline def ne(inline y: AnyRef | Null): Boolean =
+  //     !(x eq y)
 }
 
 /** The `LowPriorityImplicits` class provides implicit values that