Rename Eql to CanEqual

Author: odersky

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

@@ -840,7 +840,7 @@ class Definitions {
 
   @tu lazy val TastyReflectionClass: ClassSymbol = requiredClass("scala.tasty.Reflection")
 
-  @tu lazy val EqlClass: ClassSymbol = requiredClass("scala.Eql")
+  @tu lazy val EqlClass: ClassSymbol = getClassIfDefined("scala.Eql").orElse(requiredClass("scala.CanEqual")).asClass
     def Eql_eqlAny(using Context): TermSymbol = EqlClass.companionModule.requiredMethod(nme.eqlAny)
 
   @tu lazy val TypeBoxClass: ClassSymbol = requiredClass("scala.runtime.TypeBox")

compiler/test-resources/repl/i4184

@@ -2,8 +2,8 @@ scala> object foo { class Foo }
 // defined object foo
 scala> object bar { class Foo }
 // defined object bar
-scala> implicit def eqFoo: Eql[foo.Foo, foo.Foo] = Eql.derived
-def eqFoo: Eql[foo.Foo, foo.Foo]
+scala> implicit def eqFoo: CanEqual[foo.Foo, foo.Foo] = CanEqual.derived
+def eqFoo: CanEqual[foo.Foo, foo.Foo]
 scala> object Bar { new foo.Foo == new bar.Foo }
 1 | object Bar { new foo.Foo == new bar.Foo }
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^

compiler/test-resources/repl/i7644

@@ -1,14 +1,14 @@
-scala> class T extends Eql
-1 | class T extends Eql
+scala> class T extends CanEqual
+1 | class T extends CanEqual
   |       ^
-  |       Cannot extend sealed trait Eql in a different source file
-1 | class T extends Eql
-  |                 ^^^
-  |                 Missing type parameter for Eql
-scala> class T extends Eql
-1 | class T extends Eql
+  |       Cannot extend sealed trait CanEqual in a different source file
+1 | class T extends CanEqual
+  |                 ^^^^^^^^
+  |                 Missing type parameter for CanEqual
+scala> class T extends CanEqual
+1 | class T extends CanEqual
   |       ^
-  |       Cannot extend sealed trait Eql in a different source file
-1 | class T extends Eql
-  |                 ^^^
-  |                 Missing type parameter for Eql
+  |       Cannot extend sealed trait CanEqual in a different source file
+1 | class T extends CanEqual
+  |                 ^^^^^^^^
+  |                 Missing type parameter for CanEqual

library/src-bootstrapped/scala/Eql.scala

@@ -0,0 +1,34 @@
+package scala
+
+import annotation.implicitNotFound
+import scala.collection.{Seq, Set}
+
+/** A marker trait indicating that values of type `L` can be compared to values of type `R`. */
+@implicitNotFound("Values of types ${L} and ${R} cannot be compared with == or !=")
+sealed trait CanEqual[-L, -R]
+
+/** Companion object containing a few universally known `CanEqual` instances.
+ *  CanEqual instances involving primitive types or the Null type are handled directly in
+ *  the compiler (see Implicits.synthesizedCanEqual), so they are not included here.
+ */
+object CanEqual {
+  /** A universal `CanEqual` instance. */
+  object derived extends CanEqual[Any, Any]
+
+  /** A fall-back instance to compare values of any types.
+   *  Even though this method is not declared as given, the compiler will
+   *  synthesize implicit arguments as solutions to `CanEqual[T, U]` queries if
+   *  the rules of multiversal equality require it.
+   */
+  def eqlAny[L, R]: CanEqual[L, R] = derived
+
+  // Instances of `CanEqual` for common Java types
+  given eqlNumber as CanEqual[Number, Number] = derived
+  given eqlString as CanEqual[String, String] = derived
+
+  // The next three definitions can go into the companion objects of classes
+  // Seq and Set. For now they are here in order not to have to touch the
+  // source code of these classes
+  given eqlSeq[T, U](using eq: CanEqual[T, U]) as CanEqual[Seq[T], Seq[U]] = derived
+  given eqlSet[T, U](using eq: CanEqual[T, U]) as CanEqual[Set[T], Set[U]] = derived
+}

library/src/scala/Eql.scala …ary/src-non-bootstrapped/scala/Eql.scalalibrary/src/scala/Eql.scala renamed to library/src-non-bootstrapped/scala/Eql.scala library/src/scala/Eql.scala renamed to library/src-non-bootstrapped/scala/Eql.scala

@@ -8,7 +8,7 @@ object Enums/*<-_empty_::Enums.*/:
   enum Directions/*<-_empty_::Enums.Directions#*/:
     case North/*<-_empty_::Enums.Directions.North.*/, East/*<-_empty_::Enums.Directions.East.*/, South/*<-_empty_::Enums.Directions.South.*/, West/*<-_empty_::Enums.Directions.West.*/
 
-  enum Suits/*<-_empty_::Enums.Suits#*/ derives /*->scala::Eql.derived.*/Eql:
+  enum Suits/*<-_empty_::Enums.Suits#*/ derives /*->scala::CanEqual.derived.*/CanEqual:
     case Hearts/*<-_empty_::Enums.Suits.Hearts.*/, Spades/*<-_empty_::Enums.Suits.Spades.*/, Clubs/*<-_empty_::Enums.Suits.Clubs.*/, Diamonds/*<-_empty_::Enums.Suits.Diamonds.*/
 
   object Suits/*<-_empty_::Enums.Suits.*/:

tests/semanticdb/expect/Enums.expect.scala

@@ -8,7 +8,7 @@ object Enums:
   enum Directions:
     case North, East, South, West
 
-  enum Suits derives Eql:
+  enum Suits derives CanEqual:
     case Hearts, Spades, Clubs, Diamonds
 
   object Suits:

tests/semanticdb/expect/Enums.scala

@@ -755,7 +755,7 @@ _empty_/Enums.Suits.Clubs. => case val static enum method Clubs
 _empty_/Enums.Suits.Diamonds. => case val static enum method Diamonds
 _empty_/Enums.Suits.Hearts. => case val static enum method Hearts
 _empty_/Enums.Suits.Spades. => case val static enum method Spades
-_empty_/Enums.Suits.derived$Eql(). => implicit method derived$Eql
+_empty_/Enums.Suits.derived$CanEqual(). => implicit method derived$CanEqual
 _empty_/Enums.Suits.fromOrdinal(). => method fromOrdinal
 _empty_/Enums.Suits.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Suits.isBlack(). => method isBlack
@@ -844,7 +844,7 @@ Occurrences:
 [8:29..8:33): West <- _empty_/Enums.Directions.West.
 [10:7..10:12): Suits <- _empty_/Enums.Suits#
 [10:21..10:21): <- _empty_/Enums.Suits#`<init>`().
-[10:21..10:21): -> scala/Eql.derived.
+[10:21..10:21): -> scala/CanEqual.derived.
 [11:9..11:15): Hearts <- _empty_/Enums.Suits.Hearts.
 [11:17..11:23): Spades <- _empty_/Enums.Suits.Spades.
 [11:25..11:30): Clubs <- _empty_/Enums.Suits.Clubs.