Add Scala 3 CanEqual for Parsers.~ to support strict equality

build.sbt

@@ -67,20 +67,16 @@ lazy val parserCombinators = crossProject(JVMPlatform, JSPlatform, NativePlatfor
           version.value
         )
     }),
-    Compile / unmanagedSourceDirectories ++= {
-      (Compile / unmanagedSourceDirectories).value.map { dir =>
-        CrossVersion.partialVersion(scalaVersion.value) match {
-          case Some((2, 13)) => file(dir.getPath ++ "-2.13+")
-          case Some((3, _))  => file(dir.getPath ++ "-2.13+")
-          case _             => file(dir.getPath ++ "-2.13-")
-        }
-      }
-    },
 
     mimaBinaryIssueFilters ++= {
       Seq(
         // scala/scala-parser-combinators#605
         ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.util.parsing.input.PagedSeq.sliding"),
+        // scala/scala-parser-combinators#646
+        ProblemFilters.exclude[DirectMissingMethodProblem]("scala.util.parsing.combinator.Parsers#~.given_CanEqual_~_~"),
+        // -Yfuture-lazy-vals turns the module's <clinit> from public to private, which is not an
+        // incompatibility. Drop once the fix for scala-garden/mima#794 is released.
+        ProblemFilters.exclude[DirectMissingMethodProblem]("scala.util.parsing.input.OffsetPosition.<clinit>"),
       )
     },
   )

shared/src/main/scala-3/scala/util/parsing/input/ScalaVersionSpecificPagedSeq.scala

@@ -0,0 +1,20 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc. dba Akka
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.util.parsing.input
+
+private[input] trait ScalaVersionSpecificPagedSeq[T] {
+  self: PagedSeq[T] =>
+  // Members declared in scala.collection.Seq
+  override def iterableFactory: collection.SeqFactory[collection.IndexedSeq] = collection.IndexedSeq
+
+}

shared/src/test/scala-3/scala/util/parsing/combinator/Parsers.scala

@@ -0,0 +1,23 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc. dba Akka
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.util.parsing.combinator
+
+import scala.language.strictEquality
+import scala.util.parsing.combinator.RegexParsers
+
+class CanEqualsCompileTest extends RegexParsers {
+  val x: String ~ String = new~("a", "b")
+  val y: String ~ String = new~("a", "b")
+  x == y
+}
+