Shrinking support for Scala 2.12.

Author: SimY4

build.sbt

@@ -159,12 +159,19 @@ lazy val kotest = (project in file("kotest"))
 
 lazy val scalacheck = (project in file("scalacheck"))
   .settings(
-    name                                    := "scalacheck",
-    moduleName                              := "coregex-scalacheck",
-    description                             := "ScalaCheck bindings for coregex library.",
-    headerEndYear                           := Some(2025),
-    libraryDependencies += "org.scalacheck" %% "scalacheck" % "1.19.0" % Provided,
-    crossScalaVersions                      := supportedScalaVersions,
+    name          := "scalacheck",
+    moduleName    := "coregex-scalacheck",
+    description   := "ScalaCheck bindings for coregex library.",
+    headerEndYear := Some(2025),
+    libraryDependencies ++= (CrossVersion.partialVersion(scalaVersion.value) match {
+      case Some((2, 13) | (3, _)) => Seq("org.scalacheck" %% "scalacheck" % "1.19.0" % Provided)
+      case Some((2, 12))          =>
+        Seq(
+          "org.scala-lang.modules" %% "scala-java8-compat" % "1.0.2",
+          "org.scalacheck"         %% "scalacheck"         % "1.19.0" % Provided
+        )
+    }),
+    crossScalaVersions := supportedScalaVersions,
     Compile / unmanagedSourceDirectories ++= (CrossVersion.partialVersion(scalaVersion.value) match {
       case Some((2, 13) | (3, _)) => Seq("scala-2.13+")
       case Some((2, 12))          => Seq.empty

scalacheck/src/main/scala-2.12/com/github/simy4/coregex/scalacheck/CoregexGenVersionSpecific.scala

@@ -0,0 +1,16 @@
+package com.github.simy4.coregex
+package scalacheck
+
+import core.Coregex
+import org.scalacheck.Shrink
+
+private[scalacheck] trait CoregexGenVersionSpecific {
+  import scala.compat.java8.StreamConverters._
+
+  def shrinkFor(coregex: Coregex): Shrink[String] = {
+    val shrinks = coregex.shrink().toScala[Stream]
+    Shrink { larger =>
+      shrinks.map(coregex => coregex.generate(larger.length.toLong)).filter(_.length < larger.length)
+    }
+  }
+}

scalacheck/src/main/scala-2.13+/com/github/simy4/coregex/scalacheck/CoregexGenVersionSpecific.scala

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2021-2025 Alex Simkin
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.github.simy4.coregex
+package scalacheck
+
+import core.Coregex
+import org.scalacheck.Shrink
+
+private[scalacheck] trait CoregexGenVersionSpecific {
+  import scala.jdk.StreamConverters._
+
+  def shrinkFor(coregex: Coregex): Shrink[String] = {
+    val shrinks = coregex.shrink().toScala(LazyList)
+    Shrink.withLazyList { larger =>
+      shrinks.map(coregex => coregex.generate(larger.length.toLong)).filter(_.length < larger.length)
+    }
+  }
+}

scalacheck/src/main/scala-2.13+/com/github/simy4/coregex/scalacheck/CoregexInstances.scala

@@ -23,8 +23,6 @@ import org.scalacheck.{ Arbitrary, Gen, Shrink }
 import java.util.regex.Pattern
 
 trait CoregexInstances {
-  import scala.jdk.CollectionConverters._
-
   type StringMatching[Regex <: String with Singleton] <: String
 
   implicit def arbitraryStringMatchingRegexStringWithSingleton[
@@ -34,12 +32,6 @@ trait CoregexInstances {
 
   implicit def shrinkStringMatchingRegexStringWithSingleton[
     Regex <: String with Singleton: ValueOf
-  ]: Shrink[StringMatching[Regex]] = {
-    val shrinks = Coregex.from(Pattern.compile(valueOf[Regex])).shrink().iterator().asScala.to(LazyList)
-    Shrink.withLazyList { larger =>
-      shrinks
-        .map(coregex => coregex.generate(larger.length.toLong).asInstanceOf[StringMatching[Regex]])
-        .filter(string => string.length < larger.length)
-    }
-  }
+  ]: Shrink[StringMatching[Regex]] =
+    CoregexGen.shrinkFor(Coregex.from(Pattern.compile(valueOf[Regex]))).asInstanceOf[Shrink[StringMatching[Regex]]]
 }

scalacheck/src/main/scala/com/github/simy4/coregex/scalacheck/CoregexGen.scala

@@ -23,7 +23,7 @@ import org.scalacheck.Gen
 import java.util.regex.Pattern
 import scala.util.matching.Regex
 
-object CoregexGen {
+object CoregexGen extends CoregexGenVersionSpecific {
   def fromRegex(regex: Regex): Gen[String] = fromPattern(regex.pattern)
 
   def fromPattern(regex: Pattern): Gen[String] = apply(Coregex.from(regex))