Reuse the extractor library via a private Compat.Extractor

Make `.extract` opt-in and keep it out of `com.thoughtworks`:

- `Compat` is now `private[sbtApiMappings]` and exposes a nested `Extractor`
  member, imported with `import Compat.Extractor._`. This avoids leaking the
  `.extract` implicit onto every function via `import Compat._`.
- On Scala 2.12, `Compat.Extractor` is `val Extractor = com.thoughtworks.Extractor`,
  i.e. a re-export of the `com.thoughtworks.extractor` library (added back as a
  Scala-2.12-only dependency). The library is reused as-is; its `sealed`
  `private[thoughtworks]` traits cannot be wrapped, but a plain `val` alias
  re-exports the object so its implicits come in through `import Compat.Extractor._`.
- On Scala 3 `Compat.Extractor` is an `object` whose `extension` turns a
  function/partial function into a `PartialFunction` (already a valid pattern on
  Scala 3). No `com.thoughtworks.Extractor` shim, so the package is not polluted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Atry

build.sbt

@@ -34,6 +34,16 @@ pluginCrossBuild / sbtVersion := {
 // so most of the plugin sources can be shared across both sbt versions.
 addSbtPlugin("com.github.sbt" % "sbt2-compat" % "0.1.0")
 
+// `.extract` pattern support, reused via `Compat.Extractor`. Only published for
+// Scala 2.12; on Scala 3 a PartialFunction is already a valid pattern, so the
+// Scala 3 `Compat.Extractor` provides an equivalent extension instead.
+libraryDependencies ++= {
+  if (scalaBinaryVersion.value == "2.12")
+    Seq("com.thoughtworks.extractor" %% "extractor" % "2.1.3")
+  else
+    Seq.empty
+}
+
 libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.20" % "test"
 
 scriptedBufferLog := false

src/main/scala-2.12/com/thoughtworks/sbtApiMappings/Compat.scala

@@ -9,7 +9,7 @@ import sbtcompat.PluginCompat
 /** sbt 1.x specific bindings: only the pieces that genuinely differ from sbt
   * 2.x. Everything that sbt2-compat can express uniformly is plain shared code.
   */
-object Compat {
+private[sbtApiMappings] object Compat {
 
   /** The value type of the `apiMappings` map. */
   type DocUrl = URL
@@ -20,22 +20,9 @@ object Compat {
   def fileToDocKey: Def.Initialize[Task[File => PluginCompat.FileRef]] =
     Def.task { (file: File) => file }
 
-  // On Scala 2.12 a function/partial function cannot be used as a pattern
-  // directly, so `.extract` adapts it into an extractor object.
-
-  final class Extractor[A, B](unlifted: A => Option[B]) {
-    def unapply(a: A): Option[B] = unlifted(a)
-  }
-
-  implicit final class FunctionExtractOps[A, B](private val f: A => Option[B])
-      extends AnyVal {
-    def extract: Extractor[A, B] = new Extractor(f)
-  }
-
-  implicit final class PartialFunctionExtractOps[A, B](
-      private val pf: PartialFunction[A, B]
-  ) extends AnyVal {
-    def extract: Extractor[A, B] = new Extractor(pf.lift)
-  }
-
+  /** The `.extract` pattern support, opted into with
+    * `import Compat.Extractor._`. On Scala 2.12 it simply re-exports the
+    * `com.thoughtworks.extractor` library.
+    */
+  val Extractor = com.thoughtworks.Extractor
 }

src/main/scala-3/com/thoughtworks/sbtApiMappings/Compat.scala

@@ -10,7 +10,7 @@ import xsbti.HashedVirtualFileRef
 /** sbt 2.x specific bindings: only the pieces that genuinely differ from sbt
   * 1.x. Everything that sbt2-compat can express uniformly is plain shared code.
   */
-object Compat:
+private[sbtApiMappings] object Compat:
 
   /** The value type of the `apiMappings` map. */
   type DocUrl = URI
@@ -27,11 +27,13 @@ object Compat:
       HashedVirtualFileRef.of(file.toPath.toString, ""): PluginCompat.FileRef
     }
 
-  // On Scala 3 a PartialFunction is already a valid pattern, so `.extract` turns
-  // a function (or partial function) into one.
-
-  extension [A, B](f: A => Option[B])
-    def extract: PartialFunction[A, B] = Function.unlift(f)
-
-  extension [A, B](pf: PartialFunction[A, B])
-    def extract: PartialFunction[A, B] = pf
+  /** The `.extract` pattern support, opted into with `import Compat.Extractor._`.
+    * The `com.thoughtworks.extractor` library has no Scala 3 build, but on Scala
+    * 3 a [[scala.PartialFunction]] is already a valid pattern, so a function (or
+    * partial function) only needs to be turned into one.
+    */
+  object Extractor:
+    extension [A, B](f: A => Option[B])
+      def extract: PartialFunction[A, B] = Function.unlift(f)
+    extension [A, B](pf: PartialFunction[A, B])
+      def extract: PartialFunction[A, B] = pf

src/main/scala/com/thoughtworks/sbtApiMappings/ApiMappings.scala

@@ -18,7 +18,7 @@ package com.thoughtworks.sbtApiMappings
 
 import sbt._
 import Keys._
-import Compat._
+import Compat.Extractor._
 import sbt.plugins.JvmPlugin
 import sbtcompat.PluginCompat
 // Brings `Def.uncached`, which sbt2-compat backfills on sbt 1.x (native on 2.x).

src/main/scala/com/thoughtworks/sbtApiMappings/JavadocIoApiMappingRule.scala

@@ -1,7 +1,7 @@
 package com.thoughtworks.sbtApiMappings
 
 import sbt._
-import Compat._
+import Compat.Extractor._
 import sbtcompat.PluginCompat
 import sbt.internal.librarymanagement.mavenint.PomExtraDependencyAttributes
 

src/main/scala/com/thoughtworks/sbtApiMappings/PlayApiMappingRule.scala

@@ -1,7 +1,7 @@
 package com.thoughtworks.sbtApiMappings
 
 import sbt._
-import Compat._
+import Compat.Extractor._
 import sbtcompat.PluginCompat
 
 /** @author

src/main/scala/com/thoughtworks/sbtApiMappings/ScalaApiMappingRule.scala

@@ -2,7 +2,7 @@ package com.thoughtworks.sbtApiMappings
 
 import sbt.{AutoPlugin, ModuleID, VersionNumber, _}
 import Ordering.Implicits._
-import Compat._
+import Compat.Extractor._
 import sbtcompat.PluginCompat
 
 /** @author

src/main/scala/com/thoughtworks/sbtApiMappings/SonatypeApiMappingRule.scala

@@ -1,7 +1,7 @@
 package com.thoughtworks.sbtApiMappings
 
 import sbt._
-import Compat._
+import Compat.Extractor._
 import sbtcompat.PluginCompat
 import sbt.internal.librarymanagement.mavenint.PomExtraDependencyAttributes
 

src/main/scala/com/thoughtworks/sbtApiMappings/SonatypeApiMappingRuleForSbtPlugins.scala

@@ -1,7 +1,7 @@
 package com.thoughtworks.sbtApiMappings
 
 import sbt._
-import Compat._
+import Compat.Extractor._
 import sbtcompat.PluginCompat
 import sbt.internal.librarymanagement.mavenint.PomExtraDependencyAttributes
 

src/main/scala/com/thoughtworks/sbtApiMappings/SparkApiMappingRule.scala

@@ -1,7 +1,7 @@
 package com.thoughtworks.sbtApiMappings
 
 import sbt.{AutoPlugin, ModuleID, _}
-import Compat._
+import Compat.Extractor._
 import sbtcompat.PluginCompat
 
 /** @author