feat: implicit conversions

input/src/main/scala-3/fix/ImplicitConversionsTest.scala

@@ -0,0 +1,21 @@
+/*
+rule = ImplicitConversions
+ */
+
+package fix
+
+import scala.language.implicitConversions
+
+// format: off
+object ImplicitConversionsTest {
+  implicit def implicitDefWithFunctionArg1(x: Int): String = x.toString
+  implicit def implicitDefWithFunctionArg2(x: (Int, Long)): String = x.toString
+
+  implicit val implicitValWithFunctionType1: Long => String = _.toString
+  implicit val implicitValWithFunctionType2: (Int, Long) => String = (i, l ) => i.toString
+
+  def defWithImplicitFunctionType1(x: Int)(implicit conv: Int => String): String = x
+  def defWithImplicitFunctionType2(x: Int)(implicit conv: (Int, Long) => String): String = x
+  def defWithImplicitFunctionType3(x: Int)(using conv: (Int, Long) => String): String = x
+}
+// format: on

output/src/main/scala-3/fix/ImplicitConversionsTest.scala

@@ -0,0 +1,17 @@
+package fix
+
+import scala.language.implicitConversions
+
+// format: off
+object ImplicitConversionsTest {
+  implicit val implicitDefWithFunctionArg1: Conversion[Int, String] = (x: Int) => x.toString
+  implicit val implicitDefWithFunctionArg2: Conversion[(Int, Long), String] = (x: (Int, Long)) => x.toString
+
+  implicit val implicitValWithFunctionType1: Conversion[Long, String] = _.toString
+  implicit val implicitValWithFunctionType2: Conversion[(Int, Long), String] = (i, l ) => i.toString
+
+  def defWithImplicitFunctionType1(x: Int)(implicit conv: Conversion[Int, String]): String = x
+  def defWithImplicitFunctionType2(x: Int)(implicit conv: Conversion[(Int, Long), String]): String = x
+  def defWithImplicitFunctionType3(x: Int)(using conv: Conversion[(Int, Long), String]): String = x
+}
+// format: on

rules/src/main/resources/META-INF/services/scalafix.v1.Rule

@@ -2,4 +2,5 @@ fix.SemiAuto
 fix.GivenAndUsing
 fix.PackageObjectExport
 fix.DropModThis
-fix.WildcardInitializer
+fix.WildcardInitializer
+fix.ImplicitConversions

rules/src/main/scala/fix/ImplicitConversions.scala

@@ -0,0 +1,102 @@
+/*
+ * Copyright 2022 Arktekk
+ *
+ * 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 fix
+
+import fix.ImplicitConversions._
+import scalafix.v1.{Patch, SemanticDocument, SemanticRule}
+
+import scala.meta._
+import scala.meta.tokens.Token
+
+class ImplicitConversions extends SemanticRule("ImplicitConversions") {
+
+  override def fix(implicit doc: SemanticDocument): Patch = {
+
+    doc.tree.collect {
+
+      case ImplicitDefWithFunctionArg(d, inType, outType) =>
+        (for {
+          pathDefToVal <- d.tokens.find(_.is[Token.KwDef]).map(Patch.replaceToken(_, "val"))
+          eqSignToken <- d.tokens.find(_.is[Token.Equals])
+          argTokens = d.tokens.dropWhile(_.isNot[Token.LeftParen]).dropRightWhile(_.isNot[Token.RightParen])
+        } yield pathDefToVal +
+          Patch.removeTokens(argTokens) +
+          Patch.addRight(eqSignToken, s" ${argTokens.toString()} =>") +
+          Patch.replaceTree(outType, conversionCode(inType, outType))).asPatch
+
+      case ImplicitValWithFunctionType(ts) =>
+        Patch.replaceTree(ts, conversionCode(ts.params, ts.res))
+
+      case DefWithImplicitFunctionType(typeFunctions) =>
+        typeFunctions.foldRight(Patch.empty) { case (tf, patches) =>
+          patches + Patch.replaceTree(tf, conversionCode(tf.params, tf.res))
+        }
+    }.asPatch
+  }
+
+  private def conversionCode(inType: Type, retType: Type): String =
+    conversionCode(inType :: Nil, retType)
+
+  private def conversionCode(inType: List[Type], retType: Type): String = {
+    val inStr = inType match {
+      case one :: Nil => one.toString()
+      case many       => many.map(_.toString()).mkString("(", ", ", ")")
+    }
+    s"Conversion[$inStr, $retType]"
+  }
+}
+
+object ImplicitConversions {
+
+  object ImplicitValWithFunctionType {
+    def unapply(tree: Tree): Option[Type.Function] =
+      tree match {
+        case Defn.Val(mods, _, Some(ts: Type.Function), _) if mods.exists(_.is[Mod.Implicit]) => Some(ts)
+        case _                                                                                => None
+      }
+  }
+  object ImplicitDefWithFunctionArg {
+    def unapply(tree: Tree): Option[(Defn.Def, Type, Type)] =
+      tree match {
+        case d @ Defn.Def(mods, Term.Name(_), _, (firstParam :: Nil) :: Nil, Some(outType: Type.Name), _)
+            if mods.exists(_.is[Mod.Implicit]) && firstParam.mods.forall(_.isNot[Mod.Implicit]) =>
+          firstParam.decltpe.map(inType => (d, inType, outType))
+        case _ => None
+      }
+  }
+
+  object DefWithImplicitFunctionType {
+    def unapply(tree: Tree): Option[List[Type.Function]] = tree match {
+      case Defn.Def(_, _, _, LastImplicitTypeFunctionParams(typeFunctions), _, _) => Some(typeFunctions)
+      case _                                                                      => None
+    }
+
+    object LastImplicitTypeFunctionParams {
+      def unapply(params: List[List[Term.Param]]): Option[List[Type.Function]] = {
+        val lastParams = params.lastOption
+        if (lastParams.exists(_.exists(_.mods.exists(a => a.is[Mod.Implicit] || a.is[Mod.Using])))) {
+          val tfs = lastParams.toList
+            .flatMap(_.map(_.decltpe))
+            .collect { case Some(tf: Type.Function) => tf }
+          if (tfs.isEmpty) None
+          else Some(tfs)
+        } else None
+      }
+    }
+  }
+
+}