New ImplicitClassPrivateParams rule scalacenter#542

scalafix-core/shared/src/main/scala/scalafix/internal/rule/ImplicitClassPrivateVal.scala

@@ -0,0 +1,28 @@
+package scalafix.internal.rule
+
+import scala.meta.quasiquotes.XtensionQuasiquoteInit
+import scala.meta.{Ctor, Defn, Mod, Template, Term}
+import scalafix.rule.RuleCtx
+import scalafix.{Patch, Rule}
+
+case object ImplicitClassPrivateVal
+    extends Rule("ImplicitClassPrivateVal") {
+
+  override def description: String =
+    "Add private access modifier to val parameters of implicit value classes in order to prevent public access"
+
+  override def fix(ctx: RuleCtx): Patch = {
+    ctx.tree.collect {
+      case Defn.Class(cMods, _, _, Ctor.Primary(_, _, (Term.Param(pMods, _, _, _) :: Nil) :: Nil), Template(_, init"AnyVal" :: Nil, _, _))
+          if cMods.exists(_.is[Mod.Implicit]) =>
+        val optPatch = for {
+          anchorMod <- pMods.find(!_.is[Mod.Annot]) if !containsPrivateOrProtected(pMods)
+        } yield ctx.addLeft(anchorMod, "private ")
+        optPatch.asPatch
+
+    }.asPatch
+  }
+
+  private def containsPrivateOrProtected(pMods: List[Mod]) =
+    pMods.exists(m => m.is[Mod.Private] || m.is[Mod.Protected])
+}

scalafix-core/shared/src/main/scala/scalafix/rule/ScalafixRules.scala

@@ -14,7 +14,8 @@ object ScalafixRules {
     NoFinalize,
     DottyKeywords,
     DottyVarArgPattern,
-    DisableSyntax()
+    DisableSyntax(),
+    ImplicitClassPrivateVal
   )
   def semantic(index: SemanticdbIndex): List[Rule] = List(
     NoInfer(index, NoInferConfig.default),

scalafix-tests/input/src/main/scala/test/ImplicitClassPrivateVal.scala

@@ -0,0 +1,26 @@
+/*
+rules = ImplicitClassPrivateVal
+ */
+package test
+
+object ImplicitClassPrivateVal {
+  implicit class XtensionVal(val int: Int) extends AnyVal {
+    def doubled: Int = int + int
+  }
+
+  implicit class XtensionFinalVal(final val int: Int) extends AnyVal {
+    def doubled: Int = int + int
+  }
+
+  implicit class XtensionAnnotatedVal(@transient val str: String) extends AnyVal {
+    def doubled: String = str + str
+  }
+
+  implicit class XtensionAnnotatedFinalVal(@transient final val str: String) extends AnyVal {
+    def doubled: String = str + str
+  }
+
+  implicit class XtensionAnnotatedProtectedVal(@transient protected val int: Int) extends AnyVal {
+    def doubled: Int = int + int
+  }
+}

scalafix-tests/output/src/main/scala/test/ImplicitClassPrivateVal.scala

@@ -0,0 +1,23 @@
+package test
+
+object ImplicitClassPrivateVal {
+  implicit class XtensionVal(private val int: Int) extends AnyVal {
+    def doubled: Int = int + int
+  }
+
+  implicit class XtensionFinalVal(private final val int: Int) extends AnyVal {
+    def doubled: Int = int + int
+  }
+
+  implicit class XtensionAnnotatedVal(@transient private val str: String) extends AnyVal {
+    def doubled: String = str + str
+  }
+
+  implicit class XtensionAnnotatedFinalVal(@transient private final val str: String) extends AnyVal {
+    def doubled: String = str + str
+  }
+
+  implicit class XtensionAnnotatedProtectedVal(@transient protected val int: Int) extends AnyVal {
+    def doubled: Int = int + int
+  }
+}

website/src/main/resources/microsite/data/rules.yml

@@ -13,3 +13,4 @@ rules:
 - Disable
 - DisableSyntax
 - DisableUnless
+- ImplicitClassPrivateVal

website/src/main/tut/docs/rules/ImplicitClassPrivateVal.md

@@ -0,0 +1,25 @@
+---
+layout: docs
+title: ImplicitClassPrivateVal
+---
+
+# ImplicitClassPrivateVal
+
+`val` fields of implicit classes are accessible as an extension. 
+This rule adds the `private` access modifier in such cases in order to prevent direct access.
+
+```scala
+// before
+implicit class XtensionVal(val str: String) extends AnyVal {
+  def doubled: String = str + str
+}
+"message".str // compiles
+
+// after
+implicit class XtensionValFixed(private val str: String) extends AnyVal {
+  def doubled: String = str + str
+}
+"message".str // does not compile
+```
+
+This rule safely ignores all other modifiers.