Initial implementation

.gitignore

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+*.iml
+*.ipr
+*.iws
+.idea/
+target/
+*.log
+.DS_Store
+application.conf
+data/

build.sbt

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+name := "stringmask"
+
+version := "1.0"
+
+scalaVersion := "2.11.7"
+
+libraryDependencies ++= Seq(
+  "org.scala-lang" % "scala-reflect" % "2.11.7",
+  "org.scalatest" %% "scalatest" % "2.2.6" % "test"
+)
+
+addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)

project/build.properties

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+sbt.version=0.13.11

src/main/scala/com/softwaremill/tostringmask/CustomizeImpl.scala

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+package com.softwaremill.tostringmask
+
+import scala.annotation.StaticAnnotation
+import scala.language.experimental.macros
+import scala.reflect.macros.whitebox
+
+class customize extends StaticAnnotation {
+  def macroTransform(annottees: Any*): Any = macro CustomizeImpl.impl
+}
+
+class mask extends StaticAnnotation
+
+
+object CustomizeImpl {
+
+  def impl(c: whitebox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
+    import c.universe._
+
+    def extractCaseClassesParts(classDecl: ClassDef) = classDecl match {
+      case q"case class $className(..$fields) extends ..$parents { ..$body }" =>
+        (className, fields, parents, body)
+    }
+
+    def extractNewToString(typeName: TypeName, allFields: List[Tree]) = {
+      val fieldListTree = allFields.foldLeft(List.empty[Tree]) { case (accList, fieldTree) =>
+        fieldTree match {
+          case q"${Modifiers(fs, nm, List(q"new mask()"))} val $field: $fieldType = $sth" =>
+            accList :+ Literal(Constant("***"))
+          case q"$m val $field: $fieldType = $sth" =>
+            accList :+ q"$field.toString"
+          case _ => c.abort(c.enclosingPosition, "Cannot call .toString on tree " + showRaw(fieldTree))
+        }
+      }
+      val treesAsTuple = Apply(Select(Ident(TermName("scala")), TermName("Tuple" + fieldListTree.length)), fieldListTree)
+      val typeNameStrTree = Literal(Constant(typeName.toString))
+      q"""
+         override def toString: ${typeOf[String]} = {
+          $typeNameStrTree + $treesAsTuple
+         }
+      """
+    }
+
+    def modifiedDeclaration(classDecl: ClassDef) = {
+      val (className, fields, parents, body) = extractCaseClassesParts(classDecl)
+      val newToString = extractNewToString(className, fields)
+
+      val params = fields.asInstanceOf[List[ValDef]] map { p => p.duplicate}
+
+      c.Expr[Any](
+        q"""
+        case class $className ( ..$params ) extends ..$parents {
+          $newToString
+          ..$body
+        }
+      """
+      )
+    }
+
+    annottees map (_.tree) toList match {
+      case (classDecl: ClassDef) :: Nil =>
+        modifiedDeclaration(classDecl)
+      case _ =>
+        c.abort(c.enclosingPosition, "Invalid annottee, expected case class.")
+    }
+  }
+}

src/test/scala/ToStringMaskTest.scala

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+import java.time.ZonedDateTime
+
+import com.softwaremill.tostringmask.{customize, mask}
+import org.scalatest.{FlatSpec, Matchers}
+
+class ToStringMaskTest extends FlatSpec with Matchers {
+
+  behavior of "masking"
+
+  @customize
+  case class User20(id: Int, @mask name: String, @mask email: String, something: Long, @mask secretDob: ZonedDateTime)
+
+  it should "mask fields" in {
+    // given
+    val u = User20(1, "Secret Person", "secret@email.com", 15, ZonedDateTime.now())
+
+    // then
+    u.toString should be("User20(1,***,***,15,***)")
+  }
+}