Merge pull request #1496 from bplommer/final-object

Add rewriting rule RedundantSyntax.finalObject

docs/rules/RedundantSyntax.md

@@ -0,0 +1,16 @@
+---
+layout: docs
+id: RedundantSyntax
+title: RedundantSyntax
+---
+
+This rule removes redundant syntax. Currently the only syntax it removes is the `final` keyword on an `object`.
+
+Example:
+
+```diff
+- final object foo
++ object Foo
+```
+
+Note: in Scala 2.12 and earlier removing the `final` modifier will slightly change the resulting bytecode - see [this bug ticket](https://github.com/scala/bug/issues/11094) for further information.

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

@@ -3,5 +3,6 @@ scalafix.internal.rule.ExplicitResultTypes
 scalafix.internal.rule.NoAutoTupling
 scalafix.internal.rule.NoValInForComprehension
 scalafix.internal.rule.ProcedureSyntax
+scalafix.internal.rule.RedundantSyntax
 scalafix.internal.rule.RemoveUnused
 scalafix.internal.rule.LeakingImplicitClassVal

scalafix-rules/src/main/scala/scalafix/internal/rule/RedundantSyntax.scala

@@ -0,0 +1,33 @@
+package scalafix.internal.rule
+
+import scala.meta._
+
+import metaconfig.Configured
+import scalafix.util.TokenList
+import scalafix.v1._
+
+class RedundantSyntax(config: RedundantSyntaxConfig)
+    extends SyntacticRule("RedundantSyntax") {
+  def this() = this(RedundantSyntaxConfig())
+  override def withConfiguration(config: Configuration): Configured[Rule] =
+    config.conf
+      .getOrElse("redundantSyntax", "RedundantSyntax")(
+        RedundantSyntaxConfig.default
+      )
+      .map(new RedundantSyntax(_))
+
+  override def description: String =
+    "Removes redundant syntax such as `final` modifiers on an object"
+  override def isRewrite: Boolean = true
+
+  override def fix(implicit doc: SyntacticDocument): Patch =
+    doc.tree.collect {
+      case o: Defn.Object
+          if config.finalObject && o.mods.exists(_.is[Mod.Final]) =>
+        Patch.removeTokens {
+          o.tokens.find(_.is[Token.KwFinal]).toIterable.flatMap { finalTok =>
+            finalTok :: TokenList(o.tokens).trailingSpaces(finalTok).toList
+          }
+        }
+    }.asPatch
+}

scalafix-rules/src/main/scala/scalafix/internal/rule/RedundantSyntaxConfig.scala

@@ -0,0 +1,18 @@
+package scalafix.internal.rule
+
+import metaconfig._
+import metaconfig.annotation._
+import metaconfig.generic.Surface
+
+final case class RedundantSyntaxConfig(
+    @Description("Remove final modifier from objects")
+    finalObject: Boolean = true
+)
+
+object RedundantSyntaxConfig {
+  val default: RedundantSyntaxConfig = RedundantSyntaxConfig()
+  implicit val reader: ConfDecoder[RedundantSyntaxConfig] =
+    generic.deriveDecoder[RedundantSyntaxConfig](default)
+  implicit val surface: Surface[RedundantSyntaxConfig] =
+    generic.deriveSurface[RedundantSyntaxConfig]
+}

scalafix-tests/input/src/main/scala/test/redundantSyntax/FinalObject.scala

@@ -0,0 +1,15 @@
+/*
+rules = RedundantSyntax
+RedundantSyntax.finalObject = true
+*/
+
+package test.redundantSyntax
+
+final object FinalObject {
+  final object Foo
+  private final case object Bar
+}
+
+abstract class Class {
+  final def bar: String = "bar"
+}

scalafix-tests/output/src/main/scala/test/redundantSyntax/FinalObject.scala

@@ -0,0 +1,10 @@
+package test.redundantSyntax
+
+object FinalObject {
+  object Foo
+  private case object Bar
+}
+
+abstract class Class {
+  final def bar: String = "bar"
+}