ObjectFinal

input/src/main/scala/fix/ObjectFinalTest.scala

@@ -0,0 +1,48 @@
+/*
+rule = ObjectFinal
+ */
+package fix
+
+object ObjectFinalTest {
+  final val a1: List[String] = List.empty[String] // assert: ObjectFinal
+  final val a2 = List.empty[String]
+
+  final def b1: List[String] = List.empty[String] // assert: ObjectFinal
+  final def b2 = List.empty[String] // assert: ObjectFinal
+  final def b3 = "a" // assert: ObjectFinal
+  final def b4 = 123 // assert: ObjectFinal
+
+  final val c1: Boolean = false
+  final val c2: Byte = 2
+  final val c3: Short = 3
+  final val c4: Char = 'x'
+  final val c5: Int = 5
+  final val c6: Long = 6L
+  final val c7: Float = 1.5f
+  final val c8: Double = 2.5
+
+  final val d1: scala.Boolean = false
+  final val d2: scala.Byte = 2
+  final val d3: scala.Short = 3
+  final val d4: scala.Char = 'x'
+  final val d5: scala.Int = 5
+  final val d6: scala.Long = 6L
+  final val d7: scala.Float = 1.5f
+  final val d8: scala.Double = 2.5
+
+  final val e1: _root_.scala.Boolean = false
+  final val e2: _root_.scala.Byte = 2
+  final val e3: _root_.scala.Short = 3
+  final val e4: _root_.scala.Char = 'x'
+  final val e5: _root_.scala.Int = 5
+  final val e6: _root_.scala.Long = 6L
+  final val e7: _root_.scala.Float = 1.5f
+  final val e8: _root_.scala.Double = 2.5
+
+  final val s1: String = "s"
+  final val s2: Predef.String = "s"
+  final val s3: scala.Predef.String = "s"
+  final val s4: _root_.scala.Predef.String = "s"
+  final val s5: java.lang.String = "s"
+  final val s6: _root_.java.lang.String = "s"
+}

rules/src/main/scala/fix/ObjectFinal.scala

@@ -0,0 +1,134 @@
+package fix
+
+import scala.meta.Defn
+import scala.meta.Mod
+import scala.meta.Pat
+import scala.meta.Term
+import scala.meta.Type
+import scalafix.Patch
+import scalafix.lint.Diagnostic
+import scalafix.lint.LintSeverity
+import scalafix.v1.SyntacticDocument
+import scalafix.v1.SyntacticRule
+
+object ObjectFinal {
+  private val constantTypes: Seq[Type] = {
+    val values = Seq(
+      "Boolean",
+      "Byte",
+      "Short",
+      "Char",
+      "Int",
+      "Long",
+      "Float",
+      "Double",
+    ).map(Type.Name.apply)
+
+    Seq(
+      values.flatMap { x =>
+        Seq(
+          x,
+          Type.Select(
+            Term.Name("scala"),
+            x,
+          ),
+          Type.Select(
+            Term.Select(
+              Term.Name("_root_"),
+              Term.Name("scala")
+            ),
+            x
+          )
+        )
+      }, {
+        val str = Type.Name("String")
+
+        Seq(
+          str,
+          Type.Select(
+            Term.Name("Predef"),
+            str,
+          ),
+          Type.Select(
+            Term.Select(
+              Term.Name("scala"),
+              Term.Name("Predef")
+            ),
+            str
+          ),
+          Type.Select(
+            Term.Select(
+              Term.Select(
+                Term.Name("_root_"),
+                Term.Name("scala")
+              ),
+              Term.Name("Predef")
+            ),
+            str
+          ),
+          Type.Select(
+            Term.Select(
+              Term.Name("java"),
+              Term.Name("lang")
+            ),
+            str
+          ),
+          Type.Select(
+            Term.Select(
+              Term.Select(
+                Term.Name("_root_"),
+                Term.Name("java")
+              ),
+              Term.Name("lang")
+            ),
+            str
+          ),
+        )
+      }
+    ).flatten
+  }
+
+  private object FinalMod {
+    def unapply(values: List[Mod]): Option[Mod] = values.find(_.is[Mod.Final])
+  }
+}
+
+class ObjectFinal extends SyntacticRule("ObjectFinal") {
+
+  override def fix(implicit doc: SyntacticDocument): Patch = {
+    doc.tree.collect { case o: Defn.Object =>
+      o.templ.stats.collect {
+        case Defn.Val(
+              ObjectFinal.FinalMod(m),
+              List(Pat.Var(_: Term.Name)),
+              Some(tpe),
+              _
+            ) if ObjectFinal.constantTypes.forall(_.structure != tpe.structure) =>
+          Patch.lint(
+            Diagnostic(
+              id = "",
+              message =
+                "redundant final https://scala-lang.org/files/archive/spec/2.13/06-expressions.html#constant-expressions",
+              position = m.pos,
+              severity = LintSeverity.Warning
+            )
+          )
+        case Defn.Def.After_4_7_3(
+              ObjectFinal.FinalMod(m),
+              _,
+              _,
+              _,
+              _
+            ) =>
+          Patch.lint(
+            Diagnostic(
+              id = "",
+              message = "redundant final",
+              position = m.pos,
+              severity = LintSeverity.Warning
+            )
+          )
+      }.asPatch
+    }.asPatch
+  }
+}