Add abstract trait inspections to scala3 (#889)

* add abstract trait to scala3

* remove unused imports

* reorder imports for scalafix

Author: fntz

README.md

@@ -157,12 +157,12 @@ To suppress warnings globally for the project, use `disabledInspections` or `ove
 
 ### Inspections
 
-There are currently 122 inspections for Scala 2, and 1 for Scala 3.
+There are currently 122 inspections for Scala 2, and 2 for Scala 3.
 An overview list is given, followed by a more detailed description of each inspection after the list (todo: finish rest of detailed descriptions)
 
 | Name                                  | Brief Description                                                                                                                                            | Default Level | Scala 2 | Scala 3 |
 |---------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------|---------|
-| AbstractTrait                         | Check if trait is abstract                                                                                                                                   | Info          | Yes     | No      |
+| AbstractTrait                         | Check if trait is abstract                                                                                                                                   | Info          | Yes     | Yes     |
 | ArrayEquals                           | Checks for comparison of arrays using `==` which will always return false                                                                                    | Info          | Yes     | No      |
 | ArraysInFormat                        | Checks for arrays passed to String.format                                                                                                                    | Error         | Yes     | No      |
 | ArraysToString                        | Checks for explicit toString calls on arrays                                                                                                                 | Warning       | Yes     | No      |

src/main/scala-3/com/sksamuel/scapegoat/Inspections.scala

@@ -1,11 +1,13 @@
 package com.sksamuel.scapegoat
 
 import com.sksamuel.scapegoat.inspections.option._
+import com.sksamuel.scapegoat.inspections.traits._
 
 object Inspections {
 
   final val inspections: List[Inspection] = List(
-    new OptionGet
+    new OptionGet,
+    new AbstractTrait
   )
 
 }

src/main/scala-3/com/sksamuel/scapegoat/Plugin.scala

@@ -32,7 +32,6 @@ class ScapegoatPhase(var configuration: Configuration, override val inspections:
     extends PluginPhase
     with ScapegoatBasePlugin {
 
-
   private[scapegoat] var feedback: Option[FeedbackDotty] = None
 
   override def phaseName: String = "scapegoat"

src/main/scala-3/com/sksamuel/scapegoat/inspections/traits/AbstractTrait.scala

@@ -0,0 +1,41 @@
+package com.sksamuel.scapegoat.inspections.traits
+
+import com.sksamuel.scapegoat.*
+import dotty.tools.dotc.ast.tpd
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Flags
+import dotty.tools.dotc.core.Symbols.ClassSymbol
+import dotty.tools.dotc.core.Types.TypeRef
+import dotty.tools.dotc.util.SourcePosition
+
+class AbstractTrait
+    extends Inspection(
+      text = "Use of abstract trait",
+      defaultLevel = Levels.Info,
+      description = "Traits are automatically abstract.",
+      explanation =
+        "The abstract modifier is used in class definitions. It is redundant for traits, and mandatory for all other classes which have incomplete members."
+    ) {
+
+  import tpd.*
+
+  def inspect(feedback: Feedback[SourcePosition], tree: tpd.Tree)(using ctx: Context): Unit = {
+    val traverser = new InspectionTraverser {
+      def traverse(tree: Tree)(using Context): Unit = {
+        tree match {
+          case tDef: TypeDef =>
+            tDef.tpe match {
+              case TypeRef(_, kls: ClassSymbol)
+                  if kls.flags.is(Flags.Trait) && kls.flags.is(Flags.Abstract) =>
+                feedback.warn(tree.sourcePos, self, tree.asSnippet)
+              case _ =>
+            }
+
+          case _ =>
+            traverseChildren(tree)
+        }
+      }
+    }
+    traverser.traverse(tree)
+  }
+}

src/test/scala-3/com/sksamuel/scapegoat/inspections/traits/AbstractTraitTest.scala

@@ -0,0 +1,36 @@
+package com.sksamuel.scapegoat.inspections.traits
+
+import com.sksamuel.scapegoat.InspectionTest
+
+class AbstractTraitTest extends InspectionTest(classOf[AbstractTrait]) {
+
+  "abstract trait use" - {
+    "should report warning" in {
+      val code = "abstract trait Test { }"
+
+      val feedback = runner.compileCodeSnippet(code)
+      feedback.warnings.assertable.size shouldBe 1
+    }
+
+    "should not report warning on sealed" in {
+      val code = "sealed trait Test { val x: Int = 1 }"
+
+      val feedback = runner.compileCodeSnippet(code)
+      feedback.warnings.assertable.size shouldBe 0
+    }
+
+    "should not report warning on trait without modifiers" in {
+      val code = "trait Test1 { val x: Int = 1 }"
+
+      val feedback = runner.compileCodeSnippet(code)
+      feedback.warnings.assertable.size shouldBe 0
+    }
+
+    "should not report on private trait" in {
+      val code = "private trait Test1 { val x: Int = 1 }"
+
+      val feedback = runner.compileCodeSnippet(code)
+      feedback.warnings.assertable.size shouldBe 0
+    }
+  }
+}