UnusedSelfType

input/src/main/scala/fix/UnusedSelfTypeTest.scala

@@ -0,0 +1,19 @@
+/*
+rule = UnusedSelfType
+ */
+package fix
+
+trait UnusedSelfTypeTest {
+  class X1 { self => // assert: UnusedSelfType
+  }
+  trait X2 { self => // assert: UnusedSelfType
+  }
+  trait X3 { self =>
+    def f1 = self
+  }
+  trait X4 { self =>
+    trait B {
+      val c = self
+    }
+  }
+}

rules/src/main/scala/fix/UnusedSelfType.scala

@@ -0,0 +1,42 @@
+package fix
+
+import scala.meta.Self
+import scala.meta.Template
+import scala.meta.Term
+import scala.meta.XtensionCollectionLikeUI
+import scala.meta.contrib.XtensionTreeOps
+import scalafix.Patch
+import scalafix.lint.Diagnostic
+import scalafix.lint.LintSeverity
+import scalafix.v1.SyntacticDocument
+import scalafix.v1.SyntacticRule
+import scalafix.v1.XtensionSeqPatch
+
+class UnusedSelfType extends SyntacticRule("UnusedSelfType") {
+  override def fix(implicit doc: SyntacticDocument): Patch = {
+    doc.tree.collect {
+      case t @ Template.After_4_9_9(
+            _,
+            _,
+            Template.Body(
+              Some(Self(a, None)),
+              _
+            ),
+            _
+          )
+          if t.body.stats.forall(s =>
+            s.collectFirst {
+              case x: Term.Name if x.value == a.value => ()
+            }.isEmpty
+          ) =>
+        Patch.lint(
+          Diagnostic(
+            id = "",
+            message = "unused self type",
+            position = a.pos,
+            severity = LintSeverity.Warning
+          )
+        )
+    }.asPatch
+  }
+}