Nothing is a special bottom type; it is a subtype of every other type. The Scala compiler loves to infer Nothing as a generic type but that is almost always incorrect. Explicit type arguments should be used instead.

Author: halotukozak

analyzer/src/main/scala/com/avsystem/commons/analyzer/AnalyzerPlugin.scala

@@ -56,7 +56,7 @@ final class AnalyzerPlugin(val global: Global) extends Plugin { plugin =>
     new Any2StringAdd(global),
     new ThrowableObjects(global),
     new DiscardedMonixTask(global),
-    new ThrownExceptionNotInFunction(global),
+    new RequireExplicitNothing(global),
     new BadSingletonComponent(global),
     new ConstantDeclarations(global),
     new BasePackage(global),

analyzer/src/main/scala/com/avsystem/commons/analyzer/RequireExplicitNothing.scala

@@ -0,0 +1,21 @@
+package com.avsystem.commons
+package analyzer
+
+import scala.tools.nsc.Global
+
+final class RequireExplicitNothing(g: Global) extends AnalyzerRule(g, "requireExplicitNothing") {
+
+  import global.*
+
+  private def wasInferred(t: TypeTree) = t.original == null
+
+  def analyze(unit: CompilationUnit): Unit = unit.body.foreach(analyzeTree {
+    case tree@TypeTree() if tree.tpe <:< definitions.NothingTpe && wasInferred(tree) =>
+      tree.tpe match {
+        // Ignore existential types, they supposedly contain "any"
+        case ExistentialType(_, _) =>
+
+        case _ => report(tree.pos, "Inferred type: Nothing")
+      }
+  })
+}

analyzer/src/main/scala/com/avsystem/commons/analyzer/ThrownExceptionNotInFunction.scala

@@ -0,0 +1,32 @@
+package com.avsystem.commons
+package analyzer
+
+import org.scalatest.funsuite.AnyFunSuite
+
+final class RequireExplicitNothingTest extends AnyFunSuite with AnalyzerTest {
+  settings.pluginOptions.value ++= List("AVSystemAnalyzer:-discardedMonixTask")
+
+  test("simple") {
+    assertErrors(4,
+      //language=Scala
+      """|
+         |object Test {
+         |  //not ok
+         |  val nook1 = throw new Exception
+         |  val nook2 = throw new Exception
+         |  def nook3 = throw new Exception
+         |  val nook4: List[Int] = List.empty //covariant
+         |
+         |  //ok
+         |  val ok1: Nothing = throw new Exception
+         |  val ok2: Nothing = throw new Exception
+         |  def ok3: Nothing = throw new Exception
+         |  val ok4: List[Nothing] = List.empty[Nothing]
+         |  val ok5: List[Nothing] = Nil
+         |  val ok6: List[Int] = Nil
+         |  val ok7: Set[Int] = Set.empty //invariant
+         |}
+         |""".stripMargin
+    )
+  }
+}