Use Nothing for no Result

.github/workflows/ci.yml

@@ -27,13 +27,11 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        scala: [3.1.0, 2.12.15, 2.13.7]
+        scala: [3.1.0, 2.13.7]
         java: [corretto@8, corretto@11]
         exclude:
           - scala: 3.1.0
             java: corretto@11
-          - scala: 2.12.15
-            java: corretto@11
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout current branch (full)
@@ -120,16 +118,6 @@ jobs:
           tar xf targets.tar
           rm targets.tar
 
-      - name: Download target directories (2.12.15)
-        uses: actions/download-artifact@v2
-        with:
-          name: target-${{ matrix.os }}-2.12.15-${{ matrix.java }}
-
-      - name: Inflate target directories (2.12.15)
-        run: |
-          tar xf targets.tar
-          rm targets.tar
-
       - name: Download target directories (2.13.7)
         uses: actions/download-artifact@v2
         with:

.scalafmt.conf

@@ -1,6 +1,14 @@
 version = 3.2.1
 
 runner.dialect = Scala213Source3
+fileOverride {
+  "glob:**/scala-3/**/*.scala" {
+    runner.dialect = scala3
+  }
+  "glob:**/scala-2.13/**/*.scala" {
+    runner.dialect = scala213
+  }
+}
 
 maxColumn = 96
 

build.sbt

@@ -21,7 +21,7 @@ ThisBuild / baseVersion := "0.1"
 ThisBuild / organization := "org.typelevel"
 ThisBuild / organizationName := "Typelevel"
 
-ThisBuild / crossScalaVersions := Seq("3.1.0", "2.12.15", "2.13.7")
+ThisBuild / crossScalaVersions := Seq("3.1.0", "2.13.7")
 
 ThisBuild / developers := List(
   Developer("armanbilge", "Arman Bilge", "@armanbilge", url("https://github.com/armanbilge")),

lambda-cloudformation-custom-resource/src/main/scala/feral/lambda/cloudformation/CloudFormationCustomResource.scala

@@ -46,7 +46,7 @@ object CloudFormationCustomResource {
       client: Client[F],
       handler: CloudFormationCustomResource[F, Input, Output])(
       implicit
-      env: LambdaEnv[F, CloudFormationCustomResourceRequest[Input]]): F[Option[Unit]] = {
+      env: LambdaEnv[F, CloudFormationCustomResourceRequest[Input]]): F[Option[INothing]] = {
     val http4sClientDsl = new Http4sClientDsl[F] {}
     import http4sClientDsl._
 

lambda/shared/src/main/scala-2/feral/lambda/package.scala

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2021 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package feral
+
+import io.circe.Encoder
+
+import scala.annotation.nowarn
+
+package object lambda {
+  /**
+   * Alias for `Nothing` which works better with type inference. Inspired by fs2, but inlined
+   * here to avoid pulling in an otherwise-unnecessary dependency.
+   */
+  type INothing <: Nothing
+
+  /**
+   * This can't actually be used. It's here because `IOLambda` demands an Encoder for its result
+   * type, which should be `Nothing` when no output is desired. Userland code will return an
+   * `Option[Nothing]` which is only inhabited by `None`, and the encoder is only used when the
+   * userland code returns `Some`.
+   */
+  @nowarn("msg=dead code following this construct")
+  implicit val nothingEncoder: Encoder[INothing] = (_: INothing) => ???
+}

lambda/shared/src/main/scala-3/feral/lambda/INothing.scala

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2021 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package feral.lambda
+
+import io.circe.Encoder
+
+import scala.annotation.nowarn
+
+/**
+ * Alias for `Nothing` which works better with type inference. Inspired by fs2, but inlined here
+ * to avoid pulling in an otherwise-unnecessary dependency.
+ */
+type INothing <: Nothing
+object INothing {
+
+  /**
+   * This can't actually be used. It's here because `IOLambda` demands an Encoder for its result
+   * type, which should be `Nothing` when no output is desired. Userland code will return an
+   * `Option[Nothing]` which is only inhabited by `None`, and the encoder is only used when the
+   * userland code returns `Some`.
+   */
+  @nowarn("msg=dead code following this construct")
+  implicit val nothingEncoder: Encoder[INothing] = (_: INothing) => ???
+}