Add PekkoInlinePlugin (#2)

* Add PekkoInlinePlugin

* Make pekkoCoreProject its own general setting

src/main/scala/com/github/pjfanning/pekkobuild/PekkoCorePlugin.scala

@@ -0,0 +1,17 @@
+package com.github.pjfanning.pekkobuild
+
+import sbt._
+
+object PekkoCorePlugin extends AutoPlugin {
+
+  override def trigger: PluginTrigger = allRequirements
+
+  object autoImport extends PekkoCoreSettings
+
+  import autoImport._
+
+  override lazy val globalSettings = Seq(
+    pekkoCoreProject := false
+  )
+
+}

src/main/scala/com/github/pjfanning/pekkobuild/PekkoCoreSettings.scala

@@ -0,0 +1,8 @@
+package com.github.pjfanning.pekkobuild
+
+import sbt._
+
+trait PekkoCoreSettings {
+  lazy val pekkoCoreProject: SettingKey[Boolean] = settingKey("Whether this is the core Pekko project or a Pekko" +
+    " module. Defaults to false")
+}

src/main/scala/com/github/pjfanning/pekkobuild/PekkoInlinePlugin.scala

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * license agreements; and to You under the Apache License, version 2.0:
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * This file is part of the Apache Pekko project, derived from Akka.
+ */
+
+package com.github.pjfanning.pekkobuild
+
+import com.github.pjfanning.pekkobuild.PekkoCorePlugin.autoImport.pekkoCoreProject
+import sbt.plugins.JvmPlugin
+import sbt._
+import sbt.Keys._
+
+object PekkoInlinePlugin extends AutoPlugin {
+  override def trigger: PluginTrigger = allRequirements
+
+  override def requires: Plugins = JvmPlugin && PekkoCorePlugin
+
+  object autoImport extends PekkoInlineSettings
+
+  import autoImport._
+
+  private def flagsForScala2(coreProject: Boolean) = {
+    val baseInlineFlags = Seq(
+      "-opt-inline-from:<sources>",
+      "-opt:l:inline"
+    )
+
+    if (coreProject)
+      baseInlineFlags ++ Seq(
+        // Since the Pekko core project doesn't allow for mixing of different versions,
+        // i.e. you cannot mix pekko-actor 1.0.0 with pekko-streams 1.0.1 at runtime
+        // its safe to do inter sbt project inlining.
+        "-opt-inline-from:org.apache.pekko.**"
+      )
+    else baseInlineFlags ++ Seq(
+      // These are safe to inline even across modules since they are
+      // wrappers for cross compilation that is stable within Pekko core.
+      "-opt-inline-from:org.apache.pekko.dispatch.internal.SameThreadExecutionContext**",
+      "-opt-inline-from:org.apache.pekko.util.OptionConverters**",
+      "-opt-inline-from:org.apache.pekko.util.FutureConverters**",
+      "-opt-inline-from:org.apache.pekko.util.FunctionConverters**",
+      "-opt-inline-from:org.apache.pekko.util.PartialFunction**",
+      "-opt-inline-from:org.apache.pekko.util.JavaDurationConverters**"
+    )
+  }
+
+  // Optimizer not yet available for Scala3, see https://docs.scala-lang.org/overviews/compiler-options/optimizer.html
+  private val flagsForScala3 = Seq()
+
+  override lazy val globalSettings = Seq(
+    pekkoInlineEnabled := !sys.props.contains("pekko.no.inline")
+  )
+
+  override lazy val projectSettings = Seq(Compile / scalacOptions ++= {
+    if (pekkoInlineEnabled.value) {
+      CrossVersion.partialVersion(scalaVersion.value) match {
+        case Some((2, n)) if n == 12 | n == 13 =>
+          flagsForScala2(pekkoCoreProject.value)
+        case Some((3, _)) =>
+          flagsForScala3
+      }
+    } else Seq.empty
+  })
+}

src/main/scala/com/github/pjfanning/pekkobuild/PekkoInlineSettings.scala

@@ -0,0 +1,8 @@
+package com.github.pjfanning.pekkobuild
+
+import sbt.{SettingKey, settingKey}
+
+trait PekkoInlineSettings {
+  lazy val pekkoInlineEnabled: SettingKey[Boolean] = settingKey("Whether to enable the Scala 2 inliner for Pekko modules." +
+    "Defaults to pekko.no.inline property")
+}