FIX #1491 DockerPlugin doesn't work with multiple main classes (#1535)

* FIX #1491 DockerPlugin doesn't work with multiple main classes by default

* scalafmt

src/main/resources/com/typesafe/sbt/packager/archetypes/scripts/ash-template

@@ -109,6 +109,16 @@ ${{template_declares}}
 
 process_args "$@"
 
+# Fallback to custom mainclass if main class is not provided (this is the case if the JAR contains multiple apps)
+if [ "$app_mainclass" = "" ] || [ $custom_mainclass ];then
+  if [ "$custom_mainclass" = "" ]; then
+    echo "You need to pass -main argument."
+    exit 1
+  fi
+
+  app_mainclass=$custom_mainclass
+fi
+
 java_cmd="$(get_java_cmd)"
 
 # If a configuration file exist, read the contents to $opts

src/main/resources/com/typesafe/sbt/packager/archetypes/scripts/bash-template

@@ -246,6 +246,16 @@ run() {
     mainclass=("${app_mainclass[@]}")
   fi
 
+  # Fallback to custom mainclass if main class is not provided (this is the case if the JAR contains multiple apps)
+  if [ "$app_mainclass" = "" ] || [ $custom_mainclass ];then
+    if [ "$custom_mainclass" = "" ]; then
+      echo "You need to pass -main argument."
+      exit 1
+    fi
+
+    app_mainclass=$custom_mainclass
+  fi
+
   # Now we check to see if there are any java opts on the environment. These get listed first, with the script able to override them.
   if [[ "$JAVA_OPTS" != "" ]]; then
     java_opts="${JAVA_OPTS}"

src/main/scala/com/typesafe/sbt/packager/archetypes/scripts/CommonStartScriptGenerator.scala

@@ -89,11 +89,20 @@ trait CommonStartScriptGenerator {
   ): Seq[(File, String)] = {
     val classAndScriptNames = ScriptUtils.createScriptNames(discoveredMainClasses)
     ScriptUtils.warnOnScriptNameCollision(classAndScriptNames, log)
-    classAndScriptNames.map {
-      case (qualifiedClassName, scriptName) =>
-        val newConfig = config.withScriptName(scriptName)
-        createMainScript(qualifiedClassName, newConfig, targetDir, discoveredMainClasses)
-    }
+
+    classAndScriptNames
+      .find {
+        case (_, script) => script == config.executableScriptName
+      }
+      .map(_ => classAndScriptNames)
+      .getOrElse(
+        classAndScriptNames ++ Seq("" -> config.executableScriptName)
+      ) // empty string to enforce the custom class in scripts
+      .map {
+        case (qualifiedClassName, scriptName) =>
+          val newConfig = config.withScriptName(scriptName)
+          createMainScript(qualifiedClassName, newConfig, targetDir, discoveredMainClasses)
+      }
   }
 
   private[this] def mainScriptName(config: ScriptConfig): String =

src/sbt-test/docker/multiple-main-classes/build.sbt

@@ -0,0 +1,5 @@
+enablePlugins(JavaAppPackaging, AshScriptPlugin)
+
+name := "multi-main-name"
+
+version := "0.1.0"

src/sbt-test/docker/multiple-main-classes/project/plugins.sbt

@@ -0,0 +1 @@
+addSbtPlugin("com.github.sbt" % "sbt-native-packager" % sys.props("project.version"))

src/sbt-test/docker/multiple-main-classes/src/main/scala/Main1.scala

@@ -0,0 +1,3 @@
+object Main1 extends App {
+  println("main1")
+}

src/sbt-test/docker/multiple-main-classes/src/main/scala/Main2.scala

@@ -0,0 +1,3 @@
+object Main2 extends App {
+  println("main2")
+}

src/sbt-test/docker/multiple-main-classes/test

@@ -0,0 +1,3 @@
+# Stage the distribution and ensure files show up.
+> docker:stage
+$ exec grep -q -F 'RUN ["chmod", "u+x,g+x", "/4/opt/docker/bin/multi-main-name"]' target/docker/stage/Dockerfile