package name not observed by sbt - scala

Question

I compiled a small Scala example of Spark program called AverageAgeByName.scala
Here is the build.sbt:
$ cd /opt/LearningSparkV2-master/chapter1/main/scala/chapter3
$ vim build.sbt
// Name of the package
name := "main/scala/chapter3"
// Version of our package
version := "1.0"
// Version of Scala
scalaVersion := "2.12.14"
// Spark library dependencies
libraryDependencies ++= Seq(
"org.apache.spark" %% "spark-core" % "3.1.2",
"org.apache.spark" %% "spark-sql" % "3.1.2"
)
I ran the command:
$ sbt clean package
[info] Updated file /opt/LearningSparkV2 master/chapter1/main/scala/chapter3/project/build.properties: set sbt.version to 1.5.5
[info] welcome to sbt 1.5.5 (Oracle Corporation Java 1.8.0_242)
[info] loading project definition from /opt/LearningSparkV2-master/chapter1/main/scala/chapter3/project
[info] loading settings for project chapter3 from build.sbt ...
[info] set current project to main/scala/chapter3 (in build file:/opt/LearningSparkV2-master/chapter1/main/scala/chapter3/)
[success] Total time: 0 s, completed Aug 4, 2021 10:07:27 AM
[info] compiling 1 Scala source to /opt/LearningSparkV2-master/chapter1/main/scala/chapter3/target/scala-2.12/classes ...
[success] Total time: 9 s, completed Aug 4, 2021 10:07:36 AM
The resulting class was not placed in proper directory hierarchy according to the package name in build.sbt:
$ ls /opt/LearningSparkV2-master/chapter1/main/scala/chapter3/target/scala-2.12/classes
'AverageAgeByName$$typecreator1$1.class' 'AverageAgeByName$.class' AverageAgeByName.class
It's flat. I expect the class should be placed in /opt/LearningSparkV2-master/chapter1/main/scala/chapter3/target/scala-2.12/classes/main/scala/chapter3
Where did I get it wrong?

Answer 1

The name := "main/scala/chapter3" in the build.sbt has nothing to do with a package or a destination folder: it's the name of the project which will be used when packaging your project as a JAR for instance.
The folder in which the classes are generated is driven by the package you set in your Scala file AverageAgeByName.scala.
The following would generate class file in target/scala-2/classes/xxx/yyy:
package xxx.yyy
class AverageAgeByName {}
Also note that usually source files are also put in a directory structure matching the package you set. That is in src/main/scala/xxx/yyy in the example above.
And last, you should probably not care at all of where the class files are generated.