Why does the sbt ~compile command do not recompile on code change? - scala

Question

I currently have a problem with recompile on code change with sbt.
I was following the sbt reference 'sbt by example'
I installed sbt 1.2.8 and followed the instructions:
Create a minimum sbt build
$ mkdir foo-build
$ cd foo-build
$ touch build.sbt
Start sbt shell
$ sbt
[info] Loading global plugins from C:\Users\hce\.sbt\1.0\plugins
[info] Loading project definition from E:\learn\Scala\demo\foo-build\project
[info] Loading settings for project foo-build from build.sbt ...
[info] Set current project to foo-build (in build file:/E:/learn/Scala/demo/foo-build/)
[info] sbt server started at local:sbt-server-57c501e502d72a00d890
Recompile on code change (Note the ~ prefix before the compile command)
sbt:foo-build> ~compile
[success] Total time: 0 s, completed Jul 6, 2019 12:01:24 PM
1. Waiting for source changes in project foo-build... (press enter to interrupt)
Create a source file
Leave the previous command running. From a different shell or in your file manager create in the project directory the following nested directories: src/main/scala/example. Then, create Hello.scala in the example directory using your favorite editor as follows:
package example
object Hello extends App {
println("Hello")
}
This new file should be picked up by the running command. But it is not working on my system.
Expected Behaviour:
[info] Compiling 1 Scala source to /tmp/foo-build/target/scala-2.12/classes ...
[info] Done compiling.
[success] Total time: 2 s, completed May 6, 2018 3:53:42 PM
2. Waiting for source changes... (press enter to interrupt)
Here are some Information about my environment
$ java -version
java version "1.8.0_211"
Java(TM) SE Runtime Environment (build 1.8.0_211-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.211-b12, mixed mode)
$ sbt sbtVersion
[info] Loading global plugins from C:\Users\hce\.sbt\1.0\plugins
[info] Loading project definition from E:\learn\Scala\demo\foo-build\project
[info] Loading settings for project foo-build from build.sbt ...
[info] Set current project to foo-build (in build file:/E:/learn/Scala/demo/foo-build/)
[info] 1.2.8
$ systeminfo.exe | grep '^OS'
OS Name: Microsoft Windows 10 Enterprise LTSC
OS Version: 10.0.17763 N/A Build 17763
OS Manufacturer: Microsoft Corporation
OS Configuration: Standalone Workstation
OS Build Type: Multiprocessor Free
What I already tried:
reinstall sbt
try it with windows commad line
try it mingw64 bash
What am I missing to run the sbt ~compile command correctly?

Answer 1

I found the answer.
The instruction contains an error.
We are supposed to put the src/main/scala/example directory in the project directory.
From a different shell or in your file manager create in the project directory the following nested directories: src/main/scala/example.
But this leads to the problem described. foo-build/project/ is for build definition code.
If I put the src/main/scala/example directory in the foo-build directory it is working.
I should have executed the run command beforehand, which gives the 'No main class detected' error. Which in turn helped to discover, that the directory structure was incorrect by reading the following stackoverflow question: how to set main class in sbt project .
My mistake. Sorry for bothering you.