How to run an existing Scala project using VS Code and Metals?

Question

I am brand new to Scala and I find that Scala IDE is very slow on my machine for basic things like searching the codebase and editing code. I am used to Visual Studio Code and was very happy to find this metals extension.

I was able to "import build" and fix issues like bumping up scala version in my projects but I am not sure how to reproduce this step to set up a run configuration and actually launch our app in Scala IDE.

We have a parent folder which has a bunch of projects and a 'consoleapp' project which is the main entry point of our app - it imports the logic/routes of all other projects.

|____parent
| |____consoleapp
| |____project1
| |____project2 

I tried sbt run and sbt runMain consoleapp from within the consoleapp folder and also the parent folder but they didn't work.

I am not sure what other information from our setup is relevant - happy to provide more info as needed.

Updated to add more details below:

consoleapp/build.sbt

name := "consoleapp"

version := "1.0"

scalaVersion := "2.12.10"

packMain := Map("consoleapp" -> "consoleapp")

libraryDependencies ++=  Seq (...)

Output of commands I ran - sbt run and sbt runMain

Running from ~/scala/parent

> sbt run                                                                                                                                                                 masterstate [0a8dab85] modified
[info] Loading settings for project global-plugins from metals.sbt,build.sbt ...
[info] Loading global plugins from /Users/pradhyo/.sbt/1.0/plugins
[info] Loading project definition from /Users/pradhyo/scala/parent/project
[info] Loading settings for project consoleapp from build.sbt ...
... 
Loading settings for all other projects in parent folder
...
[info] Loading settings for project parent from build.sbt ...
[info] Resolving key references (22435 settings) ...
[info] Set current project to parent (in build file:/Users/pradhyo/scala/parent/)
[error] java.lang.RuntimeException: No main class detected.
[error]     at scala.sys.package$.error(package.scala:30)
[error] stack trace is suppressed; run last Compile / bgRun for the full output
[error] (Compile / bgRun) No main class detected.
[error] Total time: 1 s, completed 18-Dec-2019 1:41:25 PM

Running from ~/scala/parent

> sbt "runMain consoleapp.consoleapp"                                                                                                                                     masterstate [0a8dab85] modified
[info] Loading settings for project global-plugins from metals.sbt,build.sbt ...
[info] Loading global plugins from /Users/pradhyo/.sbt/1.0/plugins
[info] Loading project definition from /Users/pradhyo/scala/parent/project
[info] Loading settings for project consoleapp from build.sbt ...
... 
Loading settings for all other projects in parent folder
...
[info] Loading settings for project parent from build.sbt ...
[info] Resolving key references (22435 settings) ...
[info] Set current project to parent (in build file:/Users/pradhyo/scala/parent/)
[info] running consoleapp.consoleapp 
[error] (run-main-0) java.lang.ClassNotFoundException: consoleapp.consoleapp
[error] java.lang.ClassNotFoundException: consoleapp.consoleapp
[error]     at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
[error] stack trace is suppressed; run last Compile / bgRunMain for the full output
[error] Nonzero exit code: 1
[error] (Compile / runMain) Nonzero exit code: 1
[error] Total time: 0 s, completed 18-Dec-2019 1:46:21 PM

Running from ~/scala/parent/consoleapp

> sbt run                                                                                                                                                                 masterstate [0a8dab85] modified
[info] Loading settings for project global-plugins from metals.sbt,build.sbt ...
[info] Loading global plugins from /Users/pradhyo/.sbt/1.0/plugins
[info] Loading project definition from /Users/pradhyo/scala/parent/consoleapp/project
[info] Loading settings for project consoleapp from build.sbt ...
[info] Set current project to consoleapp (in build file:/Users/pradhyo/scala/parent/consoleapp/)
[error] java.lang.RuntimeException: No main class detected.
[error]     at scala.sys.package$.error(package.scala:30)
[error] stack trace is suppressed; run last Compile / bgRun for the full output
[error] (Compile / bgRun) No main class detected.
[error] Total time: 0 s, completed 18-Dec-2019 1:49:26 PM

Running from ~/scala/parent/consoleapp

> sbt "runMain consoleapp"                                                                                                                                                masterstate [0a8dab85] modified
[info] Loading settings for project global-plugins from metals.sbt,build.sbt ...
[info] Loading global plugins from /Users/pradhyo/.sbt/1.0/plugins
[info] Loading project definition from /Users/pradhyo/scala/parent/consoleapp/project
[info] Loading settings for project consoleapp from build.sbt ...
[info] Set current project to consoleapp (in build file:/Users/pradhyo/scala/parent/consoleapp/)
[info] running consoleapp 
[error] (run-main-0) java.lang.ClassNotFoundException: consoleapp
[error] java.lang.ClassNotFoundException: consoleapp
[error]     at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
[error] stack trace is suppressed; run last Compile / bgRunMain for the full output
[error] Nonzero exit code: 1
[error] (Compile / runMain) Nonzero exit code: 1
[error] Total time: 1 s, completed 18-Dec-2019 1:50:06 PM

Answer 1

After following the instructions in the Scala Metals VSCode Readme, use a launch configuration similar to this for the Eclipse screenshots in the question.

.vscode/launch.json

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "type": "scala",
            "name": "Debug consoleapp",
            "request": "launch",
            "mainClass": "consoleapp",
            "buildTarget": "consoleapp",
            "args": [],
            "jvmOptions": ["-J-Dconfig.file=/path/to/config/file"]
        }
    ]
}

I had trouble passing the config file for pureconfig correctly. Here's the Github issue with the correct jvmOptions line.

Answer 2

Metals supports these Scala versions 2.13.0, 2.13.1, 2.12.8, 2.12.9, 2.12.10, 2.12.7 and 2.11.12

This is something I noticed from their documentation(doc). So it could pinpoint to your and mine problem which I addressed in comments.

Your scalaVersion := "2.12.3" is not listed here.