coursier | Pure Scala Artifact Fetching | Build Tool library

We have a simple java project with unit tests written in scalatest:

• no scala library in compile scope (autoScalaLibrary := false)
• scala-compiler added to test scope to compile unit tests written in scala using scalatest
• scala-library, scalatest added to test scope for unit tests

Getting below error when executing unit tests from intellij as well as from commandline sbt console:-

I have a scala spark project that fails because of some dependency hell. Here is my build.sbt:

How to launch scala 3.1.0 using coursier?

I tried and got this ...

I installed scala from https://www.scala-lang.org/download/scala3.html using the coursier option:

I'm compiling a multi-part Scala project. It's not that large, but some of it is Scala 2.13 and some is Scala 3.

Attempting to compile generates the fatal error [UNRESOLVED DEPENDENCIES: base#base_2.12;0.1.0-SNAPSHOT: not found]

The thing is, the string {0.1.0-SNAPSHOT} doesn't occur anywhere in my build.sbt or anywhere else. It used to be there, but it's long gone. I assume some update cache contains it, but I've been unable to find it.

Here is my {build.sbt}:

If you follow the steps at the official Scala 3 sites, like Dotty or Scala Lang then it recommends using Coursier to install Scala 3. The problem is that neither or these explain how to run a compiled Scala 3 application after following the steps.

Scala 2:

I'm facing some deduplicate errors like below, which indicate that some of my dependencies import other dependencies which contains files with the same path name. Since they have the same path, they cannot be included together in the jar file that I'm trying to create with sbt-assembly.

I understand that the clean way to fix it is by fixing my dependencies. The conflicting dependencies from the example below seem to be reactive-streams and reactive-streams-flow-adapters, but I'm not sure what they are and where they come from. How can I find which of my dependencies are importing them?

If I can figure that out, how can I fix it? Is there a way other than just removing one of them?

An example of deduplicate errors:

There are multiple binary incompatible scala 2 versions, however the document says the installation is either via IDE or SBT.

DOWNLOAD SCALA 2

Then, install Scala:...either by installing an IDE such as IntelliJ, or sbt, Scala's build tool.

Spark 3 needs Scala 2.12.

Spark 3.1.2 uses Scala 2.12. You will need to use a compatible Scala version (2.12.x).

Then how can we make sure the scala version is 2.12 if we install sbt?

Or the documentation is not accurate and it should be "to use specific version of scala, need to download specific scala version on your own"?

As per the answer by mario-galic, in ONE-CLICK INSTALL FOR SCALA it is said:

Installing Scala has always been a task more challenging than necessary, with the potential to drive away beginners. Should I install Scala itself? sbt? Some other build tools? What about a better REPL like Ammonite? Oh and before all that I need to install Java?

To solve this problem, the Scala Center contracted Alexandre Archambault in January 2020 to add a one-click install of Scala through coursier. For example, on Linux, all we now need is:
$ curl -Lo cs https://git.io/coursier-cli-linux && chmod +x cs && ./cs setup

I've migrated my local coursier cache to another part of my system and changed the COURSIER_CACHE system property, as described in the coursier docs

My local installation of SBT works fine with this, via shell as well as via IntelliJ's sbt shell. However, when building my app using IntelliJ's build-in SBT using CTRL+F9, I get the following error: