sbt-tpolecat-intellij-issue is a project that demonstrates an issue with:

Test / tpolecatExcludeOptions += ScalacOptions.warnNonUnitStatement

being applied properly for a standalone sbt compilation, but not for the compilation in IntelliJ IDEA. In turn, that can cause compilation errors such as:

unused value of type org.scalatest.Assertion (add `: Unit` to discard silently)

only in IntelliJ (but not in the standalone sbt)

If we comment out/remove:

Test / tpolecatExcludeOptions += ScalacOptions.warnNonUnitStatement

from build.sbt file and reload sbt shell (reload command), then the compilation fails both in sbt and IntelliJ IDEA (as expected) with the following error:

[error] /.../sbt-tpolecat-intellij-issue/src/test/scala/intellijissue/MainTest.scala:9:7: unused value of type org.scalatest.Assertion (add `: Unit` to discard silently)
[error]     1 shouldEqual 1
[error]       ^
[error] No warnings can be incurred under -Werror.

However, if Test / tpolecatExcludeOptions is defined, the compilation succeeds only in sbt - it still fails in IntelliJ IDEA with the same error as before

This issue was reproduced in the following environment:

IntelliJ IDEA version: 2023.2
Scala plugin version: 2023.2.17
JVM version: Temurin OpenJDK 17.0.8+7
OS: macOS 13.5