How to to warn the statement if it is an expression and the type of it is not Unit?

Question
1

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As the screenshot shows above, the line 165 is an expression which has a type Tf.Tensor and this line is not the end line, the compiler does not give a warning for this line even though i have configured the scalacOption -Wvalue-discard.
Here is my sbt config:

import org.scalajs.linker.interface.ModuleSplitStyle

lazy val root = project
  .in(file("."))
  .enablePlugins(ScalaJSPlugin)
  .settings(
    name := "bm3d-scalajs",
    scalaVersion := "2.13.11",
    scalacOptions ++= Seq(
      "-encoding", "UTF-8",
      "-unchecked",
      "-deprecation",
      "-Ywarn-dead-code",
      "-Ywarn-numeric-widen",
      "-Wvalue-discard",
      "-Ywarn-unused"
    ),

    scalaJSUseMainModuleInitializer := false,
    scalaJSLinkerConfig ~= {
      _.withModuleKind(ModuleKind.CommonJSModule)
        .withModuleSplitStyle(ModuleSplitStyle.SmallModulesFor(List("bm3d")))
    },

    libraryDependencies ++= Seq(
      "org.scala-js" %%% "scalajs-dom" % "2.4.0",
      "io.github.metarank" %% "cfor" % "0.3"
    )
  )

Is there a way to make the type checker give a warning for non-Unit type of expression?

2

I fixed this issue by wartremover, but i still want to know that is there any way to fix this by scalac itself?

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3

That is not a value discard but an unused statement, which is a different flag.

Personally, I just use sbt-tpolecat which manages all those flags for me.

1 Like
4

Thanks! @BalmungSan

5

The flag is -Wnonunit-statement.

Under scalac -W:

  -Wnonunit-statement            Warn when block statements are non-Unit expressions. [false]

It has useful exclusions, such as for side-effecting methods that return this.type.

2 Likes