Refactor the build for consistency with other Scalameta builds

* tests live in `tests` project
* enable Scalafix `ExplicitResultTypes` and `RemoveUnused` rules
* enforce scalafmt and scalafix in CI
* use MUnit for ScalaCheck property tests
* use `*Suite` suffix for test suites

.github/workflows/ci.yml

@@ -21,3 +21,10 @@ jobs:
       - uses: olafurpg/setup-scala@v2
       - name: Test
         run: sbt +test
+  checks:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: olafurpg/setup-scala@v7
+      - run: ./bin/scalafmt --check
+      - run: sbt scalafixCheckAll

.scalafix.conf

@@ -0,0 +1,6 @@
+rules = [
+  RemoveUnused,
+  ExplicitResultTypes,
+]
+
+ExplicitResultTypes.rewriteStructuralTypesToNamedSubclass = false

build.sbt

@@ -1,7 +1,10 @@
 import java.util.Date
 import sbtcrossproject.CrossPlugin.autoImport.crossProject
+lazy val V = new {
+  def munit = "0.7.2"
+}
 val scala211 = "2.11.12"
-val scala212 = "2.12.10"
+val scala212 = "2.12.11"
 val scala213 = "2.13.1"
 val ScalaVersions = List(scala212, scala211, scala213)
 inThisBuild(
@@ -31,6 +34,15 @@ inThisBuild(
   )
 )
 
+addCommandAlias(
+  "scalafixAll",
+  s"; ++$scala212 ; scalafixEnable ; all scalafix test:scalafix"
+)
+addCommandAlias(
+  "scalafixCheckAll",
+  s"; ++$scala212 ;  scalafixEnable ; scalafix --check ; test:scalafix --check"
+)
+
 addCommandAlias(
   "native-image",
   "; tests/graalvm-native-image:packageBin ; taskready"
@@ -41,55 +53,24 @@ commands += Command.command("taskready") { s =>
   s
 }
 
-lazy val testSettings = List(
-  testOptions.in(Test) +=
-    Tests.Argument(TestFrameworks.ScalaCheck, "-verbosity", "2"),
-  testFrameworks := List(
-    new TestFramework("munit.Framework"),
-    new TestFramework("org.scalacheck.ScalaCheckFramework")
-  ),
-  libraryDependencies ++= {
-    if (SettingKey[Boolean]("nativeLinkStubs").?.value.contains(true))
-      List(
-        "org.scalameta" %%% "munit" % "0.4.5" % Test,
-        "com.github.lolgab" %%% "scalacheck" % "1.14.1" % Test
-      )
-    else
-      List(
-        "org.scalameta" %%% "munit" % "0.4.5" % Test,
-        "org.scalacheck" %%% "scalacheck" % "1.14.0" % Test,
-        "com.github.alexarchambault" %%% "scalacheck-shapeless_1.14" % "1.2.3" % Test
-      )
-  }
-)
+lazy val warnUnusedImport = Def.setting {
+  if (scalaVersion.value.startsWith("2.13")) "-Wunused:imports"
+  else "-Ywarn-unused-import"
+}
 
-lazy val nativeSettings = List(
-  nativeLinkStubs := true,
-  scalaVersion := scala211,
-  crossScalaVersions := List(scala211),
-  test.in(Test) := {}
+lazy val sharedSettings = List[Setting[_]](
+  scalacOptions ++= List(
+    "-Yrangepos",
+    warnUnusedImport.value
+  )
 )
 
 skip.in(publish) := true
 
-lazy val json = project
-  .in(file("metaconfig-json"))
-  .settings(
-    testSettings,
-    moduleName := "metaconfig-json",
-    libraryDependencies ++= List(
-      "org.scalameta" %% "testkit" % "4.1.12" % Test
-    ) :+ (CrossVersion.partialVersion(scalaVersion.value) match {
-      case Some((2, 11 | 12)) => "com.lihaoyi" %%% "upickle" % "0.7.4"
-      case _ => "com.lihaoyi" %% "upickle" % "0.7.5"
-    })
-  )
-  .dependsOn(coreJVM)
-
 lazy val core = crossProject(JVMPlatform, JSPlatform)
   .in(file("metaconfig-core"))
   .settings(
-    testSettings,
+    sharedSettings,
     moduleName := "metaconfig-core",
     libraryDependencies ++= List(
       "org.typelevel" %%% "paiges-core" % "0.3.0",
@@ -100,54 +81,78 @@ lazy val core = crossProject(JVMPlatform, JSPlatform)
       case _ => "com.lihaoyi" %%% "pprint" % "0.5.9"
     })
   )
-  .jsSettings(scalaJSModuleKind := ModuleKind.CommonJSModule)
-  // .nativeSettings(nativeSettings)
-  .jvmSettings(
-    libraryDependencies += "org.scalameta" %% "testkit" % "4.1.12" % Test
-  )
 lazy val coreJVM = core.jvm
 lazy val coreJS = core.js
-// lazy val coreNative = core.native
 
-lazy val typesafeConfig = "com.typesafe" % "config" % "1.2.1"
+lazy val json = project
+  .in(file("metaconfig-json"))
+  .settings(
+    sharedSettings,
+    moduleName := "metaconfig-json",
+    libraryDependencies ++= List(
+      "org.scalameta" %% "testkit" % "4.1.12" % Test
+    ) :+ (CrossVersion.partialVersion(scalaVersion.value) match {
+      case Some((2, 11 | 12)) => "com.lihaoyi" %%% "upickle" % "0.7.4"
+      case _ => "com.lihaoyi" %% "upickle" % "0.7.5"
+    })
+  )
+  .dependsOn(coreJVM)
 
 lazy val typesafe = project
   .in(file("metaconfig-typesafe-config"))
   .settings(
-    testSettings,
+    sharedSettings,
     moduleName := "metaconfig-typesafe-config",
     description := "Integration for HOCON using typesafehub/config.",
-    libraryDependencies += typesafeConfig
+    libraryDependencies += "com.typesafe" % "config" % "1.2.1"
   )
-  .dependsOn(coreJVM % "test->test;compile->compile")
+  .dependsOn(coreJVM)
 
 lazy val sconfig = crossProject(JVMPlatform)
   .in(file("metaconfig-sconfig"))
   .settings(
-    testSettings,
+    sharedSettings,
     moduleName := "metaconfig-sconfig",
     description := "Integration for HOCON using ekrich/sconfig.",
     libraryDependencies ++= List(
       "org.ekrich" %%% "sconfig" % "1.0.0"
     )
   )
-  // .nativeSettings(nativeSettings)
-  .dependsOn(core % "test->test;compile->compile")
+  .dependsOn(core)
 lazy val sconfigJVM = sconfig.jvm
-// lazy val sconfigNative = sconfig.native
 
 val scalatagsVersion = Def.setting {
   if (scalaVersion.value.startsWith("2.11")) "0.6.7"
   else "0.7.0"
 }
 
-lazy val tests = project
+lazy val tests = crossProject(JVMPlatform, JSPlatform)
   .in(file("metaconfig-tests"))
   .settings(
+    sharedSettings,
     skip in publish := true,
+    publishArtifact.in(Compile, packageDoc) := false,
+    testOptions.in(Test) +=
+      Tests.Argument(TestFrameworks.ScalaCheck, "-verbosity", "2"),
+    testFrameworks := List(
+      new TestFramework("munit.Framework")
+    ),
+    libraryDependencies ++= {
+      if (SettingKey[Boolean]("nativeLinkStubs").?.value.contains(true))
+        List(
+          "org.scalameta" %%% "munit-scalacheck" % V.munit % Test
+        )
+      else
+        List(
+          "org.scalameta" %%% "munit-scalacheck" % V.munit % Test,
+          "com.github.alexarchambault" %%% "scalacheck-shapeless_1.14" % "1.2.3" % Test
+        )
+    }
+  )
+  .jsSettings(scalaJSModuleKind := ModuleKind.CommonJSModule)
+  .jvmSettings(
     mainClass in GraalVMNativeImage := Some("metaconfig.tests.ExampleMain"),
     sources.in(Compile, doc) := Seq.empty,
-    publishArtifact.in(Compile, packageDoc) := false,
     graalVMNativeImageOptions ++= {
       val reflectionFile =
         Keys.sourceDirectory.in(Compile).value./("graal")./("reflection.json")
@@ -168,10 +173,17 @@ lazy val tests = project
       )
     }
   )
-  .enablePlugins(GraalVMNativeImagePlugin)
-  .dependsOn(coreJVM)
+  .jvmConfigure(
+    _.enablePlugins(GraalVMNativeImagePlugin)
+      .dependsOn(json, typesafe, sconfigJVM)
+  )
+  .dependsOn(core)
+lazy val testsJVM = tests.jvm
+lazy val testsJS = tests.js
+
 lazy val docs = project
   .settings(
+    sharedSettings,
     moduleName := "metaconfig-docs",
     libraryDependencies ++= List(
       "com.lihaoyi" %% "scalatags" % scalatagsVersion.value

metaconfig-core/shared/src/main/scala/metaconfig/Conf.scala

@@ -9,8 +9,6 @@ import metaconfig.internal.CliParser
 import metaconfig.internal.ConfGet
 import metaconfig.internal.ConfPatch
 import metaconfig.internal.HoconPrinter
-import org.typelevel.paiges.Doc
-import metaconfig.generic.Surface
 
 sealed abstract class Conf extends Product with Serializable {
   def dynamic: ConfDynamic = ConfDynamic(Configured.Ok(this))
@@ -115,7 +113,7 @@ object Conf {
         .getOrElse(Configured.Ok(None))
   }
   object Obj {
-    val empty = Obj()
+    val empty: Obj = Obj()
     def apply(values: (String, Conf)*): Obj = Obj(values.toList)
   }
 }

metaconfig-core/shared/src/main/scala/metaconfig/ConfCodec.scala

@@ -1,7 +1,5 @@
 package metaconfig
 
-import scala.language.higherKinds
-
 trait ConfCodec[A] extends ConfDecoder[A] with ConfEncoder[A] { self =>
   def bimap[B](in: B => A, out: A => B): ConfCodec[B] = new ConfCodec[B] {
     override def write(value: B): Conf = self.write(in(value))

metaconfig-core/shared/src/main/scala/metaconfig/ConfDecoder.scala

@@ -1,6 +1,5 @@
 package metaconfig
 
-import scala.language.experimental.macros
 import scala.language.higherKinds
 import scala.collection.compat._
 import scala.reflect.ClassTag

metaconfig-core/shared/src/main/scala/metaconfig/Input.scala

@@ -66,19 +66,21 @@ sealed abstract class Input(val path: String, val text: String)
 object Input {
 
   case object None extends Input("<none>", "") {
-    override def toString = "Input.None"
+    override def toString: Predef.String = "Input.None"
   }
 
   final case class String(override val text: Predef.String)
       extends Input("<input>", text) {
-    override def toString = s"""Input.String("$text")"""
+    override def toString: Predef.String =
+      s"""Input.String("$text")"""
   }
 
   final case class VirtualFile(
       override val path: Predef.String,
       override val text: Predef.String
   ) extends Input(path, text) {
-    override def toString = s"""Input.VirtualFile("$path", "...")"""
+    override def toString: Predef.String =
+      s"""Input.VirtualFile("$path", "...")"""
   }
 
   final case class File(file: Path, charset: Charset)

metaconfig-core/shared/src/main/scala/metaconfig/Position.scala

@@ -77,7 +77,7 @@ object Position {
     def endLine: Int = input.offsetToLine(end)
     def endColumn: Int = end - input.lineToOffset(endLine)
     override def text = new String(input.chars, start, end - start)
-    override def toString = s"[$start..$end) in $input"
+    override def toString: String = s"[$start..$end) in $input"
   }
 
 }

metaconfig-core/shared/src/main/scala/metaconfig/cli/CliApp.scala

@@ -2,9 +2,6 @@ package metaconfig.cli
 
 import java.io.PrintStream
 import java.io.InputStream
-import metaconfig.generic
-import metaconfig.ConfEncoder
-import metaconfig.generic.Surface
 import java.nio.file.Path
 import fansi.Str
 import fansi.Color

metaconfig-core/shared/src/main/scala/metaconfig/cli/Command.scala

@@ -1,11 +1,8 @@
 package metaconfig.cli
 
 import java.io.PrintStream
-import java.io.InputStream
-import metaconfig.generic
 import metaconfig.ConfEncoder
 import metaconfig.generic.Surface
-import java.nio.file.Path
 import org.typelevel.paiges.Doc
 import java.io.ByteArrayOutputStream
 import java.nio.charset.StandardCharsets

metaconfig-core/shared/src/main/scala/metaconfig/cli/HelpCommand.scala

@@ -1,20 +1,7 @@
 package metaconfig.cli
 
-import metaconfig.generic.Field
-import metaconfig.generic.Surface
-import metaconfig.ConfEncoder
-import metaconfig.Conf
 import org.typelevel.paiges.Doc
-import scala.util.control.NonFatal
-import metaconfig.Conf.Str
-import java.io.PrintStream
-import java.io.ByteArrayOutputStream
-import java.nio.charset.StandardCharsets
 import metaconfig.internal.TermInfo
-import metaconfig.annotation.ExtraName
-import metaconfig.ConfDecoder
-import metaconfig.Configured
-import metaconfig.Conf.Obj
 import metaconfig.internal.Levenshtein
 
 object HelpCommand
@@ -30,7 +17,7 @@ class HelpCommand(
     appDescription: CliApp => Doc,
     appExamples: CliApp => Doc
 ) extends Command[HelpOptions]("help") {
-  override def description = Doc.paragraph("Print this help message")
+  override def description: Doc = Doc.paragraph("Print this help message")
   override def extraNames: List[String] = List("-h", "--help", "-help")
   override def complete(
       context: TabCompletionContext