From 67a625a5df636a062b9e42430a8362d4b511bc3a Mon Sep 17 00:00:00 2001
From: David Barri <japgolly@gmail.com>
Date: Fri, 30 Jul 2021 17:30:24 +1000
Subject: [PATCH 1/5] Core compiles and passes

---
 .github/workflows/ci.yml                      |   6 +-
 build.sbt                                     |   2 +
 .../scalacss/internal/mutable/Mutex.scala     |   2 +-
 .../main/scala/scalacss/js/PlatformJs.scala   |  42 +--
 .../scalacss/internal/mutable/Mutex.scala     |   2 +-
 .../scalacss/internal/Macros.scala            |  10 +
 .../scala-3/scalacss/internal/Macros.scala    | 252 ++++++++++++++++++
 .../main/scala/scalacss/internal/Dsl.scala    |  14 +-
 .../main/scala/scalacss/internal/Media.scala  |   8 +-
 .../main/scala/scalacss/internal/Pseudo.scala |   2 +-
 .../scalacss/internal/mutable/Settings.scala  |  14 +-
 .../internal/mutable/StyleSheet.scala         |   4 +-
 .../src/main/scala/scalacss/package.scala     |   8 +-
 .../scala/scalacss/full/DefaultsTest.scala    |   6 +-
 .../scala/scalacss/internal/ColorTest.scala   |   6 +-
 .../scala/scalacss/internal/ComposeTest.scala |   2 +-
 .../scala/scalacss/internal/RandomData.scala  |  12 +-
 .../scala/scalacss/internal/UsageTest.scala   |   2 +-
 .../internal/mutable/RegisterTest.scala       |   4 +-
 project/Build.scala                           |  65 +++--
 project/Dependencies.scala                    |   5 +-
 project/Lib.scala                             |  30 +--
 22 files changed, 389 insertions(+), 109 deletions(-)
 rename core/shared/src/main/{scala => scala-2}/scalacss/internal/Macros.scala (96%)
 create mode 100644 core/shared/src/main/scala-3/scalacss/internal/Macros.scala

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 61dffb37..7fa32b7c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,12 +13,10 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - java: 8
-            scala: 2.13.6
-          - java: 11
-            scala: 2.13.6
           - java: 16
             scala: 2.13.6
+          - java: 8
+            scala: 3.0.1
 
     steps:
       - name: Git checkout
diff --git a/build.sbt b/build.sbt
index ba2eee70..aa899ac8 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,6 +1,8 @@
 name      := "ScalaCSS"
 startYear := Some(2015)
 
+ThisBuild / shellPrompt := ((s: State) => Project.extract(s).currentRef.project + "> ")
+
 // Mutability & NameGen causes occasional test failures
 ThisBuild / parallelExecution := false
 
diff --git a/core/js/src/main/scala/scalacss/internal/mutable/Mutex.scala b/core/js/src/main/scala/scalacss/internal/mutable/Mutex.scala
index db169eea..b6defa89 100644
--- a/core/js/src/main/scala/scalacss/internal/mutable/Mutex.scala
+++ b/core/js/src/main/scala/scalacss/internal/mutable/Mutex.scala
@@ -12,5 +12,5 @@ final class Mutex {
 }
 
 object Mutex {
-  implicit val mutex = new Mutex
+  implicit val mutex: Mutex = new Mutex
 }
diff --git a/core/js/src/main/scala/scalacss/js/PlatformJs.scala b/core/js/src/main/scala/scalacss/js/PlatformJs.scala
index 0eb8cf23..cbd78d65 100644
--- a/core/js/src/main/scala/scalacss/js/PlatformJs.scala
+++ b/core/js/src/main/scala/scalacss/js/PlatformJs.scala
@@ -1,7 +1,7 @@
 package scalacss.js
 
 import scala.annotation.nowarn
-import scala.scalajs.js._
+import scala.scalajs.js
 
 object PlatformJs {
 
@@ -16,38 +16,38 @@ object PlatformJs {
   /**
    * Returns `undefined` in NodeJS unit tests.
    */
-  lazy val value: UndefOr[PlatformJs] =
+  lazy val value: js.UndefOr[PlatformJs] =
     try {
-      eval(sourceCode)
-      Dynamic.global.platform.asInstanceOf[UndefOr[PlatformJs]]
+      js.eval(sourceCode)
+      js.Dynamic.global.platform.asInstanceOf[js.UndefOr[PlatformJs]]
     } catch {
       case e: Throwable =>
         e.printStackTrace(System.err)
-        undefined
+        js.undefined
     }
 }
 
 /**
  * https://github.com/bestiejs/platform.js/blob/master/doc/README.md#readme
  */
-@native
+@js.native
 @nowarn
-trait PlatformJs extends Object {
-  val description : UndefOr[String]       = native
-  val layout      : UndefOr[String]       = native
-  val manufacturer: UndefOr[String]       = native
-  val name        : UndefOr[String]       = native
-  val prerelease  : UndefOr[String]       = native
-  val product     : UndefOr[String]       = native
-  val ua          : UndefOr[String]       = native
-  val version     : UndefOr[String]       = native
-  val os          : UndefOr[PlatformJsOS] = native
+trait PlatformJs extends js.Object {
+  val description : js.UndefOr[String]       = js.native
+  val layout      : js.UndefOr[String]       = js.native
+  val manufacturer: js.UndefOr[String]       = js.native
+  val name        : js.UndefOr[String]       = js.native
+  val prerelease  : js.UndefOr[String]       = js.native
+  val product     : js.UndefOr[String]       = js.native
+  val ua          : js.UndefOr[String]       = js.native
+  val version     : js.UndefOr[String]       = js.native
+  val os          : js.UndefOr[PlatformJsOS] = js.native
 }
 
-@native
+@js.native
 @nowarn
-trait PlatformJsOS extends Object {
-  val architecture: UndefOr[Int]    = native
-  val family      : UndefOr[String] = native
-  val version     : UndefOr[String] = native
+trait PlatformJsOS extends js.Object {
+  val architecture: js.UndefOr[Int]    = js.native
+  val family      : js.UndefOr[String] = js.native
+  val version     : js.UndefOr[String] = js.native
 }
diff --git a/core/jvm/src/main/scala/scalacss/internal/mutable/Mutex.scala b/core/jvm/src/main/scala/scalacss/internal/mutable/Mutex.scala
index c54b58a0..67ccec8d 100644
--- a/core/jvm/src/main/scala/scalacss/internal/mutable/Mutex.scala
+++ b/core/jvm/src/main/scala/scalacss/internal/mutable/Mutex.scala
@@ -12,5 +12,5 @@ final class Mutex {
 }
 
 object Mutex {
-  implicit def mutex = new Mutex
+  implicit def mutex: Mutex = new Mutex
 }
diff --git a/core/shared/src/main/scala/scalacss/internal/Macros.scala b/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
similarity index 96%
rename from core/shared/src/main/scala/scalacss/internal/Macros.scala
rename to core/shared/src/main/scala-2/scalacss/internal/Macros.scala
index 59b1ab81..515a641d 100644
--- a/core/shared/src/main/scala/scalacss/internal/Macros.scala
+++ b/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
@@ -9,6 +9,11 @@ object Macros {
 
   object Dsl {
 
+    trait Base {
+      @inline final implicit def colourLiteralMacro(sc: StringContext): Macros.ColourLiteral =
+        new Macros.ColourLiteral(sc)
+    }
+
     private def name(c: Context): String = {
       val localName = c.internal.enclosingOwner.name.toString.trim
 
@@ -179,6 +184,11 @@ object Macros {
 
   // ===================================================================================================================
 
+  trait DevOrProdDefaults {
+    def devOrProdDefaults: Exports with Settings =
+      macro Macros.devOrProdDefaults
+  }
+
   def devOrProdDefaults(c: Context): c.Expr[Exports with mutable.Settings] = {
     import c.universe._
     c.Expr[Exports with mutable.Settings](q"""
diff --git a/core/shared/src/main/scala-3/scalacss/internal/Macros.scala b/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
new file mode 100644
index 00000000..5f6621bb
--- /dev/null
+++ b/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
@@ -0,0 +1,252 @@
+package scalacss.internal
+
+import java.util.regex.Pattern
+import scala.quoted._
+import scalacss.defaults.Exports
+import scala.language.`3.0`
+import scala.reflect.NameTransformer
+
+object Macros {
+
+  object Dsl {
+
+    trait Base {
+      extension (inline sc: StringContext) {
+        /** c"#fc6" provides a validates Color */
+        inline def c(inline args: Any*): Color =
+          ${ ColorLiteral.impl('sc) }
+      }
+    }
+
+    inline def name(): String =
+      ${ nameQuoted }
+
+    private def nameQuoted(using Quotes): Expr[String] = {
+      import quotes.reflect._
+
+      val owner = {
+        var o = Symbol.spliceOwner
+        while (o.flags.is(Flags.Synthetic))
+          o = o.owner
+        o
+      }
+
+      val isStyleSheet: Symbol => Boolean = {
+        val mss = TypeRepr.of[mutable.StyleSheet.Inline]
+        sym =>
+          try {
+            sym.tree match {
+              case ClassDef(_, _, parents, _, _) =>
+                parents.exists {
+                  case p: TypeTree => p.tpe <:< mss
+                  case _           => false
+                }
+              case _ => false
+            }
+          } catch {
+            case _: Throwable => false
+          }
+      }
+
+      val classOwner = {
+        var o = owner.owner
+        while (!isStyleSheet(o) && !o.maybeOwner.isNoSymbol)
+          o = o.owner
+        o
+      }
+
+      def fixName(s: String): String =
+        s.replace("$", "")
+
+      val localName =
+        fixName(owner.name)
+
+      // `style()` instead of `val x = style()` results in "<local OuterClass>"
+      val finalName =
+        if (localName startsWith "<")
+          ""
+        else {
+          // Try to extract a name, relative to the stylesheet class
+          val className = fixName(classOwner.fullName)
+          val fullName  = fixName(owner.fullName)
+          if ((fullName.length > className.length + 1) && fullName.startsWith(className + ".")) {
+            val relName = fullName.substring(className.length + 1).replace('.', '-')
+            relName
+          } else
+            // Default to local name
+            localName
+        }
+
+      Inlined(None, Nil, Literal(StringConstant(finalName))).asExprOf[String]
+    }
+
+    import DslMacros._
+
+    trait Mixin {
+      protected def __macroStyle    (name: String): MStyle
+      protected def __macroStyleF   (name: String): MStyleF
+      protected def __macroKeyframes(name: String): MKeyframes
+      protected def __macroKeyframe               : MStyle
+      protected def __macroFontFace               : MFontFace
+
+      final protected inline def style    : MStyle     = __macroStyle(name())
+      final protected inline def styleF   : MStyleF    = __macroStyleF(name())
+      final protected inline def keyframes: MKeyframes = __macroKeyframes(name())
+      final protected inline def keyframe : MStyle     = __macroKeyframe
+      final protected inline def fontFace : MFontFace  = __macroFontFace
+    }
+  }
+
+  // ===================================================================================================================
+
+  type Color = ValueT[ValueT.Color]
+
+  object ColorLiteral {
+
+    private def cssFnRegex(f: String, as: String*) = {
+      val args = as mkString ","
+      Pattern compile s"^$f\\($args\\)$$"
+    }
+
+    private def int = "(-?\\d+)"
+    private def dbl = """(-?\d+(?:\.\d+)?|\.\d+)"""
+    private def pct = s"$dbl%"
+
+    private val ws   = "\\s+".r
+    private val rgbI = cssFnRegex("rgb",  int, int, int)
+    private val rgbP = cssFnRegex("rgb",  pct, pct, pct)
+    private val rgba = cssFnRegex("rgba", int, int, int, dbl)
+    private val hsl  = cssFnRegex("hsl",  int, pct, pct)
+    private val hsla = cssFnRegex("hsla", int, pct, pct, dbl)
+
+    private def isHex: Char => Boolean =
+      c => (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')
+
+    def impl(sc: Expr[StringContext])(using Quotes): Expr[Color] = {
+      import quotes.reflect._
+
+      import report.{throwError => fail}
+
+      val arg: Expr[String] =
+        sc match {
+          case '{ StringContext(${Varargs(parts)}*) } =>
+            parts.toList match {
+              case a :: Nil => a
+              case x        => fail(s"Expected exactly 1 StringContext part, got: $x")
+            }
+          case _ =>
+            fail(s"Failed to extract StringContext parts")
+        }
+
+      val value: String =
+        arg.asTerm match {
+          case Literal(StringConstant(v))                => v
+          case Inlined(_, _, Literal(StringConstant(v))) => v
+          case x                                         => fail("Don't know how to handle: " + x)
+        }
+
+      attempt(value) match {
+        case Right(c) =>
+          val l = Inlined(None, Nil, Literal(StringConstant(c))).asExprOf[String]
+          Inlined(None, Nil, '{ Color($l) }.asTerm).asExprOf[Color]
+        case Left(e) =>
+          report.throwError(e)
+      }
+    }
+
+    def runtime(text: String): Color =
+      attempt(text) match {
+        case Right(c) => Color(c)
+        case Left(e) => throw new IllegalArgumentException(e)
+      }
+
+    def attempt(text0: String): Either[String, String] = {
+      val text = ws.replaceAllIn(text0, "").toLowerCase
+
+      var errorResult: Left[String, String] =
+        null
+
+      def pass = true
+      def undecided = false
+      def fail(err: String) = {
+        errorResult = Left(err)
+        false
+      }
+
+      def validateHex: Boolean =
+        (text.charAt(0) == '#') && {
+          val v = text.drop(1)
+          v.length match {
+            case (3 | 6 | 4 | 8) if v.forall(isHex) => pass
+            case _                                  => fail("Hex notation must be #RGB, #RRGGBB, #RGBA, or #RRGGBBAA.")
+          }
+        }
+
+      type V = String => Unit
+
+      def validateInt(name: String, max: Int): V =
+        s => {
+          val i = s.toInt
+          if (i < 0 || i > max)
+            fail(s"Invalid $name value: $s")
+        }
+
+      def validateDbl(name: String, max: Double): V =
+        s => {
+          val d = s.toDouble
+          if (d < 0 || d > max)
+            fail(s"Invalid $name value: $s")
+        }
+
+      def validatePct(name: String): V =
+        validateDbl(name, 100)
+
+      def validateFn(p: Pattern, a: V, b: V, c: V, d: V = null): Boolean = {
+        val m = p.matcher(text)
+        if (m.matches) {
+          a(m group 1)
+          b(m group 2)
+          c(m group 3)
+          if (d ne null) d(m group 4)
+          pass
+        } else
+          undecided
+      }
+
+      def ri = validateInt("red",   255)
+      def gi = validateInt("green", 255)
+      def bi = validateInt("blue",  255)
+      def rp = validatePct("red")
+      def gp = validatePct("green")
+      def bp = validatePct("blue")
+      def h  = validateInt("hue", 359)
+      def s  = validatePct("saturation")
+      def l  = validatePct("lightness")
+      def a  = validateDbl("alpha", 1)
+
+      def validateRgbI = validateFn(rgbI, ri, gi, bi)
+      def validateRgbP = validateFn(rgbP, rp, gp, bp)
+      def validateRgba = validateFn(rgba, ri, gi, bi, a)
+      def validateHsl  = validateFn(hsl,  h, s, l)
+      def validateHsla = validateFn(hsla, h, s, l, a)
+
+      val validated =
+        validateHex || validateRgbI || validateRgbP || validateRgba || validateHsl || validateHsla
+
+      if (validated && (errorResult == null))
+        Right(text)
+      else
+        Option(errorResult).getOrElse(Left("Invalid colour: \"" + text0 + "\""))
+    }
+  }
+
+  // ===================================================================================================================
+
+  trait DevOrProdDefaults {
+    inline final def devOrProdDefaults: Exports with mutable.Settings =
+      if (scalacss.internal.Platform.DevMode)
+        scalacss.DevDefaults
+      else
+        scalacss.ProdDefaults
+  }
+}
diff --git a/core/shared/src/main/scala/scalacss/internal/Dsl.scala b/core/shared/src/main/scala/scalacss/internal/Dsl.scala
index f954529d..20f56ef7 100644
--- a/core/shared/src/main/scala/scalacss/internal/Dsl.scala
+++ b/core/shared/src/main/scala/scalacss/internal/Dsl.scala
@@ -10,8 +10,8 @@ object DslBase {
   object MediaQueryEmpty extends TypeAOps[Query] with FeatureOps[Query] {
     override protected def F = f => new Query(Right(f), Vector.empty)
     override protected def T = t => new Query(Left(Just(t)), Vector.empty)
-    def not  = new MediaQueryNeedType(Not)
-    def only = new MediaQueryNeedType(Only)
+    def not  = new MediaQueryNeedType(Not.apply)
+    def only = new MediaQueryNeedType(Only.apply)
   }
 
   // media.{not,only}
@@ -154,6 +154,7 @@ import DslBase._
 // =====================================================================================================================
 abstract class DslBase
   extends AttrAliasesAndValueTRules
+     with Macros.Dsl.Base
      with TypedLiteralAliases
      with ColorOps[ValueT[Color]] {
 
@@ -186,7 +187,7 @@ abstract class DslBase
   @inline implicit final def autoDslAV   (a: AV)           : DslAV          = new DslAV(a)
   @inline implicit final def autoDslAVs  (a: AVs)          : DslAVs         = new DslAVs(a)
 
-          implicit final def DslCond[C](x: C)(implicit f: C => Cond): DslCond = new DslCond(x, this)
+          implicit final def DslCond[C](x: C)(implicit f: C => Cond): DslCond = new DslCond(f(x), this)
 
   @inline implicit final def ToAVToAV(x: ToAV): AV = x.av
 
@@ -196,8 +197,8 @@ abstract class DslBase
           implicit final def ToStyleToAV      (x: ToAV)                           : ToStyle = ToStyleAV(x.av)
           implicit final def ToStyleAV        (x: AV)                             : ToStyle = ToStyleAVs(AVs(x))
           implicit final def ToStyleAVs       (x: AVs)                            : ToStyle = new ToStyle(StyleS.data1(Cond.empty, x))
-          implicit final def ToStyleCAV [C]   (x: (C, AV)) (implicit f: C => Cond): ToStyle = new ToStyle(StyleS.data1(x._1, AVs(x._2)))
-          implicit final def ToStyleCAVs[C]   (x: (C, AVs))(implicit f: C => Cond): ToStyle = new ToStyle(StyleS.data1(x._1, x._2))
+          implicit final def ToStyleCAV [C]   (x: (C, AV)) (implicit f: C => Cond): ToStyle = new ToStyle(StyleS.data1(f(x._1), AVs(x._2)))
+          implicit final def ToStyleCAVs[C]   (x: (C, AVs))(implicit f: C => Cond): ToStyle = new ToStyle(StyleS.data1(f(x._1), x._2))
           implicit final def ToStyleUnsafeExt (x: UnsafeExt)                      : ToStyle = ToStyleUnsafeExts(Vector1(x))
           implicit final def ToStyleUnsafeExts(x: UnsafeExts)                     : ToStyle = new ToStyle(StyleS.empty.copy(unsafeExts = x))
   @inline implicit final def ToStyleStyleS    (x: StyleS)                         : ToStyle = new ToStyle(x)
@@ -230,9 +231,6 @@ abstract class DslBase
 
   def mixinIfElse(b: Boolean)(t: ToStyle*)(f: ToStyle*)(implicit c: Compose): StyleS =
     styleS((if (b) t else f): _*)(c)
-
-  @inline implicit def colourLiteralMacro(sc: StringContext) =
-    new Macros.ColourLiteral(sc)
 }
 
 // =====================================================================================================================
diff --git a/core/shared/src/main/scala/scalacss/internal/Media.scala b/core/shared/src/main/scala/scalacss/internal/Media.scala
index 2c7f3b17..044bcea0 100644
--- a/core/shared/src/main/scala/scalacss/internal/Media.scala
+++ b/core/shared/src/main/scala/scalacss/internal/Media.scala
@@ -206,13 +206,13 @@ object Media {
     `(` ~ c ~ `)`
 
   private def opt[T](ov: Option[T], name: String)(implicit tc: T => String): String =
-    ov.fold(name)(name ~ `:` ~ _)
+    ov.fold(name)(name ~ `:` ~ tc(_))
 
   private def cssValueExpr[T](e: ValueExpr[T], name: String)(implicit tc: T => String): String =
     e match {
-      case Eql(t) =>       name ~ `:` ~ t
-      case Min(t) => min ~ name ~ `:` ~ t
-      case Max(t) => max ~ name ~ `:` ~ t
+      case Eql(t) =>       name ~ `:` ~ tc(t)
+      case Min(t) => min ~ name ~ `:` ~ tc(t)
+      case Max(t) => max ~ name ~ `:` ~ tc(t)
     }
 
   private def cssValueExprO[T](o: Option[ValueExpr[T]], name: String)(implicit tc: T => String): String =
diff --git a/core/shared/src/main/scala/scalacss/internal/Pseudo.scala b/core/shared/src/main/scala/scalacss/internal/Pseudo.scala
index 0b9d204d..eed8948b 100644
--- a/core/shared/src/main/scala/scalacss/internal/Pseudo.scala
+++ b/core/shared/src/main/scala/scalacss/internal/Pseudo.scala
@@ -28,7 +28,7 @@ object PseudoType {
 sealed abstract class Pseudo extends Pseudo.ChainOps[Pseudo]  {
   import Pseudo._
 
-  val cssValue: String
+  def cssValue: String
 
   // apply() is used by Dsl
   final def modSelector(sel: CssSelector): CssSelector =
diff --git a/core/shared/src/main/scala/scalacss/internal/mutable/Settings.scala b/core/shared/src/main/scala/scalacss/internal/mutable/Settings.scala
index bdeb2bb5..776f4f5f 100644
--- a/core/shared/src/main/scala/scalacss/internal/mutable/Settings.scala
+++ b/core/shared/src/main/scala/scalacss/internal/mutable/Settings.scala
@@ -19,13 +19,13 @@ trait Settings {
 
 object Settings {
   trait Delegate extends Settings {
-    override          def cssRegisterNameGen      = cssSettings.cssRegisterNameGen
-    override          def cssRegisterMacroName    = cssSettings.cssRegisterMacroName
-    override          def cssRegisterErrorHandler = cssSettings.cssRegisterErrorHandler
-    override implicit def cssStringRenderer       = cssSettings.cssStringRenderer
-    override implicit def cssComposition          = cssSettings.cssComposition
-    override implicit def cssEnv                  = cssSettings.cssEnv
-    override implicit def cssRegister             = cssSettings.cssRegister
+    override          def cssRegisterNameGen     : NameGen          = cssSettings.cssRegisterNameGen
+    override          def cssRegisterMacroName   : MacroName        = cssSettings.cssRegisterMacroName
+    override          def cssRegisterErrorHandler: ErrorHandler     = cssSettings.cssRegisterErrorHandler
+    override implicit def cssStringRenderer      : Renderer[String] = cssSettings.cssStringRenderer
+    override implicit def cssComposition         : Compose          = cssSettings.cssComposition
+    override implicit def cssEnv                 : Env              = cssSettings.cssEnv
+    override implicit def cssRegister            : Register         = cssSettings.cssRegister
 
     protected[scalacss] def cssSettings: Settings
   }
diff --git a/core/shared/src/main/scala/scalacss/internal/mutable/StyleSheet.scala b/core/shared/src/main/scala/scalacss/internal/mutable/StyleSheet.scala
index 8bdb6325..b03e4009 100644
--- a/core/shared/src/main/scala/scalacss/internal/mutable/StyleSheet.scala
+++ b/core/shared/src/main/scala/scalacss/internal/mutable/StyleSheet.scala
@@ -38,7 +38,9 @@ object StyleSheet {
 
       @inline final def Color(literal: String) = scalacss.internal.Color(literal)
 
-      @inline implicit final def toCondOps[C](x: C)(implicit f: C => Cond) = new CondOps(x)
+      @inline implicit final def toCondOps[C](x: C)(implicit f: C => Cond): CondOps =
+        new CondOps(f(x))
+
       final class CondOps(val cond: Cond) {
         @inline def - = new DslCond(cond, dsl)
       }
diff --git a/core/shared/src/main/scala/scalacss/package.scala b/core/shared/src/main/scala/scalacss/package.scala
index 5612584e..c49edda6 100644
--- a/core/shared/src/main/scala/scalacss/package.scala
+++ b/core/shared/src/main/scala/scalacss/package.scala
@@ -1,4 +1,7 @@
-package object scalacss extends scalacss.defaults.Exports  {
+package object scalacss
+    extends scalacss.defaults.Exports
+       with internal.Macros.DevOrProdDefaults {
+
   import internal.mutable.Settings
   import defaults.{DefaultSettings, Exports}
 
@@ -11,7 +14,4 @@ package object scalacss extends scalacss.defaults.Exports  {
     "\n    3. val CssSettings = scalacss.devOrProdDefaults; import CssSettings._",
     "0.5.3")
   object Defaults extends Exports with DefaultSettings.Dev
-
-  def devOrProdDefaults: Exports with Settings =
-    macro internal.Macros.devOrProdDefaults
 }
diff --git a/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala b/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala
index 1763e2c3..c93a7b53 100644
--- a/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala
+++ b/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala
@@ -17,7 +17,7 @@ object DefaultsTest extends TestSuite {
 
   class SharedStyles(implicit reg: StyleSheet.Register) extends StyleSheet.Inline {
     import dsl._
-    implicit def compose = CssComposer.trust
+    implicit def compose: CssComposer = CssComposer.trust
     val header = style(backgroundColor(c"#333"))
     val footer = style(backgroundColor(c"#666"))
   }
@@ -39,7 +39,7 @@ object DefaultsTest extends TestSuite {
       val shared = new SharedStyles
     }
 
-    implicit def cssEnv = CssEnv.empty
+    implicit def cssEnv: CssEnv = CssEnv.empty
     val css = SS.render[String]
 
     def norm(css: String) = css.trim
@@ -92,7 +92,7 @@ object DefaultsTest extends TestSuite {
       val blah = style(width.inherit)
     }
 
-    implicit def cssEnv = CssEnv.empty
+    implicit def cssEnv: CssEnv = CssEnv.empty
     val css1 = SS1.render[String]
     val css2 = SS2.render[String]
 
diff --git a/core/shared/src/test/scala/scalacss/internal/ColorTest.scala b/core/shared/src/test/scala/scalacss/internal/ColorTest.scala
index 67733fa3..9b60dc85 100644
--- a/core/shared/src/test/scala/scalacss/internal/ColorTest.scala
+++ b/core/shared/src/test/scala/scalacss/internal/ColorTest.scala
@@ -37,10 +37,8 @@ object ColorTest extends TestSuite {
     "invalid" - {
       @nowarn("cat=unused")
       def assertFailure(e: CompileError) = ()
-      def assertErrorContains(e: CompileError, frag: String): Unit = {
-        val err = e.msg
-        assert(err contains frag)
-      }
+      def assertErrorContains(e: CompileError, frag: String): Unit =
+        assertContains(e.msg, frag)
 
       "hex" - {
         def test(e: CompileError): Unit = assertErrorContains(e, "Hex notation must be")
diff --git a/core/shared/src/test/scala/scalacss/internal/ComposeTest.scala b/core/shared/src/test/scala/scalacss/internal/ComposeTest.scala
index 44e0240c..5cdcf888 100644
--- a/core/shared/src/test/scala/scalacss/internal/ComposeTest.scala
+++ b/core/shared/src/test/scala/scalacss/internal/ComposeTest.scala
@@ -85,7 +85,7 @@ object ComposeTest extends TestSuite {
 
     "values" - {
       import Dsl._
-      implicit def c = Compose.safe
+      implicit def c: Compose = Compose.safe
 
       def test(s: StyleS)(avs: AV*)(ws: String*): Unit = {
         assertEq(s.data(Cond.empty).avIterator.toVector, avs.toVector)
diff --git a/core/shared/src/test/scala/scalacss/internal/RandomData.scala b/core/shared/src/test/scala/scalacss/internal/RandomData.scala
index db92c055..632b1bd5 100644
--- a/core/shared/src/test/scala/scalacss/internal/RandomData.scala
+++ b/core/shared/src/test/scala/scalacss/internal/RandomData.scala
@@ -35,10 +35,14 @@ object RandomData {
       Visited, After, Before, FirstLetter, FirstLine, Selection)
 
     val needNthQuery = NonEmptyList.of[NthQuery => Pseudo](
-      NthChild, NthLastChild, NthLastOfType, NthOfType)
+      NthChild.apply,
+      NthLastChild.apply,
+      NthLastOfType.apply,
+      NthOfType.apply,
+    )
 
     val needStr = NonEmptyList.of[String => Pseudo](
-      Custom(_, PseudoType.Class), Custom(_, PseudoType.Element), Lang, new Not(_), AttrExists)
+      Custom(_, PseudoType.Class), Custom(_, PseudoType.Element), Lang.apply, new Not(_), AttrExists.apply)
 
     val need2Str = NonEmptyList.of[(String, String) => Pseudo](
       Pseudo.Attr _, AttrContains _, AttrStartsWith _, AttrEndsWith _)
@@ -64,7 +68,7 @@ object RandomData {
     }
 
   def unsafeExt(g: Gen[StyleS]): Gen[UnsafeExt] =
-    Gen.apply3(UnsafeExt)(unsafeCssSelEndo, cond, g)
+    Gen.apply3(UnsafeExt.apply)(unsafeCssSelEndo, cond, g)
 
   private def sized(from: Int, jvm: Int, js: Int): SizeSpec =
     from to (jvm `JVM|JS` js)
@@ -74,7 +78,7 @@ object RandomData {
       unsafeExt(g).vector(sized(1, 8, 3)))
 
   val warning: Gen[Warning] =
-    Gen.apply2(Warning)(cond, str)
+    Gen.apply2(Warning.apply)(cond, str)
 
   val className: Gen[ClassName] =
     str1 map ClassName.apply
diff --git a/core/shared/src/test/scala/scalacss/internal/UsageTest.scala b/core/shared/src/test/scala/scalacss/internal/UsageTest.scala
index 6079db8e..15644db0 100644
--- a/core/shared/src/test/scala/scalacss/internal/UsageTest.scala
+++ b/core/shared/src/test/scala/scalacss/internal/UsageTest.scala
@@ -7,7 +7,7 @@ object UsageTest extends TestSuite {
   import Dsl._
   import Pseudo._
 
-  implicit def composition = Compose.safe
+  implicit def composition: Compose = Compose.safe
 
   val thing = 2.ex
 
diff --git a/core/shared/src/test/scala/scalacss/internal/mutable/RegisterTest.scala b/core/shared/src/test/scala/scalacss/internal/mutable/RegisterTest.scala
index 46c1506d..f98a5408 100644
--- a/core/shared/src/test/scala/scalacss/internal/mutable/RegisterTest.scala
+++ b/core/shared/src/test/scala/scalacss/internal/mutable/RegisterTest.scala
@@ -29,14 +29,14 @@ object RegisterTest extends TestSuite {
     assertEq(l, l.distinct)
   }
 
-  implicit def env = Env.empty
+  implicit def env: Env = Env.empty
 
   def stylesToCssMap(s: Vector[StyleA]) =
     Css.styles(s).map(e => (e.sel, e.content)).toMap
 
   override def tests = Tests {
     val reg = new Register(NameGen.numbered(), MacroName.Use, ErrorHandler.noisy)
-    implicit def cnh = ClassNameHint("blah")
+    implicit def cnh: ClassNameHint = ClassNameHint("blah")
 
     "registerS" - {
       val a1 = reg registerS ss1
diff --git a/project/Build.scala b/project/Build.scala
index 4837ec59..a5aa7b10 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -20,22 +20,28 @@ object ScalaCssBuild {
   private val publicationSettings =
     Lib.publicationSettings(ghProject)
 
-  def scalacFlags =
-    Seq(
-      "-deprecation",
-      "-unchecked",
-      "-feature",
-      "-language:postfixOps",
-      "-language:implicitConversions",
-      "-language:higherKinds",
-      "-language:existentials",
-      "-opt:l:inline",
-      "-opt-inline-from:japgolly.univeq.**",
-      "-opt-inline-from:scalacss.**",
-      "-Ywarn-dead-code",
-      "-Ywarn-unused",
-      // "-Ywarn-value-discard",
-    )
+  def scalacCommonFlags = Seq(
+    "-deprecation",
+    "-unchecked",
+    "-feature",
+    "-language:postfixOps",
+    "-language:implicitConversions",
+    "-language:higherKinds",
+    "-language:existentials",
+  )
+
+  def scalac2Flags = Seq(
+    "-opt:l:inline",
+    "-opt-inline-from:japgolly.univeq.**",
+    "-opt-inline-from:scalacss.**",
+    "-Ywarn-dead-code",
+    "-Ywarn-unused",
+    // "-Ywarn-value-discard",
+  )
+
+  def scalac3Flags = Seq(
+    "-source", "3.0-migration",
+  )
 
   val commonSettings = ConfigureBoth(
     _.settings(
@@ -43,9 +49,10 @@ object ScalaCssBuild {
       homepage                      := Some(url("https://github.com/japgolly/scalacss")),
       licenses                      += ("Apache-2.0", url("http://opensource.org/licenses/Apache-2.0")),
       scalaVersion                  := Ver.scala2,
-      crossScalaVersions            := Seq(Ver.scala2),
-      scalacOptions                ++= scalacFlags,
-      ThisBuild / shellPrompt       := ((s: State) => Project.extract(s).currentRef.project + "> "),
+      crossScalaVersions            := Seq(Ver.scala2, Ver.scala3),
+      scalacOptions                ++= scalacCommonFlags,
+      scalacOptions                ++= scalac2Flags.filter(_ => scalaVersion.value.startsWith("2")),
+      scalacOptions                ++= scalac3Flags.filter(_ => scalaVersion.value.startsWith("3")),
    // incOptions                    := incOptions.value.withNameHashing(true).withLogRecompileOnMacro(false),
       updateOptions                 := updateOptions.value.withCachedResolution(true),
       releasePublishArtifactsAction := PgpKeys.publishSigned.value,
@@ -54,11 +61,21 @@ object ScalaCssBuild {
 
   def definesMacros = ConfigureBoth(
     _.settings(
-      scalacOptions += "-language:experimental.macros",
-      libraryDependencies ++= Seq(
-        Dep.scalaReflect.value,
-        Dep.scalaCompiler.value % Provided,
-      ),
+      scalacOptions ++= {
+        if (scalaVersion.value.startsWith("2"))
+          "-language:experimental.macros" :: Nil
+        else
+          Nil
+      },
+      libraryDependencies ++=  {
+        if (scalaVersion.value.startsWith("2"))
+          List(
+            Dep.scalaReflect.value,
+            Dep.scalaCompiler.value % Provided,
+          )
+        else
+          Nil
+      },
     )
   )
 
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 7336cec6..8c8b79bc 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -10,6 +10,7 @@ object Dependencies {
 
     // Exported
     val scala2          = "2.13.6"
+    val scala3          = "3.0.1"
     val scalaJsDom      = "1.1.0"
     val scalaJsReact    = "2.0.0-RC2"
     val scalatags       = "0.9.4"
@@ -30,12 +31,12 @@ object Dependencies {
     val nyayaProp           = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-prop"              % Ver.nyaya)
     val nyayaTest           = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-test"              % Ver.nyaya)
     val scalaCompiler       = Def.setting("org.scala-lang"                      % "scala-compiler"          % scalaVersion.value)
-    val scalaJsDom          = Def.setting("org.scala-js"                      %%% "scalajs-dom"             % Ver.scalaJsDom)
+    val scalaJsDom          = Def.setting("org.scala-js"                      %%% "scalajs-dom"             % Ver.scalaJsDom cross CrossVersion.for3Use2_13)
     val scalaJsReactCore    = Def.setting("com.github.japgolly.scalajs-react" %%% "core"                    % Ver.scalaJsReact)
     val scalaJsReactCoreGen = Def.setting("com.github.japgolly.scalajs-react" %%% "core-generic"            % Ver.scalaJsReact)
     val scalaJsReactTest    = Def.setting("com.github.japgolly.scalajs-react" %%% "test"                    % Ver.scalaJsReact)
     val scalaReflect        = Def.setting("org.scala-lang"                      % "scala-reflect"           % scalaVersion.value)
-    val scalatags           = Def.setting("com.lihaoyi"                       %%% "scalatags"               % Ver.scalatags)
+    val scalatags           = Def.setting("com.lihaoyi"                       %%% "scalatags"               % Ver.scalatags cross CrossVersion.for3Use2_13)
     val univEq              = Def.setting("com.github.japgolly.univeq"        %%% "univeq"                  % Ver.univEq)
     val utest               = Def.setting("com.lihaoyi"                       %%% "utest"                   % Ver.utest)
   }
diff --git a/project/Lib.scala b/project/Lib.scala
index afcf7eb1..10ab5eec 100644
--- a/project/Lib.scala
+++ b/project/Lib.scala
@@ -53,24 +53,22 @@ object Lib {
     .jsConfigure(
       sourceMapsToGithub(ghProject))
 
-  def sourceMapsToGithub(ghProject: String): PE =
+  def sourceMapsToGithub(ghProject: String): Project => Project =
     p => p.settings(
-      scalacOptions ++= (if (isSnapshot.value) Seq.empty else Seq({
-        val a = p.base.toURI.toString.replaceFirst("[^/]+/?$", "")
-        val g = s"https://raw.githubusercontent.com/japgolly/$ghProject"
-        s"-P:scalajs:mapSourceURI:$a->$g/v${version.value}/"
-      }))
+      scalacOptions ++= {
+        val isDotty = scalaVersion.value startsWith "3"
+        val ver     = version.value
+        if (isSnapshot.value)
+          Nil
+        else {
+          val a = p.base.toURI.toString.replaceFirst("[^/]+/?$", "")
+          val g = s"https://raw.githubusercontent.com/japgolly/$ghProject"
+          val flag = if (isDotty) "-scalajs-mapSourceURI" else "-P:scalajs:mapSourceURI"
+          s"$flag:$a->$g/v$ver/" :: Nil
+        }
+      }
     )
 
   def preventPublication: PE =
-    _.settings(
-      publish / skip     := true,
-      publish            := (()),
-      publishLocal       := (()),
-      publishSigned      := (()),
-      publishLocalSigned := (()),
-      publishArtifact    := false,
-      publishTo          := Some(Resolver.file("Unused transient repository", target.value / "fakepublish")),
-      packagedArtifacts  := Map.empty)
-    // .disablePlugins(plugins.IvyPlugin)
+    _.settings(publish / skip := true)
 }

From 00c28ee290772c19c5f2be9ba7092aa02fb0a63c Mon Sep 17 00:00:00 2001
From: David Barri <japgolly@gmail.com>
Date: Fri, 30 Jul 2021 19:07:56 +1000
Subject: [PATCH 2/5] Disable scalatags and elisionTest for Scala 3

---
 .../src/test/scala/scalacss/ReactTest.scala     |  2 +-
 project/Build.scala                             |  7 ++++---
 project/Dependencies.scala                      |  1 +
 project/Lib.scala                               | 17 +++++++++++++++++
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/ext-react/src/test/scala/scalacss/ReactTest.scala b/ext-react/src/test/scala/scalacss/ReactTest.scala
index 04857a1f..58423754 100644
--- a/ext-react/src/test/scala/scalacss/ReactTest.scala
+++ b/ext-react/src/test/scala/scalacss/ReactTest.scala
@@ -4,13 +4,13 @@ import japgolly.scalajs.react._
 import japgolly.scalajs.react.vdom.html_<^._
 import org.scalajs.dom.document
 import org.scalajs.dom.raw.HTMLStyleElement
-import scalacss.DevDefaults._
 import scalacss.ScalaCssReact._
 import scalacss.TestUtil._
 import scalacss.internal.mutable.StyleSheetRegistry
 import utest._
 
 object ReactTest extends TestSuite {
+  import scalacss.DevDefaults._
 
   object MyStyles extends StyleSheet.Inline {
     import dsl._
diff --git a/project/Build.scala b/project/Build.scala
index a5aa7b10..e94a33d6 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -139,7 +139,7 @@ object ScalaCssBuild {
   lazy val elisionTest = crossProject(JSPlatform, JVMPlatform)
     .in(file("elision-test"))
     .configureCross(commonSettings, utestSettings)
-    .configure(preventPublication)
+    .configure(preventPublication, onlyScala2)
     .dependsOn(core)
     .settings(
       scalacOptions ++= Seq("-Xelide-below", "OFF"),
@@ -149,9 +149,9 @@ object ScalaCssBuild {
   lazy val extScalatagsJS  = extScalatags.js
   lazy val extScalatags = crossProject(JSPlatform, JVMPlatform)
     .in(file("ext-scalatags"))
-    .configureCross(commonSettings, publicationSettings)
     .dependsOn(core)
-    .configureCross(utestSettings)
+    .configureCross(commonSettings, publicationSettings, utestSettings)
+    .configure(onlyScala2)
     .settings(
       moduleName := "ext-scalatags",
       libraryDependencies ++= Seq(
@@ -170,6 +170,7 @@ object ScalaCssBuild {
       moduleName := "ext-react",
       libraryDependencies ++= Seq(
         Dep.scalaJsReactCoreGen.value % Provided,
+        Dep.scalaJsReactDummy.value % Provided,
         Dep.scalaJsReactTest.value % Test,
         Dep.cats.value % Test,
       ),
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 8c8b79bc..1beddf9c 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -34,6 +34,7 @@ object Dependencies {
     val scalaJsDom          = Def.setting("org.scala-js"                      %%% "scalajs-dom"             % Ver.scalaJsDom cross CrossVersion.for3Use2_13)
     val scalaJsReactCore    = Def.setting("com.github.japgolly.scalajs-react" %%% "core"                    % Ver.scalaJsReact)
     val scalaJsReactCoreGen = Def.setting("com.github.japgolly.scalajs-react" %%% "core-generic"            % Ver.scalaJsReact)
+    val scalaJsReactDummy   = Def.setting("com.github.japgolly.scalajs-react" %%% "util-dummy-defaults"     % Ver.scalaJsReact)
     val scalaJsReactTest    = Def.setting("com.github.japgolly.scalajs-react" %%% "test"                    % Ver.scalaJsReact)
     val scalaReflect        = Def.setting("org.scala-lang"                      % "scala-reflect"           % scalaVersion.value)
     val scalatags           = Def.setting("com.lihaoyi"                       %%% "scalatags"               % Ver.scalatags cross CrossVersion.for3Use2_13)
diff --git a/project/Lib.scala b/project/Lib.scala
index 10ab5eec..2dad17f5 100644
--- a/project/Lib.scala
+++ b/project/Lib.scala
@@ -71,4 +71,21 @@ object Lib {
 
   def preventPublication: PE =
     _.settings(publish / skip := true)
+
+  def onlyScala2(p: Project) = {
+    def clearWhenDisabled[A](key: SettingKey[Seq[A]]) =
+      Def.setting[Seq[A]] {
+        val disabled = scalaVersion.value.startsWith("3")
+        val as = key.value
+        if (disabled) Nil else as
+      }
+    p.settings(
+      libraryDependencies                  := clearWhenDisabled(libraryDependencies).value,
+      Compile / unmanagedSourceDirectories := clearWhenDisabled(Compile / unmanagedSourceDirectories).value,
+      Test / unmanagedSourceDirectories    := clearWhenDisabled(Test / unmanagedSourceDirectories).value,
+      publish / skip                       :=  ((publish / skip).value || scalaVersion.value.startsWith("3")),
+      Test / test                           := { if (scalaVersion.value.startsWith("2")) (Test / test).value },
+    )
+  }
+
 }

From 126faadfcc7fc770bcc9700cd3aff2e0c143f039 Mon Sep 17 00:00:00 2001
From: David Barri <japgolly@gmail.com>
Date: Fri, 30 Jul 2021 19:11:56 +1000
Subject: [PATCH 3/5] Fix

---
 core/shared/src/main/scala-2/scalacss/internal/Macros.scala | 2 +-
 core/shared/src/main/scala/scalacss/package.scala           | 1 -
 doc/history/0.8.md                                          | 1 +
 ext-react/src/test/scala/scalacss/ReactTest.scala           | 2 +-
 4 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/core/shared/src/main/scala-2/scalacss/internal/Macros.scala b/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
index 515a641d..8d0d26d2 100644
--- a/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
+++ b/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
@@ -185,7 +185,7 @@ object Macros {
   // ===================================================================================================================
 
   trait DevOrProdDefaults {
-    def devOrProdDefaults: Exports with Settings =
+    def devOrProdDefaults: Exports with mutable.Settings =
       macro Macros.devOrProdDefaults
   }
 
diff --git a/core/shared/src/main/scala/scalacss/package.scala b/core/shared/src/main/scala/scalacss/package.scala
index c49edda6..0e02920a 100644
--- a/core/shared/src/main/scala/scalacss/package.scala
+++ b/core/shared/src/main/scala/scalacss/package.scala
@@ -2,7 +2,6 @@ package object scalacss
     extends scalacss.defaults.Exports
        with internal.Macros.DevOrProdDefaults {
 
-  import internal.mutable.Settings
   import defaults.{DefaultSettings, Exports}
 
   object DevDefaults  extends Exports with DefaultSettings.Dev
diff --git a/doc/history/0.8.md b/doc/history/0.8.md
index 6ed7262a..d0f2efa9 100644
--- a/doc/history/0.8.md
+++ b/doc/history/0.8.md
@@ -1,3 +1,4 @@
 # 0.8.0 ([commit log](https://github.com/japgolly/scalacss/compare/v0.7.0..v0.8.0-RC1))
 
+* Add support for Scala 3 (`scalatags` module excepted)
 * Upgrade deps
diff --git a/ext-react/src/test/scala/scalacss/ReactTest.scala b/ext-react/src/test/scala/scalacss/ReactTest.scala
index 58423754..dd411962 100644
--- a/ext-react/src/test/scala/scalacss/ReactTest.scala
+++ b/ext-react/src/test/scala/scalacss/ReactTest.scala
@@ -1,4 +1,4 @@
-package scalacss
+package scalacss.external
 
 import japgolly.scalajs.react._
 import japgolly.scalajs.react.vdom.html_<^._

From c27bc5684728823fdc860e8fa32fb29b47462a5a Mon Sep 17 00:00:00 2001
From: David Barri <japgolly@gmail.com>
Date: Sat, 31 Jul 2021 08:58:20 +1000
Subject: [PATCH 4/5] Harden Scala 3 macro

---
 core/shared/src/main/scala-3/scalacss/internal/Macros.scala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/core/shared/src/main/scala-3/scalacss/internal/Macros.scala b/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
index 5f6621bb..b41b5e7b 100644
--- a/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
+++ b/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
@@ -32,13 +32,13 @@ object Macros {
       }
 
       val isStyleSheet: Symbol => Boolean = {
-        val mss = TypeRepr.of[mutable.StyleSheet.Inline]
+        val ss = TypeRepr.of[mutable.StyleSheet.Base]
         sym =>
           try {
             sym.tree match {
               case ClassDef(_, _, parents, _, _) =>
                 parents.exists {
-                  case p: TypeTree => p.tpe <:< mss
+                  case p: TypeTree => (p.tpe <:< ss)
                   case _           => false
                 }
               case _ => false

From 5680a82849e00f3c6c60cd8ebdf70d168cd07933 Mon Sep 17 00:00:00 2001
From: David Barri <japgolly@gmail.com>
Date: Sat, 31 Jul 2021 10:42:37 +1000
Subject: [PATCH 5/5] Fix up dev/prod mode selection

---
 .github/workflows/ci.yml                      |  12 +-
 bin/ci                                        |  57 ++++++++
 bin/get_scala_version                         |  11 ++
 build.sbt                                     |   2 -
 .../scalacss/internal/ModeMacros.scala        |  52 +++++++
 .../scalacss/internal/ModeMacros.scala        |  55 ++++++++
 .../scala/scalacss/internal/Platform.scala    |  11 --
 .../scalacss/internal/ModeMacros.scala        |  44 ++++++
 .../scalacss/internal/ModeMacros.scala        |  47 +++++++
 .../scala/scalacss/internal/Platform.scala    |  10 --
 .../scala-2/scalacss/internal/Macros.scala    |  18 ---
 .../scala-3/scalacss/internal/Macros.scala    |  13 +-
 .../scalacss/defaults/DefaultSettings.scala   |   6 -
 .../src/main/scala/scalacss/package.scala     |   2 +-
 .../scala/scalacss/full/DefaultsTest.scala    |   8 +-
 doc/features/basics.md                        |  19 +--
 doc/history/0.8.md                            |   5 +
 downstream-tests/build.sbt                    | 119 ++++++++++++++++
 .../js/src/main/scala/downstream/Main.scala   |  10 ++
 .../test/scala/downstream/RuntimeTest.scala   |  27 ++++
 .../test/scala/downstream/JsOutputTest.scala  |  53 +++++++
 .../jvm/src/test/scala/downstream/Props.scala |  34 +++++
 downstream-tests/project/Dependencies.scala   |   1 +
 downstream-tests/project/Lib.scala            |   1 +
 downstream-tests/project/build.properties     |   1 +
 downstream-tests/project/plugins.sbt          |   1 +
 downstream-tests/run                          | 130 ++++++++++++++++++
 downstream-tests/version.sbt                  |   1 +
 .../scala/scalacss/elision/DefaultsTest.scala |  34 -----
 project/Build.scala                           |  48 +------
 project/Dependencies.scala                    |  31 +++--
 project/Lib.scala                             |  34 +++++
 32 files changed, 713 insertions(+), 184 deletions(-)
 create mode 100755 bin/ci
 create mode 100755 bin/get_scala_version
 create mode 100644 core/js/src/main/scala-2/scalacss/internal/ModeMacros.scala
 create mode 100644 core/js/src/main/scala-3/scalacss/internal/ModeMacros.scala
 create mode 100644 core/jvm/src/main/scala-2/scalacss/internal/ModeMacros.scala
 create mode 100644 core/jvm/src/main/scala-3/scalacss/internal/ModeMacros.scala
 create mode 100644 downstream-tests/build.sbt
 create mode 100644 downstream-tests/js/src/main/scala/downstream/Main.scala
 create mode 100644 downstream-tests/js/src/test/scala/downstream/RuntimeTest.scala
 create mode 100644 downstream-tests/jvm/src/test/scala/downstream/JsOutputTest.scala
 create mode 100644 downstream-tests/jvm/src/test/scala/downstream/Props.scala
 create mode 120000 downstream-tests/project/Dependencies.scala
 create mode 120000 downstream-tests/project/Lib.scala
 create mode 120000 downstream-tests/project/build.properties
 create mode 120000 downstream-tests/project/plugins.sbt
 create mode 100755 downstream-tests/run
 create mode 120000 downstream-tests/version.sbt
 delete mode 100644 elision-test/shared/src/test/scala/scalacss/elision/DefaultsTest.scala

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7fa32b7c..b1ee65ce 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,9 +14,9 @@ jobs:
       matrix:
         include:
           - java: 16
-            scala: 2.13.6
+            scala: 2
           - java: 8
-            scala: 3.0.1
+            scala: 3
 
     steps:
       - name: Git checkout
@@ -40,12 +40,8 @@ jobs:
 
       - name: Build and test
         shell: bash
-        run: sbt ++${{ matrix.scala }} test
-
-      - name: Test fullOptJS
-        shell: bash
-        run: sbt ++${{ matrix.scala }} 'set ThisBuild / scalaJSStage := FullOptStage' JS/test
+        run: bin/ci ${{ matrix.scala }}
 
       - name: Show JS sizes
         shell: bash
-        run: sbt ++${{ matrix.scala }} cmpJsSize jsSizes
+        run: sbt "++$(bin/get_scala_version ${{ matrix.scala }})" cmpJsSize jsSizes
diff --git a/bin/ci b/bin/ci
new file mode 100755
index 00000000..92692e5f
--- /dev/null
+++ b/bin/ci
@@ -0,0 +1,57 @@
+#!/bin/bash
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+if [ $# -gt 1 ]; then
+  echo "Usage: $0 [<scala ver>]"
+  echo ""
+  echo "Where"
+  echo "  <scala ver> = 2 or 3"
+  echo
+  exit 1
+fi
+
+case "${1:-}" in
+  "")
+    "$0" 2
+    echo
+    echo
+    "$0" 3
+    exit 0
+    ;;
+  2|3)
+    SCALA_VER="$(bin/get_scala_version $1)"
+    echo "Scala version: $SCALA_VER"
+    ;;
+  *)
+    echo "Unrecognised version: $1" >&2
+    exit 2
+    ;;
+esac
+
+dryrun=
+# dryrun=-n
+
+# See how much memory is available
+free -h
+echo
+
+# Test upstream
+rm -rf */target/scala-*/{,test-}classes
+cmd=(
+  sbt
+    -J-Xmx3G
+    -J-XX:+UseG1GC
+    ++$SCALA_VER
+    'set ThisBuild / parallelExecution := false'
+    'set Global / concurrentRestrictions += Tags.limit(ScalaJSTags.Link, 1)'
+    test                                                # Test development-mode
+    'set ThisBuild / scalaJSStage := FullOptStage' test # Test production-mode
+    publishLocal                                        # For downstream tests
+)
+echo "> $(printf "%s\n    " "${cmd[@]}")"
+[[ $dryrun == "-n" ]] || "${cmd[@]}"
+
+# Test downstream
+SCALA_MAJOR_VER="${SCALA_VER:0:1}"
+downstream-tests/run -$SCALA_MAJOR_VER $dryrun
diff --git a/bin/get_scala_version b/bin/get_scala_version
new file mode 100755
index 00000000..153f69e9
--- /dev/null
+++ b/bin/get_scala_version
@@ -0,0 +1,11 @@
+#!/bin/bash
+set -euo pipefail
+cd "$(dirname "$0")/.."
+tmp="$(fgrep " scala$1 " project/Dependencies.scala)"
+r='[^"]*"([^"]*)"[^"]*'
+if [[ "$tmp" =~ $r ]]; then
+  echo "${BASH_REMATCH[1]}"
+else
+  echo "Unable to determine Scala $1 version" >&2
+  exit 3
+fi
diff --git a/build.sbt b/build.sbt
index aa899ac8..2b08041d 100644
--- a/build.sbt
+++ b/build.sbt
@@ -12,8 +12,6 @@ val rootJS            = ScalaCssBuild.rootJS
 
 val coreJVM           = ScalaCssBuild.coreJVM
 val coreJS            = ScalaCssBuild.coreJS
-val elisionTestJVM    = ScalaCssBuild.elisionTestJVM
-val elisionTestJS     = ScalaCssBuild.elisionTestJS
 val extScalatagsJVM   = ScalaCssBuild.extScalatagsJVM
 val extScalatagsJS    = ScalaCssBuild.extScalatagsJS
 val extReact          = ScalaCssBuild.extReact
diff --git a/core/js/src/main/scala-2/scalacss/internal/ModeMacros.scala b/core/js/src/main/scala-2/scalacss/internal/ModeMacros.scala
new file mode 100644
index 00000000..130f58be
--- /dev/null
+++ b/core/js/src/main/scala-2/scalacss/internal/ModeMacros.scala
@@ -0,0 +1,52 @@
+package scalacss.internal
+
+import scala.reflect.macros.whitebox.Context
+import scalacss.defaults._
+
+// ==========================
+// ====                  ====
+// ====   Scala 2 / JS   ====
+// ====                  ====
+// ==========================
+
+object ModeMacros {
+
+  private def readConfig(key: String): Option[String] =
+    (Option(System.getProperty(key, null)) orElse Option(System.getenv(key)))
+      .map(_.trim.toLowerCase)
+      .filter(_.nonEmpty)
+
+  trait DevOrProdDefaults {
+    def devOrProdDefaults: Exports with mutable.Settings =
+      macro ModeMacros.devOrProdDefaults
+  }
+
+  def devOrProdDefaults(c: Context): c.Expr[Exports with mutable.Settings] = {
+    import c.universe._
+
+    def fail(msg: String): Nothing =
+      c.abort(c.enclosingPosition, msg)
+
+    c.Expr[Exports with mutable.Settings](
+      readConfig("scalacss.mode") match {
+
+        case None =>
+          q"""
+            if (_root_.scala.scalajs.LinkingInfo.developmentMode)
+              _root_.scalacss.DevDefaults
+            else
+              _root_.scalacss.ProdDefaults
+          """
+
+        case Some("dev") =>
+          q"_root_.scalacss.DevDefaults"
+
+        case Some("prod") =>
+          q"_root_.scalacss.ProdDefaults"
+
+        case Some(x) =>
+          fail(s"Unrecognise option for scalacss.mode: $x. Legal values are 'dev' and 'prod'.")
+      }
+    )
+  }
+}
diff --git a/core/js/src/main/scala-3/scalacss/internal/ModeMacros.scala b/core/js/src/main/scala-3/scalacss/internal/ModeMacros.scala
new file mode 100644
index 00000000..539835ff
--- /dev/null
+++ b/core/js/src/main/scala-3/scalacss/internal/ModeMacros.scala
@@ -0,0 +1,55 @@
+package scalacss.internal
+
+import scalacss.defaults._
+import scala.language.`3.0`
+import scala.quoted._
+
+// ==========================
+// ====                  ====
+// ====   Scala 3 / JS   ====
+// ====                  ====
+// ==========================
+
+object ModeMacros {
+
+  private def readConfig(key: String): Option[String] =
+    (Option(System.getProperty(key, null)) orElse Option(System.getenv(key)))
+      .map(_.trim.toLowerCase)
+      .filter(_.nonEmpty)
+
+  trait DevOrProdDefaults {
+    transparent inline def devOrProdDefaults: Exports with mutable.Settings =
+      ${ ModeMacros.devOrProdDefaults }
+  }
+
+  def devOrProdDefaults(using Quotes): Expr[Exports with mutable.Settings] = {
+    import quotes.reflect._
+
+    def fail(msg: String): Nothing =
+      report.throwError(msg)
+
+    type S = Exports with mutable.Settings
+    val expr: Expr[S] =
+      readConfig("scalacss.mode") match {
+
+        case None =>
+          '{
+            if (_root_.scala.scalajs.LinkingInfo.developmentMode)
+              _root_.scalacss.DevDefaults
+            else
+              _root_.scalacss.ProdDefaults
+          }
+
+        case Some("dev") =>
+          '{ scalacss.DevDefaults }
+
+        case Some("prod") =>
+          '{ scalacss.ProdDefaults }
+
+        case Some(x) =>
+          fail(s"Unrecognise option for scalacss.mode: $x. Legal values are 'dev' and 'prod'.")
+      }
+
+    Inlined(None, Nil, expr.asTerm).asExprOf[S]
+  }
+}
diff --git a/core/js/src/main/scala/scalacss/internal/Platform.scala b/core/js/src/main/scala/scalacss/internal/Platform.scala
index 4dce0e98..9a2d13ca 100644
--- a/core/js/src/main/scala/scalacss/internal/Platform.scala
+++ b/core/js/src/main/scala/scalacss/internal/Platform.scala
@@ -1,7 +1,5 @@
 package scalacss.internal
 
-import scala.annotation.elidable
-
 // ================
 // ====        ====
 // ====   JS   ====
@@ -10,15 +8,6 @@ import scala.annotation.elidable
 
 object Platform {
 
-  /**
-   * Use the scalac `-Xelide-below` flag to switch from development- to production-mode.
-   */
-  @elidable(elidable.ASSERTION)
-  @inline def DevMode: Boolean =
-    true
-//  @inline def DevMode: Boolean =
-//    scalajs.LinkingInfo.developmentMode
-
   implicit def env: Env =
     Env.empty
 }
diff --git a/core/jvm/src/main/scala-2/scalacss/internal/ModeMacros.scala b/core/jvm/src/main/scala-2/scalacss/internal/ModeMacros.scala
new file mode 100644
index 00000000..bf451144
--- /dev/null
+++ b/core/jvm/src/main/scala-2/scalacss/internal/ModeMacros.scala
@@ -0,0 +1,44 @@
+package scalacss.internal
+
+import scala.reflect.macros.whitebox.Context
+import scalacss.defaults._
+
+// ===========================
+// ====                   ====
+// ====   Scala 2 / JVM   ====
+// ====                   ====
+// ===========================
+
+object ModeMacros {
+
+  private def readConfig(key: String): Option[String] =
+    (Option(System.getProperty(key, null)) orElse Option(System.getenv(key)))
+      .map(_.trim.toLowerCase)
+      .filter(_.nonEmpty)
+
+  trait DevOrProdDefaults {
+    def devOrProdDefaults: Exports with mutable.Settings =
+      macro ModeMacros.devOrProdDefaults
+  }
+
+  def devOrProdDefaults(c: Context): c.Expr[Exports with mutable.Settings] = {
+    import c.universe._
+
+    def fail(msg: String): Nothing =
+      c.abort(c.enclosingPosition, msg)
+
+    c.Expr[Exports with mutable.Settings](
+      readConfig("scalacss.mode") match {
+
+        case Some("dev") | None =>
+          q"_root_.scalacss.DevDefaults"
+
+        case Some("prod") =>
+          q"_root_.scalacss.ProdDefaults"
+
+        case Some(x) =>
+          fail(s"Unrecognise option for scalacss.mode: $x. Legal values are 'dev' and 'prod'.")
+      }
+    )
+  }
+}
diff --git a/core/jvm/src/main/scala-3/scalacss/internal/ModeMacros.scala b/core/jvm/src/main/scala-3/scalacss/internal/ModeMacros.scala
new file mode 100644
index 00000000..04fd09d0
--- /dev/null
+++ b/core/jvm/src/main/scala-3/scalacss/internal/ModeMacros.scala
@@ -0,0 +1,47 @@
+package scalacss.internal
+
+import scalacss.defaults._
+import scala.language.`3.0`
+import scala.quoted._
+
+// ===========================
+// ====                   ====
+// ====   Scala 3 / JVM   ====
+// ====                   ====
+// ===========================
+
+object ModeMacros {
+
+  private def readConfig(key: String): Option[String] =
+    (Option(System.getProperty(key, null)) orElse Option(System.getenv(key)))
+      .map(_.trim.toLowerCase)
+      .filter(_.nonEmpty)
+
+  trait DevOrProdDefaults {
+    transparent inline def devOrProdDefaults: Exports with mutable.Settings =
+      ${ ModeMacros.devOrProdDefaults }
+  }
+
+  def devOrProdDefaults(using Quotes): Expr[Exports with mutable.Settings] = {
+    import quotes.reflect._
+
+    def fail(msg: String): Nothing =
+      report.throwError(msg)
+
+    type S = Exports with mutable.Settings
+    val expr: Expr[S] =
+      readConfig("scalacss.mode") match {
+
+        case Some("dev") | None =>
+          '{ scalacss.DevDefaults }
+
+        case Some("prod") =>
+          '{ scalacss.ProdDefaults }
+
+        case Some(x) =>
+          fail(s"Unrecognise option for scalacss.mode: $x. Legal values are 'dev' and 'prod'.")
+      }
+
+    Inlined(None, Nil, expr.asTerm).asExprOf[S]
+  }
+}
diff --git a/core/jvm/src/main/scala/scalacss/internal/Platform.scala b/core/jvm/src/main/scala/scalacss/internal/Platform.scala
index 6309a31b..8a227a96 100644
--- a/core/jvm/src/main/scala/scalacss/internal/Platform.scala
+++ b/core/jvm/src/main/scala/scalacss/internal/Platform.scala
@@ -1,7 +1,5 @@
 package scalacss.internal
 
-import scala.annotation.elidable
-
 // =================
 // ====         ====
 // ====   JVM   ====
@@ -10,14 +8,6 @@ import scala.annotation.elidable
 
 object Platform {
 
-  /**
-   * Use the scalac `-Xelide-below` flag to switch from development- to production-mode.
-   */
-  @elidable(elidable.ASSERTION)
-  @inline def DevMode: Boolean =
-    true
-
   implicit def env: Env =
     Env.empty
-
 }
diff --git a/core/shared/src/main/scala-2/scalacss/internal/Macros.scala b/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
index 8d0d26d2..d365cf84 100644
--- a/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
+++ b/core/shared/src/main/scala-2/scalacss/internal/Macros.scala
@@ -3,7 +3,6 @@ package scalacss.internal
 import java.util.regex.Pattern
 import scala.reflect.NameTransformer
 import scala.reflect.macros.blackbox.Context
-import scalacss.defaults.Exports
 
 object Macros {
 
@@ -181,21 +180,4 @@ object Macros {
     /** c"#fc6" provides a validates Color */
     def c(args: Any*): Color = macro ColorLiteral.impl
   }
-
-  // ===================================================================================================================
-
-  trait DevOrProdDefaults {
-    def devOrProdDefaults: Exports with mutable.Settings =
-      macro Macros.devOrProdDefaults
-  }
-
-  def devOrProdDefaults(c: Context): c.Expr[Exports with mutable.Settings] = {
-    import c.universe._
-    c.Expr[Exports with mutable.Settings](q"""
-      if (_root_.scalacss.internal.Platform.DevMode)
-        _root_.scalacss.DevDefaults
-      else
-        _root_.scalacss.ProdDefaults
-       """)
-  }
 }
diff --git a/core/shared/src/main/scala-3/scalacss/internal/Macros.scala b/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
index b41b5e7b..f2104ec6 100644
--- a/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
+++ b/core/shared/src/main/scala-3/scalacss/internal/Macros.scala
@@ -1,10 +1,9 @@
 package scalacss.internal
 
 import java.util.regex.Pattern
-import scala.quoted._
-import scalacss.defaults.Exports
 import scala.language.`3.0`
 import scala.reflect.NameTransformer
+import scala.quoted._
 
 object Macros {
 
@@ -239,14 +238,4 @@ object Macros {
         Option(errorResult).getOrElse(Left("Invalid colour: \"" + text0 + "\""))
     }
   }
-
-  // ===================================================================================================================
-
-  trait DevOrProdDefaults {
-    inline final def devOrProdDefaults: Exports with mutable.Settings =
-      if (scalacss.internal.Platform.DevMode)
-        scalacss.DevDefaults
-      else
-        scalacss.ProdDefaults
-  }
 }
diff --git a/core/shared/src/main/scala/scalacss/defaults/DefaultSettings.scala b/core/shared/src/main/scala/scalacss/defaults/DefaultSettings.scala
index dcbccc3d..8e9091cd 100644
--- a/core/shared/src/main/scala/scalacss/defaults/DefaultSettings.scala
+++ b/core/shared/src/main/scala/scalacss/defaults/DefaultSettings.scala
@@ -29,10 +29,4 @@ object DefaultSettings {
     override implicit def cssStringRenderer      : Renderer[String] = StringRenderer.formatTiny
     override implicit def cssComposition         : Compose          = Compose.trust
   }
-
-  def devOrProd: Settings =
-    if (Platform.DevMode)
-      Dev
-    else
-      Prod
 }
diff --git a/core/shared/src/main/scala/scalacss/package.scala b/core/shared/src/main/scala/scalacss/package.scala
index 0e02920a..fb279631 100644
--- a/core/shared/src/main/scala/scalacss/package.scala
+++ b/core/shared/src/main/scala/scalacss/package.scala
@@ -1,6 +1,6 @@
 package object scalacss
     extends scalacss.defaults.Exports
-       with internal.Macros.DevOrProdDefaults {
+       with internal.ModeMacros.DevOrProdDefaults {
 
   import defaults.{DefaultSettings, Exports}
 
diff --git a/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala b/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala
index c93a7b53..0c0028eb 100644
--- a/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala
+++ b/core/shared/src/test/scala/scalacss/full/DefaultsTest.scala
@@ -2,17 +2,13 @@ package scalacss.full
 
 import japgolly.microlibs.testutil.TestUtil._
 import scalacss._
-import scalacss.internal.Platform
 import utest._
 
 object DefaultsTest extends TestSuite {
 
   override def tests = Tests {
-    "platform" - assert(Platform.DevMode)
-    "defaults" - assert(devOrProdDefaults eq DevDefaults)
-
-    "dev"     - Dev .test()
-    "prod"    - Prod.test()
+    "dev"  - Dev .test()
+    "prod" - Prod.test()
   }
 
   class SharedStyles(implicit reg: StyleSheet.Register) extends StyleSheet.Inline {
diff --git a/doc/features/basics.md b/doc/features/basics.md
index 1e560030..26a59718 100644
--- a/doc/features/basics.md
+++ b/doc/features/basics.md
@@ -6,7 +6,10 @@ The first thing you'll want to do is import some settings by using one of these
 import scalacss.DevDefaults._  // Always use dev settings
 import scalacss.ProdDefaults._ // Always use prod settings
 
-// This will choose between dev/prod depending on your scalac `-Xelide-below` setting
+// This will choose between dev/prod depending on:
+//   1. `sbt -Dscalacss.mode=dev` or `sbt -Dscalacss.mode=prod`
+//   2. Defaults to dev-mode unless in `fullOptJS`
+//
 val CssSettings = scalacss.devOrProdDefaults
 import CssSettings._
 ```
@@ -20,20 +23,6 @@ Error handling        | Print to `stderr` | Ignore
 Class name generation | `.<class>-<val>` <br/> Eg. `.MyStyles-outer` | `._a0` <br/> `._a1` <br/> etc
 CSS output            | Pretty-print. <br/> Indents, spaces, newlines. | Minified. <br/> No whitespace.
 
-`Defaults` will choose a mode to use based on its `devMode: Boolean` method
-which uses
-[elision](http://www.scala-lang.org/api/current/scala/annotation/elidable.html)
-to determine production-mode.
-
-For instance, in my production SBT settings I generally have:
-
-```scala
-// Prod settings
-scalacOptions ++= Seq("-Xelide-below", "OFF")
-```
-
-_Note: `-Xelide-below OFF` doesn't turn eliding off, it means "elide everything". There must've been painting going on in the building with no windows open when that was named._
-
 Defaults aren't mandatory, you're free to customise as needed.
 (See [DefaultSettings.scala](https://github.com/japgolly/scalacss/blob/master/core/shared/src/main/scala/scalacss/defaults/DefaultSettings.scala).)
 
diff --git a/doc/history/0.8.md b/doc/history/0.8.md
index d0f2efa9..28adca32 100644
--- a/doc/history/0.8.md
+++ b/doc/history/0.8.md
@@ -1,4 +1,9 @@
 # 0.8.0 ([commit log](https://github.com/japgolly/scalacss/compare/v0.7.0..v0.8.0-RC1))
 
 * Add support for Scala 3 (`scalatags` module excepted)
+
+* Changed how `scalacss.devOrProdDefaults` works:
+  * You can now control it via `sbt -Dscalacss.mode=dev` or `sbt -Dscalacss.mode=prod`
+  * Defaults to dev-mode unless in `fullOptJS`
+
 * Upgrade deps
diff --git a/downstream-tests/build.sbt b/downstream-tests/build.sbt
new file mode 100644
index 00000000..26cfcad3
--- /dev/null
+++ b/downstream-tests/build.sbt
@@ -0,0 +1,119 @@
+import java.util.Properties
+import org.scalajs.linker.interface._
+import Dependencies._
+import Lib._
+
+ThisBuild / organization := "scalacss-test"
+ThisBuild / shellPrompt  := ((s: State) => Project.extract(s).currentRef.project + "> ")
+
+def scalacCommonFlags: Seq[String] = Seq(
+  "-deprecation",
+  "-feature",
+  "-language:postfixOps",
+  "-language:implicitConversions",
+  "-language:higherKinds",
+  "-language:existentials",
+  "-unchecked",
+)
+
+def scalac2Flags = Seq(
+  "-Wconf:msg=may.not.be.exhaustive:e",            // Make non-exhaustive matches errors instead of warnings
+  "-Wconf:msg=Reference.to.uninitialized.value:e", // Make uninitialised value calls errors instead of warnings
+  "-Wunused:explicits",                            // Warn if an explicit parameter is unused.
+  "-Wunused:implicits",                            // Warn if an implicit parameter is unused.
+  "-Wunused:imports",                              // Warn if an import selector is not referenced.
+  "-Wunused:locals",                               // Warn if a local definition is unused.
+  "-Wunused:nowarn",                               // Warn if a @nowarn annotation does not suppress any warnings.
+  "-Wunused:patvars",                              // Warn if a variable bound in a pattern is unused.
+  "-Wunused:privates",                             // Warn if a private member is unused.
+  "-Xlint:adapted-args",                           // An argument list was modified to match the receiver.
+  "-Xlint:constant",                               // Evaluation of a constant arithmetic expression resulted in an error.
+  "-Xlint:delayedinit-select",                     // Selecting member of DelayedInit.
+  "-Xlint:deprecation",                            // Enable -deprecation and also check @deprecated annotations.
+  "-Xlint:eta-zero",                               // Usage `f` of parameterless `def f()` resulted in eta-expansion, not empty application `f()`.
+  "-Xlint:implicit-not-found",                     // Check @implicitNotFound and @implicitAmbiguous messages.
+  "-Xlint:inaccessible",                           // Warn about inaccessible types in method signatures.
+  "-Xlint:infer-any",                              // A type argument was inferred as Any.
+  "-Xlint:missing-interpolator",                   // A string literal appears to be missing an interpolator id.
+  "-Xlint:nonlocal-return",                        // A return statement used an exception for flow control.
+  "-Xlint:nullary-unit",                           // `def f: Unit` looks like an accessor; add parens to look side-effecting.
+  "-Xlint:option-implicit",                        // Option.apply used an implicit view.
+  "-Xlint:poly-implicit-overload",                 // Parameterized overloaded implicit methods are not visible as view bounds.
+  "-Xlint:private-shadow",                         // A private field (or class parameter) shadows a superclass field.
+  "-Xlint:stars-align",                            // In a pattern, a sequence wildcard `_*` should match all of a repeated parameter.
+  "-Xlint:valpattern",                             // Enable pattern checks in val definitions.
+  "-Xmixin-force-forwarders:false",                // Only generate mixin forwarders required for program correctness.
+  "-Yjar-compression-level", "9",                  // compression level to use when writing jar files
+  "-Ymacro-annotations",                           // Enable support for macro annotations, formerly in macro paradise.
+  "-Ypatmat-exhaust-depth", "off",
+)
+
+def scalac3Flags = Seq(
+  "-source:3.0-migration",
+)
+
+def commonSettings: Project => Project = _
+  .configure(preventPublication)
+  .settings(
+    scalaVersion       := Ver.scala2,
+    crossScalaVersions := Seq(Ver.scala2, Ver.scala3),
+    scalacOptions     ++= scalacCommonFlags,
+    scalacOptions     ++= scalac2Flags.filter(_ => scalaVersion.value.startsWith("2")),
+    scalacOptions     ++= scalac3Flags.filter(_ => scalaVersion.value.startsWith("3")),
+  )
+
+lazy val cleanTestAll = taskKey[Unit]("cleanTestAll")
+
+lazy val root = Project("root", file("."))
+  .configure(commonSettings)
+  .aggregate(jvm, js)
+  .settings(
+    cleanTestAll := (
+      Def.sequential(
+        jvm           / clean,
+        js            / clean,
+                 Test / compile,
+        jvm    / Test / test,
+        js     / Test / test,
+      ).value
+    ),
+  )
+
+val useFullOptJS = System.getProperty("downstream_tests.fullOptJS") != null
+val jsStage      = if (useFullOptJS) FullOptStage else FastOptStage
+val jsOptKey     = if (useFullOptJS) fullOptJS else fastOptJS
+
+lazy val jvm = project
+  .in(file("jvm"))
+  .configure(commonSettings, utestSettings.jvm)
+  .settings(
+    libraryDependencies ++= Seq(
+      Dep.microlibsTestUtil.value % Test,
+    ),
+    Test / fork := true,
+    Test / javaOptions ++=
+      sys.props.iterator
+        .filter(_._1.matches("(downstream_tests|japgolly|scalacss).*"))
+        .map(x => s"-D${x._1}=${x._2}")
+        .toSeq,
+    Test / javaOptions += {
+      val jsFile = (js / Compile / jsOptKey).value
+      s"-Djs_file=${jsFile.data.absolutePath}"
+    },
+  )
+
+lazy val js = project
+  .in(file("js"))
+  .enablePlugins(ScalaJSPlugin)
+  .configure(commonSettings, utestSettings.js)
+  .settings(
+    scalaJSStage := jsStage,
+    libraryDependencies ++= {
+      val ver = version.value.stripSuffix("-SNAPSHOT") + "-SNAPSHOT"
+      Seq(
+        "com.github.japgolly.scalacss" %%% "core" % ver,
+        Dep.microlibsCompileTime.value % Test,
+        Dep.microlibsTestUtil.value % Test,
+      )
+    },
+  )
diff --git a/downstream-tests/js/src/main/scala/downstream/Main.scala b/downstream-tests/js/src/main/scala/downstream/Main.scala
new file mode 100644
index 00000000..e74c5ca4
--- /dev/null
+++ b/downstream-tests/js/src/main/scala/downstream/Main.scala
@@ -0,0 +1,10 @@
+package downstream
+
+import scala.scalajs.js.annotation._
+
+@JSExportTopLevel("MAIN")
+object Main {
+
+  @JSExport
+  val CssSettings = scalacss.devOrProdDefaults
+}
diff --git a/downstream-tests/js/src/test/scala/downstream/RuntimeTest.scala b/downstream-tests/js/src/test/scala/downstream/RuntimeTest.scala
new file mode 100644
index 00000000..0ac93138
--- /dev/null
+++ b/downstream-tests/js/src/test/scala/downstream/RuntimeTest.scala
@@ -0,0 +1,27 @@
+package downstream
+
+import japgolly.microlibs.compiletime.CompileTimeInfo
+import japgolly.microlibs.testutil.TestUtil._
+import scalacss._
+import utest._
+
+object RuntimeTest extends TestSuite {
+
+  val mode       = CompileTimeInfo.sysProp("scalacss.mode")
+  val expectProd = CompileTimeInfo.sysProp("downstream_tests.expect.prod").contains("1")
+
+  override def tests = Tests {
+
+    "settings" - {
+
+      "isDev" - assertEq(
+        actual = (Main.CssSettings: AnyRef) eq DevDefaults,
+        expect = !expectProd)
+
+      "isProd" - assertEq(
+        actual = (Main.CssSettings: AnyRef) eq ProdDefaults,
+        expect = expectProd)
+    }
+
+  }
+}
diff --git a/downstream-tests/jvm/src/test/scala/downstream/JsOutputTest.scala b/downstream-tests/jvm/src/test/scala/downstream/JsOutputTest.scala
new file mode 100644
index 00000000..f2af2c8d
--- /dev/null
+++ b/downstream-tests/jvm/src/test/scala/downstream/JsOutputTest.scala
@@ -0,0 +1,53 @@
+package downstream
+
+import japgolly.microlibs.testutil.TestUtil._
+import japgolly.microlibs.testutil.TestUtilInternals._
+import scala.Console._
+import sourcecode.Line
+import utest._
+
+object JsOutputTest extends TestSuite {
+  import Props._
+
+  private def fgrep(term: String): Unit = {
+    println(s"> fgrep '$term'")
+    content
+      .linesIterator
+      .zipWithIndex
+      .filter(_._1.contains(term))
+      .map { case (s, l) => s"$GREEN$l:$RESET " + s.replace(term, MAGENTA_B + WHITE + term + RESET) }
+      .foreach(println)
+  }
+
+  private def contentTest(substrToExpect: (String, Boolean)*)(implicit l: Line): Unit = {
+    System.out.flush()
+    System.err.flush()
+    var errors = List.empty[String]
+    for ((substr, expect) <- substrToExpect) {
+      val actual = content.contains(substr)
+      val pass   = actual == expect
+      val result = if (pass) s"${GREEN}pass$RESET" else s"${RED_B}${WHITE}FAIL$RESET"
+      val should = if (expect) "should" else "shouldn't"
+      val strCol = if (expect) (GREEN + BRIGHT_GREEN) else BRIGHT_BLACK
+      println(s"[$result] JS $should contain $strCol$substr$RESET")
+      if (!pass) errors ::= s"JS $should contain $substr"
+    }
+    System.out.flush()
+    if (errors.nonEmpty) {
+      for ((substr, _) <- substrToExpect)
+        fgrep(substr)
+      fail(errors.sorted.mkString(", "))
+    }
+  }
+
+  override def tests = Tests {
+
+    "size" - "%,d bytes".format(content.length)
+
+    "defaults" - contentTest(
+      "DevDefaults"  -> !expectProd,
+      "ProdDefaults" -> expectProd,
+    )
+
+  }
+}
diff --git a/downstream-tests/jvm/src/test/scala/downstream/Props.scala b/downstream-tests/jvm/src/test/scala/downstream/Props.scala
new file mode 100644
index 00000000..bf2678eb
--- /dev/null
+++ b/downstream-tests/jvm/src/test/scala/downstream/Props.scala
@@ -0,0 +1,34 @@
+package downstream
+
+import java.io.File
+import scala.Console._
+import scala.io.Source
+
+object Props {
+
+  private object Prop {
+    def get(property: String): Option[String] = {
+      val o = Option(System.getProperty(property))
+      println(s"$CYAN$property$RESET = $YELLOW${o.getOrElse("")}$RESET")
+      o
+    }
+
+    def get(property: String, default: String): String =
+      get(property).getOrElse(default)
+
+    def need(property: String): String =
+      get(property).getOrElse(throw new RuntimeException("Property not defined: " + property))
+  }
+
+  val jsFilename = Prop.need("js_file")
+
+  val fastOptJS = jsFilename.contains("fast")
+
+  val content: String = {
+    val s = Source.fromFile(new File(jsFilename))
+    try s.mkString finally s.close()
+  }
+
+  val mode       = Prop.get("scalacss.mode")
+  val expectProd = Prop.get("downstream_tests.expect.prod").contains("1")
+}
diff --git a/downstream-tests/project/Dependencies.scala b/downstream-tests/project/Dependencies.scala
new file mode 120000
index 00000000..921dece9
--- /dev/null
+++ b/downstream-tests/project/Dependencies.scala
@@ -0,0 +1 @@
+../../project/Dependencies.scala
\ No newline at end of file
diff --git a/downstream-tests/project/Lib.scala b/downstream-tests/project/Lib.scala
new file mode 120000
index 00000000..b6d6acc2
--- /dev/null
+++ b/downstream-tests/project/Lib.scala
@@ -0,0 +1 @@
+../../project/Lib.scala
\ No newline at end of file
diff --git a/downstream-tests/project/build.properties b/downstream-tests/project/build.properties
new file mode 120000
index 00000000..5b4fb9be
--- /dev/null
+++ b/downstream-tests/project/build.properties
@@ -0,0 +1 @@
+../../project/build.properties
\ No newline at end of file
diff --git a/downstream-tests/project/plugins.sbt b/downstream-tests/project/plugins.sbt
new file mode 120000
index 00000000..ed05ef9c
--- /dev/null
+++ b/downstream-tests/project/plugins.sbt
@@ -0,0 +1 @@
+../../project/plugins.sbt
\ No newline at end of file
diff --git a/downstream-tests/run b/downstream-tests/run
new file mode 100755
index 00000000..c1491a11
--- /dev/null
+++ b/downstream-tests/run
@@ -0,0 +1,130 @@
+#!/bin/bash
+set -euo pipefail
+cd "$(dirname "$0")" || exit 1
+
+# "Skip Scala 2"
+skip2=skip2
+
+# Tests
+all_tests_values=(
+  "-Ddownstream_tests.expect.prod=0"
+  "-Ddownstream_tests.expect.prod=0 -Dscalacss.mode=dev"
+  "-Ddownstream_tests.expect.prod=1 -Dscalacss.mode=prod"
+  "-Ddownstream_tests.expect.prod=1 -Ddownstream_tests.fullOptJS"
+  "-Ddownstream_tests.expect.prod=0 -Ddownstream_tests.fullOptJS -Dscalacss.mode=dev"
+  "-Ddownstream_tests.expect.prod=1 -Ddownstream_tests.fullOptJS -Dscalacss.mode=prod"
+)
+all_tests_keys=()
+declare -A all_tests
+i=0
+for t in "${all_tests_values[@]}"; do
+  i=$((i+1))
+  all_tests_keys+=($i)
+  all_tests[$i]="$t"
+done
+
+# Parse options
+dryrun=0
+filter=0
+parse=1
+while [ $parse -eq 1 ]; do
+  case "${1:-}" in
+    -h|-help|--help)
+      echo "Usage: $0 [-2 | -3] [-n] [<test number>...]"
+      echo
+      echo "Options:"
+      echo "  -2  --  Only run Scala 2 tests."
+      echo "  -3  --  Only run Scala 3 tests."
+      echo "  -n  --  Dry-run."
+      echo
+      echo "Tests:"
+      for n in "${all_tests_keys[@]}"; do
+        echo "  $n) ${all_tests[$n]}"
+      done
+      echo
+      exit 0
+      ;;
+    -2)
+      if [ $filter -eq 3 ]; then
+        filter=0
+      else
+        filter=2
+      fi
+      shift
+      ;;
+    -3)
+      if [ $filter -eq 2 ]; then
+        filter=0
+      else
+        filter=3
+      fi
+      shift
+      ;;
+    -n)
+      dryrun=1
+      shift
+      ;;
+    *)
+      parse=0
+      ;;
+  esac
+done
+
+# Decide which tests to run
+tests=("${all_tests_keys[@]}")
+if [ $# -ne 0 ]; then
+  tests=("$@")
+fi
+
+# Make sure all declared tests actually exist
+all_good=1
+for t in "${tests[@]}"; do
+  if [ "${all_tests[$t]-x}" = x ]; then
+    echo "Invalid test: $t" >&2
+    all_good=0
+  fi
+done
+[ $all_good -eq 1 ] || exit 2
+
+# Get Scala versions
+scalaVer2="$(../bin/get_scala_version 2)"
+scalaVer3="$(../bin/get_scala_version 3)"
+
+# Declare test runner
+function run {
+  local args="$1"
+  local s2=1
+  local s3=1
+  if [[ "$args" == *"$skip2"* ]]; then
+    args="${args/$skip2/}"
+    s2=0
+  fi
+  # echo "$filter/$s2/$s3 [$args]"
+  local task=cleanTestAll
+  local sbt_cmds=()
+  if [[ "$filter-$s3" =~ [03]-1 ]]; then
+    sbt_cmds+=( ++$scalaVer3 $task )
+  fi
+  if [[ "$filter-$s2" =~ [02]-1 ]]; then
+    sbt_cmds+=( ++$scalaVer2 $task )
+  fi
+  if [ "${#sbt_cmds[@]}" -eq 0 ]; then
+    echo "Skipped."
+  else
+    local cmd=(sbt --warn $args "${sbt_cmds[@]}")
+    echo "> ${cmd[@]}"
+    [ $dryrun -eq 1 ] || "${cmd[@]}"
+  fi
+}
+
+# Run all tests
+sep="==================================================================================================="
+i=0
+for t in "${tests[@]}"; do
+  i=$((i+1))
+  echo "$sep"
+  echo "[$i/${#tests[@]}] Test #$t"
+  run "${all_tests[$t]}"
+done
+echo "$sep"
+echo "Done. All tests passed."
diff --git a/downstream-tests/version.sbt b/downstream-tests/version.sbt
new file mode 120000
index 00000000..868dd38f
--- /dev/null
+++ b/downstream-tests/version.sbt
@@ -0,0 +1 @@
+../version.sbt
\ No newline at end of file
diff --git a/elision-test/shared/src/test/scala/scalacss/elision/DefaultsTest.scala b/elision-test/shared/src/test/scala/scalacss/elision/DefaultsTest.scala
deleted file mode 100644
index b5cf0973..00000000
--- a/elision-test/shared/src/test/scala/scalacss/elision/DefaultsTest.scala
+++ /dev/null
@@ -1,34 +0,0 @@
-package scalacss.elision
-
-import scala.annotation.{elidable, nowarn}
-import scalacss._
-import scalacss.internal.Platform
-import utest._
-
-object DefaultsTest extends TestSuite {
-
-  def assert(ok: Boolean, msg: String) =
-    if (!ok) fail(msg)
-
-  def fail(msg: String) = {
-    val e = new java.lang.AssertionError(msg)
-    e.setStackTrace(Array.empty)
-    throw e
-  }
-
-  override def tests = Tests {
-
-    "elision" - {
-      var on = false
-
-      @elidable(elidable.ASSERTION)
-      @nowarn("cat=unused")
-      def test(): Unit = on = true
-
-      assert(!on, "ELISION")
-    }
-
-    "platform" - assert(!Platform.DevMode, "PLATFORM")
-    "defaults" - assert(devOrProdDefaults eq ProdDefaults, "DEFAULTS")
-  }
-}
diff --git a/project/Build.scala b/project/Build.scala
index e94a33d6..51642de7 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -4,7 +4,6 @@ import com.jsuereth.sbtpgp.PgpKeys
 import org.portablescala.sbtplatformdeps.PlatformDepsPlugin.autoImport._
 import org.scalajs.jsdependencies.sbtplugin.JSDependenciesPlugin
 import org.scalajs.jsdependencies.sbtplugin.JSDependenciesPlugin.autoImport._
-import org.scalajs.jsenv.jsdomnodejs.JSDOMNodeJSEnv
 import org.scalajs.sbtplugin.ScalaJSPlugin
 import org.scalajs.sbtplugin.ScalaJSPlugin.autoImport._
 import sbtcrossproject.CrossPlugin.autoImport.{crossProject, _}
@@ -59,38 +58,6 @@ object ScalaCssBuild {
       releaseTagComment             := s"v${(ThisBuild / version).value}",
       releaseVcsSign                := true))
 
-  def definesMacros = ConfigureBoth(
-    _.settings(
-      scalacOptions ++= {
-        if (scalaVersion.value.startsWith("2"))
-          "-language:experimental.macros" :: Nil
-        else
-          Nil
-      },
-      libraryDependencies ++=  {
-        if (scalaVersion.value.startsWith("2"))
-          List(
-            Dep.scalaReflect.value,
-            Dep.scalaCompiler.value % Provided,
-          )
-        else
-          Nil
-      },
-    )
-  )
-
-  def utestSettings = ConfigureBoth(
-    _.settings(
-      libraryDependencies ++= Seq(
-        Dep.utest.value % Test,
-        Dep.microlibsTestUtil.value % Test,
-      ),
-      testFrameworks := Seq(new TestFramework("utest.runner.Framework")),
-    )
-  ).jsConfigure(
-    _.settings(jsEnv := new JSDOMNodeJSEnv)
-  )
-
   // ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 
   lazy val root =
@@ -101,12 +68,12 @@ object ScalaCssBuild {
   lazy val rootJVM =
     Project("JVM", file(".rootJVM"))
       .configure(commonSettings.jvm, preventPublication)
-      .aggregate(coreJVM, elisionTestJVM, extScalatagsJVM)
+      .aggregate(coreJVM, extScalatagsJVM)
 
   lazy val rootJS =
     Project("JS", file(".rootJS"))
       .configure(commonSettings.jvm, preventPublication)
-      .aggregate(coreJS, elisionTestJS, extScalatagsJS, extReact)
+      .aggregate(coreJS, extScalatagsJS, extReact)
 
   // ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 
@@ -134,17 +101,6 @@ object ScalaCssBuild {
       initialCommands := "import scalacss._",
     )
 
-  lazy val elisionTestJVM = elisionTest.jvm
-  lazy val elisionTestJS  = elisionTest.js
-  lazy val elisionTest = crossProject(JSPlatform, JVMPlatform)
-    .in(file("elision-test"))
-    .configureCross(commonSettings, utestSettings)
-    .configure(preventPublication, onlyScala2)
-    .dependsOn(core)
-    .settings(
-      scalacOptions ++= Seq("-Xelide-below", "OFF"),
-    )
-
   lazy val extScalatagsJVM = extScalatags.jvm
   lazy val extScalatagsJS  = extScalatags.js
   lazy val extScalatags = crossProject(JSPlatform, JVMPlatform)
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 1beddf9c..2a441fb7 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -25,21 +25,22 @@ object Dependencies {
   }
 
   object Dep {
-    val cats                = Def.setting("org.typelevel"                     %%% "cats-core"               % Ver.cats)
-    val microlibsTestUtil   = Def.setting("com.github.japgolly.microlibs"     %%% "test-util"               % Ver.microlibs)
-    val nyayaGen            = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-gen"               % Ver.nyaya)
-    val nyayaProp           = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-prop"              % Ver.nyaya)
-    val nyayaTest           = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-test"              % Ver.nyaya)
-    val scalaCompiler       = Def.setting("org.scala-lang"                      % "scala-compiler"          % scalaVersion.value)
-    val scalaJsDom          = Def.setting("org.scala-js"                      %%% "scalajs-dom"             % Ver.scalaJsDom cross CrossVersion.for3Use2_13)
-    val scalaJsReactCore    = Def.setting("com.github.japgolly.scalajs-react" %%% "core"                    % Ver.scalaJsReact)
-    val scalaJsReactCoreGen = Def.setting("com.github.japgolly.scalajs-react" %%% "core-generic"            % Ver.scalaJsReact)
-    val scalaJsReactDummy   = Def.setting("com.github.japgolly.scalajs-react" %%% "util-dummy-defaults"     % Ver.scalaJsReact)
-    val scalaJsReactTest    = Def.setting("com.github.japgolly.scalajs-react" %%% "test"                    % Ver.scalaJsReact)
-    val scalaReflect        = Def.setting("org.scala-lang"                      % "scala-reflect"           % scalaVersion.value)
-    val scalatags           = Def.setting("com.lihaoyi"                       %%% "scalatags"               % Ver.scalatags cross CrossVersion.for3Use2_13)
-    val univEq              = Def.setting("com.github.japgolly.univeq"        %%% "univeq"                  % Ver.univEq)
-    val utest               = Def.setting("com.lihaoyi"                       %%% "utest"                   % Ver.utest)
+    val cats                 = Def.setting("org.typelevel"                     %%% "cats-core"               % Ver.cats)
+    val microlibsCompileTime = Def.setting("com.github.japgolly.microlibs"     %%% "compile-time"            % Ver.microlibs)
+    val microlibsTestUtil    = Def.setting("com.github.japgolly.microlibs"     %%% "test-util"               % Ver.microlibs)
+    val nyayaGen             = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-gen"               % Ver.nyaya)
+    val nyayaProp            = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-prop"              % Ver.nyaya)
+    val nyayaTest            = Def.setting("com.github.japgolly.nyaya"         %%% "nyaya-test"              % Ver.nyaya)
+    val scalaCompiler        = Def.setting("org.scala-lang"                      % "scala-compiler"          % scalaVersion.value)
+    val scalaJsDom           = Def.setting("org.scala-js"                      %%% "scalajs-dom"             % Ver.scalaJsDom cross CrossVersion.for3Use2_13)
+    val scalaJsReactCore     = Def.setting("com.github.japgolly.scalajs-react" %%% "core"                    % Ver.scalaJsReact)
+    val scalaJsReactCoreGen  = Def.setting("com.github.japgolly.scalajs-react" %%% "core-generic"            % Ver.scalaJsReact)
+    val scalaJsReactDummy    = Def.setting("com.github.japgolly.scalajs-react" %%% "util-dummy-defaults"     % Ver.scalaJsReact)
+    val scalaJsReactTest     = Def.setting("com.github.japgolly.scalajs-react" %%% "test"                    % Ver.scalaJsReact)
+    val scalaReflect         = Def.setting("org.scala-lang"                      % "scala-reflect"           % scalaVersion.value)
+    val scalatags            = Def.setting("com.lihaoyi"                       %%% "scalatags"               % Ver.scalatags cross CrossVersion.for3Use2_13)
+    val univEq               = Def.setting("com.github.japgolly.univeq"        %%% "univeq"                  % Ver.univEq)
+    val utest                = Def.setting("com.lihaoyi"                       %%% "utest"                   % Ver.utest)
   }
 
   def addReactJsDependencies(scope: Configuration): Project => Project =
diff --git a/project/Lib.scala b/project/Lib.scala
index 2dad17f5..870bccbd 100644
--- a/project/Lib.scala
+++ b/project/Lib.scala
@@ -1,11 +1,13 @@
 import sbt._
 import Keys._
 import com.jsuereth.sbtpgp.PgpKeys._
+import org.scalajs.jsenv.jsdomnodejs.JSDOMNodeJSEnv
 import org.scalajs.sbtplugin.ScalaJSPlugin.autoImport._
 import sbtcrossproject.CrossPlugin.autoImport._
 import sbtcrossproject.CrossProject
 import scalajscrossproject.ScalaJSCrossPlugin.autoImport._
 import xerial.sbt.Sonatype.autoImport._
+import Dependencies._
 
 object Lib {
   type CPE = CrossProject => CrossProject
@@ -88,4 +90,36 @@ object Lib {
     )
   }
 
+  def definesMacros = ConfigureBoth(
+    _.settings(
+      scalacOptions ++= {
+        if (scalaVersion.value.startsWith("2"))
+          "-language:experimental.macros" :: Nil
+        else
+          Nil
+      },
+      libraryDependencies ++=  {
+        if (scalaVersion.value.startsWith("2"))
+          List(
+            Dep.scalaReflect.value,
+            Dep.scalaCompiler.value % Provided,
+          )
+        else
+          Nil
+      },
+    )
+  )
+
+  def utestSettings = ConfigureBoth(
+    _.settings(
+      libraryDependencies ++= Seq(
+        Dep.utest.value % Test,
+        Dep.microlibsTestUtil.value % Test,
+      ),
+      testFrameworks := Seq(new TestFramework("utest.runner.Framework")),
+    )
+  ).jsConfigure(
+    _.settings(jsEnv := new JSDOMNodeJSEnv)
+  )
+
 }