Add using python directive

modules/build/src/main/scala/scala/build/preprocessing/ScalaPreprocessor.scala

@@ -55,6 +55,7 @@ case object ScalaPreprocessor extends Preprocessor {
     UsingPlatformDirectiveHandler,
     UsingPublishContextualDirectiveHandler,
     UsingPublishDirectiveHandler,
+    UsingPythonDirectiveHandler,
     UsingRepositoryDirectiveHandler,
     UsingResourcesDirectiveHandler,
     UsingScalaJsOptionsDirectiveHandler,

modules/directives/src/main/scala/scala/build/preprocessing/directives/UsingPythonDirectiveHandler.scala

@@ -0,0 +1,40 @@
+package scala.build.preprocessing.directives
+import scala.build.Logger
+import scala.build.errors.BuildException
+import scala.build.options.{BuildOptions, MaybeScalaVersion, PostBuildOptions, ScalaOptions}
+
+case object UsingPythonDirectiveHandler extends UsingDirectiveHandler {
+  def name = "Python"
+
+  def description = "Enable Python support"
+
+  def usage = "//> using python"
+
+  override def usageMd = "`//> using python"
+
+  override def examples = Seq(
+    "//> using python"
+  )
+
+  def keys = Seq("python")
+
+  override def isRestricted = true
+
+  def handleValues(
+    scopedDirective: ScopedDirective,
+    logger: Logger
+  ): Either[BuildException, ProcessedUsingDirective] = {
+    val options = BuildOptions(
+      notForBloopOptions = PostBuildOptions(
+        python = Some(true)
+      )
+    )
+    Right(ProcessedDirective(Some(options), Nil))
+  }
+
+  override def getSupportedTypes(key: String) =
+    Set()
+  override protected def getValueNumberBounds(key: String): UsingDirectiveValueNumberBounds =
+    UsingDirectiveValueNumberBounds(0, 0)
+
+}

modules/integration/src/test/scala/scala/cli/integration/RunTestDefinitions.scala

@@ -2455,24 +2455,42 @@ abstract class RunTestDefinitions(val scalaVersionOpt: Option[String])
     if (actualScalaVersion.startsWith("2.13.")) ""
     else "import me.shadaj.scalapy.py" + System.lineSeparator()
 
-  test("scalapy") {
+  def scalapyTest(useDirective: Boolean): Unit = {
+    val maybeDirective =
+      if (useDirective)
+        """//> using python
+          |""".stripMargin
+      else
+        ""
+    val maybeCliArg =
+      if (useDirective) Nil
+      else Seq("--python")
     val inputs = TestInputs(
-      os.rel / "helloscalapy.sc" ->
-        s"""$maybeScalapyPrefix
-           |import py.SeqConverters
-           |val len = py.Dynamic.global.len(List(0, 2, 3).toPythonProxy)
-           |println(s"Length is $$len")
-           |""".stripMargin
+      os.rel / "helloscalapy.sc" -> {
+        maybeDirective +
+          s"""$maybeScalapyPrefix
+             |import py.SeqConverters
+             |val len = py.Dynamic.global.len(List(0, 2, 3).toPythonProxy)
+             |println(s"Length is $$len")
+             |""".stripMargin
+      }
     )
 
     inputs.fromRoot { root =>
-      val res    = os.proc(TestUtil.cli, "run", extraOptions, ".", "--python").call(cwd = root)
+      val res    = os.proc(TestUtil.cli, "run", extraOptions, ".", maybeCliArg).call(cwd = root)
       val output = res.out.trim()
       val expectedOutput = "Length is 3"
       expect(output == expectedOutput)
     }
   }
 
+  test("scalapy from CLI") {
+    scalapyTest(useDirective = false)
+  }
+  test("scalapy via directive") {
+    scalapyTest(useDirective = true)
+  }
+
   if (actualScalaVersion.startsWith("2.12."))
     test("verify that Scala version 2.12.x < 2.12.4 is respected and compiles correctly") {
       TestInputs(os.rel / "s.sc" -> "println(util.Properties.versionNumberString)").fromRoot {

website/docs/reference/directives.md

@@ -180,6 +180,15 @@ Set contextual parameters for publishing
 
 `//> using publish.secretKey "env:PUBLISH_SECRET_KEY"`
 
+### Python
+
+Enable Python support
+
+`//> using python
+
+#### Examples
+`//> using python`
+
 ### Repository
 
 Add a repository for dependency resolution