Fix using directives not working with the shebang line in .scala files (#1639)

Author: Gedochao

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

@@ -187,8 +187,9 @@ case object ScalaPreprocessor extends Preprocessor {
     maybeRecoverOnError: BuildException => Option[BuildException],
     allowRestrictedFeatures: Boolean
   ): Either[BuildException, Option[ProcessingOutput]] = either {
+    val (contentWithNoShebang, _) = SheBang.ignoreSheBangLines(content)
     val extractedDirectives = value(ExtractedDirectives.from(
-      content.toCharArray,
+      contentWithNoShebang.toCharArray,
       path,
       logger,
       UsingDirectiveKind.values(),

modules/build/src/test/scala/scala/build/tests/ScalaPreprocessorTests.scala

@@ -0,0 +1,51 @@
+package scala.build.tests
+
+import com.eed3si9n.expecty.Expecty.expect
+
+import scala.build.input.SourceScalaFile
+import scala.build.preprocessing.{PreprocessedSource, ScalaPreprocessor}
+
+class ScalaPreprocessorTests extends munit.FunSuite {
+
+  test("should respect using directives in a .scala file with the shebang line") {
+    TestInputs(os.rel / "Main.scala" ->
+      """#!/usr/bin/env -S scala-cli shebang
+        |//> using lib "com.lihaoyi::os-lib::0.8.1"
+        |
+        |object Main {
+        |  def main(args: Array[String]): Unit = {
+        |    println(os.pwd)
+        |  }
+        |}""".stripMargin).fromRoot { root =>
+      val scalaFile = SourceScalaFile(root, os.sub / "Main.scala")
+      val Some(Right(result)) = ScalaPreprocessor.preprocess(
+        scalaFile,
+        logger = TestLogger(),
+        allowRestrictedFeatures = false
+      )
+      expect(result.nonEmpty)
+      val Some(directivesPositions) = result.head.directivesPositions
+      expect(directivesPositions.specialCommentDirectives.startPos == 0 -> 0)
+      expect(directivesPositions.specialCommentDirectives.endPos == 3   -> 0)
+    }
+  }
+
+  test("should respect using directives in a .sc file with the shebang line") {
+    TestInputs(os.rel / "sample.sc" ->
+      """#!/usr/bin/env -S scala-cli shebang
+        |//> using lib "com.lihaoyi::os-lib::0.8.1"
+        |println(os.pwd)
+        |""".stripMargin).fromRoot { root =>
+      val scalaFile = SourceScalaFile(root, os.sub / "sample.sc")
+      val Some(Right(result)) = ScalaPreprocessor.preprocess(
+        scalaFile,
+        logger = TestLogger(),
+        allowRestrictedFeatures = false
+      )
+      expect(result.nonEmpty)
+      val Some(directivesPositions) = result.head.directivesPositions
+      expect(directivesPositions.specialCommentDirectives.startPos == 0 -> 0)
+      expect(directivesPositions.specialCommentDirectives.endPos == 2   -> 0)
+    }
+  }
+}