Add line number magic comment support

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -341,6 +341,7 @@ private sealed trait XSettings:
   val Xdumpclasses: Setting[String] = StringSetting(AdvancedSetting, "Xdump-classes", "dir", "Dump the generated bytecode to .class files (useful for reflective compilation that utilizes in-memory classloaders).", "")
   val XjarCompressionLevel: Setting[Int] = IntChoiceSetting(AdvancedSetting, "Xjar-compression-level", "compression level to use when writing jar files", Deflater.DEFAULT_COMPRESSION to Deflater.BEST_COMPRESSION, Deflater.DEFAULT_COMPRESSION)
   val XkindProjector: Setting[String] = ChoiceSetting(AdvancedSetting, "Xkind-projector", "[underscores, enable, disable]", "Allow `*` as type lambda placeholder to be compatible with kind projector. When invoked as -Xkind-projector:underscores will repurpose `_` to be a type parameter placeholder, this will disable usage of underscore as a wildcard.", List("disable", "", "underscores"), "disable", legacyArgs = true)
+  val XmagicOffsetHeader: Setting[String] = StringSetting(AdvancedSetting, "Xmagic-offset-header", "header", "Specify the magic header comment that marks the start of the actual code in generated wrapper scripts. Example: -Xmagic-offset-header:///SOURCE_CODE_START", "")
 
   /** Documentation related settings */
   val XdropComments: Setting[Boolean] = BooleanSetting(AdvancedSetting, "Xdrop-docs", "Drop documentation when scanning source files.", aliases = List("-Xdrop-comments"))

compiler/src/dotty/tools/dotc/reporting/MessageRendering.scala

@@ -11,7 +11,7 @@ import core.Decorators.*
 import printing.Highlighting.{Blue, Red, Yellow}
 import printing.SyntaxHighlighting
 import Diagnostic.*
-import util.{ SourcePosition, NoSourcePosition }
+import util.{ SourcePosition, NoSourcePosition, WrappedSourceFile }
 import util.Chars.{ LF, CR, FF, SU }
 import scala.annotation.switch
 
@@ -44,7 +44,10 @@ trait MessageRendering {
     var maxLen = Int.MinValue
     def render(offsetAndLine: (Int, String)): String = {
       val (offset1, line) = offsetAndLine
-      val lineNbr = (pos.source.offsetToLine(offset1) + 1).toString
+      var magicOffset = WrappedSourceFile.locateMagicHeader(pos.source).getOrElse(0)
+      val lineId = pos.source.offsetToLine(offset1)
+      if lineId < magicOffset then magicOffset = 0
+      val lineNbr = (lineId + 1 - magicOffset).toString
       val prefix = String.format(s"%${offset - 2}s |", lineNbr)
       maxLen = math.max(maxLen, prefix.length)
       val lnum = hl(" " * math.max(0, maxLen - prefix.length - 1) + prefix)

compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala

@@ -7,7 +7,7 @@ import core.Contexts.*
 import collection.mutable
 import scala.annotation.tailrec
 import dotty.tools.dotc.reporting.Reporter
-import dotty.tools.dotc.util.SourcePosition;
+import dotty.tools.dotc.util.SourcePosition
 
 import java.io.OutputStreamWriter
 import java.nio.charset.StandardCharsets.UTF_8

compiler/src/dotty/tools/dotc/util/SourceFile.scala

@@ -61,6 +61,21 @@ object ScriptSourceFile {
   }
 }
 
+object WrappedSourceFile:
+  private val cache: mutable.HashMap[SourceFile, Int] = mutable.HashMap.empty
+  def locateMagicHeader(sourceFile: SourceFile)(using Context): Option[Int] =
+    def findOffset: Int =
+      val magicHeader = ctx.settings.XmagicOffsetHeader.value
+      if magicHeader.isEmpty then
+        -1
+      else
+        val s = new String(sourceFile.content)
+        val regex = ("(?m)^" + java.util.regex.Pattern.quote(magicHeader) + "$").r
+        val pos = regex.findFirstMatchIn(s).map(_.start).map(sourceFile.offsetToLine(_))
+        pos.getOrElse(-1)
+    val result = cache.getOrElseUpdate(sourceFile, findOffset)
+    if result >= 0 then Some(result + 1) else None
+
 class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends interfaces.SourceFile {
   import SourceFile.*
 

tests/neg/magic-offset-header-a.check

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg/magic-offset-header-a.scala:6:19 ----------------------------------------------
+1 |def test1(): Int = "无穷"  // error
+  |                   ^^^^
+  |                   Found:    ("无穷" : String)
+  |                   Required: Int
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/magic-offset-header-a.scala

@@ -0,0 +1,6 @@
+//> using options -Xmagic-offset-header:///TEST_MARKER
+val t1 = 1
+val t2 = 2
+val t3 = 3
+///TEST_MARKER
+def test1(): Int = "无穷"  // error

tests/neg/magic-offset-header-b.check

@@ -0,0 +1,14 @@
+-- [E007] Type Mismatch Error: tests/neg/magic-offset-header-b.scala:3:13 ----------------------------------------------
+3 |def x: Int = true  // error
+  |             ^^^^
+  |             Found:    (true : Boolean)
+  |             Required: Int
+  |
+  | longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/magic-offset-header-b.scala:7:13 ----------------------------------------------
+2 |def y: Int = false  // error
+  |             ^^^^^
+  |             Found:    (false : Boolean)
+  |             Required: Int
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/magic-offset-header-b.scala

@@ -0,0 +1,7 @@
+//> using options -Xmagic-offset-header:///TEST_MARKER
+
+def x: Int = true  // error
+
+///TEST_MARKER
+
+def y: Int = false  // error

tests/neg/magic-offset-header-c.check

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg/magic-offset-header-c.scala:8:18 ----------------------------------------------
+3 |  val x: String = 0  // error
+  |                  ^
+  |                  Found:    (0 : Int)
+  |                  Required: String
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/magic-offset-header-c.scala

@@ -0,0 +1,8 @@
+//> using options -Xmagic-offset-header:///SOURCE_CODE_START_MARKER
+
+val generatedCode = 123
+
+///SOURCE_CODE_START_MARKER
+
+def userCode =
+  val x: String = 0  // error