Add line number magic comment support (#23549)

  - Added compiler setting to configure magic line number comments
- Implemented line number offset reporting when magic comments are
present

fixes #21919.

Author: Linyxus

compiler/src/dotty/tools/dotc/ast/Positioned.scala

@@ -3,7 +3,8 @@ package dotc
 package ast
 
 import util.Spans.*
-import util.{SourceFile, SourcePosition, SrcPos}
+import util.{SourceFile, SourcePosition, SrcPos, WrappedSourceFile}
+import WrappedSourceFile.MagicHeaderInfo, MagicHeaderInfo.*
 import core.Contexts.*
 import core.Decorators.*
 import core.NameOps.*
@@ -51,7 +52,15 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
 
   def source: SourceFile = mySource
 
-  def sourcePos(using Context): SourcePosition = source.atSpan(span)
+  def sourcePos(using Context): SourcePosition =
+    val info = WrappedSourceFile.locateMagicHeader(source)
+    info match
+      case HasHeader(offset, originalFile) =>
+        if span.start >= offset then  // This span is in user code
+          originalFile.atSpan(span.shift(-offset))
+        else  // Otherwise, return the source position in the wrapper code
+          source.atSpan(span)
+      case _ => source.atSpan(span)
 
   /** This positioned item, widened to `SrcPos`. Used to make clear we only need the
    *  position, typically for error reporting.

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

@@ -444,6 +444,8 @@ private sealed trait YSettings:
   val YbestEffort: Setting[Boolean] = BooleanSetting(ForkSetting, "Ybest-effort", "Enable best-effort compilation attempting to produce betasty to the META-INF/best-effort directory, regardless of errors, as part of the pickler phase.")
   val YwithBestEffortTasty: Setting[Boolean] = BooleanSetting(ForkSetting, "Ywith-best-effort-tasty", "Allow to compile using best-effort tasty files. If such file is used, the compiler will stop after the pickler phase.")
 
+  val YmagicOffsetHeader: Setting[String] = StringSetting(ForkSetting, "Ymagic-offset-header", "header", "Specify the magic header comment that marks the start of the actual code in generated wrapper scripts. Example: -Ymagic-offset-header:SOURCE_CODE_START. Then, in the source, the magic comment `///SOURCE_CODE_START:<ORIGINAL_FILE_PATH>` marks the start of user code. The comment should be suffixed by `:<ORIGINAL_FILE_PATH>` to indicate the original file.", "")
+
   // Experimental language features
   @deprecated(message = "This flag has no effect and will be removed in a future version.", since = "3.7.0")
   val YnoKindPolymorphism: Setting[Boolean] = BooleanSetting(ForkSetting, "Yno-kind-polymorphism", "Disable kind polymorphism. (This flag has no effect)", deprecation = Deprecation.removed())

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}
 import util.Chars.{ LF, CR, FF, SU }
 import scala.annotation.switch
 

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

@@ -7,6 +7,7 @@ import scala.language.unsafeNulls
 import dotty.tools.io.*
 import Spans.*
 import core.Contexts.*
+import core.Decorators.*
 
 import scala.io.Codec
 import Chars.*
@@ -61,6 +62,36 @@ object ScriptSourceFile {
   }
 }
 
+object WrappedSourceFile:
+  enum MagicHeaderInfo:
+    case HasHeader(offset: Int, originalFile: SourceFile)
+    case NoHeader
+  import MagicHeaderInfo.*
+
+  private val cache: mutable.HashMap[SourceFile, MagicHeaderInfo] = mutable.HashMap.empty
+
+  def locateMagicHeader(sourceFile: SourceFile)(using Context): MagicHeaderInfo =
+    def findOffset: MagicHeaderInfo =
+      val magicHeader = ctx.settings.YmagicOffsetHeader.value
+      if magicHeader.isEmpty then NoHeader
+      else
+        val text = new String(sourceFile.content)
+        val headerQuoted = java.util.regex.Pattern.quote("///" + magicHeader)
+        val regex = s"(?m)^$headerQuoted:(.+)$$".r
+        regex.findFirstMatchIn(text) match
+          case Some(m) =>
+            val markerOffset = m.start
+            val sourceStartOffset = sourceFile.nextLine(markerOffset)
+            val file = ctx.getFile(m.group(1))
+            if file.exists then
+              HasHeader(sourceStartOffset, ctx.getSource(file))
+            else
+              report.warning(em"original source file not found: ${file.path}")
+              NoHeader
+          case None => NoHeader
+    val result = cache.getOrElseUpdate(sourceFile, findOffset)
+    result
+
 class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends interfaces.SourceFile {
   import SourceFile.*
 

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

@@ -0,0 +1,2 @@
+
+def test1(): Int = "无穷"  // error

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

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg/magic-offset-header-a.scala:2:19 ----------------------------------------------
+2 |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_wrapper.scala

@@ -0,0 +1,7 @@
+//> using options -Ymagic-offset-header:TEST_MARKER
+val t1 = 1
+val t2 = 2
+val t3 = 3
+///TEST_MARKER:tests/neg/magic-offset-header-a.scala
+
+def test1(): Int = "无穷"  // anypos-error

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

@@ -0,0 +1,2 @@
+
+def y: Int = false  // error

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

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