From dec026d615b7bf9fb85e739e1c2a0d3ec0f6d93c Mon Sep 17 00:00:00 2001
From: Jamie Thompson <bishbashboshjt@gmail.com>
Date: Mon, 14 Oct 2024 15:20:12 +0200
Subject: [PATCH] backend computes line number from source of position

[Cherry-picked c6b23cc2944c183a36bc607e1eed9361cc9e3b83]
---
 .../src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala    | 8 +++++++-
 compiler/src/dotty/tools/dotc/util/SourceFile.scala       | 3 ++-
 compiler/src/dotty/tools/dotc/util/SourcePosition.scala   | 4 ++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala b/compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala
index 0ab9ed85b6cf..3ed21a6de3e8 100644
--- a/compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala
+++ b/compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala
@@ -623,7 +623,13 @@ trait BCodeSkelBuilder extends BCodeHelpers {
       }
 
       if (emitLines && tree.span.exists && !tree.hasAttachment(SyntheticUnit)) {
-        val nr = ctx.source.offsetToLine(tree.span.point) + 1
+        val nr =
+          val sourcePos = tree.sourcePos
+          (
+            if sourcePos.exists then sourcePos.finalPosition.line
+            else ctx.source.offsetToLine(tree.span.point) // fallback
+          ) + 1
+
         if (nr != lastEmittedLineNr) {
           lastEmittedLineNr = nr
           getNonLabelNode(lastInsn) match {
diff --git a/compiler/src/dotty/tools/dotc/util/SourceFile.scala b/compiler/src/dotty/tools/dotc/util/SourceFile.scala
index 48675b6b8eae..246255ae3802 100644
--- a/compiler/src/dotty/tools/dotc/util/SourceFile.scala
+++ b/compiler/src/dotty/tools/dotc/util/SourceFile.scala
@@ -118,7 +118,8 @@ class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends
    *  For regular source files, simply return the argument.
    */
   def positionInUltimateSource(position: SourcePosition): SourcePosition =
-    SourcePosition(underlying, position.span shift start)
+    if isSelfContained then position // return the argument
+    else SourcePosition(underlying, position.span shift start)
 
   private def calculateLineIndicesFromContents() = {
     val cs = content()
diff --git a/compiler/src/dotty/tools/dotc/util/SourcePosition.scala b/compiler/src/dotty/tools/dotc/util/SourcePosition.scala
index 904704b2349c..384d2f1fb2f3 100644
--- a/compiler/src/dotty/tools/dotc/util/SourcePosition.scala
+++ b/compiler/src/dotty/tools/dotc/util/SourcePosition.scala
@@ -79,6 +79,10 @@ extends SrcPos, interfaces.SourcePosition, Showable {
     rec(this)
   }
 
+  def finalPosition: SourcePosition = {
+    source.positionInUltimateSource(this)
+  }
+
 
   override def toString: String =
     s"${if (source.exists) source.file.toString else "(no source)"}:$span"