Fix #4947: Do not replace positions of inlined arguments

compiler/src/dotty/tools/dotc/typer/Inliner.scala

@@ -149,12 +149,26 @@ object Inliner {
 
   /** Replace `Inlined` node by a block that contains its bindings and expansion */
   def dropInlined(inlined: tpd.Inlined)(implicit ctx: Context): Tree = {
-    val reposition = new TreeMap {
-      override def transform(tree: Tree)(implicit ctx: Context): Tree = {
-        super.transform(tree).withPos(inlined.call.pos)
+    if (enclosingInlineds.nonEmpty) inlined // remove in the outer inlined call
+    else {
+      val reposition = new TreeMap {
+        private[this] var pos: Position = inlined.pos
+        override def transform(tree: Tree)(implicit ctx: Context): Tree = {
+          tree match {
+            case inlined: Inlined =>
+              val last = pos
+              pos = inlined.call.pos
+              val res = tpd.seq(inlined.bindings.map(transform), transform(inlined.expansion)).withPos(last)
+              pos = last
+              res
+            case tree =>
+              if (pos.exists) super.transform(tree).withPos(pos)
+              else super.transform(tree)
+          }
+        }
       }
+      reposition.transform(inlined)
     }
-    tpd.seq(inlined.bindings, reposition.transform(inlined.expansion))
   }
 }
 

tests/run/i4947.check

@@ -0,0 +1,2 @@
+failed
+Test$.main(i4947.scala:9)

tests/run/i4947.scala

@@ -0,0 +1,18 @@
+object Test {
+
+  transparent def track[T](f: => T): T = f
+
+  def main(args: Array[String]): Unit = {
+    try {
+      track {
+        val a = 9
+        throw new Exception("failed")
+      }
+    } catch {
+      case ex: Throwable =>
+        println(ex.getMessage)
+        println(ex.getStackTrace.head)
+    }
+  }
+
+}