Make sure that trace is shown correctly in the presence of invalid li…

…ne numbers (#18930)

Make sure that trace is shown correctly in the presence of invalid line
numbers (-1) in TASTy.

Before:

```Scala
Reading mutable state of object Array during initialization of object Parent.
Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. Calling trace: 
-> object Parent {                    // error  [ t9312.scala:11 ]
   ^
-> final val children = Set(Child1, Child2)     [ t9312.scala:21 ]
                        ^^^^^^^^^^^^^^^^^^^
-> BitmapIndexedSetNode.this.originalHashes.apply(index)
```

After:

```Scala
Reading mutable state of object Array during initialization of object Parent.
Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. Calling trace:
├── object Parent {                    // error	[ t9312.scala:11 ]
│      ^
├── final val children = Set(Child1, Child2)	[ t9312.scala:21 ]
│                        ^^^^^^^^^^^^^^^^^^^
├── scala.collection.IterableFactory.apply
├── IterableFactory.this.from[A](elems)
├── scala.collection.immutable.Set.from
├── scala.collection.immutable.Set.newBuilder[E].addAll(it)
├── scala.collection.immutable.SetBuilderImpl.addAll
├── super.addAll(xs)
├── scala.collection.mutable.Growable.addAll
├── Growable.this.addOne(it.next())
├── scala.collection.immutable.SetBuilderImpl.addOne
├── SetBuilderImpl.this.hashSetBuilder.addOne(elem)
├── scala.collection.immutable.HashSetBuilder.addOne
├── HashSetBuilder.this.update(HashSetBuilder.this.rootNode, elem, h, im, 0)
├── scala.collection.immutable.HashSetBuilder.update
├── bm.getHash(index)
├── scala.collection.immutable.BitmapIndexedSetNode.getHash
└── BitmapIndexedSetNode.this.originalHashes.apply(index)
```

 Ref: #18882

compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -380,7 +380,7 @@ object Objects:
       case Some(theValue) =>
         theValue
       case _ =>
-        report.warning("[Internal error] Value not found " + x.show + "\nenv = " + data.show + ". Calling trace:\n" + Trace.show, Trace.position)
+        report.warning("[Internal error] Value not found " + x.show + "\nenv = " + data.show + ". " + Trace.show, Trace.position)
         Bottom
 
     def getVal(x: Symbol)(using data: Data, ctx: Context): Option[Value] = data.getVal(x)
@@ -619,7 +619,7 @@ object Objects:
   def call(value: Value, meth: Symbol, args: List[ArgInfo], receiver: Type, superType: Type, needResolve: Boolean = true): Contextual[Value] = log("call " + meth.show + ", this = " + value.show + ", args = " + args.map(_.value.show), printer, (_: Value).show) {
     value match
     case Cold =>
-      report.warning("Using cold alias. Calling trace:\n" + Trace.show, Trace.position)
+      report.warning("Using cold alias. " + Trace.show, Trace.position)
       Bottom
 
     case Bottom =>
@@ -792,15 +792,15 @@ object Objects:
               errorReadOtherStaticObject(State.currentObject, addr.owner)
               Bottom
           else if ref.isObjectRef && ref.klass.hasSource then
-            report.warning("Access uninitialized field " + field.show + ". Call trace: " + Trace.show, Trace.position)
+            report.warning("Access uninitialized field " + field.show + ". " + Trace.show, Trace.position)
             Bottom
           else
             // initialization error, reported by the initialization checker
             Bottom
         else if ref.hasVal(target) then
           ref.valValue(target)
         else if ref.isObjectRef && ref.klass.hasSource then
-          report.warning("Access uninitialized field " + field.show + ". Call trace: " + Trace.show, Trace.position)
+          report.warning("Access uninitialized field " + field.show + ". " + Trace.show, Trace.position)
           Bottom
         else
           // initialization error, reported by the initialization checker
@@ -847,7 +847,7 @@ object Objects:
       report.warning("[Internal error] unexpected tree in assignment, array = " + arr.show + Trace.show, Trace.position)
 
     case Cold =>
-      report.warning("Assigning to cold aliases is forbidden. Calling trace:\n" + Trace.show, Trace.position)
+      report.warning("Assigning to cold aliases is forbidden. " + Trace.show, Trace.position)
 
     case Bottom =>
 
@@ -862,7 +862,7 @@ object Objects:
         else
           Heap.writeJoin(addr, rhs)
       else
-        report.warning("Mutating a field before its initialization: " + field.show + ". Calling trace:\n" + Trace.show, Trace.position)
+        report.warning("Mutating a field before its initialization: " + field.show + ". " + Trace.show, Trace.position)
     end match
 
     Bottom
@@ -947,7 +947,7 @@ object Objects:
             Bottom
           end if
         case _ =>
-          report.warning("[Internal error] Variable not found " + sym.show + "\nenv = " + env.show + ". Calling trace:\n" + Trace.show, Trace.position)
+          report.warning("[Internal error] Variable not found " + sym.show + "\nenv = " + env.show + ". " + Trace.show, Trace.position)
           Bottom
       else
         given Env.Data = env
@@ -959,17 +959,17 @@ object Objects:
             given Env.Data = fun.env
             eval(fun.code, fun.thisV, fun.klass)
           case Cold =>
-            report.warning("Calling cold by-name alias. Call trace: \n" + Trace.show, Trace.position)
+            report.warning("Calling cold by-name alias. " + Trace.show, Trace.position)
             Bottom
           case _: ValueSet | _: Ref | _: OfArray =>
-            report.warning("[Internal error] Unexpected by-name value " + value.show  + ". Calling trace:\n" + Trace.show, Trace.position)
+            report.warning("[Internal error] Unexpected by-name value " + value.show  + ". " + Trace.show, Trace.position)
             Bottom
         else
           value
 
     case _ =>
       if isByNameParam(sym) then
-        report.warning("Calling cold by-name alias. Call trace: \n" + Trace.show, Trace.position)
+        report.warning("Calling cold by-name alias. " + Trace.show, Trace.position)
         Bottom
       else
         Cold
@@ -994,10 +994,10 @@ object Objects:
         else
           Heap.writeJoin(addr, value)
       case _ =>
-        report.warning("[Internal error] Variable not found " + sym.show + "\nenv = " + env.show + ". Calling trace:\n" + Trace.show, Trace.position)
+        report.warning("[Internal error] Variable not found " + sym.show + "\nenv = " + env.show + ". " + Trace.show, Trace.position)
 
     case _ =>
-      report.warning("Assigning to variables in outer scope. Calling trace:\n" + Trace.show, Trace.position)
+      report.warning("Assigning to variables in outer scope. " + Trace.show, Trace.position)
 
     Bottom
   }
@@ -1726,15 +1726,13 @@ object Objects:
   def errorMutateOtherStaticObject(currentObj: ClassSymbol, otherObj: ClassSymbol)(using Trace, Context) =
     val msg =
       s"Mutating ${otherObj.show} during initialization of ${currentObj.show}.\n" +
-      "Mutating other static objects during the initialization of one static object is forbidden. " +
-      "Calling trace:\n" + Trace.show
+      "Mutating other static objects during the initialization of one static object is forbidden. " + Trace.show
 
     report.warning(msg, Trace.position)
 
   def errorReadOtherStaticObject(currentObj: ClassSymbol, otherObj: ClassSymbol)(using Trace, Context) =
     val msg =
       "Reading mutable state of " + otherObj.show + " during initialization of " + currentObj.show + ".\n" +
-      "Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. " +
-      "Calling trace: " + Trace.show
+      "Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. " + Trace.show
 
     report.warning(msg, Trace.position)

compiler/src/dotty/tools/dotc/transform/init/Trace.scala

@@ -22,12 +22,17 @@ object Trace:
 
   val empty: Trace = Vector.empty
 
+  val EMPTY_PADDING     = "    "
+  val CONNECTING_INDENT = "\u2502   "               // "|   "
+  val CHILD             = "\u251c\u2500\u2500 "     // "|-- "
+  val LAST_CHILD        = "\u2514\u2500\u2500 "     // "\-- "
+
   extension (trace: Trace)
     def add(node: Tree): Trace = trace :+ node
     def toVector: Vector[Tree] = trace
     def ++(trace2: Trace): Trace = trace ++ trace2
 
-  def show(using trace: Trace, ctx: Context): String = buildStacktrace(trace, "\n")
+  def show(using trace: Trace, ctx: Context): String = buildStacktrace(trace, "Calling trace:" + System.lineSeparator())
 
   def position(using trace: Trace): Tree = trace.last
 
@@ -41,8 +46,8 @@ object Trace:
     var lastLineNum = -1
     var lines: mutable.ArrayBuffer[String] = new mutable.ArrayBuffer
     trace.foreach { tree =>
+      val isLastTraceItem = tree `eq` trace.last
       val pos = tree.sourcePos
-      val prefix = "-> "
       val line =
         if pos.source.exists then
           val loc = "[ " + pos.source.file.name + ":" + (pos.line + 1) + " ]"
@@ -52,19 +57,22 @@ object Trace:
           tree match
             case defDef: DefTree =>
               // The definition can be huge, avoid printing the whole definition.
-              defDef.symbol.show
+              defDef.symbol.showFullName
             case _ =>
-              tree.show
+              tree.show.split(System.lineSeparator(), 2).nn.head.nn
+
       val positionMarkerLine =
         if pos.exists && pos.source.exists then
-          positionMarker(pos)
-        else ""
+          (if isLastTraceItem then EMPTY_PADDING else CONNECTING_INDENT)+ positionMarker(pos)
+        else
+          ""
 
       // always use the more precise trace location
-      if lastLineNum == pos.line then
+      if lastLineNum >= 0 && lastLineNum == pos.line then
         lines.dropRightInPlace(1)
 
-      lines += (prefix + line + "\n" + positionMarkerLine)
+      val prefix = if isLastTraceItem then LAST_CHILD else CHILD
+      lines += (prefix + line + System.lineSeparator() + positionMarkerLine)
 
       lastLineNum = pos.line
     }
@@ -78,10 +86,10 @@ object Trace:
    */
   private def positionMarker(pos: SourcePosition): String =
     val trimmed = pos.source.lineContent(pos.start).takeWhile(c => c.isWhitespace).length
-    val padding = pos.startColumnPadding.substring(trimmed).nn + "   "
+    val padding = pos.startColumnPadding.substring(trimmed).nn
     val carets =
       if (pos.startLine == pos.endLine)
         "^" * math.max(1, pos.endColumn - pos.startColumn)
       else "^"
 
-    s"$padding$carets\n"
+    s"$padding$carets" + System.lineSeparator()

tests/init-global/neg/global-cycle1.check

@@ -2,19 +2,19 @@
 1 |object A {             // error
   |       ^
   |       Cyclic initialization: object A -> object B -> object A. Calling trace:
-  |       -> object A {             // error	[ global-cycle1.scala:1 ]
-  |          ^
-  |       -> val a: Int = B.b	[ global-cycle1.scala:2 ]
-  |                       ^
-  |       -> object B {	[ global-cycle1.scala:5 ]
-  |          ^
-  |       -> val b: Int = A.a     // error	[ global-cycle1.scala:6 ]
-  |                       ^
+  |       ├── object A {             // error	[ global-cycle1.scala:1 ]
+  |       │   ^
+  |       ├── val a: Int = B.b	[ global-cycle1.scala:2 ]
+  |       │                ^
+  |       ├── object B {	[ global-cycle1.scala:5 ]
+  |       │   ^
+  |       └── val b: Int = A.a     // error	[ global-cycle1.scala:6 ]
+  |                        ^
 -- Error: tests/init-global/neg/global-cycle1.scala:6:17 ---------------------------------------------------------------
 6 |  val b: Int = A.a     // error
   |               ^^^
-  |               Access uninitialized field value a. Call trace: 
-  |               -> object B {	[ global-cycle1.scala:5 ]
-  |                  ^
-  |               -> val b: Int = A.a     // error	[ global-cycle1.scala:6 ]
-  |                               ^^^
+  |               Access uninitialized field value a. Calling trace:
+  |               ├── object B {	[ global-cycle1.scala:5 ]
+  |               │   ^
+  |               └── val b: Int = A.a     // error	[ global-cycle1.scala:6 ]
+  |                                ^^^

tests/init-global/neg/line-spacing.check

@@ -2,12 +2,12 @@
 3 |    B
 4 |      .s.length // error
   |    ^
-  |    Access uninitialized field value s. Call trace: 
-  |    -> object B {	[ line-spacing.scala:7 ]
-  |       ^
-  |    -> val s: String = s"${A.a}a"	[ line-spacing.scala:8 ]
-  |                           ^^^
-  |    -> def a: Int =	[ line-spacing.scala:2 ]
-  |       ^
-  |    -> .s.length // error	[ line-spacing.scala:4 ]
-  |       ^
+  |    Access uninitialized field value s. Calling trace:
+  |    ├── object B {	[ line-spacing.scala:7 ]
+  |    │   ^
+  |    ├── val s: String = s"${A.a}a"	[ line-spacing.scala:8 ]
+  |    │                       ^^^
+  |    ├── def a: Int =	[ line-spacing.scala:2 ]
+  |    │   ^
+  |    └── .s.length // error	[ line-spacing.scala:4 ]
+  |        ^

tests/init-global/neg/patmat-unapplySeq.check

@@ -2,10 +2,10 @@
 8 |  def apply(i: Int): Box = array(i)             // error
   |                           ^^^^^^^^
   |Reading mutable state of object A during initialization of object B.
-  |Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. Calling trace: 
-  |-> object B:	[ patmat-unapplySeq.scala:15 ]
-  |   ^
-  |-> case A(b) =>	[ patmat-unapplySeq.scala:17 ]
-  |        ^^^^
-  |-> def apply(i: Int): Box = array(i)             // error	[ patmat-unapplySeq.scala:8 ]
-  |                            ^^^^^^^^
+  |Reading mutable state of other static objects is forbidden as it breaks initialization-time irrelevance. Calling trace:
+  |├── object B:	[ patmat-unapplySeq.scala:15 ]
+  |│   ^
+  |├── case A(b) =>	[ patmat-unapplySeq.scala:17 ]
+  |│        ^^^^
+  |└── def apply(i: Int): Box = array(i)             // error	[ patmat-unapplySeq.scala:8 ]
+  |                             ^^^^^^^^

tests/init/neg/closureLeak.check

@@ -2,13 +2,13 @@
 11 |    l.foreach(a => a.addX(this)) // error
    |              ^^^^^^^^^^^^^^^^^
    |Could not verify that the method argument is transitively initialized (Hot). It was found to be a function where "this" is (the original object of type (class Outer) where initialization checking started). Only transitively initialized arguments may be passed to methods (except constructors). Calling trace:
-   |-> class Outer {	[ closureLeak.scala:1 ]
-   |   ^
-   |-> l.foreach(a => a.addX(this)) // error	[ closureLeak.scala:11 ]
-   |             ^^^^^^^^^^^^^^^^^
+   |├── class Outer {	[ closureLeak.scala:1 ]
+   |│   ^
+   |└── l.foreach(a => a.addX(this)) // error	[ closureLeak.scala:11 ]
+   |              ^^^^^^^^^^^^^^^^^
    |
    |Promoting the value to transitively initialized (Hot) failed due to the following problem:
    |Could not verify that the method argument is transitively initialized (Hot). It was found to be the original object of type (class Outer) where initialization checking started. Only transitively initialized arguments may be passed to methods (except constructors).
    |Non initialized field(s): value p. Promotion trace:
-   |-> l.foreach(a => a.addX(this)) // error	[ closureLeak.scala:11 ]
-   |                         ^^^^
+   |└── l.foreach(a => a.addX(this)) // error	[ closureLeak.scala:11 ]
+   |                          ^^^^

tests/init/neg/cycle-structure.check

@@ -2,29 +2,29 @@
 3 |    val x = B(this)   // error
   |            ^^^^^^^
   |            Problematic object instantiation: arg 1 is not transitively initialized (Hot). Calling trace:
-  |            -> case class A(b: B) {	[ cycle-structure.scala:1 ]
-  |               ^
-  |            -> val x = B(this)   // error	[ cycle-structure.scala:3 ]
-  |                       ^^^^^^^
+  |            ├── case class A(b: B) {	[ cycle-structure.scala:1 ]
+  |            │   ^
+  |            └── val x = B(this)   // error	[ cycle-structure.scala:3 ]
+  |                        ^^^^^^^
   |
   |            It leads to the following error during object initialization:
   |            Access field value x on an uninitialized (Cold) object. Calling trace:
-  |            -> case class B(a: A) {	[ cycle-structure.scala:7 ]
-  |               ^
-  |            -> val x1 = a.x	[ cycle-structure.scala:8 ]
-  |                        ^^^
+  |            ├── case class B(a: A) {	[ cycle-structure.scala:7 ]
+  |            │   ^
+  |            └── val x1 = a.x	[ cycle-structure.scala:8 ]
+  |                         ^^^
 -- Error: tests/init/neg/cycle-structure.scala:9:13 --------------------------------------------------------------------
 9 |    val x = A(this)   // error
   |            ^^^^^^^
   |            Problematic object instantiation: arg 1 is not transitively initialized (Hot). Calling trace:
-  |            -> case class B(a: A) {	[ cycle-structure.scala:7 ]
-  |               ^
-  |            -> val x = A(this)   // error	[ cycle-structure.scala:9 ]
-  |                       ^^^^^^^
+  |            ├── case class B(a: A) {	[ cycle-structure.scala:7 ]
+  |            │   ^
+  |            └── val x = A(this)   // error	[ cycle-structure.scala:9 ]
+  |                        ^^^^^^^
   |
   |            It leads to the following error during object initialization:
   |            Access field value x on an uninitialized (Cold) object. Calling trace:
-  |            -> case class A(b: B) {	[ cycle-structure.scala:1 ]
-  |               ^
-  |            -> val x1 = b.x	[ cycle-structure.scala:2 ]
-  |                        ^^^
+  |            ├── case class A(b: B) {	[ cycle-structure.scala:1 ]
+  |            │   ^
+  |            └── val x1 = b.x	[ cycle-structure.scala:2 ]
+  |                         ^^^

tests/init/neg/default-this.check

@@ -3,11 +3,11 @@
   |        ^^^^^^^
   |Could not verify that the method argument is transitively initialized (Hot). It was found to be the original object of type (class B) where initialization checking started. Only transitively initialized arguments may be passed to methods (except constructors).
   |Non initialized field(s): value result. Calling trace:
-  |-> class B extends A {	[ default-this.scala:6 ]
-  |   ^
-  |-> val result = updateThenCompare(5)	[ default-this.scala:11 ]
-  |                ^^^^^^^^^^^^^^^^^^^^
-  |-> def updateThenCompare(c: Int): Boolean = {	[ default-this.scala:7 ]
-  |   ^
-  |-> compare() // error	[ default-this.scala:9 ]
-  |   ^^^^^^^
+  |├── class B extends A {	[ default-this.scala:6 ]
+  |│   ^
+  |├── val result = updateThenCompare(5)	[ default-this.scala:11 ]
+  |│                ^^^^^^^^^^^^^^^^^^^^
+  |├── def updateThenCompare(c: Int): Boolean = {	[ default-this.scala:7 ]
+  |│   ^
+  |└── compare() // error	[ default-this.scala:9 ]
+  |    ^^^^^^^

tests/init/neg/i15363.check

@@ -2,14 +2,14 @@
 3 |  val b = new B(this) // error
   |          ^^^^^^^^^^^
   |          Problematic object instantiation: arg 1 is not transitively initialized (Hot). Calling trace:
-  |          -> class A:	[ i15363.scala:1 ]
-  |             ^
-  |          -> val b = new B(this) // error	[ i15363.scala:3 ]
-  |                     ^^^^^^^^^^^
+  |          ├── class A:	[ i15363.scala:1 ]
+  |          │   ^
+  |          └── val b = new B(this) // error	[ i15363.scala:3 ]
+  |                      ^^^^^^^^^^^
   |
   |          It leads to the following error during object initialization:
   |          Access field value m on an uninitialized (Cold) object. Calling trace:
-  |          -> class B(a: A):	[ i15363.scala:7 ]
-  |             ^
-  |          -> val x = a.m	[ i15363.scala:8 ]
-  |                     ^^^
+  |          ├── class B(a: A):	[ i15363.scala:7 ]
+  |          │   ^
+  |          └── val x = a.m	[ i15363.scala:8 ]
+  |                      ^^^

tests/init/neg/i15459.check

@@ -3,9 +3,9 @@
   |          ^^^^
   |Could not verify that the method argument is transitively initialized (Hot). It was found to be the original object of type (class Sub) where initialization checking started. Only transitively initialized arguments may be passed to methods (except constructors).
   |Non initialized field(s): value b. Calling trace:
-  |-> class Sub extends Sup:	[ i15459.scala:5 ]
-  |   ^
-  |-> class Sup:	[ i15459.scala:1 ]
-  |   ^
-  |-> println(this)  // error	[ i15459.scala:3 ]
-  |           ^^^^
+  |├── class Sub extends Sup:	[ i15459.scala:5 ]
+  |│   ^
+  |├── class Sup:	[ i15459.scala:1 ]
+  |│   ^
+  |└── println(this)  // error	[ i15459.scala:3 ]
+  |            ^^^^