Improve trace for TASTy without valid line numbers

Ref: #18882

Author: liufengyun

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 =>
@@ -781,15 +781,15 @@ 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
@@ -836,7 +836,7 @@ 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 =>
 
@@ -851,7 +851,7 @@ 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
@@ -936,7 +936,7 @@ 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
@@ -948,17 +948,17 @@ 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
@@ -983,10 +983,10 @@ 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
   }
@@ -1716,14 +1716,14 @@ object Objects:
     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
+      "Calling trace:" + 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
+      "Calling trace:" + Trace.show
 
     report.warning(msg, Trace.position)

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

@@ -22,12 +22,16 @@ object Trace:
 
   val empty: Trace = Vector.empty
 
+  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 +45,8 @@ 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 +56,22 @@ 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 "" 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
     }
@@ -84,4 +91,4 @@ object Trace:
         "^" * math.max(1, pos.endColumn - pos.startColumn)
       else "^"
 
-    s"$padding$carets\n"
+    s"$padding$carets" + System.lineSeparator()