More friendly stack trace

Author: liufengyun

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

@@ -86,6 +86,12 @@ class CycleChecker(cache: Cache) {
   val classesInCurrentRun = mutable.Set.empty[Symbol]
   val objectsInCurrentRun = new mutable.ListBuffer[Symbol]
 
+  /** The limit of stack trace shown to programmers
+   *
+   *  TODO: make it configurable from command-line for debugging purposes
+   */
+  val traceNumberLimit = 10
+
   /** Checking state */
   case class State(visited: mutable.Set[Dependency], path: Vector[Symbol], trace: Vector[Dependency]) {
     def visit[T](dep: Dependency)(op: State ?=> T): T =
@@ -138,11 +144,25 @@ class CycleChecker(cache: Cache) {
       val obj = dep.symbol
       if state.path.contains(obj) then
         val cycle = state.path.dropWhile(_ != obj)
-        val trace = state.trace.dropWhile(_.symbol != obj).flatMap(_.source) ++ dep.source
+        val ctor = obj.moduleClass.primaryConstructor
+        var trace = state.trace.dropWhile(_.symbol != ctor) :+ dep
+
+        val traceSuppress = trace.size > traceNumberLimit
+        if traceSuppress then
+          // truncate trace up to the first escape of object
+          val iter = trace.iterator
+          trace = Vector.empty
+          var elem = iter.next()
+          trace = trace :+ elem
+          while iter.hasNext && !elem.isInstanceOf[InstanceUsage] do
+            elem = iter.next()
+            trace = trace :+ elem
+
+        val locations = trace.flatMap(_.source)
         if cycle.size > 1 then
-          CyclicObjectInit(cycle, trace) :: Nil
+          CyclicObjectInit(cycle, locations, traceSuppress) :: Nil
         else
-          ObjectLeakDuringInit(obj, trace) :: Nil
+          ObjectLeakDuringInit(obj, locations, traceSuppress) :: Nil
       else
         val constr = obj.moduleClass.primaryConstructor
         state.visitObject(dep) {

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

@@ -23,12 +23,18 @@ object Errors {
     def trace: Seq[Tree]
     def show(using Context): String
 
+    def traceSuppressed: Boolean = false
+
     def issue(using Context): Unit =
       report.warning(show + stacktrace, source.srcPos)
 
     def toErrors: Errors = this :: Nil
 
-    def stacktrace(using Context): String = if (trace.isEmpty) "" else " Calling trace:\n" + {
+    private def stacktracePrefix: String =
+      val str = if traceSuppressed then "suppressed" else "full"
+      " Calling trace (" +  str + "):\n"
+
+    def stacktrace(using Context): String = if (trace.isEmpty) "" else stacktracePrefix + {
       var indentCount = 0
       var last: String = ""
       val sb = new StringBuilder
@@ -69,7 +75,7 @@ object Errors {
       report.warning(show + stacktrace, field.srcPos)
   }
 
-  case class CyclicObjectInit(objs: Seq[Symbol], trace: Seq[Tree]) extends Error {
+  case class CyclicObjectInit(objs: Seq[Symbol], trace: Seq[Tree], override val traceSuppressed: Boolean) extends Error {
     def source: Tree = trace.last
     def show(using Context): String =
       "Cyclic object initialization for " + objs.map(_.show).mkString(", ") + "."
@@ -78,10 +84,9 @@ object Errors {
       report.warning(show + stacktrace, objs.head.srcPos)
   }
 
-  case class ObjectLeakDuringInit(obj: Symbol, trace: Seq[Tree]) extends Error {
+  case class ObjectLeakDuringInit(obj: Symbol, trace: Seq[Tree], override val traceSuppressed: Boolean) extends Error {
     def source: Tree = trace.last
-    def show(using Context): String =
-      obj.show + " leaked during its initialization " + "."
+    def show(using Context): String = obj.show + " leaked during its initialization " + "."
 
     override def issue(using Context): Unit =
       report.warning(show + stacktrace, obj.srcPos)