Fix missing stacktrace item

Author: liufengyun

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

@@ -21,10 +21,7 @@ object Errors:
     def issue(using Context): Unit =
       report.warning(show + stacktrace, this.pos)
 
-    private def isTraceInformative(using Context): Boolean =
-      trace.size > 1 || trace.size == 1 && trace.head.sourcePos.ne(pos)
-
-    def stacktrace(using Context): String = if !isTraceInformative then "" else " Calling trace:\n" + {
+    def stacktrace(using Context): String = if trace.isEmpty then "" else " Calling trace:\n" + {
       var lastLineNum = -1
       var lines: mutable.ArrayBuffer[String] = new mutable.ArrayBuffer
       trace.foreach { tree =>
@@ -107,10 +104,8 @@ object Errors:
     override def issue(using Context): Unit =
       report.warning(show, this.pos)
 
-    def show(using Context): String = {
-      var index = 0
+    def show(using Context): String =
       msg + stacktrace + "\n" +
         "Promoting the value to fully initialized failed due to the following problem:\n" +
         error.show + error.stacktrace
-    }
   }

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

@@ -1145,7 +1145,7 @@ object Semantic {
 
       case id @ Ident(name) if !id.symbol.is(Flags.Method)  =>
         assert(name.isTermName, "type trees should not reach here")
-        cases(expr.tpe, thisV, klass)
+        withTrace(trace2) { cases(expr.tpe, thisV, klass) }
 
       case NewExpr(tref, New(tpt), ctor, argss) =>
         // check args

tests/init/neg/t3273.check

@@ -8,7 +8,9 @@
   |                                       ^^^^^^^^^^^^^^^
   |
   |    Promoting the value to fully initialized failed due to the following problem:
-  |    Access non-initialized value num1.
+  |    Access non-initialized value num1. Calling trace:
+  |    -> val num1: LazyList[Int] = 1 #:: num1.map(_ + 1)                        // error	[ t3273.scala:4 ]
+  |                                       ^^^^
 -- Error: tests/init/neg/t3273.scala:5:61 ------------------------------------------------------------------------------
 5 |  val num2: LazyList[Int] = 1 #:: num2.iterator.map(_ + 1).to(LazyList)  // error
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -19,4 +21,6 @@
   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   |    Promoting the value to fully initialized failed due to the following problem:
-  |    Access non-initialized value num2.
+  |    Access non-initialized value num2. Calling trace:
+  |    -> val num2: LazyList[Int] = 1 #:: num2.iterator.map(_ + 1).to(LazyList)  // error	[ t3273.scala:5 ]
+  |                                       ^^^^