Fix #15363: Improve error messages of leaked non-hot values

Author: liufengyun

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

@@ -19,9 +19,9 @@ object Errors:
     def pos(using Context): SourcePosition = trace.last.sourcePos
 
     def issue(using Context): Unit =
-      report.warning(show + stacktrace, this.pos)
+      report.warning(show + stacktrace(), this.pos)
 
-    def stacktrace(using Context): String = if trace.isEmpty then "" else " Calling trace:\n" + {
+    def stacktrace(preamble: String = " Calling trace:\n")(using Context): String = if trace.isEmpty then "" else preamble + {
       var lastLineNum = -1
       var lines: mutable.ArrayBuffer[String] = new mutable.ArrayBuffer
       trace.foreach { tree =>
@@ -99,6 +99,16 @@ object Errors:
       report.warning(show, this.pos)
 
     def show(using Context): String =
-      msg + stacktrace + "\n" +
+      msg + stacktrace() + "\n" +
         "Promoting the value to fully initialized failed due to the following problem:\n" +
-        error.show + error.stacktrace
+        error.show + error.stacktrace()
+
+  /** Unsafe leaking a non-hot value as constructor arguments */
+  case class UnsafeLeaking(trace: Seq[Tree], error: Error) extends Error:
+    override def issue(using Context): Unit =
+      report.warning(show, this.pos)
+
+    def show(using Context): String =
+      "Unsafe leaking of uninitialized value: the leaked value is used. " + stacktrace() + "\n" +
+        "The leaked uninitialized value is used as follows:\n" +
+        error.stacktrace(preamble = "")

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

@@ -793,8 +793,16 @@ object Semantic:
             val outer = Hot
             val warm = Warm(klass, outer, ctor, args2).ensureObjectExists()
             val argInfos2 = args.zip(args2).map { (argInfo, v) => argInfo.copy(value = v) }
-            warm.callConstructor(ctor, argInfos2)
-            warm
+            val errors = Reporter.stopEarly {
+              given Trace = Trace.empty
+              warm.callConstructor(ctor, argInfos2)
+            }
+            if errors.nonEmpty then
+              val error = UnsafeLeaking(trace.toVector, errors.head)
+              reporter.report(error)
+              Hot
+            else
+              warm
 
         case Cold =>
           val error = CallCold(ctor, trace.toVector)

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

@@ -86,7 +86,7 @@ object Implicits:
    */
   abstract class ImplicitRefs(initctx: Context) {
     val irefCtx =
-      if (initctx == NoContext) initctx else initctx.retractMode(Mode.ImplicitsEnabled)
+      if (initctx eq NoContext) initctx else initctx.retractMode(Mode.ImplicitsEnabled)
     protected given Context = irefCtx
 
     /** The nesting level of this context. Non-zero only in ContextialImplicits */
@@ -549,16 +549,16 @@ object Implicits:
     override def msg(using Context) = _msg
     def explanation(using Context) = msg.toString
 
-  /** A search failure type for failed synthesis of terms for special types */ 
+  /** A search failure type for failed synthesis of terms for special types */
   class SynthesisFailure(reasons: List[String], val expectedType: Type) extends SearchFailureType:
     def argument = EmptyTree
 
-    private def formatReasons = 
-      if reasons.length > 1 then 
-        reasons.mkString("\n\t* ", "\n\t* ", "") 
-      else 
+    private def formatReasons =
+      if reasons.length > 1 then
+        reasons.mkString("\n\t* ", "\n\t* ", "")
+      else
         reasons.mkString
-      
+
     def explanation(using Context) = em"Failed to synthesize an instance of type ${clarify(expectedType)}: ${formatReasons}"
 
 end Implicits
@@ -871,7 +871,7 @@ trait Implicits:
             SearchFailure(new SynthesisFailure(errors, formal), span).tree
           else
             tree.orElse(failed)
-          
+
 
   /** Search an implicit argument and report error if not found */
   def implicitArgTree(formal: Type, span: Span)(using Context): Tree = {

tests/init/neg/i15363.check

@@ -0,0 +1,15 @@
+-- Warning: tests/init/neg/i15363.scala:3:10 -----------------------------------
+3 |  val b = new B(this) // error
+  |          ^^^^^^^^^^^
+  |Unsafe leaking of uninitialized values: the leaked value is used.  Calling trace:
+  |-> class A:	[ i15363.scala:1 ]
+  |   ^
+  |-> val b = new B(this) // error	[ i15363.scala:3 ]
+  |           ^^^^^^^^^^^
+  |
+  |The leaked uninitialized value is used as follows:
+  |-> class B(a: A):	[ i15363.scala:7 ]
+  |   ^
+  |-> val x = a.m	[ i15363.scala:8 ]
+  |           ^^^
+1 warning found

tests/init/neg/i15363.scala

@@ -0,0 +1,9 @@
+class A:
+  // should report one error here
+  val b = new B(this) // error
+  val m = 10
+  val n = 20
+
+class B(a: A):
+  val x = a.m
+  val y = a.n