Add debugging of constness

src/main/scala/millfork/env/Environment.scala

@@ -787,6 +787,21 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
     }
   }.map(_.quickSimplify)
 
+  def debugConstness(item: Expression): Unit = {
+    if (!log.debugEnabled) return
+    if (eval(item).isEmpty) {
+      log.debug(s"$item is not const!")
+      item match {
+        case FunctionCallExpression(_, expressions) => expressions.foreach(debugConstness)
+        case SumExpression(expressions, _) => expressions.map(_._2).foreach(debugConstness)
+        case SeparateBytesExpression(b1, b2) =>
+          debugConstness(b1)
+          debugConstness(b2)
+        case _ =>
+      }
+    }
+  }
+
   private def constantOperation(op: MathOperator.Value, params: List[Expression]) = {
     params.map(eval).reduceLeft[Option[Constant]] { (oc, om) =>
       for {

src/main/scala/millfork/error/ConsoleLogger.scala

@@ -51,6 +51,8 @@ class ConsoleLogger extends Logger {
 
   override def traceEnabled: Boolean = verbosity >= 2
 
+  override def debugEnabled: Boolean = verbosity >= 1
+
   override def trace(msg: String, position: Option[Position] = None): Unit = {
     if (verbosity < 2) return
     println("TRACE: " + f(position) + msg)

src/main/scala/millfork/error/ErrorsOnlyLogger.scala

@@ -17,6 +17,8 @@ class ErrorsOnlyLogger(inner: Logger) extends Logger {
 
   override def traceEnabled: Boolean = false
 
+  override def debugEnabled: Boolean = false
+
   override def warn(msg: String, position: Option[Position]): Unit = ()
 
   override def error(msg: String, position: Option[Position]): Unit = inner.error(msg, position)

src/main/scala/millfork/error/Logger.scala

@@ -18,6 +18,8 @@ trait Logger {
 
   def traceEnabled: Boolean
 
+  def debugEnabled: Boolean
+
   def warn(msg: String, position: Option[Position] = None): Unit
 
   def error(msg: String, position: Option[Position] = None): Unit

src/test/scala/millfork/NullLogger.scala

@@ -18,6 +18,8 @@ class NullLogger extends Logger {
 
   override def traceEnabled: Boolean = false
 
+  override def debugEnabled: Boolean = false
+
   override def warn(msg: String, position: Option[Position]): Unit = ()
 
   override def error(msg: String, position: Option[Position]): Unit = ()