Fixes and improvements to trace logging

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1370,13 +1370,6 @@ class Definitions {
     else if arity >= 0 then FunctionType(arity)
     else NoType
 
-  val predefClassNames: Set[Name] =
-    Set("Predef$", "DeprecatedPredef", "LowPriorityImplicits").map(_.toTypeName.unmangleClassName)
-
-  /** Is `cls` the predef module class, or a class inherited by Predef? */
-  def isPredefClass(cls: Symbol): Boolean =
-    (cls.owner eq ScalaPackageClass) && predefClassNames.contains(cls.name)
-
   private val JavaImportFns: List[RootRef] = List(
     RootRef(() => JavaLangPackageVal.termRef)
   )

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -36,7 +36,7 @@ object Formatting {
               case _ => ex.getMessage
             s"[cannot display due to $msg, raw string = ${arg.toString}]"
         }
-      case _ => arg.toString
+      case _ => String.valueOf(arg)
     }
 
     private def treatArg(arg: Any, suffix: String)(using Context): (Any, String) = arg match {

compiler/src/dotty/tools/dotc/reporting/trace.scala

@@ -7,13 +7,23 @@ import config.Config
 import config.Printers
 import core.Mode
 
+/** Exposes the {{{ trace("question") { op } }}} syntax.
+ *
+ * Traced operations will print indented messages if enabled.
+ * Tracing depends on [[Config.tracingEnabled]] and [[dotty.tools.dotc.config.ScalaSettings.Ylog]].
+ * Tracing can be forced by replacing [[trace]] with [[trace.force]] or [[trace.log]] (see below).
+ */
 object trace extends TraceSyntax:
   inline def isEnabled = Config.tracingEnabled
   protected val isForced = false
 
   object force extends TraceSyntax:
     inline def isEnabled: true = true
     protected val isForced = true
+
+  object log extends TraceSyntax:
+    inline def isEnabled: true = true
+    protected val isForced = false
 end trace
 
 /** This module is carefully optimized to give zero overhead if Config.tracingEnabled
@@ -73,7 +83,7 @@ trait TraceSyntax:
       var logctx = ctx
       while logctx.reporter.isInstanceOf[StoreReporter] do logctx = logctx.outer
       def margin = ctx.base.indentTab * ctx.base.indent
-      def doLog(s: String) = if isForced then println(s) else report.log(s)
+      def doLog(s: String) = if isForced then println(s) else report.log(s)(using logctx)
       def finalize(msg: String) =
         if !finalized then
           ctx.base.indent -= 1