Avoid using show or toText before an error is reported

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -393,9 +393,10 @@ object Trees {
     def isBackquoted: Boolean = hasAttachment(Backquoted)
   }
 
-  class SearchFailureIdent[-T >: Untyped] private[ast] (name: Name)(implicit @constructorOnly src: SourceFile)
+  class SearchFailureIdent[-T >: Untyped] private[ast] (name: Name, expl: => String)(implicit @constructorOnly src: SourceFile)
     extends Ident[T](name) {
-    override def toString: String = s"SearchFailureIdent($name)"
+    def explanation = expl
+    override def toString: String = s"SearchFailureIdent($explanation)"
   }
 
   /** qualifier.name, or qualifier#name, if qualifier is a type */

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -359,7 +359,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   // ------ Creation methods for untyped only -----------------
 
   def Ident(name: Name)(implicit src: SourceFile): Ident = new Ident(name)
-  def SearchFailureIdent(name: Name)(implicit src: SourceFile): SearchFailureIdent = new SearchFailureIdent(name)
+  def SearchFailureIdent(name: Name, explanation: => String)(implicit src: SourceFile): SearchFailureIdent = new SearchFailureIdent(name, explanation)
   def Select(qualifier: Tree, name: Name)(implicit src: SourceFile): Select = new Select(qualifier, name)
   def SelectWithSig(qualifier: Tree, name: Name, sig: Signature)(implicit src: SourceFile): Select = new SelectWithSig(qualifier, name, sig)
   def This(qual: Ident)(implicit src: SourceFile): This = new This(qual)

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

@@ -317,7 +317,7 @@ object Denotations {
 
     def requiredMethod(pname: PreName, argTypes: List[Type])(using Context): TermSymbol = {
       val name = pname.toTermName
-      info.member(name).requiredSymbol(i"method", name, this, argTypes) { x =>
+      info.member(name).requiredSymbol("method", name, this, argTypes) { x =>
         x.is(Method) && {
           x.info.paramInfoss match {
             case paramInfos :: Nil => paramInfos.corresponds(argTypes)(_ =:= _)

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

@@ -143,6 +143,8 @@ object StdNames {
     val QUOTE: N                      = "'"
     val TYPE_QUOTE: N                 = "type_'"
     val TRAIT_SETTER_SEPARATOR: N     = str.TRAIT_SETTER_SEPARATOR
+    val AMBIGUOUS: N                  = "/* ambiguous */"
+    val MISSING: N                    = "/* missing */"
 
     // value types (and AnyRef) are all used as terms as well
     // as (at least) arguments to the @specialize annotation.

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

@@ -352,10 +352,10 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       case id: Trees.SearchFailureIdent[?] =>
         tree.typeOpt match {
           case reason: Implicits.SearchFailureType =>
-            toText(id.name)
+            Str(id.explanation)
             ~ ("summon[" ~ toText(reason.clarify(reason.expectedType)) ~ "]").close
           case _ =>
-            toText(id.name)
+            Str(id.explanation)
         }
       case id @ Ident(name) =>
         val txt = tree.typeOpt match {

compiler/src/dotty/tools/dotc/report.scala

@@ -43,7 +43,7 @@ object report:
   def featureWarning(msg: Message, pos: SrcPos = NoSourcePosition)(using Context): Unit =
     issueWarning(new FeatureWarning(msg, pos.sourcePos))
 
-  def featureWarning(feature: String, featureDescription: String,
+  def featureWarning(feature: String, featureDescription: => String,
       featureUseSite: Symbol, required: Boolean, pos: SrcPos)(using Context): Unit = {
     val req = if (required) "needs to" else "should"
     val fqname = s"scala.language.$feature"
@@ -56,7 +56,7 @@ object report:
            |See the Scala docs for value $fqname for a discussion
            |why the feature $req be explicitly enabled.""".stripMargin
 
-    val msg = s"""$featureDescription $req be enabled
+    def msg = s"""$featureDescription $req be enabled
                  |by adding the import clause 'import $fqname'
                  |or by setting the compiler option -language:$feature.$explain""".stripMargin
     if (required) error(msg, pos)

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

@@ -17,7 +17,6 @@ import util.NoSourcePosition
 
 import java.io.{ BufferedReader, PrintWriter }
 
-
 object Reporter {
   /** Convert a SimpleReporter into a real Reporter */
   def fromSimpleReporter(simple: interfaces.SimpleReporter): Reporter =
@@ -142,9 +141,14 @@ abstract class Reporter extends interfaces.ReporterResult {
   var unreportedWarnings: Map[String, Int] = Map.empty
 
   def report(dia: Diagnostic)(using Context): Unit =
-    if (!isHidden(dia)) {
+    val isSummarized = dia match
+      case dia: ConditionalWarning => !dia.enablingOption.value
+      case _ => false
+    if isSummarized  // avoid isHidden test for summarized warnings so that message is not forced
+       || !isHidden(dia)
+    then
       withMode(Mode.Printing)(doReport(dia))
-      dia match {
+      dia match
         case dia: ConditionalWarning if !dia.enablingOption.value =>
           val key = dia.enablingOption.name
           unreportedWarnings =
@@ -155,8 +159,6 @@ abstract class Reporter extends interfaces.ReporterResult {
           _errorCount += 1
         case dia: Info => // nothing to do here
         // match error if d is something else
-      }
-    }
 
   def incomplete(dia: Diagnostic)(using Context): Unit =
     incompleteHandler(dia, ctx)

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

@@ -617,7 +617,7 @@ trait Applications extends Compatibility {
         case nil =>
           args match {
             case arg :: args1 =>
-              val msg = arg match
+              def msg = arg match
                 case untpd.Tuple(Nil)
                 if applyKind == ApplyKind.InfixTuple && funType.widen.isNullaryMethod =>
                   i"can't supply unit value with infix notation because nullary $methString takes no arguments; use dotted invocation instead: (...).${methRef.name}()"

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

@@ -393,9 +393,11 @@ object Implicits:
   object SearchFailure {
     def apply(tpe: SearchFailureType)(using Context): SearchFailure = {
       val id = tpe match
-        case tpe: AmbiguousImplicits => i"/* ambiguous: ${tpe.explanation} */"
-        case _ => "/* missing */"
-      SearchFailure(untpd.SearchFailureIdent(id.toTermName).withTypeUnchecked(tpe))
+        case tpe: AmbiguousImplicits =>
+          untpd.SearchFailureIdent(nme.AMBIGUOUS, s"/* ambiguous: ${tpe.explanation} */")
+        case _ =>
+          untpd.SearchFailureIdent(nme.MISSING, "/* missing */")
+      SearchFailure(id.withTypeUnchecked(tpe))
     }
   }