Improve message when tree cannot be shown as source (#19906)

Closes #19905

compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala

@@ -188,7 +188,7 @@ object SourceCode {
           case Select(newTree: New, _) =>
             printType(newTree.tpe)(using Some(cdef.symbol))
           case parent: Term =>
-            throw new MatchError(parent.show(using Printer.TreeStructure))
+            cannotBeShownAsSource(parent.show(using Printer.TreeStructure))
         }
 
         def printSeparated(list: List[Tree /* Term | TypeTree */]): Unit = list match {
@@ -536,7 +536,7 @@ object SourceCode {
         printCaseDef(tree)
 
       case _ =>
-        throw new MatchError(tree.show(using Printer.TreeStructure))
+        cannotBeShownAsSource(tree.show(using Printer.TreeStructure))
 
     }
 
@@ -934,7 +934,7 @@ object SourceCode {
           case Ident("unapply" | "unapplySeq") =>
             this += fun.symbol.owner.fullName.stripSuffix("$")
           case _ =>
-            throw new MatchError(fun.show(using Printer.TreeStructure))
+            cannotBeShownAsSource(fun.show(using Printer.TreeStructure))
         }
         inParens(printPatterns(patterns, ", "))
 
@@ -953,7 +953,7 @@ object SourceCode {
         printTree(v)
 
       case _ =>
-        throw new MatchError(pattern.show(using Printer.TreeStructure))
+        cannotBeShownAsSource(pattern.show(using Printer.TreeStructure))
 
     }
 
@@ -1079,7 +1079,7 @@ object SourceCode {
         printTypeTree(tpt)
 
       case _ =>
-        throw new MatchError(tree.show(using Printer.TreeStructure))
+        cannotBeShownAsSource(tree.show(using Printer.TreeStructure))
 
     }
 
@@ -1248,7 +1248,7 @@ object SourceCode {
         printType(rhs)
 
       case _ =>
-        throw new MatchError(tpe.show(using Printer.TypeReprStructure))
+        cannotBeShownAsSource(tpe.show(using Printer.TypeReprStructure))
     }
 
     private def printSelector(sel: Selector): this.type = sel match {
@@ -1287,7 +1287,7 @@ object SourceCode {
           val sym = annot.tpe.typeSymbol
           sym != Symbol.requiredClass("scala.forceInline") &&
           sym.maybeOwner != Symbol.requiredPackage("scala.annotation.internal")
-        case x => throw new MatchError(x.show(using Printer.TreeStructure))
+        case x => cannotBeShownAsSource(x.show(using Printer.TreeStructure))
       }
       printAnnotations(annots)
       if (annots.nonEmpty) this += " "
@@ -1458,6 +1458,9 @@ object SourceCode {
       }
     }
 
+    private def cannotBeShownAsSource(x: String): Nothing =
+      throw new Exception(s"$x does not have a source representation")
+
     private object SpecialOp {
       def unapply(arg: Tree): Option[(String, List[Term])] = arg match {
         case arg @ Apply(fn, args) =>

tests/run-macros/i19905.check

@@ -0,0 +1,3 @@
+java.lang.Exception: NoPrefix() does not have a source representation
+java.lang.Exception: NoPrefix() does not have a source representation
+NoPrefix()

tests/run-macros/i19905/Macro_1.scala

@@ -0,0 +1,31 @@
+import scala.quoted.*
+
+inline def noPrefixShortCode: String =
+  ${ noPrefixShortCodeImpl }
+
+inline def noPrefixCode: String =
+  ${ noPrefixCodeImpl }
+
+inline def noPrefixStructure: String =
+  ${ noPrefixStructure }
+
+def noPrefix(using Quotes): quotes.reflect.TypeRepr =
+  import quotes.reflect.*
+  TypeRepr.of[Unit] match
+    case TypeRef(ThisType(TypeRef(prefix, _)), _) => prefix
+
+def noPrefixShortCodeImpl(using Quotes): Expr[String] =
+  import quotes.reflect.*
+  try Expr(Printer.TypeReprShortCode.show(noPrefix))
+  catch case ex: Exception =>
+    Expr(s"${ex.getClass.getName}: ${ex.getMessage}")
+
+def noPrefixCodeImpl(using Quotes): Expr[String] =
+  import quotes.reflect.*
+  try Expr(Printer.TypeReprCode.show(noPrefix))
+  catch case ex: Exception =>
+    Expr(s"${ex.getClass.getName}: ${ex.getMessage}")
+
+def noPrefixStructure(using Quotes): Expr[String] =
+  import quotes.reflect.*
+  Expr(Printer.TypeReprStructure.show(noPrefix))

tests/run-macros/i19905/Test_2.scala

@@ -0,0 +1,5 @@
+@main
+def Test: Unit =
+  println(noPrefixShortCode)
+  println(noPrefixCode)
+  println(noPrefixStructure)