Fix #6795: Print flagString

Author: nicolasstucki

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1697,7 +1697,7 @@ object messages {
   case class ModifiersNotAllowed(flags: FlagSet, printableType: Option[String])(implicit ctx: Context)
     extends Message(ModifiersNotAllowedID) {
     val kind: String = "Syntax"
-    val msg: String = em"Modifier(s) $flags not allowed for ${printableType.getOrElse("combination")}"
+    val msg: String = em"Modifier(s) ${flags.flagsString} not allowed for ${printableType.getOrElse("combination")}"
     val explanation: String = {
       val first = "sealed def y: Int = 1"
       val second = "sealed lazy class z"

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

@@ -284,7 +284,7 @@ class Namer { typer: Typer =>
           case _ => (flags.isTermFlags, flags.toTermFlags, "value")
         }
         if (!ok)
-          ctx.error(i"modifier(s) `$flags' incompatible with $kind definition", tree.sourcePos)
+          ctx.error(i"modifier(s) `${flags.flagsString}' incompatible with $kind definition", tree.sourcePos)
         adapted
       }
 

tests/neg/i6795-b.check

@@ -0,0 +1,6 @@
+-- [E083] Syntax Error: tests/neg/i6795-b.scala:1:11 -------------------------------------------------------------------
+1 |sealed def y: Int = 1 // error
+  |           ^
+  |           Modifier(s) sealed not allowed for method
+
+longer explanation available when compiling with `-explain`

tests/neg/i6795-b.scala

@@ -0,0 +1 @@
+sealed def y: Int = 1 // error

tests/neg/i6795.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i6795.scala:1:13 -----------------------------------------------------------------------------------
+1 |erased class Foo // error
+  |^^^^^^^^^^^^^^^^
+  |modifier(s) `erased' incompatible with type definition

tests/neg/i6795.scala

@@ -0,0 +1 @@
+erased class Foo // error