Fix #9517: Do not print contents of ErrorType on -Xprint-types

Author: nicolasstucki

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

@@ -4706,11 +4706,12 @@ object Types {
 
   object ErrorType:
     def apply(m: Message)(using Context): ErrorType =
-      val et = new ErrorType:
+      class PreviousErrorType extends ErrorType:
         def msg(using Context): Message =
           ctx.base.errorTypeMsg.get(this) match
             case Some(m) => m
             case None => "error message from previous run no longer available"
+      val et = new PreviousErrorType
       ctx.base.errorTypeMsg(et) = m
       et
   end ErrorType

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

@@ -695,7 +695,9 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         }
         else tp2
 
-      if (!suppressTypes)
+      if tp3.isInstanceOf[ErrorType] then
+        txt = ("<" ~ txt ~ ":ERROR>").close
+      else if !suppressTypes then
         txt = ("<" ~ txt ~ ":" ~ toText(tp3) ~ ">").close
       else if (tree.isType && !homogenizedView)
         txt = toText(tp3)

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -149,6 +149,7 @@ class CompilationTests extends ParallelTesting {
       compileFile("tests/neg-custom-args/i3882.scala", allowDeepSubtypes),
       compileFile("tests/neg-custom-args/i4372.scala", allowDeepSubtypes),
       compileFile("tests/neg-custom-args/i1754.scala", allowDeepSubtypes),
+      compileFile("tests/neg-custom-args/i9517.scala", defaultOptions.and("-Xprint-types")),
       compileFile("tests/neg-custom-args/interop-polytypes.scala", allowDeepSubtypes.and("-Yexplicit-nulls")),
       compileFile("tests/neg-custom-args/conditionalWarnings.scala", allowDeepSubtypes.and("-deprecation").and("-Xfatal-warnings")),
       compileFilesInDir("tests/neg-custom-args/isInstanceOf", allowDeepSubtypes and "-Xfatal-warnings"),

tests/neg-custom-args/i9517.scala

@@ -0,0 +1,3 @@
+
+def test():Unit = foo({ case 1 => 10 }) // error
+def foo(x: Any): Boolean = true