From cf38826926e59ac38b36912fab50420885385155 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Mon, 10 Aug 2020 17:35:47 +0200
Subject: [PATCH] Fix #9517: Do not print recursively ErrorType on
 -Xprint-types

---
 compiler/src/dotty/tools/dotc/core/Types.scala       | 12 +++++++-----
 .../src/dotty/tools/dotc/printing/PlainPrinter.scala |  2 ++
 .../test/dotty/tools/dotc/CompilationTests.scala     |  1 +
 tests/neg-custom-args/i9517.scala                    |  3 +++
 4 files changed, 13 insertions(+), 5 deletions(-)
 create mode 100644 tests/neg-custom-args/i9517.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 777f43931e13..da5ce2eada1a 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -4706,15 +4706,17 @@ object Types {
 
   object ErrorType:
     def apply(m: Message)(using Context): ErrorType =
-      val et = new 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
 
+  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"
+
   object UnspecifiedErrorType extends ErrorType {
     override def msg(using Context): Message = "unspecified error"
   }
diff --git a/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala b/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
index 8b41983bad27..0d05928b1de6 100644
--- a/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
+++ b/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
@@ -177,6 +177,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
             keywordStr(" match ") ~ "{" ~ casesText ~ "}" ~
             (" <: " ~ toText(bound) provided !bound.isAny)
         }.close
+      case tp: PreviousErrorType if ctx.settings.XprintTypes.value =>
+        "<error>" // do not print previously reported error message because they may try to print this error type again recuresevely
       case tp: ErrorType =>
         s"<error ${tp.msg.rawMessage}>"
       case tp: WildcardType =>
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index 7b3fd7c6f04a..e927ba8d31a4 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/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"),
diff --git a/tests/neg-custom-args/i9517.scala b/tests/neg-custom-args/i9517.scala
new file mode 100644
index 000000000000..d1201d8ca39e
--- /dev/null
+++ b/tests/neg-custom-args/i9517.scala
@@ -0,0 +1,3 @@
+
+def test():Unit = foo({ case 1 => 10 }) // error
+def foo(x: Any): Boolean = true