From deb945669e677ab817838342910dd502137cc4c7 Mon Sep 17 00:00:00 2001
From: friendseeker <66892505+Friendseeker@users.noreply.github.com>
Date: Mon, 25 Dec 2023 15:27:28 -0800
Subject: [PATCH] Flag class file collision as error

---
 compiler/src/dotty/tools/backend/jvm/PostProcessor.scala | 2 +-
 tests/pos-with-compiler-cc/backend/jvm/GenBCode.scala    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/src/dotty/tools/backend/jvm/PostProcessor.scala b/compiler/src/dotty/tools/backend/jvm/PostProcessor.scala
index 45c6d6ecad44..571058cbe0f4 100644
--- a/compiler/src/dotty/tools/backend/jvm/PostProcessor.scala
+++ b/compiler/src/dotty/tools/backend/jvm/PostProcessor.scala
@@ -73,7 +73,7 @@ class PostProcessor(val frontendAccess: PostProcessorFrontendAccess, val bTypes:
           else s" (defined in ${pos2.source.file.name})"
         def nicify(name: String): String = name.replace('/', '.').nn
         if name1 == name2 then
-          backendReporting.warning(
+          backendReporting.error(
             em"${nicify(name1)} and ${nicify(name2)} produce classes that overwrite one another", pos1)
         else
           backendReporting.warning(
diff --git a/tests/pos-with-compiler-cc/backend/jvm/GenBCode.scala b/tests/pos-with-compiler-cc/backend/jvm/GenBCode.scala
index 1af7e5dd705a..3bc9fb5592ee 100644
--- a/tests/pos-with-compiler-cc/backend/jvm/GenBCode.scala
+++ b/tests/pos-with-compiler-cc/backend/jvm/GenBCode.scala
@@ -214,7 +214,7 @@ class GenBCodePipeline(val int: DottyBackendInterface, val primitives: DottyPrim
           val same = classSymbol.effectiveName.toString == dupClassSym.effectiveName.toString
           atPhase(typerPhase) {
             if (same)
-              report.warning( // FIXME: This should really be an error, but then FromTasty tests fail
+              report.error(
                 em"$cl1 and ${cl2.showLocated} produce classes that overwrite one another", cl1.sourcePos)
             else
               report.warning(