From be88dfd7448fd84f2289bd6161912a32c243266a Mon Sep 17 00:00:00 2001
From: Richard Smith <richard@metafoo.co.uk>
Date: Thu, 26 Feb 2026 17:02:53 -0800
Subject: [PATCH] Formatter: don't crash on unexpected SemIR. (#6787)

The formatter is used as a debugging tool, so shouldn't crash if the
SemIR is in an unexpected shape.
---
 toolchain/sem_ir/formatter.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/toolchain/sem_ir/formatter.cpp b/toolchain/sem_ir/formatter.cpp
index efd3d0ed861b..6c4dba205fbb 100644
--- a/toolchain/sem_ir/formatter.cpp
+++ b/toolchain/sem_ir/formatter.cpp
@@ -733,7 +733,9 @@ auto Formatter::FormatParamList(InstBlockId params_id, InstId return_form_id)
       out() << "invalid";
       continue;
     }
-    CARBON_CHECK(!sem_ir_->insts().Is<OutParam>(param_id));
+    if (sem_ir_->insts().Is<OutParam>(param_id)) {
+      out() << "<unexpected out> ";
+    }
     FormatNameAndForm(param_id, sem_ir_->insts().Get(param_id));
   }