From 506d12848787b9e5eb2a926ebcaea67a0d72e28b Mon Sep 17 00:00:00 2001
From: Evan Wilde <ewilde@apple.com>
Date: Sat, 19 Apr 2025 23:32:17 -0700
Subject: [PATCH] Fix Bootstrap: UTF8EncoddingError

The pass that annotated control-flow positions unreachable after an
infinite loop was migrated to pure Swift in PR 79186
(https://github.com/swiftlang/swift/pull/79186). As a result, the
C++-only bootstrap compiler is unable to determine that the
code-location is unreachable. Placing a fatalError after the infinite
while loop.

Fixes: rdar://149568740
(cherry picked from commit 783c969e103a3cb424eb660faa3d5222568c1abc)
---
 stdlib/public/core/UTF8EncodingError.swift | 1 +
 1 file changed, 1 insertion(+)

diff --git a/stdlib/public/core/UTF8EncodingError.swift b/stdlib/public/core/UTF8EncodingError.swift
index 9956b5ec35750..aeaaee5f50866 100644
--- a/stdlib/public/core/UTF8EncodingError.swift
+++ b/stdlib/public/core/UTF8EncodingError.swift
@@ -256,6 +256,7 @@ extension UTF8 {
           errors.append(adjustedErr)
         }
       }
+      fatalError()
     }
   }
 }