From 542f355853fcae25e788c4514fe57494200797ce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Steffen=20Schu=CC=88mann?= <s.schuemann@pobox.com>
Date: Sat, 11 Jul 2026 18:29:40 +0200
Subject: [PATCH] lexically_normal() preserves IPv6 components in device UNC
 paths (#170)

---
 README.md                  | 2 ++
 include/ghc/filesystem.hpp | 7 ++++++-
 test/filesystem_test.cpp   | 8 ++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 64e079e..fb3ef3c 100644
--- a/README.md
+++ b/README.md
@@ -653,6 +653,8 @@ to the expected behavior.
   support, with iteration errors terminating the process.
 * Fix for [#191](https://github.com/gulrak/filesystem/issues/191), appending
   to a host-only UNC path now inserts the missing separator.
+* Fix for [#170](https://github.com/gulrak/filesystem/issues/170),
+  `lexically_normal()` now preserves IPv6 components in device UNC paths.
 * Fix for [#185](https://github.com/gulrak/filesystem/issues/185),
   `lexically_normal()` now preserves unresolved parent components in relative
   paths.
diff --git a/include/ghc/filesystem.hpp b/include/ghc/filesystem.hpp
index 70e21b7..463cf4f 100644
--- a/include/ghc/filesystem.hpp
+++ b/include/ghc/filesystem.hpp
@@ -3290,7 +3290,12 @@ GHC_INLINE path path::lexically_normal() const
             }
         }
         if (!(s.empty() && lastDotDot)) {
-            dest /= s;
+            if (dest.has_relative_path()) {
+                dest.append_name(s.c_str());
+            }
+            else {
+                dest /= s;
+            }
         }
         lastDotDot = s == "..";
     }
diff --git a/test/filesystem_test.cpp b/test/filesystem_test.cpp
index 9502882..f95506f 100644
--- a/test/filesystem_test.cpp
+++ b/test/filesystem_test.cpp
@@ -972,6 +972,14 @@ TEST_CASE("fs.path.gen - path generation", "[filesystem][path][fs.path.gen]")
     CHECK(fs::path("a/b/..\\//..///\\/../c\\\\/").lexically_normal() == "../c/");
     CHECK(fs::path("..a/b/..\\//..///\\/../c\\\\/").lexically_normal() == "../c/");
     CHECK(fs::path("..\\").lexically_normal() == "..");
+    CHECK(fs::path("//?/UNC/::1/c$/foo").lexically_normal() == R"(\\?\UNC\::1\c$\foo)");
+    CHECK(fs::path(R"(\\?\UNC\a::1\c$\foo)").lexically_normal() == R"(\\?\UNC\a::1\c$\foo)");
+    CHECK(fs::path(R"(\\?\UNC\fe80::1\c$\foo)").lexically_normal() == R"(\\?\UNC\fe80::1\c$\foo)");
+    CHECK(fs::path(R"(\\?\UNC\server\share\foo)").lexically_normal() == R"(\\?\UNC\server\share\foo)");
+    CHECK(fs::path(R"(\\server\share\foo)").lexically_normal() == R"(\\server\share\foo)");
+    CHECK(fs::path(R"(\\?\C:\foo\..\bar)").lexically_normal() == R"(\\?\C:\bar)");
+    CHECK(fs::path(R"(\??\C:\foo\..\bar)").lexically_normal() == R"(\??\C:\bar)");
+    CHECK(fs::path(R"(C:foo\..\bar)").lexically_normal() == R"(C:bar)");
 #endif
 
     // lexically_relative()