Do not extend an already extended path.

Author: evoskuil

src/unicode/utf8_everywhere/paths.cpp

@@ -140,9 +140,14 @@ std::filesystem::path extended_path(const std::filesystem::path& path) NOEXCEPT
     // However this includes "considered relative" paths (with ".." segments).
     // That is of no consequence here because those will also be converted.
     // MAX_PATH includes the terminator, so a path of that length requires it.
+    // An already extended path (e.g. by a shell) is not extended again.
     BC_PUSH_WARNING(NO_THROW_IN_NOEXCEPT)
+    constexpr std::wstring_view prefix{ L"\\\\?\\" };
     const auto full = qualified_path(path).wstring();
-    return { (full.length() >= MAX_PATH) ? L"\\\\?\\" + full : full };
+    if (full.starts_with(prefix) || full.length() < MAX_PATH)
+        return { full };
+
+    return { std::wstring{ prefix } + full };
     BC_POP_WARNING()
 }
 

test/unicode/utf8_everywhere/paths.cpp

@@ -193,6 +193,12 @@ BOOST_AUTO_TEST_CASE(paths__extended_path__maximum__extended)
     BOOST_REQUIRE_EQUAL(extended_path({ test_maximum }), test_maximum_extended);
 }
 
+BOOST_AUTO_TEST_CASE(paths__extended_path__extended__unchanged)
+{
+    BOOST_REQUIRE_EQUAL(extended_path(test_extended), test_extended);
+    BOOST_REQUIRE_EQUAL(extended_path(test_maximum_extended), test_maximum_extended);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 BC_POP_WARNING()