From 625d8965bfb00e7e749b90024e48c8be1cb079d5 Mon Sep 17 00:00:00 2001
From: Junyoung Lee <leejy31415@outlook.com>
Date: Mon, 2 Mar 2026 16:05:30 -0600
Subject: [PATCH 1/2] Make `fs::absolute("", ec)` set the error code.

---
 stl/inc/filesystem                          | 20 +++++++++-----------
 tests/libcxx/expected_results.txt           |  5 ++---
 tests/std/tests/P0218R1_filesystem/test.cpp |  8 ++++++++
 3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/stl/inc/filesystem b/stl/inc/filesystem
index 7d838ea2d17..b9cc15336ea 100644
--- a/stl/inc/filesystem
+++ b/stl/inc/filesystem
@@ -3013,17 +3013,15 @@ namespace filesystem {
         // calls GetFullPathNameW
         _Ec.clear(); // for exception safety
         path _Result;
-        if (!_Input._Text.empty()) {
-            _Result._Text.resize(__std_fs_max_path);
-            for (;;) {
-                const auto _Requested_size = static_cast<unsigned long>(_Result._Text.size());
-                const auto _Full_path_result =
-                    __std_fs_get_full_path_name(_Input._Text.c_str(), _Requested_size, _Result._Text.data());
-                _Result._Text.resize(_Full_path_result._Size);
-                if (_Full_path_result._Size < _Requested_size) {
-                    _Ec = _Make_ec(_Full_path_result._Error);
-                    break;
-                }
+        _Result._Text.resize(__std_fs_max_path);
+        for (;;) {
+            const auto _Requested_size = static_cast<unsigned long>(_Result._Text.size());
+            const auto _Full_path_result =
+                __std_fs_get_full_path_name(_Input._Text.c_str(), _Requested_size, _Result._Text.data());
+            _Result._Text.resize(_Full_path_result._Size);
+            if (_Full_path_result._Size < _Requested_size) {
+                _Ec = _Make_ec(_Full_path_result._Error);
+                break;
             }
         }
         return _Result;
diff --git a/tests/libcxx/expected_results.txt b/tests/libcxx/expected_results.txt
index 971a27c8889..cdccea195d3 100644
--- a/tests/libcxx/expected_results.txt
+++ b/tests/libcxx/expected_results.txt
@@ -714,6 +714,8 @@ std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/indirec
 # Not analyzed, likely bogus test. constexpr fails with "vector iterators incompatible".
 std/ranges/range.adaptors/range.join.with/range.join.with.iterator/ctor.default.pass.cpp FAIL
 
+# libc++ treats `fs::absolute("", ec)` as a success case, whereas we emit an error and return an empty `path`.
+std/input.output/filesystems/fs.op.funcs/fs.op.absolute/absolute.pass.cpp FAIL
 
 # *** LIKELY STL BUGS ***
 # Not analyzed, likely STL bugs. Various assertions.
@@ -1122,9 +1124,6 @@ std/input.output/filesystems/class.path/path.member/path.generic.obs/generic_str
 # Not analyzed. Assertion failed: std::equal(p.begin(), p.end(), TC.elements.begin(), ComparePathExact())
 std/input.output/filesystems/class.path/path.member/path.decompose/path.decompose.pass.cpp FAIL
 
-# Not analyzed. Assertion failed: ret.is_absolute()
-std/input.output/filesystems/fs.op.funcs/fs.op.absolute/absolute.pass.cpp FAIL
-
 # Not analyzed. Assertion failed: ret == TC.p
 std/input.output/filesystems/fs.op.funcs/fs.op.temp_dir_path/temp_directory_path.pass.cpp FAIL
 
diff --git a/tests/std/tests/P0218R1_filesystem/test.cpp b/tests/std/tests/P0218R1_filesystem/test.cpp
index de836655bc4..76b4c25c323 100644
--- a/tests/std/tests/P0218R1_filesystem/test.cpp
+++ b/tests/std/tests/P0218R1_filesystem/test.cpp
@@ -1537,6 +1537,14 @@ void test_absolute() {
     longPath.resize(260);
     expect_absolute(longPath, longPath);
 
+    EXPECT(absolute(L"", ec).empty());
+    if (ec.value() != 123) {
+        wcerr << L"Warning: Expected absolute on an empty path to report ERROR_INVALID_NAME, "
+                 L"but it reported "
+              << ec.value() << L"\n";
+    }
+    EXPECT(ec.category() == system_category());
+
     expect_absolute({}, {});
 }
 

From 3271d11e057bb7e5df404463bc5b5d19f47bbe87 Mon Sep 17 00:00:00 2001
From: Junyoung Lee <leejy31415@outlook.com>
Date: Mon, 2 Mar 2026 17:15:50 -0600
Subject: [PATCH 2/2] remove existing empty test

---
 tests/std/tests/P0218R1_filesystem/test.cpp | 2 --
 1 file changed, 2 deletions(-)

diff --git a/tests/std/tests/P0218R1_filesystem/test.cpp b/tests/std/tests/P0218R1_filesystem/test.cpp
index 76b4c25c323..edd4b60ce03 100644
--- a/tests/std/tests/P0218R1_filesystem/test.cpp
+++ b/tests/std/tests/P0218R1_filesystem/test.cpp
@@ -1544,8 +1544,6 @@ void test_absolute() {
               << ec.value() << L"\n";
     }
     EXPECT(ec.category() == system_category());
-
-    expect_absolute({}, {});
 }
 
 void test_canonical() {