MinGW C++ filesystem glitches

Readme.md

C++ UNC path filesystem bug with MinGW

MinGW currently has bugs with UNC paths in C++ filesystem library. MSVC, Clang-CL, oneAPI work correctly.

A convenience script runs the tests from the oneAPI command prompt (or MSVC if oneAPI not available).

cmake -P main.cmake

MSVC

cl /std:c++17 test_unc.cpp && test_unc.exe

PASSED: path: "\\\\server\\share\\path\\" == "\\\\server\\share\\path\\"
PASSED: path: "\\\\host\\a\\c" == "\\\\host\\a\\c"
PASSED: string: \\host\a\c == \\host\a\c
PASSED: generic string: //host/a/c == //host/a/c
OK: UNC tests passed

MSYS2 G++

g++ --version && g++ test_unc.cpp && ./a.exe

g++.exe (Rev3, Built by MSYS2 project) 13.2.0
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

PASSED: path: "\\server\\share\\path\\" == "\\server\\share\\path\\"
PASSED: path: "\\host\\a\\c" == "\\\\host\\a\\c"
FAILED: string: \host\a\c != \\host\a\c
FAILED: generic string: /host/a/c != //host/a/c
FAILED: UNC tests

MSYS2 Clang

clang++ --version && clang++ test_unc.cpp && ./a.exe

clang version 17.0.6
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:/msys64/mingw64/bin
PASSED: path: "\\server\\share\\path\\" == "\\server\\share\\path\\"
PASSED: path: "\\host\\a\\c" == "\\\\host\\a\\c"
FAILED: string: \host\a\c != \\host\a\c
FAILED: generic string: /host/a/c != //host/a/c
FAILED: UNC tests

Intel oneAPI

ICX (MSVC-like) driver

icx test_unc.cpp && test_unc.exe

Intel(R) oneAPI DPC++/C++ Compiler 2024.0.0 (2024.0.0.20231017)
Target: x86_64-pc-windows-msvc
Thread model: posix

PASSED: path: "\\\\server\\share\\path\\" == "\\\\server\\share\\path\\"
PASSED: path: "\\\\host\\a\\c" == "\\\\host\\a\\c"
PASSED: string: \\host\a\c == \\host\a\c
PASSED: generic string: //host/a/c == //host/a/c
OK: UNC tests passed

ICPX (GNU-like) driver

icpx --version && icpx test_unc.cpp && a.exe

Intel(R) oneAPI DPC++/C++ Compiler 2024.0.0 (2024.0.0.20231017)
Target: x86_64-pc-windows-msvc
Thread model: posix

PASSED: path: "\\\\server\\share\\path\\" == "\\\\server\\share\\path\\"
PASSED: path: "\\\\host\\a\\c" == "\\\\host\\a\\c"
PASSED: string: \\host\a\c == \\host\a\c
PASSED: generic string: //host/a/c == //host/a/c
OK: UNC tests passed

CMakeLists.txt

cmake_minimum_required(VERSION 3.10...3.28)

if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR)
  message(FATAL_ERROR "In-source builds are not allowed.
  cmake -Bbuild")
endif()

project(fs_unc LANGUAGES CXX)

enable_testing()

set(CMAKE_CXX_STANDARD 17)

add_executable(test_unc test_unc.cpp)

add_test(NAME ${CMAKE_CXX_COMPILER_ID}_unc COMMAND test_unc)

file(GENERATE OUTPUT .gitignore CONTENT "*")

main.cmake

cmake_minimum_required(VERSION 3.21)

# run this script from Windows Intel oneAPI command prompt,
# or MSVC prompt if you don't have oneAPI.

set(compilers cl clang-cl clang++ g++ icx)
# icpx not yet enabled on Windows in CMake


function(run_compiler exe)

find_program(cexe NAMES ${exe} NO_CACHE)
if(NOT cexe)
  message(STATUS "Compiler ${exe} not found")
  return()
endif()

set(bindir ${CMAKE_CURRENT_LIST_DIR}/build_${exe})

execute_process(COMMAND ${CMAKE_COMMAND}
    -B${bindir} -S${CMAKE_CURRENT_LIST_DIR}
    -DCMAKE_CXX_COMPILER=${cexe}
  RESULT_VARIABLE ret
)

if(NOT ret EQUAL 0)
  message(WARNING "Compiler ${c} failed to configure")
  return()
endif()

execute_process(COMMAND ${CMAKE_COMMAND} --build ${bindir}
  RESULT_VARIABLE ret
)

if(NOT ret EQUAL 0)
  message(WARNING "Compiler ${c} build failed")
  return()
endif()

execute_process(COMMAND ${CMAKE_CTEST_COMMAND} --test-dir ${bindir} --verbose
  RESULT_VARIABLE ret
)

if(NOT ret EQUAL 0)
  message(WARNING "Compiler ${c} tests failed")
  return()
endif()

endfunction(run_compiler)


foreach(c IN LISTS compilers)
  run_compiler(${c})
endforeach()

test_unc.cpp

#include <filesystem>
#include <cstdlib>
#include <iostream>

static_assert(__cpp_lib_filesystem, "C++17 std::filesystem is not available.");

namespace fs = std::filesystem;

int main(){

  int err = 0;

  fs::path bserv("\\\\server\\share\\\\path\\");
  fs::path rserv("//server/share//path/");

  fs::path n_bserv = bserv.lexically_normal();
  fs::path n_rserv = rserv.lexically_normal();
  if (n_bserv == n_rserv){
    std::cout << "PASSED: path: " << n_bserv << " == " << n_rserv << "\n";
  }
  else {
    err++;
    std::cerr << "FAILED: path: " << n_bserv << " != " << n_rserv << "\n";
  }

  fs::path p3("//host/a/b/../c");
  fs::path p3n = p3.lexically_normal();
  fs::path p3n_r("\\\\host\\a\\c");

  if (p3n == p3n_r){
    std::cout << "PASSED: path: " << p3n << " == " << p3n_r << "\n";
  }
  else {
    err++;
    std::cerr << "FAILED: path: " << p3n << " != " << p3n_r << "\n";
  }

  std::string p3s = p3n.string();
  if (p3s == "\\\\host\\a\\c"){
    std::cout << "PASSED: string: " << p3s << " == \\\\host\\a\\c\n";
  }
  else {
    err++;
    std::cerr << "FAILED: string: " << p3s << " != \\\\host\\a\\c\n";
  }

  std::string p3gs = p3n.generic_string();
  if (p3gs == "//host/a/c"){
    std::cout << "PASSED: generic string: " << p3gs << " == //host/a/c\n";
  }
  else {
    err++;
    std::cerr << "FAILED: generic string: " << p3gs << " != //host/a/c\n";
  }

  fs::path dlocal("\\\\?\\C:\\path\\x\\..");
  fs::path blocal("C:\\path\\y\\..\\");

  fs::path n_dlocal = fs::weakly_canonical(dlocal);
  fs::path n_blocal = blocal.lexically_normal();

  if (n_dlocal == n_blocal){
    std::cout << "PASSED: long_path: " << n_dlocal << " == " << n_blocal << "\n";
  }
  else {
    err++;
    std::cerr << "FAILED: long_path: " << n_dlocal << " != " << n_blocal << "\n";
  }

  if (err != 0){
    std::cerr << "FAILED: UNC tests\n";
    return EXIT_FAILURE;
  }

  std::cout << "OK: UNC tests passed\n";
  return EXIT_SUCCESS;
}