From cbdc6670a1b20d28cde1455ece1ef5002cc60f7c Mon Sep 17 00:00:00 2001
From: scawful <justin.scofield@outlook.com>
Date: Thu, 20 Nov 2025 02:15:00 -0500
Subject: [PATCH] fix(windows): properly detect clang-cl and add /std:c++latest
 for std::filesystem

Root cause analysis:
- clang-cl on GitHub Actions Windows Server 2022 cannot find std::filesystem
- The compiler defaults to pre-C++17 compatibility, exposing only std::experimental::filesystem
- Build logs show: -std=c++23 (Unix-style flag) instead of /std:c++latest (MSVC-style flag)

Key insight: CMAKE_CXX_COMPILER_FRONTEND_VARIANT is needed to distinguish:
- "MSVC": clang-cl (Clang with MSVC command-line interface)
- "GNU": regular Clang on Windows

Solution:
1. Use CMAKE_CXX_COMPILER_FRONTEND_VARIANT to properly detect clang-cl
2. Add /std:c++latest flag specifically to yaze_util target (where filesystem is used)
3. Apply as PUBLIC compile option so it propagates to dependent targets

This targets the exact source of the problem - clang-cl needs MSVC-style /std:c++latest
flag to access modern MSVC STL features including std::filesystem.

Tested approach based on CMake 3.16+ feature CMAKE_CXX_COMPILER_FRONTEND_VARIANT.

Related commits: 19196ca87c, c2bb90a3f1, b556b155a5

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 cmake/utils.cmake   | 28 ++++++----------------------
 src/util/util.cmake | 24 +++++++++++++++---------
 2 files changed, 21 insertions(+), 31 deletions(-)

diff --git a/cmake/utils.cmake b/cmake/utils.cmake
index ff320346..f50baa44 100644
--- a/cmake/utils.cmake
+++ b/cmake/utils.cmake
@@ -40,28 +40,12 @@ function(yaze_add_compiler_flags)
 
     # Compiler-specific settings
     if(MSVC)
-        # Check if we're using clang-cl (Clang with MSVC-compatible command line)
-        if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-            # clang-cl requires explicit /std:c++latest to access C++23 features including <filesystem>
-            # Without this, clang-cl only sees std::experimental::filesystem from older MSVC STL
-            target_compile_options(yaze_common INTERFACE
-                /EHsc
-                /W4 /permissive-
-                /bigobj
-                /utf-8
-                /std:c++latest
-            )
-            message(STATUS "Windows clang-cl: Added /std:c++latest for C++23 and std::filesystem support")
-        else()
-            # Regular MSVC compiler
-            target_compile_options(yaze_common INTERFACE
-                /EHsc
-                /W4 /permissive-
-                /bigobj
-                /utf-8
-            )
-        endif()
-
+        target_compile_options(yaze_common INTERFACE
+            /EHsc
+            /W4 /permissive-
+            /bigobj
+            /utf-8
+        )
         target_compile_definitions(yaze_common INTERFACE
             _CRT_SECURE_NO_WARNINGS
             _CRT_NONSTDC_NO_WARNINGS
diff --git a/src/util/util.cmake b/src/util/util.cmake
index 3fe0b416..f4ba062e 100644
--- a/src/util/util.cmake
+++ b/src/util/util.cmake
@@ -105,15 +105,21 @@ elseif(APPLE)
   target_compile_definitions(yaze_util PRIVATE MACOS)
 elseif(WIN32)
   target_compile_definitions(yaze_util PRIVATE WINDOWS)
-  # Windows-specific: Some clang-cl versions need help finding filesystem
-  # Ensure we're using the right C++ standard library headers
-  if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    # Verify clang-cl can find MSVC STL headers with filesystem support
-    include(CheckIncludeFileCXX)
-    check_include_file_cxx("filesystem" HAVE_FILESYSTEM)
-    if(NOT HAVE_FILESYSTEM)
-      message(WARNING "std::filesystem not found - this may cause build failures on Windows")
-    endif()
+
+  # CRITICAL FIX: clang-cl on Windows needs explicit /std:c++latest for std::filesystem
+  # clang-cl uses Clang's compiler but must interface with MSVC STL. Without this flag,
+  # it only finds std::experimental::filesystem (pre-C++17 version).
+  #
+  # The CMAKE_CXX_COMPILER_FRONTEND_VARIANT check distinguishes:
+  # - "MSVC": clang-cl (Clang with MSVC-compatible command line)
+  # - "GNU": regular Clang on Windows
+  if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "MSVC")
+    # Use MSVC-style flag for clang-cl
+    target_compile_options(yaze_util PUBLIC /std:c++latest)
+    message(STATUS "Windows clang-cl detected: Added /std:c++latest for std::filesystem support")
+  elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    # Regular Clang on Windows - already has proper flags from parent
+    message(STATUS "Windows Clang (non-cl) detected: Using inherited C++23 flags")
   endif()
 endif()