From: Tyler Erickson <tyler.erickson@seagate.com>
Date: Mon, 20 Oct 2025 17:39:04 +0000 (-0600)
Subject: bug: Fixing Cmake build when using clang-cl
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=461d9f90c41b90aaa01a0405aabc86c4947fc0fb;p=thirdparty%2Fjson-c.git

bug: Fixing Cmake build when using clang-cl

Clang-cl will fail to build and produce warnings about redefining existing symbols, mostly for float.h and math.h compatibility.

To resolve this, this moves the clang-cl detection earlier in the CMakeLists.txt so that CLANG_CL can be checked properly where there is an existing MSVC workaround for these symbols.
This resolves the build using the latest clang-cl from the LLVM clang repo as well as clang-cl that can be installed with MSVC 2022.

Signed-off-by: Tyler Erickson <tyler.erickson@seagate.com>
---

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e599244..4ebba27 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -177,7 +177,17 @@ endif()
 check_symbol_exists(_isnan          "float.h" HAVE_DECL__ISNAN)
 check_symbol_exists(_finite         "float.h" HAVE_DECL__FINITE)
 
-if ((MSVC AND NOT (MSVC_VERSION LESS 1800)) OR MINGW OR CYGWIN OR UNIX OR AMIGA)
+if ("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
+    # Detect clang-cl.exe, it is Clang but with MSVC compatible command line arguments
+    execute_process (COMMAND ${CMAKE_C_COMPILER} -? ERROR_QUIET OUTPUT_QUIET RESULT_VARIABLE _clang_result)
+    if (_clang_result EQUAL 0)
+        set(CLANG_CL TRUE)
+    else()
+        set(CLANG_CL FALSE)
+    endif()
+endif()
+
+if ((MSVC AND NOT (MSVC_VERSION LESS 1800)) OR MINGW OR CYGWIN OR UNIX OR AMIGA OR CLANG_CL)
     check_symbol_exists(INFINITY    "math.h" HAVE_DECL_INFINITY)
     check_symbol_exists(isinf       "math.h" HAVE_DECL_ISINF)
     check_symbol_exists(isnan       "math.h" HAVE_DECL_ISNAN)
@@ -328,9 +338,7 @@ if (NOT DEFINED CMAKE_C_COMPILER_FRONTEND_VARIANT OR "${CMAKE_C_COMPILER_FRONTEN
 	elseif ("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU")
 		set(CMAKE_C_COMPILER_FRONTEND_VARIANT "GNU")
 	elseif ("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
-		# Detect clang-cl.exe, it is Clang but with MSVC compatible command line arguments
-		execute_process (COMMAND ${CMAKE_C_COMPILER} -? ERROR_QUIET OUTPUT_QUIET RESULT_VARIABLE _clang_result)
-		if (_clang_result EQUAL 0)
+		if (CLANG_CL)
 			set(CMAKE_C_COMPILER_FRONTEND_VARIANT "MSVC")
 		else()
 			set(CMAKE_C_COMPILER_FRONTEND_VARIANT "GNU")