Add CMake option to disable XCHAR support

This is useful in some embedded scenarios where the libc's wchar_t
support is disabled.

CMakeLists.txt

@@ -83,6 +83,7 @@ option(FMT_TEST "Generate the test target." ${FMT_MASTER_PROJECT})
 option(FMT_FUZZ "Generate the fuzz target." OFF)
 option(FMT_CUDA_TEST "Generate the cuda-test target." OFF)
 option(FMT_OS "Include OS-specific APIs." ON)
+option(FMT_XCHAR "Include wchar_t and exotic character support" ON)
 option(FMT_MODULE "Build a module library." ${FMT_USE_CMAKE_MODULES})
 option(FMT_SYSTEM_HEADERS "Expose headers with marking them as system." OFF)
 option(FMT_UNICODE "Enable Unicode support." ON)
@@ -294,6 +295,10 @@ else ()
   target_compile_definitions(fmt PRIVATE FMT_OS=0)
 endif ()
 
+if (NOT FMT_XCHAR)
+  target_compile_definitions(fmt PRIVATE FMT_XCHAR=0)
+endif ()
+
 if (FMT_WERROR)
   target_compile_options(fmt PRIVATE ${WERROR_FLAG})
 endif ()

doc/api.md

@@ -725,6 +725,8 @@ configuring CMake.
 ### CMake Options
 
 - **`FMT_OS`**: When set to `OFF`, disables OS-specific APIs (`fmt/os.h`).
+- **`FMT_XCHAR`**: When set to `OFF`, disables wchar_t and exotic character
+  support.
 - **`FMT_UNICODE`**: When set to `OFF`, disables Unicode support on
   Windows/MSVC. Unicode support is always enabled on other platforms.
 
@@ -761,6 +763,7 @@ some features, you can use the following configuration:
 
 - CMake options:
     - `FMT_OS=OFF`
+    - `FMT_XCHAR=OFF`
 - Macros:
     - `FMT_BUILTIN_TYPES=0`
     - `FMT_OPTIMIZE_SIZE=2`

src/fmt.cc

@@ -121,6 +121,10 @@ extern "C++" {
 #  define FMT_OS 1
 #endif
 
+#ifndef FMT_XCHAR
+#  define FMT_XCHAR 1
+#endif
+
 // All library-provided declarations and definitions must be in the module
 // purview to be exported.
 #include "fmt/args.h"
@@ -135,7 +139,9 @@ extern "C++" {
 #include "fmt/printf.h"
 #include "fmt/ranges.h"
 #include "fmt/std.h"
-#include "fmt/xchar.h"
+#if FMT_XCHAR
+#  include "fmt/xchar.h"
+#endif
 
 #ifdef FMT_ATTACH_TO_GLOBAL_MODULE
 }