MSVC: lower C4100 warning level from 4 to 3

The C4100 warning is related to unused formal parameters in functions.

Enabling it better aligns with "-Wunused-parameter" option in other
compilers.

While suppressing it with `__pragma(warning(suppress:4100))` is not the
same as using `__attribute__((__unused__))` in GCC or Clang, it is
still preferable to use it over completely hiding the warning.

This ensures consistent warning behavior across compilers and improves
code quality by addressing unused function parameters.

(Note that some warnings in Windows-specific code have already been
silenced in 7fcb262dfd2f48a73f9cf794944ff677c36e3783)

Pull Request: https://projects.blender.org/blender/blender/pulls/105534

CMakeLists.txt

@@ -1607,6 +1607,7 @@ elseif(CMAKE_C_COMPILER_ID MATCHES "MSVC")
     # warning level:
     "/W3"
     "/w34062"  # switch statement contains 'default' but no 'case' labels
+    "/w34100"  # 'identifier' : unreferenced formal parameter
     "/w34115"  # 'type' : named type definition in parentheses
     "/w34189"  # local variable is initialized but not referenced
     # see https://docs.microsoft.com/en-us/cpp/error-messages/compiler-warnings/c5038?view=vs-2017

build_files/cmake/macros.cmake

@@ -702,6 +702,7 @@ macro(remove_strict_flags)
   endif()
 
   if(MSVC)
+    remove_cc_flag(/w34100) # Restore warn C4100 (unreferenced formal parameter) back to w4
     remove_cc_flag(/w34189) # Restore warn C4189 (unused variable) back to w4
   endif()
 
@@ -721,7 +722,7 @@ macro(remove_extra_strict_flags)
   endif()
 
   if(MSVC)
-    # TODO
+    remove_cc_flag(/w34100) # Restore warn C4100 (unreferenced formal parameter) back to w4
   endif()
 endmacro()
 

intern/guardedalloc/intern/mallocn_intern.h

@@ -10,6 +10,9 @@
 
 #ifdef __GNUC__
 #  define UNUSED(x) UNUSED_##x __attribute__((__unused__))
+#elif defined(_MSC_VER)
+/* NOTE: This suppresses the warning for the line, not the attribute. */
+#  define UNUSED(x) UNUSED_##x __pragma(warning(suppress : 4100))
 #else
 #  define UNUSED(x) UNUSED_##x
 #endif

intern/mantaflow/CMakeLists.txt

@@ -15,6 +15,13 @@ if(WIN32)
   add_definitions(-D_USE_MATH_DEFINES)
 endif()
 
+if(WIN32)
+  # Some files in extern are being included which brings up a bunch of
+  # "unreferenced formal parameter" warnings.
+  # So restore warn C4100 (unreferenced formal parameter) back to w4
+  remove_cc_flag(/w34100)
+endif()
+
 
 set(INC
   extern

source/blender/blenlib/BLI_utildefines.h

@@ -668,6 +668,9 @@ extern bool BLI_memory_is_zero(const void *arr, size_t arr_size);
 /* UNUSED macro, for function argument */
 #  if defined(__GNUC__) || defined(__clang__)
 #    define UNUSED(x) UNUSED_##x __attribute__((__unused__))
+#  elif defined(_MSC_VER)
+/* NOTE: This suppresses the warning for the line, not the attribute. */
+#    define UNUSED(x) UNUSED_##x __pragma(warning(suppress : 4100))
 #  else
 #    define UNUSED(x) UNUSED_##x
 #  endif

source/blender/io/usd/CMakeLists.txt

@@ -35,6 +35,13 @@ if(USD_IMAGING_HEADERS)
   add_definitions(-DUSD_HAS_IMAGING)
 endif()
 
+if(WIN32)
+  # Some USD library headers trigger the "unreferenced formal parameter"
+  # warning alert.
+  # Silence them by restore warn C4100 back to w4
+  remove_cc_flag(/w34100)
+endif()
+
 set(INC
   .
   ../common

source/blender/makesrna/intern/CMakeLists.txt

@@ -140,6 +140,9 @@ if(CMAKE_COMPILER_IS_GNUCC OR (CMAKE_C_COMPILER_ID MATCHES "Clang"))
 endif()
 if(CMAKE_C_COMPILER_ID MATCHES "Clang")
   string(APPEND GENSRC_CFLAGS " -Wno-missing-variable-declarations")
+elseif(MSVC)
+  # Restore warn C4100 (unreferenced formal parameter) back to w4
+  remove_cc_flag(/w34100)
 endif()
 
 if(GENSRC_CFLAGS)

source/blender/python/intern/stubs.c

@@ -12,6 +12,9 @@
 #if defined(__GNUC__) || defined(__clang__)
 #  pragma GCC diagnostic error "-Wmissing-prototypes"
 #  pragma GCC diagnostic ignored "-Wunused-parameter"
+#elif defined(_MSC_VER)
+/* Suppress unreferenced formal parameter warning. */
+#  pragma warning(disable : 4100)
 #endif
 
 /* python, will come back */