build: Disable clang18 warnings about deprecated unicode conversion (A…

…cademySoftwareFoundation#4246)

clang/llvm 18 (and probably other compilers soon) has made noisy
warnings about the C++17-deprecated unicode conversions. Actually
replacing them enirely with something else is rather hairy, we will
tackle that later.

In the mean time, this patch seems to be the minimal change to disable
the warnings that should be totally easy to backport.

These seem to be the only changes necessary to make a clean build with
clang 18.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

INSTALL.md

@@ -18,7 +18,7 @@ NEW or CHANGED MINIMUM dependencies since the last major release are **bold**.
      * The default build mode is C++14. This can be controlled by via the
        CMake configuration flag: `-DCMAKE_CXX_STANDARD=17`, etc.
      * ADVISORY: We expect that OIIO 2.6 in 2024 will require C++17 or higher.
- * Compilers: gcc 6.1 - 13.1, clang 3.4 - 17, MSVS 2017 - 2019,
+ * Compilers: gcc 6.1 - 13.1, clang 3.4 - 18, MSVS 2017 - 2019,
    Intel icc 17+, Intel OneAPI C++ compiler 2022+.
  * **CMake >= 3.15** (tested through 3.28)
  * **OpenEXR/Imath >= 2.4** (recommended: 3.1 or higher; tested through 3.2

src/include/OpenImageIO/detail/fmt.h

@@ -48,6 +48,7 @@
 #    define FMT_USE_FLOAT128 0
 #endif
 
+// Suppress certain warnings generated in the fmt headers themselves
 OIIO_PRAGMA_WARNING_PUSH
 #if OIIO_GNUC_VERSION >= 70000
 #    pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
@@ -58,6 +59,9 @@ OIIO_PRAGMA_WARNING_PUSH
 #if OIIO_INTEL_LLVM_COMPILER
 #    pragma GCC diagnostic ignored "-Wtautological-constant-compare"
 #endif
+#if OIIO_CLANG_VERSION >= 180000
+#    pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#endif
 
 #include <OpenImageIO/detail/fmt/format.h>
 #include <OpenImageIO/detail/fmt/ostream.h>

src/libutil/strutil.cpp

@@ -3,15 +3,24 @@
 // https://github.com/AcademySoftwareFoundation/OpenImageIO
 
 
-#include <cmath>
+#include <OpenImageIO/platform.h>
+
+// Special dance to disable warnings in the included files related to
+// the deprecation of unicode conversion functions.
+OIIO_PRAGMA_WARNING_PUSH
+OIIO_CLANG_PRAGMA(clang diagnostic ignored "-Wdeprecated-declarations")
 #include <codecvt>
+#include <locale>
+OIIO_PRAGMA_WARNING_POP
+
+#include <algorithm>
+#include <cmath>
 #include <cstdarg>
 #include <cstdint>
 #include <cstdlib>
 #include <ctime>
 #include <iostream>
 #include <limits>
-#include <locale>
 #include <mutex>
 #include <numeric>
 #include <sstream>
@@ -25,7 +34,6 @@
 #include <boost/algorithm/string/find.hpp>
 
 #include <OpenImageIO/dassert.h>
-#include <OpenImageIO/platform.h>
 #include <OpenImageIO/string_view.h>
 #include <OpenImageIO/strutil.h>
 #include <OpenImageIO/thread.h>