Add a warning to catch 0 to pointer conversion. (#2742)

This could help finding some weird casts (like bool to ptr)

Author: vrabaud

CMakeLists.txt

@@ -302,6 +302,7 @@ elseif(CMAKE_C_COMPILER_ID MATCHES "Clang")
     message(STATUS "libavif: Enabling warnings for Clang")
     target_compile_options(
         avif_enable_warnings INTERFACE -Wall -Wextra -Wgnu-empty-initializer -Wshorten-64-to-32 -Wstrict-prototypes
+                                       -Wzero-as-null-pointer-constant
     )
 elseif(CMAKE_C_COMPILER_ID MATCHES "GNU")
     message(STATUS "libavif: Enabling warnings for GCC")

apps/avifgainmaputil/extractgainmap_command.cc

@@ -18,7 +18,7 @@ ExtractGainMapCommand::ExtractGainMapCommand()
 
 avifResult ExtractGainMapCommand::Run() {
   DecoderPtr decoder(avifDecoderCreate());
-  if (decoder == NULL) {
+  if (decoder == nullptr) {
     return AVIF_RESULT_OUT_OF_MEMORY;
   }
   decoder->imageContentToDecode = AVIF_IMAGE_CONTENT_GAIN_MAP;

apps/avifgainmaputil/imageio.cc

@@ -98,15 +98,15 @@ avifResult ReadImage(avifImage* image, const std::string& input_filename,
     return AVIF_RESULT_INVALID_ARGUMENT;
   } else if (input_format == AVIF_APP_FILE_FORMAT_AVIF) {
     DecoderPtr decoder(avifDecoderCreate());
-    if (decoder == NULL) {
+    if (decoder == nullptr) {
       return AVIF_RESULT_OUT_OF_MEMORY;
     }
     avifResult result = ReadAvif(decoder.get(), input_filename, ignore_profile);
     if (result != AVIF_RESULT_OK) {
       return result;
     }
     if (decoder->image->imageOwnsYUVPlanes &&
-        (decoder->image->alphaPlane == NULL ||
+        (decoder->image->alphaPlane == nullptr ||
          decoder->image->imageOwnsAlphaPlane)) {
       std::swap(*image, *decoder->image);
     } else {

apps/avifgainmaputil/printmetadata_command.cc

@@ -38,7 +38,7 @@ PrintMetadataCommand::PrintMetadataCommand()
 
 avifResult PrintMetadataCommand::Run() {
   DecoderPtr decoder(avifDecoderCreate());
-  if (decoder == NULL) {
+  if (decoder == nullptr) {
     return AVIF_RESULT_OUT_OF_MEMORY;
   }
 

apps/avifgainmaputil/swapbase_command.cc

@@ -128,7 +128,7 @@ SwapBaseCommand::SwapBaseCommand()
 
 avifResult SwapBaseCommand::Run() {
   DecoderPtr decoder(avifDecoderCreate());
-  if (decoder == NULL) {
+  if (decoder == nullptr) {
     return AVIF_RESULT_OUT_OF_MEMORY;
   }
   decoder->imageContentToDecode |= AVIF_IMAGE_CONTENT_GAIN_MAP;

apps/avifgainmaputil/tonemap_command.cc

@@ -68,7 +68,7 @@ avifResult TonemapCommand::Run() {
   const bool tone_mapping_to_hdr = (headroom > 0.0f);
 
   DecoderPtr decoder(avifDecoderCreate());
-  if (decoder == NULL) {
+  if (decoder == nullptr) {
     return AVIF_RESULT_OUT_OF_MEMORY;
   }
   decoder->imageContentToDecode |= AVIF_IMAGE_CONTENT_GAIN_MAP;