Invalid conversion from int to int

[Kzer-Za]

The compilation throws this error:

/home/denis/Downloads/DevIL/DevIL/src-IL/src/il_jp2.cpp:353:2: error: invalid conversion from ‘int (*)(jas_stream_obj_t*, char*, int)’ {aka ‘int (*)(void*, char*, int)’} to ‘int (*)(jas_stream_obj_t*, char*, unsigned int)’ {aka ‘int (*)(void*, char*, unsigned int)’} [-fpermissive]
  353 |  iJp2_file_read,
      |  ^~~~~~~~~~~~~~
      |  |
      |  int (*)(jas_stream_obj_t*, char*, int) {aka int (*)(void*, char*, int)}
/home/denis/Downloads/DevIL/DevIL/src-IL/src/il_jp2.cpp:354:2: error: invalid conversion from ‘int (*)(jas_stream_obj_t*, char*, int)’ {aka ‘int (*)(void*, char*, int)’} to ‘int (*)(jas_stream_obj_t*, char*, unsigned int)’ {aka ‘int (*)(void*, char*, unsigned int)’} [-fpermissive]
  354 |  iJp2_file_write,
      |  ^~~~~~~~~~~~~~~
      |  |
      |  int (*)(jas_stream_obj_t*, char*, int) {aka int (*)(void*, char*, int)}
make[2]: *** [src-IL/CMakeFiles/IL.dir/build.make:511: src-IL/CMakeFiles/IL.dir/src/il_jp2.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:215: src-IL/CMakeFiles/IL.dir/all] Error 2
make: *** [Makefile:160: all] Error 2

[mitchblank]

The problem is that the jasper library changed their API so now the write call takes a const ponter. Also some int got changed to unsigned int the most recent version. For example, see https://github.com/jasper-software/jasper/commit/46dbba47210c7e16f7304f67a896b2f0faea4859#diff-251b049c7bd7658b9d34baa3ace6a1af0445780f3013f5e6181fe4784d8cdb86

It's pretty ugly from DevIL's perspective... if you want to support building against different versions of jasper we'll either need to do some decltype tricks or cmake autodetection

[mitchblank]

Digging into the jasper history a bit more:

Up through 2.0.16 the callbacks were:

int (*read_)(jas_stream_obj_t *obj, char *buf, int cnt);
int (*write_)(jas_stream_obj_t *obj, char *buf, int cnt);

Then for 2.0.17 - 2.0.19 the count changed to unsigned (729996abbeabe698b7ee249c2146405b9a347a01):

int (*read_)(jas_stream_obj_t *obj, char *buf, unsigned cnt);
int (*write_)(jas_stream_obj_t *obj, char *buf, unsigned cnt);

before finally in 2.0.20 the write interface became more const-correct (46dbba47210c7e16f7304f67a896b2f0faea4859):

int (*write_)(jas_stream_obj_t *obj, const char *buf, unsigned cnt);

so far, no changes to the other callbacks like seek_()

It would be handy if there were a simple way of detecting what version of jasper we are building against directly using #ifdef. There is a jasper/jas_version.h header available, but unfortunate it only exports a JAS_VERSION string, nothing like major/minor as numbers...

So basically twice in the last few months the API for jas_stream_ops_t has changed in source-incompatible ways :-(

cc @MaxKellermann

[mitchblank]

Looks like this is the hack that gdal went with to deal with the API drift: https://github.com/OSGeo/gdal/commit/9ef8e16e27c5fc4c491debe50bf2b7f3e94ed334