gdal.pxi CSLConstList type change in GDAL

[schwehr]

Fiona/fiona/gdal.pxi

Line 20 in ec9768a

ctypedef char **CSLConstList

Should become:

cdef extern from "cpl_port.h":
    ctypedef const char * const * CSLConstList

And here:

Fiona/fiona/ogrext.pyx

Line 1266 in ec9768a

cdef char **metadata = NULL

• https://github.com/OSGeo/gdal/blob/a071ab3fc60cd94fcc94728cc3d5382995f447e2/port/cpl_port.h#L1280
• https://github.com/OSGeo/gdal/blob/a071ab3fc60cd94fcc94728cc3d5382995f447e2/gcore/gdaldataset.cpp#L5218

[sgillies]

@schwehr which GDAL introduced the change?

[schwehr]

CSLConstList started being available with OSGeo/gdal@07238f4:

Apr 2, 2018 -- GDAL 2.4.4

The typedef const char* const* CSLConstList; has been behind a #ifdef since:

#if defined(__cplusplus) && !defined(CPL_SUPRESS_CPLUSPLUS) && !defined(DOXYGEN_SKIP)

Otherwise, it is this less constrained version:

typedef char** CSLConstList;

https://github.com/OSGeo/gdal/blob/a3165a6975ae52c56267d3e1cc63c4cb6306774b/port/cpl_port.h#L1276-L1285

[sgillies]

@schwehr I don't think fiona and rasterio use CSLConstList in a C++ context. Why would we want to change?

[schwehr]

It's just a bit more tight definition that lets the compiler be more certain about how the pointers are use. I It's always possible that some compilers might be able to optimize a bit more or slightly reduce compile time. An more importantly, I've found lots of little bugs found over the years this way. It's usually an assumption being off.

t should work fine in C too.