Unbreak IO extensions on BSDs (1.68 regression)

[jbeich]

alloca is defined in <stdlib.h> even on Linux (see Notes on the GNU version). FreeBSD, DragonFly, OpenBSD don't support <malloc.h> while GNU libc uses <malloc.h> for non-standard extensions: malloc_usable_size, mallinfo, memalign, pvalloc, etc. FreeBSD (but not other BSDs) also supports non-standard extensions: malloc_usable_size, mallctl*, *allocx, etc.

$ echo '#include <boost/gil/extension/io/png/read.hpp>' | c++ -xc++ - -isystem/usr/local/include
In file included from <stdin>:1:
In file included from /usr/local/include/boost/gil/extension/io/png/read.hpp:29:
In file included from /usr/local/include/boost/gil/io/get_reader.hpp:22:
In file included from /usr/local/include/boost/gil/io/get_read_device.hpp:26:
In file included from /usr/local/include/boost/gil/io/path_spec.hpp:23:
/usr/include/malloc.h:3:2: error: "<malloc.h> has been replaced by <stdlib.h>"
#error "<malloc.h> has been replaced by <stdlib.h>"
 ^
1 error generated.

[jbeich]

Windows appears to have _alloca in <malloc.h>. I wonder if alloca is a compiler builtin instead.

[mloskot]

LGTM

[mloskot]

@jbeich Thanks!

Next, we shall watch the regression tests if this does not cause any issues
www.boost.org/development/tests/develop/developer/gil.html

Once that's confirmed, we may still have time to merge it into master for release with Boost 1.68 (/cc @stefanseefeld )

[jbeich]

http://www.boost.org/development/tests/develop/developer/gil.html

How to filter out expected (i.e., pre-existing) fallout? Some cerr links even go nowhere: "Error extracting file: Error code 11 - No matching files were found." And it doesn't look like develop can be replaced with arbitrary commit in order to track when the fallout was introduced.

[jbeich]

Ah, this is hilarious. https://www.boost.org/development/tests/develop/developer/gil-io.html has been showing bustage on FreeBSD but no one payed an attention.

[stefanseefeld]

or to be a little less harsh: no-one with either FreeBSD experience or a suitable system to test locally is available. Read: your contributions would be very much appreciated ! :-)

[mloskot]

Indeed, in a team of three, there is never enough man power!

@jbeich I confess, proposing to watch the regression tests, I failed to check them myself.