need to check for libxml2 in configure

[edwardhartnett]

Some time ago (I'm not sure when), the handling of szip was changed.

It used to be that if szip was detected in the HDF5 library, szip was turned on.

But now, configure checks for the szip library presence as well as checking for its use in HDF5. So none of my builds in CI were really including szip. ;-)

When I finally fixed this, I get an immediate compile error. ;-)

make[1]: Entering directory '/home/ed/netcdf-c/libncxml'
depbase=`echo ncxml_xml2.lo | sed 's|[^/]*$|.deps/&|;s|\.lo$||'`;\
/bin/bash ../libtool  --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. -I..  -I../include -I../include -I../oc2 -I../libnczarr  -I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include  -g -fno-strict-aliasing -MT ncxml_xml2.lo -MD -MP -MF $depbase.Tpo -c -o ncxml_xml2.lo ncxml_xml2.c &&\
mv -f $depbase.Tpo $depbase.Plo
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -I../include -I../include -I../oc2 -I../libnczarr -I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include -g -fno-strict-aliasing -MT ncxml_xml2.lo -MD -MP -MF .deps/ncxml_xml2.Tpo -c ncxml_xml2.c  -fPIC -DPIC -o .libs/ncxml_xml2.o
ncxml_xml2.c:5:10: fatal error: libxml2/libxml/parser.h: No such file or directory
    5 | #include <libxml2/libxml/parser.h>
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[1]: *** [Makefile:562: ncxml_xml2.lo] Error 1
make[1]: Leaving directory '/home/ed/netcdf-c/libncxml'
make: *** [Makefile:760: check-recursive] Error 1
ed@koko:~/netcdf-c$ 

Here's more info:

CFLAGS='-g' CPPFLAGS="-I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include" LDFLAGS="-L/usr/local/szip-2.1.1/lib -L/usr/local/hdf5-1.12.2_szip/lib" ./configure --disable-dap-remote-tests --prefix=/usr/local/netcdf-c-4.9.0_hdf5-1.12.2_szip && make -j check
configure: netCDF 4.9.1-development
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking target system type... x86_64-pc-linux-gnu
checking for gcc... gcc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking whether gcc understands -c and -o together... yes
checking whether compiler supports -fno-strict-aliasing... yes
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /usr/bin/mkdir -p
checking for gawk... no
checking for mawk... mawk
checking whether make sets $(MAKE)... yes
checking whether make supports the include directive... yes (GNU style)
checking whether make supports nested variables... yes
checking dependency style of gcc... gcc3
./configure: line 5032: systeminfo: command not found
configure: checking supported formats
checking whether we should build with netcdf4 (alias for HDF5)... yes (deprecated; Please use with --disable-hdf5)
checking whether we should build with netcdf-4 (alias for HDF5)... yes
checking whether we should build with HDF5... yes
checking whether CDF5 support should be disabled... auto
checking whether reading of HDF4 SD files is to be enabled... no
checking whether parallel I/O for classic files is to be enabled... no
checking for curl_easy_setopt in -lcurl... yes
checking for library containing curl_easy_setopt... -lcurl
checking whether DAP client(s) are to be built... yes
checking whether netcdf zarr storage format should be disabled... yes
checking whether netcdf-4 should be forcibly enabled... yes
configure: checking user options
checking whether a NCIO_MINBLOCKSIZE was specified... 256
checking for valgrind... no
checking if fsync support is enabled... no
checking if jna bug workaround is enabled... no
checking if unit tests should be disabled... yes
checking do we require hdf5 dynamic-loading support... yes
checking whether to fetch some sample HDF4 files from Unidata ftp site to test HDF4 reading (requires wget)... no
checking whether we should attempt to install netcdf-fortran (EXPERIMENTAL)... no
checking whether parallel IO tests should be run... no
checking whether a user specified program to run mpi programs... mpiexec
checking whether a default chunk size in bytes was specified... 4194304
checking whether a maximum per-variable cache size for HDF5 was specified... 67108864
checking whether a number of chunks for the default per-variable cache was specified... 10
checking whether a default file cache size for HDF5 was specified... 16777216
checking whether a default file cache maximum number of elements for HDF5 was specified... 4133
checking whether a default cache preemption for HDF5 was specified... 0.75
checking whether netCDF-4 logging is enabled... no
checking whether nc_set_log_level() function is included (will do nothing unless enable-logging is also used)... yes
checking whether CURLOPT_USERNAME is defined... yes
checking whether CURLOPT_PASSWORD is defined... yes
checking whether CURLOPT_KEYPASSWD is defined... yes
checking whether CURLINFO_RESPONSE_CODE is defined... yes
checking whether CURLOPT_BUFFERSIZE is defined... yes
checking whether CURLOPT_TCP_KEEPALIVE is defined... yes
checking whether libcurl is version 7.66 or later?... yes
checking whether to search for and use external libxml2... yes
checking for xmlReadMemory in -lxml2... no
checking whether dap remote testing should be enabled... no
checking whether dap remote authorization testing should be enabled (default off)... no
checking which remote test server(s) to use... remotetest.unidata.ucar.edu
checking whether the time-consuming dap tests should be enabled (default off)... no
checking for blosc_init in -lblosc... no
checking for ZSTD_compress in -lzstd... no
checking whether libzstd library is available... no
checking for BZ2_bzCompress in -lbz2... no
checking whether libbz2 library is available... no
configure: Defaulting to internal libbz2
checking for SZ_BufftoBuffCompress in -lsz... yes
checking for library containing SZ_BufftoBuffCompress... -lsz
checking whether libsz library is available... yes
checking for zip_open in -lzip... no
checking whether libzip library is available... no
checking whether nczarr zip support is enabled... no
checking whether netcdf zarr S3 support should be enabled... no
checking whether AWS S3 SDK library is available... no
configure: WARNING: No S3 library available; disabling S3 support
checking whether netcdf zarr S3 testing should be enabled... no
checking whether a default file cache size for NCZarr was specified... 4194304
checking whether multi-filter support is enabled... yes
checking whether to enable strict null-byte header padding when reading (default off)... no
checking whether FFIO will be used... no
checking whether STDIO will be used... no
checking whether examples should be built... yes
checking whether v2 netCDF API should be built... yes
checking whether the ncgen/ncdump/nccopy should be built... yes
checking whether test should be built and run... yes
checking whether large file (> 2GB) tests should be run... no
checking whether benchmarks should be run... no
checking whether extreme numbers should be used in tests... yes
checking where to put large temp files if large file tests are run... .
checking Extra values for _NCProperties... 
checking whether user-defined format 0 was specified... 
checking whether a magic number for user-defined format 0 was specified... 
checking whether user-defined format 1 was specified... 
checking whether a magic number for user-defined format 1 was specified... 
configure: finding C compiler
checking for gcc... (cached) gcc
checking whether we are using the GNU C compiler... (cached) yes
checking whether gcc accepts -g... (cached) yes
checking for gcc option to accept ISO C89... (cached) none needed
checking whether gcc understands -c and -o together... (cached) yes
checking for g++... g++
checking whether we are using the GNU C++ compiler... yes
checking whether g++ accepts -g... yes
checking dependency style of g++... gcc3
checking for an ANSI C-conforming const... yes
configure: setting up libtool
checking how to print strings... printf
checking for a sed that does not truncate output... /usr/bin/sed
checking for grep that handles long lines and -e... /usr/bin/grep
checking for egrep... /usr/bin/grep -E
checking for fgrep... /usr/bin/grep -F
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking whether ln -s works... yes
checking the maximum length of command line arguments... 1879296
checking how to convert x86_64-pc-linux-gnu file names to x86_64-pc-linux-gnu format... func_convert_file_noop
checking how to convert x86_64-pc-linux-gnu file names to toolchain format... func_convert_file_noop
checking for /usr/bin/ld option to reload object files... -r
checking for objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for dlltool... no
checking how to associate runtime and link libraries... printf %s\n
checking for ar... ar
checking for archiver @FILE support... @
checking for strip... strip
checking for ranlib... ranlib
checking command to parse /usr/bin/nm -B output from gcc object... ok
checking for sysroot... no
checking for a working dd... /usr/bin/dd
checking how to truncate binary pipes... /usr/bin/dd bs=4096 count=1
checking for mt... mt
checking if mt is a manifest tool... no
checking how to run the C preprocessor... gcc -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking for dlfcn.h... yes
checking for objdir... .libs
checking if gcc supports -fno-rtti -fno-exceptions... no
checking for gcc option to produce PIC... -fPIC -DPIC
checking if gcc PIC flag -fPIC -DPIC works... yes
checking if gcc static flag -static works... yes
checking if gcc supports -c -o file.o... yes
checking if gcc supports -c -o file.o... (cached) yes
checking whether the gcc linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
checking how to run the C++ preprocessor... g++ -E
checking for ld used by g++... /usr/bin/ld -m elf_x86_64
checking if the linker (/usr/bin/ld -m elf_x86_64) is GNU ld... yes
checking whether the g++ linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking for g++ option to produce PIC... -fPIC -DPIC
checking if g++ PIC flag -fPIC -DPIC works... yes
checking if g++ static flag -static works... yes
checking if g++ supports -c -o file.o... yes
checking if g++ supports -c -o file.o... (cached) yes
checking whether the g++ linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking dynamic linker characteristics... (cached) GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
configure: finding other utilities
checking for m4... m4
checking for doxygen... doxygen
checking for dot... no
configure: WARNING: dot not found - will use simple charts in documentation
checking for special C compiler options needed for large files... no
checking for _FILE_OFFSET_BITS value needed for large files... no
configure: displaying some results
checking CPPFLAGS... -I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include
checking CC CFLAGS... gcc -g -fno-strict-aliasing
checking type gcc... gcc is /usr/bin/gcc
checking CXX... g++
checking CXXFLAGS... -g -O2
checking type g++... g++ is /usr/bin/g++
checking FC... unset
checking F90... unset
checking AR... ar
checking AR_FLAGS... cr
checking type ar... ar is /usr/bin/ar
checking NM... /usr/bin/nm -B
checking NMFLAGS... 
configure: checking types, headers, and functions
checking sys/param.h usability... yes
checking sys/param.h presence... yes
checking for sys/param.h... yes
checking libgen.h usability... yes
checking libgen.h presence... yes
checking for libgen.h... yes
checking for ANSI C header files... (cached) yes
checking locale.h usability... yes
checking locale.h presence... yes
checking for locale.h... yes
checking stdio.h usability... yes
checking stdio.h presence... yes
checking for stdio.h... yes
checking stdarg.h usability... yes
checking stdarg.h presence... yes
checking for stdarg.h... yes
checking fcntl.h usability... yes
checking fcntl.h presence... yes
checking for fcntl.h... yes
checking malloc.h usability... yes
checking malloc.h presence... yes
checking for malloc.h... yes
checking for stdlib.h... (cached) yes
checking for string.h... (cached) yes
checking for strings.h... (cached) yes
checking for unistd.h... (cached) yes
checking for sys/stat.h... (cached) yes
checking getopt.h usability... yes
checking getopt.h presence... yes
checking for getopt.h... yes
checking sys/time.h usability... yes
checking sys/time.h presence... yes
checking for sys/time.h... yes
checking for sys/types.h... (cached) yes
checking time.h usability... yes
checking time.h presence... yes
checking for time.h... yes
checking dirent.h usability... yes
checking dirent.h presence... yes
checking for dirent.h... yes
checking sys/resource.h usability... yes
checking sys/resource.h presence... yes
checking for sys/resource.h... yes
checking ftw.h usability... yes
checking ftw.h presence... yes
checking for ftw.h... yes
checking execinfo.h usability... yes
checking execinfo.h presence... yes
checking for execinfo.h... yes
checking for strlcat... no
checking for snprintf... yes
checking for strcasecmp... yes
checking for fileno... yes
checking for strdup... yes
checking for strtoll... yes
checking for strtoull... yes
checking for mkstemp... yes
checking for mktemp... yes
checking for random... yes
checking for getrlimit... yes
checking for gettimeofday... yes
checking for fsync... yes
checking for MPI_Comm_f2c... no
checking for MPI_Info_f2c... no
checking for strncasecmp... yes
checking for clock_gettime... yes
checking for struct timespec... yes
checking for memmove... yes
checking for getpagesize... yes
checking for sysconf... yes
checking whether mmap is enabled for in-memory files... no
checking for mmap... yes
checking for mremap... yes
checking whether MAP_ANONYMOUS is defined... yes
configure: mmap functionality is not available: disabling mmap
checking whether byte range support is enabled... no
checking whether nc_finalize should be invoked at exit... yes
checking for atexit... yes
checking for dlopen in -ldl... yes
checking for library containing dlopen... -ldl
checking whether dynamically loaded plugins is enabled... yes
checking for size_t... yes
checking for working alloca.h... yes
checking for alloca... yes
checking whether isnan is declared... yes
checking whether isinf is declared... yes
checking whether isfinite is declared... yes
checking for struct stat.st_blksize... yes
checking for IEEE floating point format... yes
checking for size_t... (cached) yes
checking for ssize_t... yes
checking for schar... no
checking for uchar... no
checking for longlong... no
checking for ushort... yes
checking for uint... yes
checking for int64... no
checking for uint64... no
checking for size64_t... no
checking for ssize64_t... no
checking for _off64_t... no
checking for uint64_t... yes
checking for ptrdiff_t... yes
checking for off_t... yes
checking for uintptr_t... yes
checking whether char is unsigned... no
checking whether byte ordering is bigendian... no
checking size of short... 2
checking size of int... 4
checking size of long... 8
checking size of long long... 8
checking size of float... 4
checking size of double... 8
checking size of off_t... 8
checking size of size_t... 8
checking size of unsigned long long... 8
checking size of unsigned char... 1
checking size of ushort... 2
checking size of uint... 4
checking size of ushort... (cached) 2
checking size of uint... (cached) 4
checking size of ssize_t... 8
checking size of void*... 8
checking for library containing deflate... -lz
checking for floor in -lm... yes
checking for library containing H5Fflush... -lhdf5
checking for library containing H5DSis_scale... -lhdf5_hl
checking hdf5.h usability... yes
checking hdf5.h presence... yes
checking for hdf5.h... yes
checking for H5Pget_fapl_mpio... no
checking for H5Pset_deflate... yes
checking for H5Z_SZIP... yes
checking for H5Pset_all_coll_metadata_ops... no
checking for H5Literate... no
checking whether parallel io is enabled in hdf5... no
checking for library containing H5Dread_chunk... none required
checking for library containing H5Pset_fapl_ros3... no
checking whether HDF5 allows parallel filters... yes
checking whether szlib was used when building HDF5... yes
checking whether HDF5 library is version 1.10.6 or later... yes
configure: WARNING: Parallel io disabled for netcdf-4 because hdf5 does not support
checking whether parallel I/O is enabled for netcdf-4... no
checking whether we should enable NCZarr filters... yes
checking whether filter testing should be run... yes
checking for unsigned long long int... yes
checking for long long int... yes
checking for unsigned long long int... (cached) yes
checking what to call the output of the ftpbin target... binary-netcdf-4.9.1-development.tar  g++
checking if libtool needs -no-undefined flag to build shared libraries... no
checking value of LIBS... -lhdf5_hl -lhdf5 -lm -lz -ldl -lsz -lcurl 
checking whether and where we should install plugins... no
configure: generating header files and makefiles
checking that generated files are newer than configure... done
configure: creating ./config.status
config.status: creating test_common.sh
config.status: creating nc_test4/findplugin.sh
config.status: creating nczarr_test/findplugin.sh
config.status: creating plugins/findplugin.sh
config.status: creating examples/C/findplugin.sh
config.status: creating ncdap_test/findtestserver.c
config.status: creating nc_test/run_pnetcdf_tests.sh
config.status: creating dap4_test/findtestserver4.c
config.status: creating dap4_test/pingurl4.c
config.status: creating h5_test/run_par_tests.sh
config.status: creating nc_test4/run_par_test.sh
config.status: creating nc_perf/run_par_bm_test.sh
config.status: creating nc_perf/run_gfs_test.sh
config.status: creating nczarr_test/timer_utils.h
config.status: creating nczarr_test/timer_utils.c
config.status: creating nczarr_test/test_filter.c
config.status: creating nczarr_test/test_filter_misc.c
config.status: creating nczarr_test/tst_multifilter.c
config.status: creating nczarr_test/test_filter_repeat.c
config.status: creating nczarr_test/test_filter_order.c
config.status: creating examples/C/run_par_test.sh
config.status: creating nc-config
config.status: creating Makefile
config.status: creating netcdf.pc
config.status: creating libnetcdf.settings
config.status: creating postinstall.sh
config.status: creating include/netcdf_meta.h
config.status: creating include/netcdf_dispatch.h
config.status: creating include/Makefile
config.status: creating h5_test/Makefile
config.status: creating hdf4_test/Makefile
config.status: creating libsrc/Makefile
config.status: creating libsrc4/Makefile
config.status: creating libhdf5/Makefile
config.status: creating libsrcp/Makefile
config.status: creating ncdump/Makefile
config.status: creating ncgen3/Makefile
config.status: creating ncgen/Makefile
config.status: creating examples/Makefile
config.status: creating examples/C/Makefile
config.status: creating examples/CDL/Makefile
config.status: creating oc2/Makefile
config.status: creating libdap2/Makefile
config.status: creating libdap4/Makefile
config.status: creating libhdf4/Makefile
config.status: creating libnczarr/Makefile
config.status: creating libncpoco/Makefile
config.status: creating libncxml/Makefile
config.status: creating libdispatch/Makefile
config.status: creating liblib/Makefile
config.status: creating ncdump/cdl/Makefile
config.status: creating ncdump/expected/Makefile
config.status: creating docs/Makefile
config.status: creating docs/images/Makefile
config.status: creating unit_test/Makefile
config.status: creating nctest/Makefile
config.status: creating nc_test4/Makefile
config.status: creating nc_perf/Makefile
config.status: creating nc_test/Makefile
config.status: creating ncdap_test/Makefile
config.status: creating ncdap_test/testdata3/Makefile
config.status: creating ncdap_test/expected3/Makefile
config.status: creating ncdap_test/expectremote3/Makefile
config.status: creating dap4_test/Makefile
config.status: creating plugins/Makefile
config.status: creating nczarr_test/Makefile
config.status: creating config.h
config.status: linking dap4_test/baselinethredds/GOES16_TEST1.nc4.thredds to dap4_test/baselinethredds/GOES16_CONUS_20170821_020218_0.47_1km_33.3N_91.4W.nc4.thredds
config.status: executing depfiles commands
config.status: executing libtool commands
# NetCDF C Configuration Summary
==============================

# General
-------
NetCDF Version:		4.9.1-development
Dispatch Version:       5
Configured On:		Sun Jun 19 10:09:50 CEST 2022
Host System:		x86_64-pc-linux-gnu
Build Directory: 	/home/ed/netcdf-c
Install Prefix:         /usr/local/netcdf-c-4.9.0_hdf5-1.12.2_szip
Plugin Install Prefix:  N.A.

# Compiling Options
-----------------
C Compiler:		/usr/bin/gcc
CFLAGS:			-g -fno-strict-aliasing
CPPFLAGS:		-I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include
LDFLAGS:		-L/usr/local/szip-2.1.1/lib -L/usr/local/hdf5-1.12.2_szip/lib
AM_CFLAGS:		
AM_CPPFLAGS:		
AM_LDFLAGS:		
Shared Library:		yes
Static Library:		yes
Extra libraries:	-lhdf5_hl -lhdf5 -lm -lz -ldl -lsz -lcurl 
XML Parser:             libxml2

# Features
--------
NetCDF-2 API:		yes
HDF4 Support:		no
HDF5 Support:		yes
NetCDF-4 API:		yes
NC-4 Parallel Support:	no
PnetCDF Support:	no
DAP2 Support:		yes
DAP4 Support:		yes
Byte-Range Support:	no
Diskless Support:	yes
MMap Support:		no
JNA Support:		no
CDF5 Support:		yes
ERANGE Fill Support:	no
Relaxed Boundary Check:	yes
Parallel Filters:       yes
NCZarr Support:		yes
Multi-Filter Support:	yes
Quantization:		yes
Logging:     		no
SZIP Write Support:     yes
Standard Filters:       deflate bz2 szip
ZSTD Support:           no
Benchmarks:		no
Making check in include
make[1]: Entering directory '/home/ed/netcdf-c/include'
make[1]: Nothing to be done for 'check'.
make[1]: Leaving directory '/home/ed/netcdf-c/include'
Making check in libncxml
make[1]: Entering directory '/home/ed/netcdf-c/libncxml'
depbase=`echo ncxml_xml2.lo | sed 's|[^/]*$|.deps/&|;s|\.lo$||'`;\
/bin/bash ../libtool  --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. -I..  -I../include -I../include -I../oc2 -I../libnczarr  -I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include  -g -fno-strict-aliasing -MT ncxml_xml2.lo -MD -MP -MF $depbase.Tpo -c -o ncxml_xml2.lo ncxml_xml2.c &&\
mv -f $depbase.Tpo $depbase.Plo
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -I../include -I../include -I../oc2 -I../libnczarr -I/usr/local/szip-2.1.1/include -I/usr/local/hdf5-1.12.2_szip/include -g -fno-strict-aliasing -MT ncxml_xml2.lo -MD -MP -MF .deps/ncxml_xml2.Tpo -c ncxml_xml2.c  -fPIC -DPIC -o .libs/ncxml_xml2.o
ncxml_xml2.c:5:10: fatal error: libxml2/libxml/parser.h: No such file or directory
    5 | #include <libxml2/libxml/parser.h>
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[1]: *** [Makefile:562: ncxml_xml2.lo] Error 1
make[1]: Leaving directory '/home/ed/netcdf-c/libncxml'
make: *** [Makefile:760: check-recursive] Error 1
ed@koko:~/netcdf-c$ 

[edwardhartnett]

This problem went away when I did:

sudo apt install libxml2-dev
So we need to check for that library in configure.

[DennisHeimbigner]

The reason we have to test for libsz specifically is because nczarr can use it
even if hdf5 is disabled.

[WardF]

Agreed we should catch this in the configure script instead of as a compilation error. I can put a PR up fence posting nczarr with the presence of this header, although I don't want to get derailed from netcdf-fortran too badly.

[WardF]

Ok, taking a look, I think the actual solution is that we need this file ncxml_xml2.c to work (if possible) with the bundled tinyxml that is used when libxml2 is either disabled or unavailable. There is some logic we will need to worry about when libxml2 (the library) is available, but the development headers are not. Working on the PR right now.

[WardF]

Adding an AC_COMPILE_IFELSE block to check to see if we can actually compile libxml2-based test code; in some situations, it appears that detecting the library isn't sufficient. Also, testing the mermaid-based flowchart syntax, ignore below XD.

flowchart TD
A[Enable libxml2] --> B[AC_CHECK_LIB xml2 via xmlReadMemory];
B -- Yes --> C[AC_SEARCH_LIBS for xmlReadMemory, xml2, xml2.dll, cygxml2.dll];
B -- No --> E[Switch over to tinyxml, bundled with libnetcdf];
C -- What purpose does this serve? --> D[We need a check for header libraries, but th];

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[DennisHeimbigner]

can put a PR up fence posting nczarr with the presence of this header

But remember that nczarr can work even if szip is not available. So we need
to include nczarr with or without szip.

[WardF]

@DennisHeimbigner No problem, szip is incidental to this, the issue is when the libxml2 library is available to link against, but the header file is not installed, resulting in the related #include causing a compile failure in ncxml_xml2.c

[DennisHeimbigner]

Ok, taking a look, I think the actual solution is that we need this file 'ncxml_xml2.cto work (if possible) with the bundledtinyxmlthat is used whenlibxml2`

I do not understand this comment. When the external libxml2 is chosen, then we need to build with ncxml_xml2.c, but when we choose tinyxml2,then we need
to build with ncxml_tinyxml2.cpp (Note that one is C and one is C++)

[WardF]

@DennisHeimbigner That comment can be ignored; it was mistaken. I'll go cross it out.