can't compile a file containting C-API

[Balsa Sarenac]

I was following a tutorial on writing external modules with Cython: https://lxml.de/capi.html#writing-external-modules-in-cython and couldn't compile the given example. Here is the error:

> python setup.py build_ext --inplace
running build_ext
building 'helloworld' extension
C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30037\bin\HostX86\x64\cl.exe /c /nologo /Ox /W3 /GL /DNDEBUG /MT -IC:\Users\Balsa\Envs\oll\lib\site-packages\lxml -IC:\Users\Balsa\Envs\oll\lib\site-packages\lxml\includes -IC:\Users\Balsa\Envs\oll\include -Ic:\users\balsa\appdata\local\programs\python\python36\include -Ic:\users\balsa\appdata\local\programs\python\python36\include "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30037\ATLMFC\include" "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30037\include" "-IC:\Program Files (x86)\Windows Kits\NETFXSDK\4.8\include\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\winrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\cppwinrt" /Tchelloworld.c /Fobuild\temp.win-amd64-3.6\Release\helloworld.obj
helloworld.c
C:\Users\Balsa\Envs\oll\lib\site-packages\lxml\includes\libxml/encoding.h(28): fatal error C1083: Cannot open include file: 'iconv.h': No such file or directory
error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise\\VC\\Tools\\MSVC\\14.29.30037\\bin\\HostX86\\x64\\cl.exe' failed with exit status 2

Versions:

Python : sys.version_info(major=3, minor=6, micro=8, releaselevel='final', serial=0)
lxml.etree : (4, 3, 2, 0)
libxml used : (2, 9, 5)
libxml compiled : (2, 9, 5)
libxslt used : (1, 1, 30)
libxslt compiled : (1, 1, 30)

Note: I have also tried with the newest version of lxml and the same error happened.

[scoder (scoder)]

Thanks for the report. It seems reasonable to include the libiconv header files in the static wheels, if they are a direct dependency of the libxml2 headers.

PR welcome. See "setup_extra_options()" in setup.py. Currently, it only includes the header files of libxml2 and libxslt, which etree directly depends on. libiconv should be added.

[scoder (scoder)]

https://github.com/lxml/lxml/commit/e6c925f8c61bc62a572dc4ff945569ee59b2128a