building with cmake and iconv

[userdocs]

I have encountered a few issues with this setup and was wondering if some things could be clarified.

https://github.com/arvidn/libtorrent/blob/RC_1_2/CMakeLists.txt#L677

When building on Alpine i need to set -D Iconv_LIBRARY="${lib_dir}/libiconv.a" otherwise the cmake files libtorrent generates tries to load an so file which give me a linking error. From the build/CMakeCache.txt

-D Iconv_LIBRARY="/usr/lib/libc.so"

Regarding ICU

iconv has become problematic for a consistent build usage when factoring in qtbase and boost seem to prefer ICU if it is available. Whilst I am unsure if that means it is actually used by libtorrent, this defaulting to iconv behaviour in cmake has created the issue I do not have when using b2

Now I know this is not a specific problem of this project, but what I think would make sense for a direct route to build on top of this with qbittorrent would be to support ICU?

https://bugreports.qt.io/browse/QTBUG-63529 and specifically this comment

https://bugreports.qt.io/browse/QTBUG-84708 + the required fix

From the linked fix conversation above will allow a locally built libiconv to work with qt using -iconv

QMAKE_CXXFLAGS=-fpermissive

https://bugreports.qt.io/browse/QTBUG-84687

Would it be possible to get an ICU support option to not have this iconv dependency with cmake?

It makes more sense to me to do this as the main deps all have a preference for ICU over iconv.

ICU > boost > libtorrent > qt > qbittorrent

[userdocs]

The cmake pkconfig

v1.2.13

prefix=/root/qb-build
libdir=${prefix}/lib

Name: libtorrent
Description: Bittorrent library
Version: 1.2.13
Libs: -L${libdir} -ltorrent-rasterbar -lIconv::Iconv -lssl -lcrypto -ldl -ldl -lcrypto
Cflags: -fexceptions -I/root/qb-build/include -I/root/qb-build/boost -I/root/qb-build/include -DBOOST_ASIO_ENABLE_CANCELIO -DTORRENT_USE_ICONV -DTORRENT_USE_OPENSSL -DTORRENT_USE_LIBCRYPTO

v2.0.3.0

prefix=/root/qb-build
libdir=${prefix}/lib

Name: libtorrent
Description: Bittorrent library
Version: 2.0.3
Libs: -L${libdir} -ltorrent-rasterbar -lssl -lcrypto -ldl -ldl
Cflags: -fexceptions -I/root/qb-build/include -I/root/qb-build/boost -I/root/qb-build/include -DBOOST_ASIO_ENABLE_CANCELIO -DBOOST_ASIO_NO_DEPRECATED -DTORRENT_USE_OPENSSL -DTORRENT_USE_LIBCRYPTO -DTORRENT_SSL_PEERS -DOPENSSL_NO_SSL2

Two things

Why do we have a double -ldl -ldl - I am not sure we even need -ldl here?

v1 has this -lIconv::Iconv but v2 does not.

[arvidn]

libtorrent 2.x no longer depends on iconv

[userdocs]

What does it do instead or is it just not needed to display unicode?

[arvidn]

iconv was used to convert from UTF-8 to the local locale of the filesystem. On windows MultiByteToWideChar() is used directly, and otherwise wcrtomb() is used to convert a unicode codepoint into the native locale. Which is extremely likely to be UTF-8 also.