[icu-support] discussion about ICU 64.1 and MSYS2+mingw-w64 : linking error

[Vincent T. <vin...@gm...>]

Hello

I have had some issues with ICU 64.1 and MSYS2+mingw-w64 when linking
with libraries using ICU (namely harfbuzz and libxml2).

This is related to ticket ICU-20322
(https://unicode-org.atlassian.net/browse/ICU-20322)

When I compile ICU, the list of installed files in libdir is (mainly) :

/home/vtorri/icu_64/lib/icudt.dll
/home/vtorri/icu_64/lib/icudt64.dll
/home/vtorri/icu_64/lib/icuin.dll
/home/vtorri/icu_64/lib/icuin64.dll
/home/vtorri/icu_64/lib/icuio.dll
/home/vtorri/icu_64/lib/icuio64.dll
/home/vtorri/icu_64/lib/icutest.dll
/home/vtorri/icu_64/lib/icutest64.dll
/home/vtorri/icu_64/lib/icutu.dll
/home/vtorri/icu_64/lib/icutu64.dll
/home/vtorri/icu_64/lib/icuuc.dll
/home/vtorri/icu_64/lib/icuuc64.dll
/home/vtorri/icu_64/lib/libicudt.dll.a
/home/vtorri/icu_64/lib/libicuin.dll.a
/home/vtorri/icu_64/lib/libicuio.dll.a
/home/vtorri/icu_64/lib/libicutest.dll.a
/home/vtorri/icu_64/lib/libicutu.dll.a
/home/vtorri/icu_64/lib/libicuuc.dll.a
/home/vtorri/icu_64/lib/pkgconfig
/home/vtorri/icu_64/lib/pkgconfig/icu-i18n.pc
/home/vtorri/icu_64/lib/pkgconfig/icu-io.pc
/home/vtorri/icu_64/lib/pkgconfig/icu-uc.pc

Here, there are 3 kind of files

1) DLL files. As explained in issue ICU-20322, they should be in bin
dir and not lib dir
2) import library (*.dll.a) : they are mainly stub DLL files
3) *.pc files

To limit the list of files, let's take only icu uc files :

/home/vtorri/icu_64/lib/icuuc.dll
/home/vtorri/icu_64/lib/icuuc64.dll
/home/vtorri/icu_64/lib/libicuuc.dll.a
/home/vtorri/icu_64/lib/pkgconfig/icu-uc.pc

So, i follow what i have written in issue ICU-20322 : i have moved the
DLL files in bin dir, so I have now :

/home/vtorri/icu_64/bin/icuuc.dll
/home/vtorri/icu_64/bin/icuuc64.dll
and
/home/vtorri/icu_64/lib/libicuuc.dll.a
/home/vtorri/icu_64/lib/pkgconfig/icu-uc.pc

but now, when I link against icu using icu-uc.pc, the link flags are
(see the content of icu-uc.pc) :
-L${libdir} -licuuc64 -licudt64

that is (with my installation):

-L/home/vtorri/icu_64/lib -licuuc64 -licudt64

Hence a linking error as the import library is libicuuc.dll.a and not
libicuuc64.dll.a

According to the "direct linking to a dll" paragraph of
https://sourceware.org/binutils/docs/ld/WIN32.html I propose the
following changes for this platform (MSYS2 (or cygwin) + mingw-w64) :

1) move DLL in the bin directory. Actually, only 1 DLL is useful :
icuuc64.dll, the other one (icuuc.dll) is useless. It is also a *copy*
of icuuc64.dll and not a symbolic link like on UNIX file systems, so
it as a waste of disk space

2) change the pc file flags to -L${libdir} -licuuc -licudt (that is
removing the '64' suffix)

Note that the change in the pc file will work for UNIX too as the
symbolic link libicuuc.does exist

Final remark :

icu-uc.pc link flags are -L${libdir} -licuuc64 -licudt64

but icu-io.pc and icu-i18n.pc are lacking -L${libdir}. I would add it.

What do you think of this proposal ?

thank you for reading

Vincent Torri