bug#38610: Two libtool 2.4.6 issues

[Roumen Petrov]

Hello,

Sergey Poznyakoff wrote:
> Dear maintainers,
>
> When working on GNU mailutils we have discovered two issues with libtool,
> which probably qualify as bugs.
> [SNIP]

Build with installed library into non-default locations most of the time 
is painful.

In one of models each library set(package) is installed in separate 
directory in format like this: <install>/<package>-<version>.
This model prevents load of headers and library from unexpected location 
but build use many -I and -L flags. Let skip -R/-rpath flags for simplify.

Another model is installation in common path. In this case flags are 
less but build is more tricky - user must ensure precedence of headers 
(-I) and libraries (-L) from source tree.

So report is for libtool and samples are for libraries but case is 
applicable for header files as well. And for headers we cannot blame 
libtool.

Tips:
I prefer first model but in one case I use second.
Let headers are in <INSTALL>/include and libraries are in <INSTALL>/lib
In the second with limited number of projects:
- if build uses shell script to return path to headers and libraries 
script must be modified do not output -I and -L flags.
- if build uses pkgconfig environment must be set so that command do not 
output -I and -L flags.
- libtool is tuned with new "system library path" : variable 
lt_cv_sys_lib_dlsearch_path_spec, work fine on unixes.
- CC is overridden to use flags like --sysroot, -isystem, -B and etc. 
Unfortunately clang lack flag to add item to "system library search 
path" and so gcc is preferred.


Remark:
In one of the provided samples is hard coded path -L $(libdir), i.e. 
-L<path> -l<lib> This should be $(FOO_LIBS) and depending from model at 
configuration time is should be set either to -L<path> -l<lib> or only 
to -l<lib>. First is usable for model with separate directories 
otherwise should be used second one.


Regards,
Roumen Petrov

P.S. samples:
$ pkg-config --libs openssl
-lssl -lcrypto
$ PKG_CONFIG_SYSTEM_LIBRARY_PATH=/bon/go pkg-config --libs openssl
-L/usr/lib64 -lssl -lcrypto

So with PKG_CONFIG_* environment variables build could be tuned to 
exclude -I and -L flags.
Note pkg-config flags lib-only* and cflags-only* are out of scope.