[cmake-developers] [PATCH] FindProtobuf: fix wrong library list for Unix

[Rolf Eike Beer]

Am 09.02.2016 11:10, schrieb Antonio Pérez Barrero:
>> 
>> On 02/08/2016 04:24 PM, Antonio Pérez Barrero wrote:
>> > Yes, it is possible, but currently it's not looking for the debug
>> > library with a different name, just in a different path that is
>> > unlikely to exist in a Unix system.
>> 
>> The fact that a separate find_library is called for it and the result
>> is stored in a separate (user-settable) cache entry means that it is
>> possible to get two different values.  This convention is well 
>> established
>> in several find modules.
>> 
>> > Having the PROTOBUF_LIBRARIES variable getting the afore mentioned
>> > value messes up the client code using `find_package(Protobuf)` on Unix.
>> 
>> The only supported use for PROTOBUF_LIBRARIES is to pass it to
>> target_link_libraries, and that interprets the 'optimized' and 'debug'
>> keywords.  This is shown in the module documentation example:
>> 
>>     target_link_libraries(bar ${PROTOBUF_LIBRARIES})
>> 
>> The documentation makes no other guarantees about the variable value.
>> 
> 
> Thanks for your explanantion, that makes sense. I had issues because I 
> was
> appending the value of PROTOBUF_LIBRARIES to a list and then removing
> duplicates before calling `target_link_libraries(bar ${LIST})`. So when 
> the
> PROTOBUF_LIBRARIES values was
> `optimized;/usr/lib/libprotobuf.so;debug;/usr/lib/libprotobuf.so` I was
> missing the link flag for /usr/lib/libprotobuf.so in Debug builds. 
> Skipping
> the duplicates removal step solves my issue.
> 
> Anyway, the root cause is the `find_library` is finding the same 
> library
> for optimized and debug configuration. So, would a patch like this be
> benefial?
> 
> diff --git a/Modules/FindProtobuf.cmake b/Modules/FindProtobuf.cmake
> index 2f13b09..35929a4 100644
> --- a/Modules/FindProtobuf.cmake
> +++ b/Modules/FindProtobuf.cmake
> @@ -224,7 +224,7 @@ function(_protobuf_find_libraries name filename)
>         PATHS
> ${PROTOBUF_SRC_ROOT_FOLDER}/vsprojects/${_PROTOBUF_ARCH_DIR}Debug)
>     mark_as_advanced(${name}_LIBRARY_DEBUG)
> 
> -   if(NOT ${name}_LIBRARY_DEBUG)
> +   if((NOT ${name}_LIBRARY_DEBUG) OR (${name}_LIBRARY STREQUAL
> ${name}_LIBRARY_DEBUG))
>        # There is no debug library
>        set(${name}_LIBRARY_DEBUG ${${name}_LIBRARY} PARENT_SCOPE)
>        set(${name}_LIBRARIES     ${${name}_LIBRARY} PARENT_SCOPE)

Just use SelectLibraryConfigurations, that does the same automatically 
if they are identical, and also handles the cases where only debug, but 
not release is found.

Greetings,

Eike