[CMake] Problem building libraries with no sources with Visual Studio 9 (2008)

[Michael Hertling]

On 12/21/2010 04:13 PM, Pere Mato Vila wrote:
> Dear all,
> 
>   I am trying to build shared libraries on Windows exporting all symbols. This is as an alternative of instrumenting the code with dllimport/dllexport declarations. For this I do build first a static library from which I get all the defined symbols to write a .DEF file which is then used to build the shared library. The CMake code (using version 2.8.3)  looks like this:
> 
> add_library( ${library}-static STATIC ${sources} ) 
> add_custom_command( OUTPUT {library}.def COMMAND <using ${library}-static> DEPENDS ${library}-static )
> add_library(${library} SHARED ${library}.def)
> target_link_libraries(${library}  ${library}-static ${other-libs} )
> set_target_properties(${library} PROPERTIES LINK_INTERFACE_LIBRARIES ${other-libs})
> 
>    This works just fine when using the nmake generator. The library is created and has all the symbols are exported as desired. But, when using Visual C++ 2008 express edition I get the following error message:
> 
> 1>.\mylib.dir\Debug\mylib.dll.intermediate.manifest : general error c1010070: Failed to load and parse the manifest. The system cannot find the file specified.
> 
>   The problem is that the shared library has been defined without any 'real' source file (only the .def file is declared) and somehow the generated code does not produce the required manifest file. Does anybody see a problem with these kind of constructs?  Should it just work from within the IDE? 
>   Experimentally I have found a workaround, which consists in adding a dummy source file in the shared library definition. 
> 
> ...
> file( WRITE ${library}.cpp "// empty file!!!\n" )
> add_library( ${library} SHARED ${library}.cpp ${library}.def)
> ... 
> 
> 
> I have also noticed that the dependency of the shared library to the .def file is also missing. This is, newer versions of the .def file does not trigger a re-build of the shared library. 

AFAIK, this is because CMake does not know how to handle a .def file
for incorporation in the target, i.e. ${library}.def has no LANGUAGE
property. Thus, its inclusion in the target's sources results in the
execution of the custom command only. Perhaps, you can enhance your
workaround with the dummy ${library}.cpp as follows:

ADD_CUSTOM_COMMAND(
    OUTPUT {library}.def
    COMMAND <using ${library}-static>
    COMMAND ${CMAKE_COMMAND} -E touch ${library}.cpp
    DEPENDS ${library}-static
)

This would invalidate ${library}.cpp each time ${library}.def is
regenerated, so the dummy is recompiled and ${library} relinked.

Regards,

Michael

PS: Don't write to the source directory with FILE(WRITE ...) or the like.