Hi,
I recently learned that the COMMAND line in a custom command supports
generator expressions. In particular, what makes this powerful is that if
the expression evaluates to the empty string, no corresponding code will be
added to the target (as documented in the docs
<https://cmake.org/cmake/help/v3.11/command/add_custom_command.html?highlight=add_custom_command>
).
While this works very nicely for single-string command, I fail to make it
work for commands consisting of multiple space-separated strings:
```
~/tmp/genex_with_spaces$ cat CMakeLists.txt
cmake_minimum_required(VERSION 3.6)
add_custom_target(foo)
add_custom_command(TARGET foo POST_BUILD
COMMAND $<1:echo bar>
)
~/tmp/genex_with_spaces$ grep bar build/CMakeFiles/foo.dir/build.make
"\$$<1:echo" bar>
```
As can be seen, the generator expression is not expanded.
My question is now whether I am doing something wrong (is there a correct
way of dealing with spaces in the context of generator expressions?) or
might this be an inherent limitation of generator expression in general?
As a workaround, the only thing that seems to work is to put each of the
space-separated components of the command in (typically identical) genexes:
```
~/tmp/genex_with_spaces$ cat CMakeLists.txt
cmake_minimum_required(VERSION 3.6)
add_custom_target(foo)
add_custom_command(TARGET foo POST_BUILD
COMMAND $<1:echo> $<1:bar>
)
~/tmp/genex_with_spaces$ grep bar build/CMakeFiles/foo.dir/build.make
echo bar
```
Of course, while this works, things becomes very unreadable if the genex is
more complex.
Other things that I have tried but failed:
- escape the space with a backslash -> this quotes the entire expression
inside the genex.
- define the command directly as a list inside the genex -> this removes
spaces between the different components of the command and quotes that
result.
- treat the command as a list, perform string operations to wrap each
element in the desired regex and convert semicolon to spaces -> again
results in the command being quoted as a whole.
Any advice is highly appreciated.
Thanks,
Yves
--
Powered by www.kitware.com
Please keep messages on-topic and check the CMake FAQ at:
http://www.cmake.org/Wiki/CMake_FAQ
Kitware offers various services to support the CMake community. For more
information on each offering, please visit:
CMake Support: http://cmake.org/cmake/help/support.html
CMake Consulting: http://cmake.org/cmake/help/consulting.html
CMake Training Courses: http://cmake.org/cmake/help/training.html
Visit other Kitware open-source projects at
http://www.kitware.com/opensource/opensource.html
Follow this link to subscribe/unsubscribe:
https://cmake.org/mailman/listinfo/cmake
