[CMake] Generator expressions containing spaces

Tue Apr 24 15:37:57 EDT 2018

There is no real need to go through an intermediate variable. The following
should work:

add_compile_options(
   "$<$<CXX_COMPILER_ID:GNU>:-Wall;-Wextra;-Werror>"
)

Yves

On Tue, Apr 24, 2018 at 6:58 PM, Elvis Stansvik <
elvis.stansvik at orexplore.com> wrote:

> 2018-04-23 14:11 GMT+02:00 CHEVRIER, Marc <marc.chevrier at sap.com>:
> > The space is used to separate arguments passed to COMMAND. So your
> generator
> > expression is splitted before evaluation and elements are no longer valid
> > generator expression.
> >
> >
> >
> > So, to solve your problem, encapsulate the generator expression inside
> > quotes. And apply the following advices for correct result:
> >
> > Separate command from args
> > Use variable to list your arguments and add option COMMAND_EXPAND_LISTS
> > (available with version 3.8) to avoid “spurious” semi-colons in the
> result
> >
> >
> >
> > Your example reworked:
> >
> >
> >
> > Set (args foo bar)
> >
> > add_custom_target(foo)
> >
> > add_custom_command(TARGET foo POST_BUILD
> >
> >   COMMAND $<1:echo> "$<1 :${args}>"
> >
> >   COMMAND_EXPAND_LISTS
> >
> >   )
> >
>
> Interesting thread. I was sort of in the same boat, having a
>
> add_compile_options(
>     "$<$<CXX_COMPILER_ID:GNU>:-Wall>"
>     "$<$<CXX_COMPILER_ID:GNU>:-Wextra>"
>     "$<$<CXX_COMPILER_ID:GNU>:-Werror>"
>
>     "$<$<CXX_COMPILER_ID:Clang>:-Wall>"
>     "$<$<CXX_COMPILER_ID:Clang>:-Wextra>"
>     "$<$<CXX_COMPILER_ID:Clang>:-Werror>"
>
>     "$<$<CXX_COMPILER_ID:AppleClang>:-Wall>"
>     "$<$<CXX_COMPILER_ID:AppleClang>:-Wextra>"
>     "$<$<CXX_COMPILER_ID:AppleClang>:-Werror>"
> )
>
> and of course wishing I could just write something like
>
> add_compile_options(
>     $<$<CXX_COMPILER_ID:GNU>:-Wall -Wextra -Werror>
>     $<$<CXX_COMPILER_ID:Clang>:-Wall -Wextra -Werror>
>     $<$<CXX_COMPILER_ID:AppleClang>:-Wall -Wextra -Werror>
> )
>
> instead.
>
> I can't depend on CMake 3.8+ just yet, but I'll remember your solution
> for when I can.
>
> I don't quite like having to introduce variables though. Is there no
> way to solve this without having to first stuff the elements in a list
> and use that?
>
> Cheers,
> Elvis
>
> >
> >
> >
> >
> > From: CMake <cmake-bounces at cmake.org> on behalf of Yves Frederix
> > <yves.frederix+cmake at gmail.com>
> > Date: Monday 23 April 2018 at 13:08
> > To: "cmake at cmake.org" <cmake at cmake.org>
> > Subject: [CMake] Generator expressions containing spaces
> >
> >
> >
> > 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).
> >
> >
> >
> > 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
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > --
> >
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