[CMake] Generator expressions containing spaces

Wed Apr 25 01:53:18 EDT 2018

2018-04-24 21:37 GMT+02:00 Yves Frederix <yves.frederix+cmake at gmail.com>:
> 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>"
> )

Ah, of course. Thanks.

Elvis

>
> 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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