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<p class="MsoNormal"><span lang="EN-US">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 So your generator expression is splitted before evaluation and elements are no longer valid generator expression.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">So, to solve your problem, encapsulate the generator expression inside quotes. And apply the following advices for correct result:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo2"><span lang="EN-US">Separate command from args<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo2"><span lang="EN-US">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<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Your example reworked:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Set (args foo bar)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">add_custom_target(foo)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">add_custom_command(TARGET foo POST_BUILD<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> COMMAND $<1:echo> "$<1 :${args}>"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> COMMAND_EXPAND_LISTS<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> </span>)<o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">CMake <cmake-bounces@cmake.org> on behalf of Yves Frederix <yves.frederix+cmake@gmail.com><br>
<b>Date: </b>Monday 23 April 2018 at 13:08<br>
<b>To: </b>"cmake@cmake.org" <cmake@cmake.org><br>
<b>Subject: </b>[CMake] Generator expressions containing spaces<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><a name="_MailOriginalBody">Hi, <o:p></o:p></a></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">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 </span><a href="https://cmake.org/cmake/help/v3.11/command/add_custom_command.html?highlight=add_custom_command"><span style="mso-bookmark:_MailOriginalBody">docs</span><span style="mso-bookmark:_MailOriginalBody"></span></a><span style="mso-bookmark:_MailOriginalBody">).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">While this works very nicely for single-string command, I fail to make it work for commands consisting of multiple space-separated strings:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">```<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">~/tmp/genex_with_spaces$ cat CMakeLists.txt cmake_minimum_required(VERSION 3.6)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">add_custom_target(foo)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">add_custom_command(TARGET foo POST_BUILD<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"> COMMAND $<1:echo bar><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"> )<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">~/tmp/genex_with_spaces$ grep bar build/CMakeFiles/foo.dir/build.make "\$$<1:echo" bar><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">```<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">As can be seen, the generator expression is not expanded.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">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?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">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:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">```<o:p></o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">~/tmp/genex_with_spaces$ cat CMakeLists.txt
cmake_minimum_required(VERSION 3.6)<o:p></o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222"><o:p> </o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">add_custom_target(foo)<o:p></o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">add_custom_command(TARGET foo POST_BUILD<o:p></o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">
<span style="background:white">COMMAND $<1:echo> $<1:bar></span> <o:p></o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222"> )<o:p></o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222"><o:p> </o:p></span></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">~/tmp/genex_with_spaces$ grep bar build/CMakeFiles/foo.dir/build.make echo bar<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">```<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><br>
Of course, while this works, things becomes very unreadable if the genex is more complex.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Other things that I have tried but failed:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
<span style="mso-bookmark:_MailOriginalBody">escape the space with a backslash -> this quotes the entire expression inside the genex.<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
<span style="mso-bookmark:_MailOriginalBody">define the command directly as a list inside the genex -> this removes spaces between the different components of the command and quotes that result.<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
<span style="mso-bookmark:_MailOriginalBody">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.<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Any advice is highly appreciated.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Thanks,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody">Yves<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-bookmark:_MailOriginalBody"><o:p> </o:p></span></p>
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