[CMake] Need suggestions for implementation of new feature in cmake.

[Hendrik Sattler]

Hi Carlo,

The answer is already right in front of you: "a && b" executes b only if a returns positive (zero exit code). This is already done for the mkdir.

And to answer the other question: no, you cannot assume a POSIX shell in a Makefile.

HS


Am 27. März 2020 05:53:39 MEZ schrieb Carlo Wood <carlo at alinoe.com>:
>Hello!
>
>I'm writing a patch for cmake to address
>https://gitlab.kitware.com/cmake/cmake/issues/19703
>
>but I need a little help; I'm only familiar with
>GNU/Linux and single target generator Makefile.
>
>In terms of a Makefile, if one uses ExternalProject_Add_Step, see
>
>https://cmake.org/cmake/help/latest/module/ExternalProject.html#explicit-step-management
>
>then something like this is generated:
>
>    /path/to/stamp_dir/myname-mystep: /path/to/some/dependency
>            @$(CMAKE_COMMAND) -E cmake_echo_color --switch=$(COLOR) \
>                --blue --bold \
>                --progress-dir=/path/to/buildir/CMakeFiles \
>                --progress-num=$(CMAKE_PROGRESS_9) "My Comment"
>            cd /path/to/workingdir && \
>                my_COMMAND my_arg1 my_arg2 ... \
>            cd /path/to/workingdir && \
>                cmake -E touch /path/to/stamp_dir/myname-mystep
>
>Now, I'm not sure about the portability of the COMMAND that
>is passed to ExternalProject_Add_Step. Are we assuming that
>every operating system supports a POSIX (unix) shell, like bash?
>
>Otherwise it seems that the only way to be portable is to run
>cmake in script mode there.
>
>Note how the last command does this: it runs cmake in order to portably
>'touch' the target file (a stamp file).
>
>What I need is way to generate a rule where depending on a
>condition (to be decided by the COMMAND (my_COMMAND)) that
>touch is or is not done.
>
>In the single target target POSIX Makefile case this could look like
>this (I'm leaving out the COMMENT here for brevity),
>
>     /path/to/stamp_dir/myname-mystep: /path/to/some/dependency
>            (cd /path/to/workingdir && \
>                if my_COMMAND my_arg1 my_arg2 ...; then \
>                  cmake -E touch /path/to/stamp_dir/myname-mystep; \
>                fi)
>
>which uses the return value of my_COMMAND to decide whether or
>not to touch the stamp file.
>
>However, this is pure shell coding: using a '(' to open a sub shell
>and then using 'if ...; then ... fi'.
>
>I'm looking for ideas on how to implement this in a portable way.
>
>How can I extract a boolean from a user defined COMMAND and then
>use that to conditionally execute the touch?