[CMake] custom target like add_executable

[Bill Newcomb]

A contrived example:

$ ls ..
b  CMakeLists.txt  foo

$ cat ../CMakeLists.txt 
cmake_minimum_required(VERSION 3.1)

add_custom_target(foo.sha1 ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/foo.sha1)

add_custom_command(
    OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/foo.sha1
    COMMAND openssl sha1 -out ${CMAKE_CURRENT_BINARY_DIR}/foo.sha1 ${CMAKE_CURRENT_SOURCE_DIR}/foo
    )

$ cmake ..
-- The C compiler identification is GNU 4.1.2
-- The CXX compiler identification is GNU 4.1.2
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/bnewcomb/tmp/cmake-tests/test-fail/b

$ make
Scanning dependencies of target foo.sha1
make[2]: Circular CMakeFiles/foo.sha1 <- foo.sha1 dependency dropped.
make[2]: Circular foo.sha1 <- foo.sha1 dependency dropped.
[100%] Generating foo.sha1
[100%] Built target foo.sha1

$ ls --full-time foo.sha1 
-rw-rw-r-- 1 bnewcomb hardware 93 2015-02-05 10:10:48.984606000 -0800 foo.sha1

$ make
make[2]: Circular CMakeFiles/foo.sha1 <- foo.sha1 dependency dropped.
make[2]: Circular foo.sha1 <- foo.sha1 dependency dropped.
[100%] Generating foo.sha1
[100%] Built target foo.sha1

$ ls --full-time foo.sha1 
-rw-rw-r-- 1 bnewcomb hardware 93 2015-02-05 10:11:05.432925000 -0800 foo.sha1

$ 

I read in a years-old bug that I should always use absolute paths
with add_custom_command, but I don't know if that's still necessary.
Using relative paths doesn't seem to change the outcome.

Thanks,
B.

On 02/04/2015 06:59 PM, Alan W. Irwin wrote:
> On 2015-02-04 13:45-0800 Bill Newcomb wrote:
> 
>> Oops, so I guess it's not that it doesn't work at all, but that the 
>> add_custom_command gets run every time I 'make all', and that gnu make 
>> emits some warnings about circular dependencies.  The first is more of 
>> a problem, but both are kind of annoying.
> 
> Neither of those "issues" occurs if you have set up add_custom_command
> and the corresponding add_custom_target with the appropriate
> dependencies between them.
> 
> If re-reading the CMake documentation for add_custom_command and
> add_custom_target doesn't help, then I suggest you give a simple example
> that is not working for you.  I assume you have some dependency
> issue, but until you give an example, it is hard to anticipate what
> that might be.
> 
> Alan
> __________________________
> Alan W. Irwin
> 
> Astronomical research affiliation with Department of Physics and Astronomy,
> University of Victoria (astrowww.phys.uvic.ca).
> 
> Programming affiliations with the FreeEOS equation-of-state
> implementation for stellar interiors (freeeos.sf.net); the Time
> Ephemerides project (timeephem.sf.net); PLplot scientific plotting
> software package (plplot.sf.net); the libLASi project
> (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
> and the Linux Brochure Project (lbproject.sf.net).
> __________________________
> 
> Linux-powered Science
> __________________________

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