[CMake] call already made makefile

[Alan W. Irwin]

On 2010-11-05 14:12-0400 David Cole wrote:

> On Fri, Nov 5, 2010 at 2:00 PM, SK <sk at metrokings.com> wrote:
>> On Thu, Nov 4, 2010 at 9:23 PM, SK <sk at metrokings.com> wrote:
>>> On Thu, Nov 4, 2010 at 6:09 PM, Alan W. Irwin <irwin at beluga.phys.uvic.ca> wrote:
>>>> then the custom make command
>>>> should always be run (since it has no DEPENDS option),
>>>
>>> Alan, you are absolutely right!!
>>
>> No, sorry.  Only if the add_custom_command output does not exist as
>> other have mentioned too.  My build is so ridiculously complex I'm
>> fooling myself right and left.  Here's a small test case to show this.
>>  Hopefully other suggestions on this thread will work.
>>
>>> cat external_makefile
>> bar : foo
>>        touch bar
>>
>>> cat CMakeLists.txt
>>
>> CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
>> PROJECT( makefile_test )
>>
>> ADD_CUSTOM_COMMAND( OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/bar
>>        COMMAND make -f ${CMAKE_CURRENT_SOURCE_DIR}/external_makefile
>>        COMMENT "Running external makefile"
>>        )
>>
>> ADD_CUSTOM_TARGET( external_target ALL
>>        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/bar
>>        )
>>
>>
>> After running cmake, we see
>>> make
>> [ 0%] Running external makefile <=== Builds bar fine first time
>> [100%] Built target external_target
>>> touch foo
>>> make
>> [100%] Built target external_target <=== DOES NOT BUILD BAR!!
>>> rm bar
>>> make
>> [ 0%] Running external makefile <=== Builds bar only after delete
>> [100%] Built target external_target
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>
>
>
> Change it to this:
>
>> ADD_CUSTOM_COMMAND( OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/NO_SUCH_FILE_AS_bar
> ...
>> ADD_CUSTOM_TARGET( external_target ALL
>>        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/NO_SUCH_FILE_AS_bar
>
> Now, because NO_SUCH_FILE_AS_bar NEVER exists, ever... the command
> will always run, because the custom target is always out of date.
> Then, when your makefile actually runs, *it* will decide (hopefully
> correctly) whether or not it needs to build 'bar'.
>
> Non-obvious, I know. I struggled with this over and over while
> developing ExternalProject... But it does work.

I agree the above idea should work, but dropping add_custom_command
completely and moving the COMMAND to add_custom_target instead (and
dropping all file DEPENDS for the custom target) is even a simpler way
to insure COMMAND gets executed every time the custom target is
built.  This situation is summarized in the documentation.

add_custom_target
    Add a target with no output so it will always be built.

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); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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Linux-powered Science
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