[CMake] --debug-trycompile not working as documented with the results being overwritten

[Alan W. Irwin]

I have the usual try_compile debug scenario; all but one of them in my
project (PLplot) is working (some with expected false results some with true),
and I would like to debug the one that isn't working (the result
is expected to be true, but it is false).

The (CMake-2.8.12.1) documentation says:

"If you use --debug-trycompile, you can only debug one try_compile call
at a time. The recommended procedure is to configure with cmake all
the way through once, then delete the cache entry associated with the
try_compile call of interest, and then re-run cmake again with
--debug-trycompile."

I have followed exactly that procedure on Linux with CMake-2.8.12.1,
but at least one of the PLplot build system's other try_compile calls 
is overwriting ./CMakeFiles/CMakeTmp/CMakeLists.txt so I cannot debug
the try_compile I want to debug.

Here are the details of all those different cached try_compile results.
I run the following commands:

software at raven> cmake \
-DCMAKE_INSTALL_PREFIX=/home/software/plplot/installcmake \
-DBUILD_TEST=ON ../plplot.git >& cmake.out

edit CMakeCache to remove the two lines relevant to the try_compile
I want to debug:
//Result of TRY_COMPILE
CONSISTENT_HEADER_ITCL_VERSION:INTERNAL=FALSE

software at raven> cmake --debug-trycompile \
-DCMAKE_INSTALL_PREFIX=/home/software/plplot/installcmake
-DBUILD_TEST=ON ../plplot.git >& cmake.out1

software at raven> grep -A1 TRY_COMPILE CMakeCache.txt
//Result of TRY_COMPILE
CMAKE_BROKEN_ISNAN_CXX:INTERNAL=TRUE
--
//Result of TRY_COMPILE
CMAKE_CXX_STDINT_H:INTERNAL=TRUE
--
//Result of TRY_COMPILE
CMAKE_D_TANGO_WORKS:INTERNAL=FALSE
--
//Result of TRY_COMPILE
CMAKE_FORTRAN_HAVE_ISNAN:INTERNAL=FALSE
--
//Result of TRY_COMPILE
CMAKE_HIGH_BIT_CHARACTERS:INTERNAL=TRUE
--
//Result of TRY_COMPILE
CMAKE_TEST_SIGNAL_TYPE:INTERNAL=TRUE
--
//Result of TRY_COMPILE
CMAKE_USE_NAMESPACE:INTERNAL=TRUE
--
//Result of TRY_COMPILE
CONSISTENT_HEADER_ITCL_VERSION:INTERNAL=FALSE
//Result of TRY_COMPILE
COMPILE_RESULT:INTERNAL=TRUE
//Result of TRY_COMPILE
CONSISTENT_HEADER_ITK_VERSION:INTERNAL=TRUE
--
//Result of TRY_COMPILE
HAVE_SAHOOKS:INTERNAL=TRUE

By looking at CMakeFiles/CMakeTmp/CMakeLists.txt I have discovered it
is the HAVE_SAHOOKS one that last overwrites the
CMakeFiles/CMakeTmp/CMakeLists.txt file for the second CMake
invocation.  Also, notice that the one I removed,
CONSISTENT_HEADER_ITCL_VERSION is restored indicating that try_compile
was executed (and returned a failure which I am trying to debug, but I
cannot do that with CMakeFiles/CMakeTmp/CMakeLists.txt being
overwritten).

The last time I had to debug a try_compile was years ago, but as far
as I can remember in that case --debug-trycompile worked as
documented.  And technically --debug-trycompile works for this case as
well (CMakeFiles/CMakeTmp/CMakeLists.txt is retained for each
try_compile). But in practice it is useless because the other
try_compiles are overwriting the results.  Is there some known bugs
for cmake-2.8.12.x such that try_compiles are repeated even if a
cached result (whether true of false) is found for the resulting
variable?  (For what it is worth, note that HAVE_SAHOOKS is true
above.)

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).
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Linux-powered Science
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