[cmake-developers] new ninja rebuild too much issue

[Bill Hoffman]

It seems that if the CMakeCache.txt changes, and cmake re-runs, ninja 
rebuilds almost ever single .obj file.  For example, if I turn on and 
off CMAKE_ENABLE_NINJA,   Then it rebuilds all the .obj files instead of 
relinking just a few executables since the .obj files are there all 
ready.  I had a report of this from someone else at Kitware working on a 
larger project.   They said if they changed options with ccmake, that 
ninja rebuild the whole thing.

Is there a way to debug ninja and have it print out why it is building 
something?


Here is the example:

$ ninja
[1/1] Re-running CMake...
-- Enable ninja generator.
-- Found Qt4: 
C:/Users/hoffman/Work/qt-everywhere-opensource-src-4.7.4/bin/qmake.exe 
(found suitable version "4.7.4", required is "4.4.0")
-- Found Qt4: 
C:/Users/hoffman/Work/qt-everywhere-opensource-src-4.7.4/bin/qmake.exe 
(found version "4.7.4")
-- No CTest.UpdateCVS test with cygwin cvs.exe outside cygwin!
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Users/hoffman/Work/My 
Builds/cmake-ninja
[1/206] Building CXX object 
Source\CMakeFiles\CMakeLib.dir\cmGlobalVisualStudio7[2/206] Building CXX 
object Source\CMakeFiles\CMakeLib.dir\cmGlobalVisualStudio7

This should be an almost no-op.   Is it because everything depends on 
the build.ninja file?


-Bill