[Octave-bug-tracker] [bug #46063] Build system re-makes certain files 2 or even 3 times

[John W. Eaton]

Follow-up Comment #21, bug #46063 (project octave):

I checked in the following chanagesets:

  http://hg.savannah.gnu.org/hgweb/octave/rev/df859661e31e
  http://hg.savannah.gnu.org/hgweb/octave/rev/7e8a410e6124

In the past, the build system was trying to handle things like


configure libdir=SOME_VALUE
make
make libdir=SOME_OTHER_VALUE


but I don't think this was ever really working correctly.  Now it won't work
at all as the new setting will be ignored, so files that have the value of
"libdir" inserted into them won't be updated, and if you try to do make
install with a modified variable like this, even if the installation step
succeeded, Octave will not have matching information compiled in so it will
not run properly

I don't think we've lost much feature-wise, but setting variables like this on
the make command line doesn't currently generate any warning or error, so
that's probably not good.

I'm not sure of the best way to go about generating an error.  I mean, there
are a lot of variables that could be set, and I don't know that we have a good
way to maintain the entire list.  If we did, maybe we could have make check
the definitions of all the variables against what was set at configure time
and issue an error if there is a mismatch?  Is it worth the trouble?

You should see some improvement if you have to run configure (or
config.status) again for an existing build because generated files do not
depend on Makefile.  And just adding a new file to a module.mk file should not
trigger a complete rebuild of everything since the timestamps of config.h,
oct-conf-post.h, and other generated files should not change just because some
module.mk file changed.

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