Storing generated files (was: Re: Make cvs ignore some changes in files)

[Mike Ayers]

Riechers, Matthew W wrote:
> > From: Christian Andersson [mailto:address@hidden
> >
> > I have some genereated source-files that I need to have in the cvs
>
>
> Why must they be in CVS?

	For those who cannot fathom why generated files may need to be 
archived, I will, without knowing the details of Mr. Andersson's 
problem, give reasonable and common scenarios for storing generated files:

	1)  The generation process itself is too expensive.  Hardware (FPGA 
and ASIC) design tools and 3D graphics come to mind, where generation 
can require several days on a cluster.  One cannot simply expect each 
developer to generate their own result file, unless one owns 
controlling interest in the server supplier.

	2)  The generation will not necessarily produce the same result.  A 
good example is lex/flex and yacc/bison generation.  Lex and yacc are 
different tools on most of the machines on which they occur, yet tend 
to produce better (and, as I recall, more portable(?!)) results than 
flex/bison on those systems.  A project I worked on would generate 
files using lex/yacc on a specific platform and archive them into the 
sources.  Those building the project would compile, and most would get 
satisfactory results.  Those who did not could clean out the generated 
files and rebuild; this usually worked.  We could not require 
generation of these files, as not all systems had lex/yacc or flex/bison.

        3)  The generation tool is not available on all supported platforms.

	4)  The generation tool is nondeterministic.  There are two cases of 
this that I know of.  First, there is Altera's FPGA compiler (at least 
last time I checked).  Next is cryptography:  one would want to start 
by generating random seeds.  However, for test runs, one would like to 
archive a seed file so that results are consistent.

        I hope this helps explain why generated files may need to be stored.


/|/|ike