[Scons-dev] User-specified signature function (was: Re: Feature request / patch)

[Eric W. Anderson]

Hi Jason (and list),

To be clear, I'm not proposing that that particular signature function should
become part of SCons.  What I want to add to the "core" SCons code is the
necessary set of hooks to accept and run user-supplied signature-generating
functions.  Indeed, the whole point is to allow users to supply something which
we wouldn't want _in general_, but is right for their needs.  I see this as the
missing half of the user-specified Decider: You can write a much broader range
of functions if you can ensure that whatever information your decider needs has
been gathered.

In my particular situation, the build tools themselves cause "spurious" changes
to the source files.  Unless those changes are somehow filtered out, the files
are _always_ changed, so a false rebuild occurs every single time.  That's
mostly an issue of poor tool design, but I'm stuck with it.  

-Eric

Thus spake Kenny, Jason L (jason.l.kenny at intel.com):


> Interesting idea. However here are some cons to consider.

> 

> 1) this will take longer to process ( increase startup time) as one has to parse the file for a certain type of comment(s)

> 2) a number of tools process values that are in the comments

> 

> In your case you point out how a comment that is updated by a VCS tool with a value of a new date, etc can cause a false rebuild of the code. That same value can be used by another tools to make documentation updates, or define many other values. Maybe in your case this is not so. You are suggesting that we have a tool based MD5 for a given node... i.e. I want a MD5 only of the content that the tool cares about, which could be one or more different signature per node.

> 

> Jason

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-- 
Eric W. Anderson                     Electrical and Computer Engineering
andersoe at ece.cmu.edu                          Carnegie Mellon University
phone: +1-412-268-1908                                  Roberts Hall 244

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