FW: Signature configurability

[Gary Oberbrunner]

I like it!  Having this will also help expose the signature behavior
of cons so people can understand how it works (it took me a while to figure
it out when I was getting started).

Quick question: the doc for cons 2.2 says that
  SourceSignature '*' => qw(consign content);
is the current behavior, I think, rather than just 'content':
  The signature of a non-derived file is computed, by default, by
taking the
  current modification time of the file and the file's entry name
(unless
  there happens to be a current .consign entry for that file, in
which case
  that signature is used).
Is that right?


Also, since the content method is a little different than the other
signature methods, we need to make sure it's well-documented.  The
current doc says "when considering whether to derive a particular
file, it first computes the expected signature;" so perhaps we could
add a section something like this:

After the file is derived, if 'content' is set for this file, its
content-signature is computed and compared to any existing content
signature in the .consign; if they match, it's considered just like
an unmodified source file when considering later files that depend on
it.  This way even if the command or dependencies of a file change in
such a way that the generated file is the same, dependents of that
file won't needlessly be rebuilt.  Note that if your compiler puts
timestamps or other varying information in object files, this can
cause more rebuilding than would otherwise have happened: without
'content', cons says that if a file is derived from the same sources,
and with the same command, as it was previously, then it's considered
unmodified when considering its dependents (even if the content
doesn't match).  This behavior may or may not be what you want.


. . . . . . . . . . . . . . . . . . . . . . . . .
Gary Oberbrunner                address@hidden
GenArts, Inc.                   Tel: 617-492-2888
8 Clinton Street                Fax: 617-492-2852
Cambridge, MA 02139 USA         http://web.genarts.com