Re: gEDA-user: Handling symbol change gschem]

[DJ Delorie <dj@xxxxxxxxxxx>]

> In addition, a SHA1 hash (for example) would also ensure the tools can
> detect when a symbol has changed in the library - without requiring the
> person changing the symbol to update a version field. (An alternative
> would be an embedded copy of the original symbol to compare against).

Note we have a similar problem in pcb, and it *does* embed symbols,
and they're highly likely to be edited by the user.

> The embedding idea would actually work well to make schematics portable,
> but would lead to cluttered schematic files.

I've thought about the idea of embedding the *origin* footprint in a
pcb file, as a sort of project-specific embedded library, and having
"elements" store only the deltas.  This is very similar to jpd's
"always copy the symbol locally" scheme.  I haven't figured out how to
merge user changes with library changes, though.

> FWIW, I'm not a big fan of UUIDs, assigned, random or otherwise.

We need a way to uniquely identify, say, different gates in the same
package in a schematic.  Consider a sheet with three NAND gates, both
U4.  How do you tell which is which when you want to swap gates across
physical packages in the layout?  Since the swap changes the refdes,
you can't rely on the refdes as a unique identifier any more.

Worse is when you want to have one package provide gates for different
sub-circuits in a heirarchy - the instances of the gates refer to the
*same* symbol!  Now what?  Now we need not only a UUID for the symbol
on the sheet, but for the path to the symbol in the design as well.


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