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Date: Sun, 26 Sep 2021 16:53:37 +0200 (CEST)
From: Roland Lutz <rlutz AT hedmen DOT org>
To: "karl AT aspodata DOT se [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Subject: Re: [geda-user] empty attributes
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On Sun, 26 Sep 2021, karl AT aspodata DOT se [via geda-user AT delorie DOT com] wrote:
> http://wiki.geda-project.org/geda:symbols
> says about the same, but also that you can use "unknown" to specify
> a empty value.

The value "unknown" is not the same thing as an empty value; it means the 
value inherited from the symbol file should be discarded.  However, this 
doesn't apply to certain attributes which, like refdes=, are handled 
specially.

> I cannot find anything in the wiki that says a final space isn't 
> permitted.

As far as I know, a trailing space is perfectly legal, but I'd expect all 
kinds of problems with the resulting netlists (most output formats aren't 
"space-safe"), so I wouldn't recommend using this.

> Prepending a space:
> $ grep unknown top.sch
> refdes= unknown
> […]
> $ cat top.net
> U?/unnamed_net4 U?R2-2 U?R1-2
> unnamed_net2    U?R2-1 R3-1
> unnamed_net1    U?R1-1 R3-2
>
> makes lepton puke, geda just applies the default refdes.

"refdes= unknown" is not a valid attribute, so it's treated like any other 
non-attribute text object, which means it's ignored for netlisting 
purposes (unless a backend explicitly looks for text objects, which is a 
rather new mechanic which I don't believe any backend uses).

> And geda folks, just stuffing in the default refdes, just makes the user 
> scratching its head, just what in the **** went wrong.

In the absence of a refdes= attribute, the value inherited from the symbol 
file is used.  Since this is pretty obviously not what the user intended, 
gnetlist treats this as an error from version 1.10.0 on.

> Now, thoose spaces will probably confuse any netlist reader downstream, 
> so I don't know why they are allowed, required to be within citation 
> marks or quoted.

Applying proper quoting is done in the netlist backend.  gEDA/gaf's 
`tedax' backend does this correctly, as well.  I'm not sure what the 
proper quoting for PCB would be, but patches to src/backend/gnet_pcbfwd.py 
are welcome.

> so it would probably be best to drop the old netlist format and replace 
> it with tEDAx

It would be best to fix the backend.  If you prefer exporting your 
schematics in tEDAx format (and your layout program supports this), you 
are free to do so.

Roland

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