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To: geda-user ailing list <geda-user AT delorie DOT com>
From: "Glenn (glimrick AT epilitimus DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Subject: [geda-user] recursive subsheet issue
Message-ID: <d3f9a609-d761-8646-8f4f-0f3fb3fa6b33@epilitimus.com>
Date: Mon, 1 Feb 2021 21:33:46 -0800
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Reply-To: geda-user AT delorie DOT com

Roland,
I came across what I think is a potential bug in gaf/netlist/netlist.py
lines 256-275.

If traverse-hierarchy is true and a subsheet sheet has as a subsheet a
sheet from higher up in the hierarchy there is no check to prevent run
away recursion.

For example:
Sheet A has as a subsheet Sheet B
Sheet B has as a subsheet Sheet C
Sheet C has as a subsheet Sheet A

A loads B loads C loads A loads B ...

No idea why this would ever be done, except by mistake.

possible solutions:
- traverse back up the hierarchy to see if the file is mentioned.
- have a level count and a recursion limit config variable.
- keep a list of all sheets traversed so far up to the current sheet and
check it.

I can think of no reason recursion would be a good idea in this situation.

Actually I see no reason why it wouldn't happen with a self referencing
sheet: A -> A -> A ...
Also it doesn't actually load the sheet each time as that is done
earlier (which actually does prevent recursion at that point, see
gaf.netlist.netlist.load_schematic), but it does consume memory by
creating a new sheet for the subsheet, and if encountered processing
would hang until you ran out of memory.

Or am I missing something? If not let me know and I write a fix.

I came across it because I am trying to figure out a way to extract the
hierarchy from the netlist.

Glenn