changing layer grouping breaks polygon plowing

[Ben Jackson]

I created my board with gsch2pcb (as opposed to starting with a blank
file in PCB).

I did lots of layout work...

I wanted a layer for the board outline, so I hijacked an existing unused
layer and removed it from its layer group.

After a save and reload, all of my nets were shorted. It turned out that
the planes had quit clearing the pads on my board (they still cleared the
pins). However, the ratsnest still knew they were on the same layer and
saw all the shorts. Nothing I could do to the layer groups in PCB fixed
the problem. Eventually diffing with my previous version showed that
I had started with this (from gsch2pcb):

        Groups("1,2,3,s:4,5,6,c:s:c")

Notice how 's' and 'c' are duplicated. PCB itself (via the lesstif HID,
anyway) will never duplicate them, as far as I can tell. When I had:

        Groups("1,2,3:4,5:s:c:6")

(which is what pcb did after I manipulated the layer stack in the GUI)
It did not work right. I was also able to move 's' and 'c' into the
groups with 1,2,3 and 4,5, but that ALSO didn't work. The only thing
that worked was manually editing the file to be more like the gsch2pcb
version:

        Groups("1,2,3,s:4,5,c:6:s:c")

-----

> Did you use the add/remove/move layers option?

Yes. Now that I think about it, I actually removed layer 6 and re-created
it. Then I pulled up the layer grouping to make sure it wasn't in any
of my copper layers. That dialog enforces that 's' and 'c' only go in
one group, whereas they seem to need to go in two.

------
DJ Delorie wrote:

Sounds like yet another variable that needs to be updated when layers
are edited. I think I've seen it myself before. Go ahead and
register the bug.

[DJ Delorie (djdelorie)]

Still broken in 20100929 - if the "solder" layer is deleted and you save the file, a reload or revert corrupts it The saved file has no 's' layer.

[DJ Delorie (djdelorie)]

Git commit c2f52c71e6b199ae2196924b0d1cfd4fa8f23446 should prevent you from getting into this situation again.