lyx2lyx regression? Malformed LyX document after roundtrip

[José Abílio Matos]

On Sunday, September 13, 2020 5:42:55 AM WEST Scott Kostyshak wrote:
> On current master I get the following:
> 
> $ lyx -e lyx20x Beamer.lyx && lyx Beamer.20.lyx
> Warning: Malformed LyX document: Missing layout name on line 1876
> Warning: Malformed LyX document: Missing layout name on line 3053
> Warning: Malformed LyX document: Missing layout name on line 4716
> 
> The reason this might be a regression is that if I first export to 2.3.x
> format, and then in 2.3.0 I do the roundtrip with 2.0.x format, I do not
> get those warnings:
> 
> $ lyx -e lyx23x Beamer.lyx
> $ lyx230 -e lyx20x Beamer.23.lyx && lyx230 Beamer.23.20.lyx

First the general consideration:
LyX 2.1 was the version where Jürgen's overhaul of the beamer layout was 
implemented. I like and I prefer it to the previous version but this change 
implied a significant change from the previous layout.

The conversion from lyx 2.0 format (from a beamer layout) to 2.1 is a tricky 
issue. The reversion is even more difficult and is done on a best effort 
basis.
The round trip for a beamer layout, 2.1 -> 2.0 -> 2.1 is useless in practical 
terms.

FWIW in the general case it would also be nice to be able to assess in the 
roundtrip the delta from the pdf output although that can not easily be done 
in an automatic way. :-)


Second consideration:
If there is difference by doing the reversion by stages between 2.3 and 2.4 
codes we need to see how the lyx2lyx code for reversions has changed for 
lyx_23.py, lyx_22.py and lyx_21.py. The list should be very small.

Now after this long preamble I do not see the problem you describe. The lyx 
files loads correctly but on the other hand I can not compile the resulting 
document it fails in the same way for all the versions complaining that:
! Argument of \beamer at decodegobble has an extra }.

FWIW I am using Fedora 33 (with python 3.9 beta) but I do not see how this 
could make a difference. :-)

-- 
José Abílio
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