Current data file incompatibility of branch-2.0 vs. SVN-trunk

[Christian Stimming]

Ok, maybe it's just me, but I've been hit by the recent "data file 
compatibility" discussion, and it came as quite a surprise.

Problem description: I've been working on a data file (which contains a small 
number of scheduled transactions) by SVN-trunk and later tried to open the 
same data file with the current SVN-branch/2.0. When trying to open the file 
in branch-2.0, I get the error dialog "There was an error parsing the 
file /my/file/name." [1] and gnucash just shows an empty window. On the 
command line, I see several tens of lines like these: 
<gnc:schedxaction version="1.0.0">
  <sx:id type="guid">f79b0b0a55fa114e2852db2a33e5da6c</sx:id>...
but this also doesn't say what is going on.

What has happened: Turns out in r15486 [2] Peter McAlpine added the 
<sx:enabled>y</sx:enabled>  field to the <gnc:schedxaction...> sections, and 
because the branch-2.0 code of the XML parser doesn't know the sx:enabled 
field, it will refuse to load this data file altogether.

My suggestions:

* First of all, I would like to have a quick'n'dirty solution for us 
developers who frequently swith back and forth between SVN-trunk and 
branch-2.0, but still want to use the same data file. This could even be an 
external command line script [3], but it should be in SVN anyway so that we 
keep track of what it does.

* Secondly, the error message of the parser error needs to be revised to be 
much more helpful. IIRC the parser itself is a problem here, as it either 
reads all or nothing. But at least we should extend the user message into 
something like this:
 "There was an error parsing the file /my/file/name, although the file could 
be loaded correctly [making sure people can distinguish this error from file 
permission problems]. This probably means the file has been saved by a newer 
version of gnucash and cannot be parsed by this older version because of new 
data elements. " 
If we had the abovementioned command line script available, we might even add 
a suggestion of what to do: "If you want to remove the new data elements, 
please use the program 'gnucash-datafile-stripnew-justwhatevername' of the 
newer gnucash version, then open the data file again in this version."

* Thirdly, as 2.0.x is still around for some months to come, we really really 
really need a solution here. Either one at the SVN-trunk side: "Disable new 
data file elements" or, in other wording, "save data file in 2.0 
compatibility mode" as a preference. Or one at the branch-2.0 side: "Ignore 
unknown data file elements instead of refusing this file" either as a 
preference or as one potential choice when this error message is encountered, 
with a later summary of what has been ignored/removed. An extra menu 
item "Export to 2.0" should IMHO rather be avoided, as nobody will notice it 
or use it anyway but people will rather expect to be able to deal with this 
at loading time in 2.0.

Ideas, suggestions, flames?

Christian


[1] That's the QofBackendError ERR_FILEIO_PARSE_ERROR and the message text is 
in src/gnome-utils/gnc-file.c:402.

[2] 
http://svn.gnucash.org/trac/changeset/15486/gnucash/trunk/src/backend/file/gnc-schedxaction-xml-v2.c

[3] Something along these lines, but with additional sanity checks whether the 
file is gzip'd and to make sure not to overwrite any existing file:
#!/bin/sh
gunzip -d $1 > $1.orig
grep -v '<sx:enabled>.</sx:enabled>' $1.orig > $1.tmp
echo "Removed the following elements:"
diff -u $1.orig $1.tmp
echo "Keeping old data file as $1.orig.gz"
gzip $1.orig
gzip -d $1.tmp > $1
rm $1.tmp