Provide a python script to dia on the command line

[Martin Metzker <martinmetzker gmx net>]

Hello list,

while exploring ways to generate beautiful(TM) PDFs from dia diagrams 
(cf. 
https://mail.gnome.org/archives/dia-list/2014-August/msg00006.html), I 
noticed there isn't an acceptable way of telling dia to execute a python 
script from the command line.

Working with the python console a little more, I came to lament this 
lack of ability a little more. Working with plain XML is not always easy 
and never pretty, so I set out to give dia the ability to run python 
scripts. I am done with my initial development and I would like to offer 
this for discussion, before git HEAD moves on and I have to redo some of 
my implementation.

I can "dia -i foo.py" to make dia execute foo.py. The script is executed 
_after_ all modules have been loaded, right before handle_all_diagrams() 
is called. (This allows using dia's python capabilities to modify 
diagrams right before they are exported.)

I'm having "dia_is_interactive = FALSE" if the -i option is provided, 
however I already have half a mind to remove this limitation, but there 
are implications to consider first.

I use this feature to, ...
... select some objects from a diagram and copy them to their own 
diagram (for export and submodels),
... change fonts and colors ( of selections of objects) in all diagrams 
at once,
... put/extract meta information and comments from UML objects, and
... synchronise UML objects used in multiple diagrams.

These are not necessarily new features, but it I get more use out of dia 
with them.

To implement this feature, I ...

... split off the part where the python plug-in's dia_plugin_init() runs 
'python-startup.py' into its own function run_script_oneshot().
... made the python plug-in's dia_plugin_init() use run_script_oneshot() 
to avoid code redundancy.
... moved the definition of struct _PluginInfo from lib/plug-ins.c to 
lib/plug-ins.h, because I need this struct in app/app_procs.c.
... modified app/app_procs.c app_init() to include the -i option and 
stores the provided filename in a local variable python_script.
... appended python_script to the list of variables that triffer 
dia_is_interactive=FALSE
... added a block if(python_script) which checks if the python plug-in 
is loaded, and does run_script_oneshot(python_script) when sensible.

I am not certain how to feel about moving a struct definition into a .h 
file and I want to be able to pass the GList "files" to 
run_script_oneshot() and the python interpreter before this is done. 
Then I also consider creating patch sets to put as enhancement into the 
bugtracker. For now, there is one big patch attached.

What do you people think about this feature?

Cheers

Martin

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