Add option to list all variables in all templates

[jayvdb]

It is important to be able to see a list of variables which are available to be set in the yaml, or re-used in new templates.

The new option would load all of the templates, display a list of "template.ext:variable" pairs, and not write any targets. --list-template-variables seems like a good name.

Due to moban supporting many template processors, this will need to be part of the template engine API

For jinja, this is quite easy:

http://jinja.pocoo.org/docs/dev/api/#jinja2.meta.find_undeclared_variables

[jayvdb]

Similar upstream jinja2 issue: pallets/jinja#174

SO thread https://stackoverflow.com/questions/26694767/jinja2-variables-in-included-template

And something similar has been built for statik and coala-mobans
thanethomson/statik#105
https://gitlab.com/jayvdb/mobans/commit/3eedcea1ec450599de08b9c3f7cb91739f2acef6

One solution is to add another global __context__ to hold the dictionary of all variables. Then moban can have its own/internal templates like list_template_variables.jj2 which render command line output.

[PrajwalM2212]

Another thread: https://stackoverflow.com/questions/8260490/how-to-get-list-of-all-variables-in-jinja-2-templates

[jayvdb]

For 0.4.0, ill do this feature without plugin api changes, which will be done in 0.5.0

[chfw]

waiting for @jayvdb 's time.

[chfw]

Stale issue.