configure default jinja2 variables globally

[oliver-sanders]

Motivation

Rose had an unpublicised feature for site portability where the name of the "site" could be configured in the Rose config. It would then be provided as a Jinja2 variable called ROSE_SITE.

Note: The ROSE_SITE variable provided by rose stem is set in an entirely different way and will remain in Rose2.

This is a pretty useful feature, however, it was never actually adopted by any sites making it totally useless.

This feature doesn't really fit into the role of Rose very well so would suggest moving it into Cylc.

Two options:

1. Create a special global config called cylc site or something like that.
   • Provide this as a Jinja2 variable called CYLC_SITE or something like that.
2. Create a global config section called template variables or something like that.
   • Provide all items defined here as Jinja2 variables.
   • This allows new portability features to develop, however, with some risk to suite portability.
3. Create a global config [meta] section
   • Provide these items as Jinja2 variables called SITE_* or something like that.

We could encourage sites to adopt the site convention with the Cylc8 transition.

See the related cylc/cylc-rose#13

[hjoliver]

Of the "two options" I prefer the second, and not the first or the third 😁

• 1. "site" may be unnecessarily specific and presumptuous, e.g. sites with multiple distinct platforms might prefer several platform variables?
• 2. maximum flexibility without presuming anything 👍 (we can recommend using a SITE variable, as an example)
• 3. "meta" is supposed to be descriptive, but these variables may be more than merely descriptive.

[oliver-sanders]

VC - Option (2) it is.