Enable variable modifications to layer changes on the same variable

[douglasjacobsen]

This merge allows modifiers that modify the same variable to layer their changes onto the modified variable.

Previously, only the last modifier to modify a variable would have it's modification stick.

[linsword13]

LGTM. Do you think it'd be good to add a test for it?

[douglasjacobsen]

I added a test, and updated existing modifiers to include the space separator as part of their variable modifications (given I removed the auto-injected space)

[linsword13]

I added a test, and updated existing modifiers to include the space separator as part of their variable modifications (given I removed the auto-injected space)

Do you feel having the separator auto-injected would be less error-prone than relying on modifier author to remember adding the space?

Perhaps a more general approach is to have the directive to accept a template_func ((prev_value, new_mod) => new_value)? (More just for a discussion, no need to add to the current PR though.)

[douglasjacobsen]

Yes, I actually have an internal task tracking this which I think is a high priority.

Injecting a space manually is definitely a hack for the time being, and we should have a nicer interface for this.