(#127) Allow escaping %{...} in hiera data so that hiera does not try to...

[ChrisPortman]

... perform a replacement

This change allows the escaping of %{...} with %%{...} so that the result is literally '%{...}'

It also support escaping the escape eg:
var = 'value of var'

%{var} : 'value of var'
%%{literal} : '%{literal}'
%%%{var} : '%value of var'
%%%%{literal} : '%%{literal}'

[zaphod42]

Hi @ChrisPortman, thanks for the contribution. Unfortunately we can't take this since it is backwards incompatible, as discussed in HI-127. I think the only way we are going to be able to get this is with the suggested escape "function" or some variation thereof.

[ChrisPortman]

Hi @zaphod42,

What if this approach were to be a hiera configurable so that:
a) it is off by default and impactless unless explicitly enabled; and
b) the escape sequence can be defined as the value for the cofigurable so that if using the '%' were to break people manifests, they could specify something else, potentially even a multichar sequence

Would that address the compatibility concerns?

Thanks,
Chris

[zaphod42]

@ChrisPortman, I'd like to keep more this kind of configurability out of hiera. Configurability at this level (how it interprets what is essentially the hiera language) makes it harder to share hiera data, and I think would just add to confusion, especially if people start putting hiera data inside modules and use one of the various systems that have been published to that end.

I added a comment to HI-127 where it looks like we can actually get "escaping" behavior by simply defining a variable named % to have a value of % and so you can do %{%}{something} to get an output of %{something}