Update Configuration doc to use double underscores instead of colons for hierarchical config keys

[danroth27]

Currently the config doc tells you to use colons for hierarchical config keys, which don't work on all platforms. Let's switch to using double scores and then update the note about double underscores to say that colons can also be used, but may not work on all platforms.

[guardrex]

Related to (or dup of) #4927.

[isaacrlevin]

@danroth27 do you want the samples in this doc updated as well? Or just lines 46 and 53?

[guardrex]

Note that the topic is getting an (unrelated) update. It could get messy before that merges 👉 #5169

[isaacrlevin]

@guardrex is there an interest in hitting this low hanging fruit in that PR?

[guardrex]

I don't think so ... it's approved. It should merge any second. I just meant you could work with a clean, updated topic as soon as that goes in. Merge conflicts are something I really try to avoid. 😨 lol

[isaacrlevin]

ohhhhh maybe I should actually click the link ;)

[guardrex]

@isaac2004 #5169 is merged now, so if they give you the green light, ur good.

[guardrex]

Note that on #5241 @scottaddie remarks for aspnetcore/fundamentals/configuration/index.md where it states ...

If a colon (:) can't be used in environment variables on a system, replace the colon (:) with a double-underscore (__).

I recommend adding an example of where the double underscore may be necessary. Maybe we have this documented somewhere already, in which case you could just link to that info.

[scottaddie]

@danroth27 @guardrex I'm hoping we can provide a bit more guidance in this statement. For example, which specific platforms are known to need the double underscore? It's going to be a question in the Feedback section of the doc if we don't specify.

[rachelappel]

@guardrex I was looking around and don't see it documented anywhere. Agree with @scottaddie that we could use more guidance here and which platforms and all that or else the question tidal wave will hit us.

[guardrex]

@danroth27's OP ☝️ suggests that making every topic go with the double-underscore approach should (in theory) just about eliminate concern over platform behavior. However, I agree that being able to say which platforms have trouble with colons would be helpful.

[rachelappel]

@guardrex I only see him mentioning the config doc. Did I miss something?
Totally agree that consistency is going to be a better thing, so if there are multiple docs that could use the mod we should look at those too.

[guardrex]

Nah ... just wondering if they'll be found in a few other topics/samples floating around the repo. Hopefully not, and then this won't be a big deal.

[isaacrlevin]

So the goal here is to update ALL samples and docs that use : and replace with __? Just want to make sure I am following this.

[scottaddie]

@isaac2004 That's my understanding.
\cc: @rachelappel

[rachelappel]

@isaac2004 @scottaddie Yep. The first to change should be the configuration doc but at some point all docs that use this

[isaacrlevin]

@rachelappel @danroth27 @scottaddie Does it really make sense to update all the samples? The more I think about it, it may just make sense to update the note to something like

A colon (:) may also be used for hierarchical config keys, but may not work on all platforms. Double underscore (__) is supported by all platforms.

[scottaddie]

This was addressed in #5876