Add NewNames and Value.NormalizeNames

[dsnet]

The NewNames function produces a map of canonical names from a Go struct.
It can be passed to Value.NormalizeNames to normalizes case-insensitive
matches to a JSON object name to the canonical name.

[bradfitz]

GitHub just pinged me about this. Do you still need a review here? Sitting since September 9th makes me think this wasn't needed?

[dsnet]

It's still helpful so that we can auto-format the ACL files to use consistent names. It's not critical.

[bradfitz]

Talked to @josharian; he's taking this over from me.

[josharian]

So far, I've looked just at the new API, not the implementation.

I think I understand the goal, but I'm not sure the API quite matches.

Consider:

type LL struct {
  S string
  Next *LL `json:"ref"`
}

I don't think there's a way to write a Names map that does the right thing for LL.

It seems like we want a mapping per type, but there's nothing good to use as a key. reflect.Type, any, and reflect.Value would all be annoying when used with JSON with anonymous struct types, which are reasonably common.

Maybe instead the "Names" type should be a single any value, and do the name mapping on the fly as needed? Then you lose the ability to provide your own independent of struct fields, but maybe that's a feature? You also lose the ability to do that computation once and then re-use it, but...oh well?

Maybe instead the "Names" type should embrace this shortcoming and be a single flat map. And if you need to rename keys differently based on context, oh well?

[josharian]

Using the official "request changes" button to get GitHub to stop nagging at me that it's my turn on this PR. :)