KVv2 json cursor jumps on "enter"

[Monkeychip]

• enterprise tests pass

Description

Fixes Issue #27524. Took the scenic route to get to this solution. The heart of the problem is the KVv2 secret engine parses the secretData on every change to the json editor (detailed steps below). So when a user hits enter, the codemirror modifier is called and it compares a parsed json blob to a non parsed blob, determining they are different. That determination caused the cursor to jump to the beginning of the text editor—an annoying UX experience.

I tried a variety of solutions and landed on the last option:

1. Only parse on save. This fails miserably, We do various actions that require the model.secretData to be updated before save. Things like toggling between kv form fields, revealing obscured values, and diff views.
2. Tried parsing and saving the model.secretData on a new blur event I added to codemirror. This borks the same set of things as solution one. Changing the parsing event will always bork things because we need the kv form field data and json editor data to be in sync and they get out of sync if we save them at different events (kv form field saves on change). However, these approaches were worth a shot because it's how the other json editor instances all work and why none of them run into this issue.
3. Tried the current solution once, realized it borked for all instances where comments (think policies) were used because a comment can't be parsed (you can use comments in the jsonEditor when the mode is "ruby" otherwise it defaults to Javascript which does not allow them). Came back to this solution after Claire also landed on this separately. I then made it work by adding in a try / catch and using the stringify helper to keep the shape of the object.

Details for reference

codemirrors .setValue—see here. Granted, we're on an older version, so here's the setValue we're actually using (I've tested the updated codemirror, it doesn't fix this).

Code walk through of why it wasn't working before:

1. When someone is using or toggling to the JSON editor for KVv2 when "creating" or "creating a new version" of a secret we parse the json onChange.
2. This triggers the codemirror-modifier modify function here.
3. If you hit a value like "enter" (a whitespace value), then the namedArgs.content has been parsed, before the this._editor.getValue() has been. Meaning that for a whitespace value like "enter" we're comparing:
   {foo: 'beep'} vs { "foo": "beep" /n }

So this only happens on the KVv2 Secrets engine and on whitespace events. The other JsonEditor instances (policies, cubbyhole, etc) all parse the json value onSave like workflows.

TODO only if you're a HashiCorp employee

• Labels: If this PR is the CE portion of an ENT change, and that ENT change is
  getting backported to N-2, use the new style backport/ent/x.x.x+ent labels
  instead of the old style backport/x.x.x labels.
• Labels: If this PR is a CE only change, it can only be backported to N, so use
  the normal backport/x.x.x label (there should be only 1).
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
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  in the PR description, commit message, or branch name.
• RFC: If this change has an associated RFC, please link it in the description.
• ENT PR: If this change has an associated ENT PR, please link it in the
  description. Also, make sure the changelog is in this PR, not in your ENT PR.

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[hashishaw]

Beautiful job, and thanks for the detailed description!