Fix global validation not firing after submit with ArrayInput

[slax57]

Fixes #7594

Todo

• Change getSimpleValidationResolver.ts according to Global validation not firing after submit with ArrayInput #7594 (comment)
• Update tests
• Add story
• Add integration test based on story
• Figure out why error for the whole array is still not cleared up properly each time ('Backlinks' still appear in red even after fixing all the errors) --> Couldn't figure it out. It might be a bug in react-hook-form. But this PR is still an improvement over what we had before
• Figure out why we decided to flatten the error fields in the first place (following RA v4 blocks validation due to empty array #7500 (comment) , but this is contradictory to Global validation not firing after submit with ArrayInput #7594 (comment))
• Add documentation

Screenshots

Before

After

Additional info

• how to write a global validator for array inputs is documented neither in RA v3 docs, nor in RA v4 docs
• how to write a Resolver for array inputs is not documented either in react-hook-form docs

So here is some testing I made by myself:

In RA v3:

validate's result's shape	works to display errors	works to clear errors
flat	❌️	❌️
tree	✅️	✅️

In RA v4 - before this PR:

validate's result's shape	works to display errors	works to clear errors
flat	✅️	❌️
tree	✅️	❌️

In RA v4 - after this PR:

validate's result's shape	works to display errors	works to clear errors
flat	✅️	❌️
tree	✅️	✅️

Where:

• flat syntax is like: {backlinks.1.date: 'A date is required'}
• tree syntax is like: {backlinks: [{}, {date: 'A date is required'}]}

[fzaninotto]

Excellent work! But I think that now that you've done all the digging, we should write down the proper format in the documentation.

Also, do we still need the flattenErrors utility?

[fzaninotto]

How does one specify errors in some of the items but not all? Does this work?

backlinks: [null, null, { url: { type: 'manual', message: 'url too short' }}, null]

I think it's worth a test.

Edit: I see you've made that test later. Well, it's worth some documentation in ArrayInput and in the global validation section.

[slax57]

I've added some documentation. Please tell me if this is enough or if I need to emphasize that returning something like [{}, {}] is supported

[fzaninotto]

Why do we flatten in the first place if react-hook-form requires a tree structure?

[slax57]

dunno 🤷

I was able to track its origin down to this issue and especially this comment: #7500 (comment)

But as I said I don't know what made you say this at the time. Since this is currently not documented on rhf's side either I can't tell if there was a change on their side or not...

[fzaninotto]

How is this possible? Please elaborate in the comment.

[slax57]

it can happen if the validator returns an error object like:

        {
            backlinks: [{}, {}],
        }

in this case we first need to transform the error field to realize it actually contains no errors.

I'll add this in the comment.

[fzaninotto]

Also, needs rebase.

[WiXSL]

This looks great!

[fzaninotto]

The added doc is fine!