Fix: useInput should call a custom validator with the final source in respect to the <SourceContext>

[slax57]

Problem

When passing a custom validator function to an input, the source prop it recieves is the original source prop declared on the input, instead of the 'final' source computed using the <SourceContext>.

This is an issue when the input is inside a component wrapping it with a custom <SourceContext>, such as <SimpleFormIterator>.

Example:

<ArrayInput source="posts">
  <SimpleFormIterator>
    <TextInput source="title" validate={validator} />
  </SimpleFormIterator>
</ArrayInput>

In that case, validator will be called like so: validator("value", { posts: [{ title: "value" }] }, { source: "title", /* ... */ })
Although it should have been: validator("value", { posts: [{ title: "value" }] }, { source: "posts.0.title", /* ... */ })

Solution

Use the <SourceContext> and pass a prop called finalSource when calling the custom validator in addition to the original source prop.

validator("value", { posts: [{ title: "value" }] }, { source: "title", finalSource: "posts.0.title", /* ... */ })

How To Test

Run unit tests.
Alternatively, use a custom validator inside an <ArrayInput> in one of the demos.

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why) <- did not find it useful for such a technical case
• The documentation is up to date

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