[TypeScript] Make types more strict in ra-core, part III

[fzaninotto]

This PR finally turns strictNullChecks to true in ra-core, and solves the remaining 63 TS compilation errors on ra-core.

Refs #9622
Follows #9644, #9741 , #9743

useRecordContext Returns undefined When No Record Is Available

The useRecordContext hook reads the current record from the RecordContext. This context may be empty (e.g. while the record is being fetched). The return type for useRecordContext has been modified to Record | undefined instead of Record to denote this possibility.

As a consequence, the TypeScript compilation of your project may fail if you don't check the existence of the record before reading it.

To fix this error, your code should handle the case where useRecordContext returns undefined:

const MyComponent = () => {
    const record = useRecordContext();
+   if (!record) return null;
    return (
        <div>
            <h1>{record.title}</h1>
            <p>{record.body}</p>
        </div>
    );
};

[fzaninotto]

Stricter types revealed a bug: Using a Datagrid in controlled mode with an EditButton as a child used to fail silently (the EditButton link didn't work), because the resource set on the Datagrid was never propagated to the child. Now the failure is loud ans forces to add this ResourceContext.

[djhi]

I don't think we have an unsubscribe method. We should add one

[fzaninotto]

Yes we do:

react-admin/packages/ra-core/src/form/FormGroupsProvider.tsx

Lines 34 to 38 in 131619a

	return () => {
	subscribers.current[group] = subscribers.current[
	group
	].filter(s => s !== subscriber);
	};

[djhi]

Why is this necessary? linkType is optional in SingleFieldList props

[fzaninotto]

Because the test doesn't define a ResourceContext, and <SingleFieldList> defaults to creating a link. It's not possible to create a link without a Resource. Before this PR, this caused an empty/invalid link. Now, it throws an error. To avoid this error, we must disable the ink or define a ResourceContext.

[djhi]

Users might need more information to solve this

[fzaninotto]

I agree, but this error should never occur (check the source code). To be honest, I added it just to please TypeScript.

[fzaninotto]

Now that you mention it, throwing an error may break the app in legitimate cases (e.g. two successive changeParams calls). I've converted it to an early return.

[slax57]

Just found out this is a BC, because now all admins have a default non-null authProvider.
So this breaks code like the following:

        <Root
            label={
                authProvider != null
                    ? 'ra.auth.user_menu'
                    : 'ra.configurable.customize'
            }
            icon={
                authProvider ? (
                    <Avatar src={identity.avatar} />
                ) : (
                    <SettingsIcon />
                )
            }
            {...props}
        />

Is there a way to avoid it?

[slax57]

#9861 attempts to fix this BC