Block Variations: Support dot notation in `isActive` string array

[ockham]

What problem does this address?

Block variations support an isActive property which can be either a function, or an array of strings (string[]), documented here. tl;dr: Given a block instance, that variation is used to determine which variation is currently active: If isActive is a function, it is given the block instance's attributes and the variation's attributes as arguments. It will return true if the block instance matches the variation. The string[] version of isActive is thought of as a shorthand of the above, where all items in the array are attribute names that will be compared.

As documented here and here, it's possible that multiple variations' isActive criteria match a given block instance, which can lead to the wrong variation being determined to be active.

There's a potential fix that solves this problem by choosing the matching variation with the highest specificity (i.e. number of items in the isActive array), but that only works if all matching variations have isActive arrays rather than functions.

One notable case where it's impossible to use an array for isActive is when an attribute is an object, and only one of its properties must be compared to determine if its active, for example:

gutenberg/packages/block-library/src/query/variations.js

Lines 41 to 59 in fe40df6

	attributes: {
	namespace: 'core/posts-list',
	query: {
	perPage: 4,
	pages: 1,
	offset: 0,
	postType: 'post',
	order: 'desc',
	orderBy: 'date',
	author: '',
	search: '',
	sticky: 'exclude',
	inherit: false,
	},
	},
	scope: [ 'inserter' ],
	isActive: ( { namespace, query } ) => {
	return namespace === 'core/posts-list' && query.postType === 'post';
	},

What is your proposed solution?

If we allow dots as "property accessors" in isActive array items, we wouldn't need to resort to isArray functions in cases like the above. The example could instead be rewritten as

isActive: [ 'namespace', 'query.postType' ]

[ockham]

FYI @ntsekouras @tjcafferkey @gziolo

[ockham]

We have the getValueFromObjectPath util function that should help with this.

[ntsekouras]

I think this is an enhancement that could be done independently from the specificity issue you mention. The isActive API as a function is still useful and can accommodate more complex cases (example in template parts).