wp post create: Add JSON input support for tax_input

[caribe]

Fixes this 10 year old issue wp-cli/wp-cli#1323 (closed, but not fixed).

wp post create parameter --tax_input is supposed to be an array, but no JSON parsing is done and therefore is unusable.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[swissspidy]

Thanks for opening this PR.

Would you also be up for adding some tests to cover this change? See #133 for inspiration.

[swissspidy]

I just added a test now, but it fails because tax_input requires the current user (which there technically isn't one with WP-CLI) to have the necessary capabilities. So we need to figure that one out first...

Related: https://github.com/orgs/wp-cli/discussions/6052

[seanlanglands]

@swissspidy, in this scenario, would passing --user=admin in this step be acceptable in your opinion?

Suggested change

	And I run `wp post create --post_title='Test Post' --post_content='Test post content' --tax_input='{"category":[{CAT_1},{CAT_2}],"post_tag":["term-one", "term-two"]}' --porcelain`
	And I run `wp post create --post_title='Test Post' --post_content='Test post content' --tax_input='{"category":[{CAT_1},{CAT_2}],"post_tag":["term-one", "term-two"]}' --user=admin --porcelain`

This user is the default administrator when core is installed during testing:
https://github.com/wp-cli/wp-cli-tests/blob/5b42c271c96efd1072cecaa8b2923db52318b056/src/Context/FeatureContext.php#L1392

[swissspidy]

That would fix the test but not the user experience in general.

We would need to document that tax_input only works in combination with --user, which is odd.

Another option could be to temporarily filter user_has_cap for this particular code path so that it would always work. But not sure if there's precedence in WP-CLI.

Perhaps @schlessera has a good idea.