REST API: Handle api-request query parameters with plain permalinks

[aduth]

Related: #40919
See: ​https://github.com/WordPress/gutenberg/issues/3215

When a site is configured to use plain permalinks, passing an endpoint or path argument containing query parameters prefixed by ? will fail:

Example:

wp.apiRequest( {
	namespace: '/wp/v2/',
	endpoint: '/posts?orderby=title'
} )

This is because we perform a simple concatenation on the API root which in the case of plain permalinks results in a URL like:

/index.php?rest_route=/wp/v2/posts?orderby=title

(Note the two ?)

Attached is a patch which resolves this issue by checking whether the API root already contains ? and, if so, converting the path of the endpoint request to replace ? with &.

QUnit tests have been updated accordingly.

[rachelbaker]

@adamsilverstein still want to pick this up? Handling the edge cases of permalinks is a frustrating game of whack-a-mole.

[adamsilverstein]

sure, i've got it on my list :)

[aduth]

Sample workaround fix for plugins encountering this bug: ​https://github.com/WordPress/gutenberg/pull/4877

[aduth]

Alternatively, since it's a common use-case, maybe apiRequest could accept a query object, which is normalized internally. Doesn't help existing usage though.

[adamsilverstein]

Verified this works as expected, marking for commit.

[adamsilverstein]

In 42965:

REST API: Handle api-request query parameters with plain permalinks.

When constructing the request URL, ensure that ? is replaced with & when the API root already contains a ?. Fixes an issue where requests were broken when sites had permalinks set to plain.

Props aduth.
Fixes #42382.

[SergeyBiryukov]

[42965] should be backported to the 5.0 branch.

[danielbachhuber]

In 43771:

REST API: Handle api-request query parameters with plain permalinks.

When constructing the request URL, ensure that ? is replaced with & when the API root already contains a ?. Fixes an issue where requests were broken when sites had permalinks set to plain.

Props aduth.
Merges [42965] to the 5.0 branch.
Fixes #42382.