The current code includes a check for a noindex value in the metatags robots element using strpos, but this element can be an array. PHP 8 has stricter type checking than PHP 7, so this mismatch in the use of strpos triggers a fatal error. which can lead to a page crash:
TypeError: strpos(): Argument #1 ($haystack) must be of type string, array given in strpos() (line 2574 of xmlsitemap.module)
This problem is present on both the 8.x-1.x-dev branch and 2.x
1. Site is running on PHP 8
2. The contrib module "Metatag" is installed and enabled on a content type that also has XMLSitemap enabled.
3. Upon trying to save a node, the PHP error above will be produced.
Provide a legacy check for the string value of noindex and provide a new check for the array value of the Robots metatag value.
1.0
Code
The attached patch provides the resolution stated in the issue description.
Reviewed the code and tested the patch locally. Looks like it is working perfect. Moving to RTBC