Thank you for your contribution.

I am open to the change you propose. However, if I look at https://bitbucket.org/atlassian/clover/raw/master/etc/schema/clover.xsd and understand ...

<xs:element name="project">
    <xs:annotation>
        <xs:documentation>
            Project metrics relating to non-test source.
            @name - project name (optional)
            @timestamp - seconds since UTC
        </xs:documentation>
    </xs:annotation>
    <xs:complexType>
        <xs:sequence>
            <xs:element name="metrics" type="projectMetrics"/>
            <xs:element maxOccurs="unbounded" ref="package"/>
        </xs:sequence>
        <xs:attribute name="name"/>
        <xs:attribute name="timestamp" use="required" type="xs:integer"/>
    </xs:complexType>
</xs:element>

... correctly then the name attribute is optional whereas the timestamp attribute is not. It is interesting that your parser seems to choke on the optional attribute that is missing but not on the non-optional attribute that is missing.

I totally missed in my first comment that the Clover XML writer in fact does generate the timestamp attribute, my bad.

I am open to accepting the change you propose. I am reluctant to change PHPUnit 8.5, PHPUnit 9.6, and PHPUnit 10.5 as these versions have reached the end of their bugfix support. The proposed change should go into 11.5, 12.1, and main.

It would help me if somebody could look into whether https://bitbucket.org/atlassian/clover/raw/master/etc/schema/clover.xsd is, in fact, the official/canonical schema for Clover XML and, if it is, look into whether there are any other changes PHPUnit (or phpunit/php-code-coverage, rather) needs to implement to comply with the schema.

I cherry-picked this into 11.5 and merged it to 12.1 and main from there.