Create a solution on our side:

• apply one patch operation at a time, introduce an index and count
• Include the index in the PatchPathException

Background:

we're currently applying patch documents by doing something like the following (pseudo code):

$patcher->patch( $target, $patchDocument );

where $patchDocument is a list of patch operations [ $op1, $op2, ..., $opN ].

the workaround (to be removed once we have the proper solution upstream, see T368414) would be to do the following

foreach ( $patchDocument as $i => $op ) {
    try {
        $patcher->patch( $target, [ $op ] );
    } catch ( PathException $e ) {
        // $i is the index of the operation with the bad path
    }
}

the advantage of applying them one by one is that we know which one exactly is problematic because we have access to the index $i whereas in the code snippet above we don't.