Custom fields can have different visibilities, depending on the custom field type and the current user:

• Custom fields are always visible to admins
• They are not visible for anonymous unless explicitly checked
• They are visible if the visible flag is checked (or the user in in a checked group for issue custom fields)

Now, to confirm whether a custom field is visible in a certain project, we use @CustomField#visibility_by_project_condition@. Given the following conditions:

• We are a non-admin user
• We defined a ProjectCustomField of type List which is not visible

Now, when we show a time entry report and select the ProjectCustomField as an aggregation criteria, we get an error because of invalid SQL:

ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'projects.project_id' in 'IN/ALL/ANY subquery':
SELECT Sum(`time_entries`.`hours`) AS sum_hours, 
       Coalesce(cf_9.value, '')    AS coalesce_cf_9_value, 
       `time_entries`.`tyear`      AS time_entries_tyear, 
       `time_entries`.`tmonth`     AS time_entries_tmonth, 
       `time_entries`.`tweek`      AS time_entries_tweek, 
       `time_entries`.`spent_on`   AS time_entries_spent_on 
FROM   `time_entries` 
       INNER JOIN `projects` 
               ON `projects`.`id` = `time_entries`.`project_id` 
       LEFT OUTER JOIN `enumerations` 
                    ON `enumerations`.`id` = `time_entries`.`activity_id` 
                       AND `enumerations`.`type` IN ( 'TimeEntryActivity' ) 
       LEFT OUTER JOIN `issues` 
                    ON `issues`.`id` = `time_entries`.`issue_id` 
       LEFT OUTER JOIN custom_values cf_9 
                    ON cf_9.customized_type = 'Project' 
                       AND cf_9.customized_id = projects.id 
                       AND cf_9.custom_field_id = 9 
                       AND ( projects.project_id IN 
                             (SELECT DISTINCT m.project_id 
                              FROM   members m 
                                     INNER JOIN member_roles mr 
                                             ON mr.member_id = 
                                                m.id 
                             INNER JOIN custom_fields_roles cfr 
                                     ON cfr.role_id = mr.role_id 
                                                     WHERE  m.user_id = 3 
                                                            AND 
                             cfr.custom_field_id = 9 
                                                    ) ) 
                       AND cf_9.value <> '' 
                       AND cf_9.id = (SELECT Max(cf_9_2.id) 
                                      FROM   custom_values cf_9_2 
                                      WHERE  cf_9_2.customized_type = 
                                             cf_9.customized_type 
                                             AND cf_9_2.customized_id = 
                                                 cf_9.customized_id 
                                             AND cf_9_2.custom_field_id = 
                                                 cf_9.custom_field_id) 
WHERE  (( ( projects.status <> 9 
            AND projects.id IN ( 1, 2, 3, 5, 
                                 12, 14, 15, 19, 25 ) ) 
          AND ( projects.id IN ( 1, 2, 4, 5 ) ) )) 
       AND (( time_entries.spent_on IS NOT NULL )) 
GROUP  BY Coalesce(cf_9.value, ''), 
          `time_entries`.`tyear`, 
          `time_entries`.`tmonth`, 
          `time_entries`.`tweek`, 
          `time_entries`.`spent_on`

The reason for that is the SQL generated by the @CustomField#visibility_by_project_condition@ method called for @Redmine::FieldFormat::Base#join_for_order_statement@ Here, we are using the final @else@ case and attempt to use the @project_id@ field on the @projects@ table.

The correct column here would however simply be @id@ instead of @project_id@. The attached patch fixes this behavior and avoids the SQL error. Unfortunately, I'm not really sure how to properly test this. This whole area seems to be not well tested currently...