[Bug 47193] New: Diff links between revdeleted versions in deleted histories causing a PHP error

[bugzilla-daemon]

https://bugzilla.wikimedia.org/show_bug.cgi?id=47193

       Web browser: ---
            Bug ID: 47193
           Summary: Diff links between revdeleted versions in deleted
                    histories causing a PHP error
           Product: MediaWiki
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: Unprioritized
         Component: History/Diffs
          Assignee: wikibugs-l@lists.wikimedia.org
          Reporter: orlod...@wiki256.net
    Classification: Unclassified
   Mobile Platform: ---

Some diff links in deleted histories between DELETED_TEXT+DELETED_RESTRICTED
revisions and DELETED_TEXT revisions raise an error in SpecialUndelete.php for
sysops.

I first noticed this bug in the deleted history of [[fr:FC Lyon 13]], that
contains the link
http://fr.wikipedia.org/w/index.php?title=Sp%C3%A9cial:Restaurer&target=FC+Lyon+13&timestamp=20120112092914&diff=prev.
It causes a PHP error when logged in with a sysop (but not oversight) account:
"PHP fatal error in
/usr/local/apache/common-local/php-1.22wmf1/includes/diff/DifferenceEngine.php
line 752:
Argument 1 passed to DifferenceEngine::generateContentDiffBody() must implement
interface Content, null given, called in
/usr/local/apache/common-local/php-1.22wmf1/includes/specials/SpecialUndelete.php
on line 1015 and defined"

Steps to reproduce (it requires an account with sysop and oversight rights, and
a second account with sysop but no oversight rights):
1. Create a page and edit it twice, so that there are three versions (say that
#1 the oldest version, then come #2 and #3 the current version).
2. With the sysop+oversight account, set the visibility parameters of revision
#1 to DELETED_TEXT + DELETED_RESTRICTED ("Hide revision text" and "Suppress
data from administrators as well as others") and set the visibility parameters
of revision #2 to DELETED_TEXT ("Hide revision text")
3. With the sysop-only account, delete the page and go the deleted history. For
revision #2, a diff link is visible (this is already a minor bug, as a sysop
cannot see the diff between #1 and #2).
4. Clicking on this diff link causes the error described at the beginning.

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