Last modified: 2007-11-14 11:12:27 UTC

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Bug 9739 - Call to a non-object when error_page used in parser hook.
Call to a non-object when error_page used in parser hook.
Product: MediaWiki
Classification: Unclassified
General/Unknown (Other open bugs)
All All
: Normal normal (vote)
: ---
Assigned To: Nobody - You can work on this!
: patch, patch-need-review
Depends on:
  Show dependency treegraph
Reported: 2007-04-30 14:48 UTC by Mark Clements (HappyDog)
Modified: 2007-11-14 11:12 UTC (History)
0 users

See Also:
Web browser: ---
Mobile Platform: ---
Assignee Huggle Beta Tester: ---

Patch to check $wgArticle is defined. (477 bytes, patch)
2007-04-30 14:49 UTC, Mark Clements (HappyDog)

Description Mark Clements (HappyDog) 2007-04-30 14:48:27 UTC
I have written a parser hook that adds a new tag to the markup, which in certain
situations redirects to the error page, using $wgOut->errorpage().

When this happens, I get the following error (which did not occur in 1.5.8, but
occurs in 1.9.3 and HEAD):

 Fatal error: Call to a member function isCurrent() on a non-object in
includes\Skin.php on line 1259

The offending line is:

 if( $this->mRevisionId && ! $wgArticle->isCurrent() ) {

and this causes an error because $wgArticle is not defined at this stage (it
contains NULL).

It can be fixed by adding a check that $wgArticle is defined, which returns the
code to its original behaviour.

This bug was introduced in r11890.
Comment 1 Mark Clements (HappyDog) 2007-04-30 14:49:17 UTC
Created attachment 3548 [details]
Patch to check $wgArticle is defined.

Patch, as described above.
Comment 2 Rob Church 2007-04-30 16:00:44 UTC
Parser hook extensions should not be touching globals such as $wgOut, $wgTitle
or $wgArticle, because parse operations can be called in situations where these
are not defined, e.g. job queue.
Comment 3 Mark Clements (HappyDog) 2007-04-30 16:23:19 UTC
Then how should a parser-hook redirect to an error page?
Comment 4 Brion Vibber 2007-04-30 19:55:42 UTC
It must not do so.

(You _might_ be able to get away with adding a header field in the parser output
object in 1.10, however I would recommend against such a thing. The concept
appears to be fundamentally flawed, and you should consider a different way of
displaying your error message -- for instance returning error text into the
page, which will not disrupt the entire wiki when you have a localized problem.)
Comment 5 Mark Clements (HappyDog) 2007-04-30 22:02:24 UTC
The hook works like this: <protect>bob,john</protect> will prevent the page from
being viewable by anyone except bob and john.  I am aware of the issues
regarding MW security, and how easy this is to bypass, but for my trusted
user-base a simple 'keep out' notice such as this is sufficient. 

Previously it called the error page to generate a 'protected page' error
message.  This works fine in 1.5.8 (and maybe higher) but is now broken.  It
would be fixed by a simple check that $wgArticle is actually a valid object...

If you can suggest an alternative way to replace the entire page output (not
just the content within the tags) then that would be sufficient, however I was
under the impression that you could only modify the tag text itself.  Feel free
to take this to private e-mail if this is an inappropriate place to continue the
Comment 6 Brion Vibber 2007-10-15 17:29:47 UTC
Pages may be rendered in batch processing or at many other times. Parsing/HTML rendering is not a UI operation, and must not attempt to manipulate the UI which may be completely unrelated.

To change page permissions, you should be hooking into the permissions system; see hooks in the Title and User classes.
Comment 7 Mark Clements (HappyDog) 2007-11-14 11:12:27 UTC
Understood.  I have written a new version using the userCan hook and it seems to be working well. 

Thanks for taking the time to elaborate.

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