Issues such as https://gerrit.wikimedia.org/r/#/c/266662/6/includes/specials/SpecialContributions.php shouldn't be possible without leaving something behind in the PHP error log. It's essentially a PHP Notice for undefined variable, except that it's through indirection of TemplateParser (and LightNCandy).
These are still immature and shows in lack of error handling.
It seems LightNCandy has some error options. Not sure which ones to use and how we'll forward it to the appropiate logs.
| Project | Branch | Lines +/- | Subject | |
|---|---|---|---|---|
| mediawiki/core | master | +30 -6 | POC: Refuse to process templates with assumed null values |
Having actual error detection for this run-time failure would have prevented T219359: lang attribute of page title is empty.
Having an error raised would have also prevented T248010: Vector sidebar missing on test.wikipedia.org and weird footer.
So I suppose we'd be checking variables are defined. It would mean we'd have to ensure certain template values were defined as null (and not undefined) as null is a perfectly valid template value.
For this to be feasible we'd need a way to access the variable names used inside a template.
I have another use case for that - see addMessagesToTemplateData - but the solution I came up with there didn't seem very optimal:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/584068/18/includes/skins/SkinMustache.php#71
I think having access to that information is the difficult part here. If that's in place however such complaints should be easy to deal with.
I came across this today - https://github.com/zordius/lightncandy#template-debugging - seems this should be built into Lightncandy.
Change 611418 had a related patch set uploaded (by Jdlrobson; owner: Jdlrobson):
[mediawiki/core@master] POC: Refuse to process templates with assumed null values
FYI from the mustache spec "By default a variable "miss" returns an empty string. This can usually be configured in your Mustache library. The Ruby version of Mustache supports raising an exception in this situation, for instance."
I don't know if lightncandy supports a miss variable. If it does, that would be useful (but I can't find one!)
If we're okay with an error, it looks like FLAG_ERROR_EXCEPTION will do the trick.
This one might be overkill, but does make missing variables visible: FLAG_RENDER_DEBUG.
I think we already use FLAG_ERROR_EXCEPTION ?
https://github.com/wikimedia/mediawiki/blob/master/includes/TemplateParser.php#L67
I don't think missing variables count as errors in Lightncandy? So we might need an upstream feature request?
Change 611418 abandoned by Jdlrobson:
[mediawiki/core@master] POC: Refuse to process templates with assumed null values
Reason:
Was an experiment. Not good for production - but we've had a few high priority regressions without this.
Removing task assignee due to inactivity as this open task has been assigned for more than two years. See the email sent to the task assignee on August 22nd, 2022.
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