515455 - Backward compatibility when layout.css.devPixelsPerPx is an integer

Status: RESOLVED WONTFIX

(Core :: Graphics, defect)

Description

[Sylvain Pasche]

Attachment: patch, v1

Should prevent issues for apps that haven't migrated the pref (such as bug 515424).

I also don't do the atof if the string is empty, which might have prevented the Fennec issue.

Comment 1

[Brad Lassey [:blassey] (use needinfo?)]

pushed http://hg.mozilla.org/mozilla-central/rev/e4abfec25e38

Comment 2

[Brad Lassey [:blassey] (use needinfo?)]

reopening because we're not actually backwards compatible due to all.js setting the pref as a string.

Comment 3

[Sylvain Pasche]

I tested the patch by modifying all.js to either an int or a string. That works in this case, but unfortunately that's not helping for scenarios like bug 515424.

Comment 4

[Sylvain Pasche]

I propose to back out my patch because it doesn't address the real issue.

One way to fix this correctly would be to make nsIPrefBranch::getPrefType return the type set at the application level (and interpret the value accordingly). For instance when a preference is set in all.js as a string and the application overrides it with an int, getPrefType and getIntPref should return int and the int value respectively. If the preference system would behave this way, the patch here would fix the compatibility problem.

I'll leave this bug open for the real fix. Now that bug 513439 has landed on 1.9.2, this would only be an issue for an application that:
1. Needs to override layout.css.devPixelsPerPx
2. Has to support both 1.9.1 and 1.9.2 XRE with the same application package.
I believe this affects very few consumers, if any.

I've opened bug 517218 for the back out.

Comment 5

[Stuart Parmenter]

imho, we simply shouldn't be changing pref values, and should instead create a new pref name

Comment 6

[:Gavin Sharp [email: [e-mail]]]

I guess this is WONTFIX now?

Comment 7

[Sylvain Pasche]

yeah, in theory it could still be an issue for some applications (see comment 4), but that shouldn't be worth fixing unless someone is affected by this and wants to work on it.