1488419 - Font editor: axis value replaces whole font-variation-settings declaration

Status: RESOLVED FIXED

(DevTools :: Inspector, defect, P2)

Description

[Razvan Caliman [:rcaliman]]

Steps: 
- Go to v-fonts.com
- Find the "Renner" font example and inspect the preview text in DevTools
- Switch to 3-pane mode with the Fonts panel alongside the CSS rules panel
- Drag the Italic slider in the Fonts panel

Expected:
- Both the "wdth" and the "ital" values show up in the `font-variation-settings` property on the selected element's inline styles.

Actual
- Sometimes, as you drag the slider, the "ital" axis value replaces the whole value. The behavior is inconsistent.

Suspected root cause:
Race condition between previewing the changes on the page and writing them to the CSS rule view.

Comment 1

[Razvan Caliman [:rcaliman]]

Attachment: Bug 1488419 - Re-attach listener for Rule view change after writing new value. r=gl

Comment 2

[Gabriel Luong [:gl] (ΦωΦ)]

Comment on attachment 9006255 [details]
Bug 1488419 - Re-attach listener for Rule view change after writing new value. r=gl

Gabriel [:gl] (ΦωΦ) has approved the revision.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/46f7c652efca
Re-attach listener for Rule view change after writing new value. r=gl

Comment 4

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/46f7c652efca

Comment 5

[Razvan Caliman [:rcaliman]]

Comment on attachment 9006255 [details]
Bug 1488419 - Re-attach listener for Rule view change after writing new value. r=gl

Approval Request Comment
[Feature/Bug causing the regression]:
https://bugzilla.mozilla.org/show_bug.cgi?id=1488419

[User impact if declined]:
While using the new Font Editor in Devtools some users can lose changes made to the `font-variation-settings` CSS property.

[Is this code covered by automated tests?]:
No. The current test infrastructure uses OS configurations which don't support variable fonts (current: OSX 10.10, needed: macOS 10.13)

[Has the fix been verified in Nightly?]:
Yes

[Needs manual test from QE? If yes, steps to reproduce]:
No
 
[List of other uplifts needed for the feature/fix]:
None

[Is the change risky?]:
No

[Why is the change risky/not risky?]:
Minimal impact on Font Editor users (subset of DevTools users) editing a variable fonts (even smaller subset of users). The patch fixes a race condition which made the issue very frequent for this subset of users.

[String changes made/needed]:
None

Comment 6

[Pascal Chevrel:pascalc (PTO until April 26)]

Comment on attachment 9006255 [details]
Bug 1488419 - Re-attach listener for Rule view change after writing new value. r=gl

Uplift approved for 63 beta 5

Comment 7

[Eliza Balazs [:ebalazs_]]

https://hg.mozilla.org/releases/mozilla-beta/rev/b359fee9b67a