1656477 - Track Changes: CSS changes not collected while Changes panel is not visible

Status: RESOLVED FIXED

(DevTools :: Inspector: Changes, defect, P1)

Description

[Razvan Caliman [:rcaliman]]

Attachment: no-changes-collected-regression.mp4

CSS changes should be collected in the background and displayed when the Changes panel is visible.

Mozregression points to this pushlog.

Bug 1625957 has regressed this functionality.

Now, the Changes panel must have been invoked at least once before changes are collected in the background.
Most likely, the corresponding ChangesActor is not created on Inspector init. Actors are lazy. If not explicitly invoked, they are not instantiated.

EDIT: The changes do get collected in the background. They're erroneously cleared as soon as the Changes panel is first focused.
This happens because the Changes panel reacts to cached DOCUMENT_EVENT resources from resource watcher (which is also watching for CSS_CHANGE resources) leading it to mistakenly believe that the document is refreshing, thus clearing the list of changes.

Steps to reproduce

• Run the following in the URL bar:

data:text/html,<style>body {color: red}</style>TEST

• Open DevTools > Inspector
• Ensure the Changes panel is NOT active; if it is, switch to another panel, close DevTools, refresh the page and start over.
• In the Rules view, change the value of color: red to color: blue
• Switch to the Changes panel

Expected result
The Changes panel shows a diff view of the changed CSS declaration

Actual result
The Changes panel behaves as if no changes have happened.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1625957

Comment 2

[Razvan Caliman [:rcaliman]]

Attachment: Bug 1656477 - Do not react to cached DOCUMENT_EVENT resources in Changes panel. r=daisuke

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6037c7a2a7de
Do not react to cached DOCUMENT_EVENT resources in Changes panel. r=daisuke

Comment 4

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

https://hg.mozilla.org/mozilla-central/rev/6037c7a2a7de

Comment 5

[Razvan Caliman [:rcaliman]]

Comment on attachment 9167349 [details]
Bug 1656477 - Do not react to cached DOCUMENT_EVENT resources in Changes panel. r=daisuke

Beta/Release Uplift Approval Request

• User impact if declined: CSS changes made in the DevTools Inspector and collected in the background are cleared when opening the Changes panel for the first time. This causes data loss for users who expect to find and export the list of changes.
  This functionality has been regressed by a Fission-related change in Bug 1625957 and has slipped undetected to Firefox 79 (current Firefox Release). An automated test was missing (one was added now with this patch).
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): The fix in this patch addresses a regression to restore previously working functionality. Any impact is isolated to the Changes panel in the DevTools Inspector.
• String changes made/needed:

Comment 6

[Julien Cristau [:jcristau] (back April 22)]

Comment on attachment 9167349 [details]
Bug 1656477 - Do not react to cached DOCUMENT_EVENT resources in Changes panel. r=daisuke

devtools regression fix, with test, approved for 80.0b4

Comment 7

[Julien Cristau [:jcristau] (back April 22)]

https://hg.mozilla.org/releases/mozilla-beta/rev/08a5ca074e7b

Comment 8

[Julien Cristau [:jcristau] (back April 22)]

Comment on attachment 9167349 [details]
Bug 1656477 - Do not react to cached DOCUMENT_EVENT resources in Changes panel. r=daisuke

80 ships next week, there are no plans for a 79 dot release.