https://searchfox.org/mozilla-central/search?q=symbol:F_%3CT_mozilla%3A%3AEditorBase%3A%3ATopLevelEditSubActionData%3E_mNewBlockElement&redirect=false

It's used only for ensuring caret in the block at the post-processing of top level edit sub-actions. First, the name is hard to understand the meaning, and this runs as stateful so that it may change selection after sub-action handlers explicitly collapsing Selection.

So I think that each sub-action handler should manage Selection instead.

The following patches touch the logic to restore selection after handling
commands. However, it seems that they are not tested because I found some
regressions by manual testing, but didn't cause orange on tryserver.

outdent-preserving-selection.tentative.html causes a crash due to the
MOZ_ASSERTION in HTMLEditor::HandleOutdentAtSelectionInternal. It means
that I misunderstand the logic and had put the assertion. I should fix it
later with reading the complicated code again. For now, I just change it
to NS_WARNING_ASSERTION instead.

And also test_cmd_absPos.html is the first test to check toggling position
between static and absolute. Therefore, it detects wrong MOZ_ASSERTs
which test whether EditActionData or TopLevelEditSubActionData is created
or not before they create them by themselves. So, this patch removes the
wrong assertions.

Depends on D152962

They set TopLevelEditSubActionData::mNewBlockElement and their root callers
in edit sub-action level are only InsertParagraphSeparatorAsSubAction and
FormatBlockContainerAsSubAction, and they are called each other. Therefore,
this patch changes these 3 methods once.

Depends on D152963

Depends on D152964

It oddly retrieve an ancestor list element which contains one range in the
selection ranges. So, working it with AutoRangeArray which is initialized
with Selection makes HTMLEditor smaller...

Depends on D152965

Depends on D152966

Depends on D152967

With taking an AutoRangeArray which is initialized with Selection, it can
restore selection and check if it's collapsed and if collapsed in the expected
list element. Then, its caller can apply the returned range to Selection
because it's an edit sub-action handler.

Depends on D152968

And also this patch makes it and an its caller stop computing editing host
with the latest Selection.

Depends on D152969

Depends on D152970

It's called only by HTMLEditor::HandleCSSIndentAtSelection which is called
only by HTMLEditor::HandleIndentAtSelection. They don't touch Selection
after calling it. Therefore, we can make it adjust collapsing selection point
by itself.

Depends on D152971

The change of expected assertion count in the crash test is caused by that the
test calls execCommand recursively from the legacy mutation event listeners.
Therefore, stopping updating Selection for each DOM tree change causes that
the target range in the nested edit action is changed. However, the nested
handling has already been disabled by default, so this should not be a problem
for the users.

Depends on D152972

Depends on D152973

Depends on D152974

Depends on D152975

Depends on D152976

It's only caller is HTMLEditor::AlignContentsAtSelection which is called only
by HTMLEditor::AlignAsSubAction at almost last of it. Therefore, it's safe
to handle mNewBlockElement at the caller of
AlignContentsAtSelectionWithEmptyDivElement is safe.

Depends on D152977

Depends on D152978

For doing that, this patch also making HTMLEditor::AlignContentsAtSelection
which the only caller of HTMLEditor::AlignNodesAndDescendants handle
Selection with AutoRangeArray because it uses AutoSelectionRestorer and
we need to adjust Selection after restored.

Depends on D152979

Depends on D152980

Depends on D152981

https://hg.mozilla.org/mozilla-central/rev/d554ca7850eb
https://hg.mozilla.org/mozilla-central/rev/b9a3b6f27a8d
https://hg.mozilla.org/mozilla-central/rev/bb54603e50c7
https://hg.mozilla.org/mozilla-central/rev/9893b8c357a2
https://hg.mozilla.org/mozilla-central/rev/d61ac9d43588
https://hg.mozilla.org/mozilla-central/rev/310cd44cff95
https://hg.mozilla.org/mozilla-central/rev/23d50b5617de

https://hg.mozilla.org/mozilla-central/rev/32d794b2a45a
https://hg.mozilla.org/mozilla-central/rev/661e25343a15
https://hg.mozilla.org/mozilla-central/rev/80ed14c716a2
https://hg.mozilla.org/mozilla-central/rev/695d708318a5
https://hg.mozilla.org/mozilla-central/rev/1e9e0b9b8536
https://hg.mozilla.org/mozilla-central/rev/f9d7d41f5043
https://hg.mozilla.org/mozilla-central/rev/3efbfdf889b4
https://hg.mozilla.org/mozilla-central/rev/511a7e64402c
https://hg.mozilla.org/mozilla-central/rev/808c433c7774
https://hg.mozilla.org/mozilla-central/rev/27d5779ea393
https://hg.mozilla.org/mozilla-central/rev/7f56b90bd017
https://hg.mozilla.org/mozilla-central/rev/a0dd784acd4c
https://hg.mozilla.org/mozilla-central/rev/8896439912aa
https://hg.mozilla.org/mozilla-central/rev/3ea6eaf0dc16

== Change summary for alert #35027 (as of Sat, 06 Aug 2022 07:46:45 GMT) ==

Improvements:

For up to date results, see: https://treeherder.mozilla.org/perfherder/alerts?id=35027