I'm unsure about the time format; TS_MW != TS_ISO_8601 which is what ExpiryDef uses; I think they should match or formatting before comparing will still be needed. An option would be to add a format param to getExpiry()(?). What do you think we should do?

Change 623052 had a related patch set uploaded (by HMonroy; owner: HMonroy):
[mediawiki/core@master] Normalize WatchedItem expiry field

https://gerrit.wikimedia.org/r/623052

Change 623052 merged by jenkins-bot:
[mediawiki/core@master] Normalize WatchedItem expiry field

https://gerrit.wikimedia.org/r/623052

Change 632675 had a related patch set uploaded (by MusikAnimal; owner: HMonroy):
[mediawiki/core@REL1_35] Normalize WatchedItem expiry field

https://gerrit.wikimedia.org/r/632675

Change 632675 merged by jenkins-bot:
[mediawiki/core@REL1_35] Normalize WatchedItem expiry field

https://gerrit.wikimedia.org/r/632675

• Expiry should be normalized and store as either MWTimestamp or CovertibleTimestamp (whatever makes more sense)

Formats like "20201016142841" get interpreted as $wgLocaltimezone and converted to UTC.

Formats like "1 week" are also interpreted in $wgLocaltimezone and converted to UTC (I think, hard to tell).

It has not changed the format the expiries are stored in the database, so should not affect things like Special:Watchlist, Special:EditWatchlist and the watch star, which query the DB directly.

• Creating a WatchedItem with an unsupported string should fail

Validation is much the same as before.

One of the only differences is that submitting an invalid expiry via action=watch or while editing time will raise an exception. Previously, it just created a permanent watch without an exception.

This would only happen if an invalid expiry option had been entered into MediaWiki:Watchlist-expiry-options or the respective translation (e.g. en.json, fr.json). I think only trusted users can edit these, although mistakes can happen like T258583.

• getExpiry() to return formatted as TS_MW or whatever makes more sense

The caller of the function can specify which format they would like it to be in.

When updating a watched item, it is important that the new and old expiry values are in the same format when they are compared.

I tested updating a watched item's expiry via action=watch and while editing. It updated when the expiry was different, and did not update when the expiry did not change.

• Confirm that the $wgLocaltimezone > UTC bug detailed in T260009 is resolved with the changes implemented in this ticket

This was fixed before this change. I made sure that it is still fixed after this change.

Also tested that a similar bug does not occur when editing a page and leaving the expiry time unchanged. (Such a bug did not occur before this change either.)

In T260868#6585108, @ifried wrote:

The one difference (submitting an invalid expiry via action=watch or while editing) is acceptable behavior. This work is now complete, so I'm marking it as Done.

@ifried what do you mean by submitting an invalid expiry via action=watch or while editing?

@dmaza I'm responding to the above comment from Dom: "One of the only differences is that submitting an invalid expiry via action=watch or while editing time will raise an exception. Previously, it just created a permanent watch without an exception."