When I ask Special:MergeItems to merge two items, I want to know all conflicts at once, so that I can resolve them all at once (or desist from the merge) and then ask merge only once. Currently, I have to continuously switch from one tab to the other: resolve conflict, submit the merge form again, get told of another conflict, and so on.
|Open||None||T96040 Wikibase special pages (tracking)|
|Open||None||T101629 Merge.js should not check conflicts itself but rely on API|
|Open||None||T91210 Special:MergeItems should report all conflicts at once|
Briefly looking at the code the issue lies in the API module.
Currently exceptions are thrown in each of the methods contained in the linked code https://github.com/wikimedia/mediawiki-extensions-Wikibase/blob/master/repo/includes/ChangeOp/ChangeOpsMerge.php#L157
Once one exception is thrown the processing stops thus on the first conflict is ever reported.