Menu rebuild on module enable reverts moved menu links to their default menus

[alanmels]

Description of the bug

Enabling any module triggers a menu rebuild that can undo previously moved menu links (and their children) by relocating them back to their original menu, breaking custom menu structures even when the enabled module doesn’t change menus.

Steps To Reproduce

1. Go to /admin/structure/menu/manage/management and move system-provided links (e.g., “Add content” and its children Card/Page/Post) from the default Administration/management menu into main-menu; save.
2. Confirm the links now appear in main-menu.
3. Enable an unrelated module (e.g., devel) via /admin/modules or drush en devel.
4. After enable completes, revisit /admin/structure/menu/manage/main-menu.

Actual behavior

Some or all moved links (e.g., Card/Page/Post under “Add content”) disappear from main-menu because the enable-time menu rebuild reassigns them back to their default menu. Parent links that were marked customized may remain, while unmarked children revert.

Expected behavior

Enabling a module should not alter existing menu placement. Links moved by a site admin should remain in their chosen menus (including children) after any module enable.

Additional information

• Notes: Backdrop performs a menu rebuild on module enable. Links not marked customized=1 can be reset to their router-default menu during that rebuild.

[alanmels]

Until this issue is addressed in core, https://github.com/backdrop-contrib/menu_tools can be used.

[quicksketch]

@alanmels Is your contrib solution adaptable to core?

[alanmels]

@quicksketch Thanks for checking in. I’m honestly not sure whether this contrib approach can be adapted to core, because the module is essentially working around a limitation that comes from core itself. The underlying issue is that Backdrop triggers a full menu rebuild whenever any module is enabled, even if that module has nothing to do with the menu system.

Ideally, core would avoid triggering a rebuild unless the module actually implements menu-related hooks. That would prevent menu link positions from being unintentionally reverted. I’m not certain whether proposing such a change would be considered too bold for core, but it feels like the cleaner long-term fix compared to trying to patch around the behavior in contrib.