Load the folder-access editor lazily to fix multi-minute freeze on large libraries

[janpospis]

Problem

On a large library, loading the folder list freezes for minutes. It is most visible in the admin Folder access editor (the user × folder permission matrix), but it also affects other places that request the full folder list (the file browser's startup default-folder detection, the "move to folder" picker, portals).

Root cause

getFolderList.php (via FolderModel::getFolderList() → getSubfolders()) does a full recursive walk of the whole tree when no folder= is given — O(n) over the entire library. Several callers hit this:

• the folder-access ACL editor (loaded every folder up front and rendered one row per folder),
• AclAdminController::getUserGrants() — calls it with no arguments once per user, so it dominates the matrix load,
• the file browser's startup/move-target folder list, portals, etc.

On a ~50k-folder library, getUserGrants('<user>') measured ~239 s; the walk returned 50,293 folders in 239 s vs 24 top-level folders in 0.11 s.

Changes

• FolderController::getFolderList — when no explicit folder= is given, default to a shallow (top-level) listing instead of the full recursive walk. This fixes every caller that pulled the whole list at once. The full recursive list is still available via &deep=1, and directory navigation (which passes an explicit folder=) is unaffected.
• AclAdminController::getUserGrants — read grants directly from folder_acl.json (the only folders that can carry a grant) instead of walking the tree. ~239 s → ~0.006 s.
• adminFolderAccess.js — the folder-access editor now loads one level at a time (using the shallow folder=<path> mode) with a breadcrumb and per-row drill-in to reach and set permissions on subfolders. In-progress edits are collected into the existing fallback map before navigating, so the batched save still persists grants from every visited level.

Notes

• Callers that previously enumerated the whole tree into a flat list (e.g. the "move to folder" picker) now show the top level; they can request the full list with &deep=1 where needed. On large libraries the full flat list was effectively unusable anyway.
• No new dependencies or schema/config changes. New i18n key open_subfolders (falls back to "Open subfolders").

Testing

Verified on a ~50k-folder local library: the folder-access editor and folder-list loading no longer freeze, drill-in reaches subfolders, and saving persists grants set across multiple levels.

[error311]

Thank you

This addresses a real performance problem, and the ACL-file optimization plus lazy editor loading look valuable. I found a few compatibility issues that need adjustment before merge.

Please preserve the existing default recursive behavior of getFolderList.php; several portal, folder-picker, and startup callers still depend on it. The lazy ACL editor already sends an explicit folder= value, so changing the global API default is not necessary.

Drill-in rendering also needs to reapply inherited group locks and read-only group-preview state, and administrator permissions should remain visibly enabled on newly loaded levels. Please add focused regression coverage for these cases and saving permissions across multiple visited levels.

Once those points are addressed, I’m happy to target the change for next release..