Function migrate_layout 

pub fn migrate_layout(
    root: &Path,
    options: LayoutMigrationOptions,
) -> Result<LayoutMigrationResult, DatabaseError>

Moves a database between the flat and nested on-disk arrangements.

Idempotent: a database already in the target arrangement, under the target document name, reports changed: false and moves nothing. Never automatic — in a repository this is a visible change to tracked files, so it has to be asked for. Only files the database accounts for are moved; anything else in the root is reported in unclaimed and left alone.

The directory is held under the writer lock for the length of the move (see [hold_for_move]), so nothing here races a writer that has the directory open. The lock is released before the directories the move emptied are removed, because in a nested database the lock file itself lives in one of them.

A format-1 database is moved without being migrated: its <table>.schema.json files travel with it and its manifest is left in format 1, so what open() says about it afterwards is exactly what it said before.

@param root the database directory @param options the arrangement to move into, the document names on either side of the move, and whether to only report the plan @returns what was moved, or would be moved under dry_run