Function designated_initializer_owner 

pub fn designated_initializer_owner(
    visibility: &VisibilityIndex<'_>,
    file: &ProjectFile,
    source: &str,
    node: Node<'_>,
) -> Option<DesignatedInitializerOwner>

Recognize a designated-initializer field and, when possible, resolve its aggregate owner.

Covers both the grammar’s ordinary field_designator shape and the exact recovery used for .field = value after a preprocessor-split array initializer. Nested aggregate levels are deliberately left unresolved unless the single outer level is the containing array initializer: resolving those would require following the enclosing field’s declared type. None means the node is not a designator at all; an unresolved designator remains classified so callers cannot fall through to unrelated global/member heuristics.