Module ra_ap_hir_expand::ast_id_map

AstIdMap allows to create stable IDs for "large" syntax nodes like items and macro calls.

Specifically, it enumerates all items in a file and uses position of a an item as an ID. That way, id's don't change unless the set of items itself changes.

Structs

AstIdMap	Maps items' SyntaxNodes to ErasedFileAstIds and back.
FileAstId	AstId points to an AST node in a specific file.