A global definition identifier consisting of a crate number and a definition index.
- let def_id = crate_num.as_def_id();
- let def_id = local_def_id.to_def_id();
- let def_id = owner_id.to_def_id();
- let def_id = mir_source.def_id();
- let def_id = [tcx](https://doc.rust-lang.org/beta/nightly-rustc/rustc_middle/ty/struct.TyCt