Macro location_id 

location_id!() { /* proc-macro */ }

Generate a globally unique identifier for a source code position

Every time you invoke this macro it will return generate a unique LocationId that corresponds to the position in the source code where it was invoked. This works even across crates, so even if two crates in your project invoke this macro on the exact same line and column of the exact same file the ID will still be unique.

How?

The ids are stored in a file in the compiler’s OUT_DIR, where it’s outputting all the object code for every crate. The file contains a btreemap of ids where the key is crate_name::file_path::line_number::column_number and the value is the id.

Failure Modes

• Your build system is so exceedingly strange that somehow you are calling rustc without passing the crate name or the out dir through any known mechanism (several are tried.). In this case the macro may produce a compile error.

• You are dynamicaly loading separately compiled code. In this case the ids may conflict, however in our use case (poolshark) we don’t care about this case because separately compiled code will have separate thread local structures and thus poolshark will still work fine