fmt-debug

The tracking issue for this feature is: #129709.

Option -Z fmt-debug=val controls verbosity of derived Debug implementations and debug formatting in format strings ({:?}).

• full — #[derive(Debug)] prints types recursively. This is the default behavior.

• shallow — #[derive(Debug)] prints only the type name, or name of a variant of a fieldless enums. Details of the Debug implementation are not stable and may change in the future. Behavior of custom fmt::Debug implementations is not affected.

• none — #[derive(Debug)] does not print anything at all. {:?} in formatting strings has no effect. This option may reduce size of binaries, and remove occurrences of type names in the binary that are not removed by striping symbols. However, it may also cause panic! and assert! messages to be incomplete.