Function get_type_diagnostic_name 

pub fn get_type_diagnostic_name(
    cx: &LateContext<'_>,
    ty: Ty<'_>,
) -> Option<Symbol>

Get the diagnostic name of a type, e.g. sym::HashMap. To check if a type implements a trait marked with a diagnostic item use implements_trait.

For a further exploitation what diagnostic items are see diagnostic items in rustc-dev-guide.