warning: unknown lint: `rustc::foo::bar::default_hash_types`
  --> $DIR/issue-83477.rs:5:9
   |
LL | #[allow(rustc::foo::bar::default_hash_types)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean: `rustc::default_hash_types`
   |
   = note: `#[warn(unknown_lints)]` on by default

warning: unknown lint: `rustc::foo::default_hash_types`
  --> $DIR/issue-83477.rs:9:9
   |
LL | #[allow(rustc::foo::default_hash_types)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean: `rustc::default_hash_types`

warning: prefer `FxHashMap` over `HashMap`, it has better performance
  --> $DIR/issue-83477.rs:14:13
   |
LL |     let _ = std::collections::HashMap::<String, String>::new();
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: a `use rustc_data_structures::fx::FxHashMap` may be necessary
note: the lint level is defined here
  --> $DIR/issue-83477.rs:3:9
   |
LL | #![warn(rustc::internal)]
   |         ^^^^^^^^^^^^^^^
   = note: `#[warn(rustc::default_hash_types)]` implied by `#[warn(rustc::internal)]`

warning: 3 warnings emitted