error[E0573]: expected type, found built-in attribute `export_name`
  --> $DIR/issue-83471.rs:15:13
   |
LL |     fn call(export_name);
   |             ^^^^^^^^^^^ not a type

error[E0658]: language items are subject to change
  --> $DIR/issue-83471.rs:7:1
   |
LL | #[lang = "sized"]
   | ^^^^^^^^^^^^^^^^^
   |
   = help: add `#![feature(lang_items)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: language items are subject to change
  --> $DIR/issue-83471.rs:11:1
   |
LL | #[lang = "fn"]
   | ^^^^^^^^^^^^^^
   |
   = help: add `#![feature(lang_items)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

warning: anonymous parameters are deprecated and will be removed in the next edition
  --> $DIR/issue-83471.rs:15:13
   |
LL |     fn call(export_name);
   |             ^^^^^^^^^^^ help: try naming the parameter or explicitly ignoring it: `_: export_name`
   |
   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2018!
   = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
   = note: `#[warn(anonymous_parameters)]` on by default

error[E0718]: `fn` language item must be applied to a trait with 1 generic argument
  --> $DIR/issue-83471.rs:11:1
   |
LL | #[lang = "fn"]
   | ^^^^^^^^^^^^^^
...
LL | trait Fn {
   |         - this trait has 0 generic arguments

error[E0425]: cannot find function `a` in this scope
  --> $DIR/issue-83471.rs:21:5
   |
LL |     a()
   |     ^ not found in this scope

error: aborting due to 5 previous errors; 1 warning emitted

Some errors have detailed explanations: E0425, E0573, E0658, E0718.
For more information about an error, try `rustc --explain E0425`.