tests/ui/parser/fn-defined-using-def.rs - third_party/rust - Git at Google

 // Check what happens when `def` is used to define a function, instead of `fn`
 //@ edition:2021

 #![allow(dead_code)]

 def foo() {}
 //~^ ERROR expected one of `!` or `::`, found `foo`
 //~^^ HELP write `fn` instead of `def` to declare a function

 fn main() {}
	// Check what happens when `def` is used to define a function, instead of `fn`
	//@ edition:2021

	#![allow(dead_code)]

	def foo() {}
	//~^ ERROR expected one of `!` or `::`, found `foo`
	//~^^ HELP write `fn` instead of `def` to declare a function

	fn main() {}