tests/ui/variance/variance-unused-region-param.rs - toolchain/rustc - Git at Google

 // Test that we report an error for unused type parameters in types.

 struct SomeStruct<'a> { x: u32 } //~ ERROR parameter `'a` is never used
 enum SomeEnum<'a> { Nothing } //~ ERROR parameter `'a` is never used
 trait SomeTrait<'a> { fn foo(&self); } // OK on traits.

 fn main() {}
	// Test that we report an error for unused type parameters in types.

	struct SomeStruct<'a> { x: u32 } //~ ERROR parameter `'a` is never used
	enum SomeEnum<'a> { Nothing } //~ ERROR parameter `'a` is never used
	trait SomeTrait<'a> { fn foo(&self); } // OK on traits.

	fn main() {}