tests/ui/btreemap/btreemap-index-mut.rs - toolchain/rustc - Git at Google

 use std::collections::BTreeMap;

 fn main() {
     let mut map = BTreeMap::<u32, u32>::new();
     map[&0] = 1; //~ ERROR cannot assign
 }
	use std::collections::BTreeMap;

	fn main() {
	let mut map = BTreeMap::<u32, u32>::new();
	map[&0] = 1; //~ ERROR cannot assign
	}