error[E0433]: failed to resolve: use of undeclared crate or module `alloc` --> $DIR/undeclared-module-alloc.rs:3:5 | LL | use alloc::rc::Rc; | ^^^^^ use of undeclared crate or module `alloc` | = help: add `extern crate alloc` to use the `alloc` crate error: aborting due to previous error For more information about this error, try `rustc --explain E0433`.