error[E0308]: mismatched types --> $DIR/issue-15783.rs:8:19 | LL | let msg = foo(x); | ^ expected slice `[&str]`, found array `[&str; 1]` | = note: expected enum `std::option::Option<&[&str]>` found enum `std::option::Option<&[&str; 1]>` error: aborting due to previous error For more information about this error, try `rustc --explain E0308`.