error: unused variable: `xyza`
  --> $DIR/issue-100584.rs:2:8
   |
LL | fn foo(xyza: &str) {
   |        ^^^^ unused variable
LL |
LL |     let _ = "{xyza}";
   |             -------- you might have meant to use string interpolation in this string literal
   |
note: the lint level is defined here
  --> $DIR/issue-100584.rs:1:9
   |
LL | #![deny(unused)]
   |         ^^^^^^
   = note: `#[deny(unused_variables)]` implied by `#[deny(unused)]`
help: string interpolation only works in `format!` invocations
   |
LL |     let _ = format!("{xyza}");
   |             ++++++++        +
help: if this is intentional, prefix it with an underscore
   |
LL | fn foo(_xyza: &str) {
   |        ~~~~~

error: unused variable: `xyza`
  --> $DIR/issue-100584.rs:7:9
   |
LL | fn foo3(xyza: &str) {
   |         ^^^^ unused variable
LL |
LL |     let _ = "aaa{xyza}bbb";
   |             -------------- you might have meant to use string interpolation in this string literal
   |
help: string interpolation only works in `format!` invocations
   |
LL |     let _ = format!("aaa{xyza}bbb");
   |             ++++++++              +
help: if this is intentional, prefix it with an underscore
   |
LL | fn foo3(_xyza: &str) {
   |         ~~~~~

error: aborting due to 2 previous errors