error[E0599]: cannot write into `String`
  --> $DIR/missing-writer-issue-139830.rs:7:20
   |
LL |     let _ = write!(buf, "foo");
   |                    ^^^
   |
  --> $SRC_DIR/core/src/fmt/mod.rs:LL:COL
   |
   = note: the method is available for `String` here
note: must implement `io::Write`, `fmt::Write`, or have a `write_fmt` method
  --> $DIR/missing-writer-issue-139830.rs:7:20
   |
LL |     let _ = write!(buf, "foo");
   |                    ^^^
   = help: items from traits can only be used if the trait is in scope
help: trait `Write` which provides `write_fmt` is implemented but not in scope; perhaps you want to import it
   |
LL + use std::fmt::Write;
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0599`.