error[E0631]: type mismatch in function arguments
  --> $DIR/suggest-option-asderef-unfixable.rs:24:40
   |
LL | fn takes_str_but_too_many_refs(_: &&str) -> Option<()> {
   | ------------------------------------------------------ found signature defined here
...
LL |     let _ = produces_string().and_then(takes_str_but_too_many_refs);
   |                               -------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected due to this
   |                               |
   |                               required by a bound introduced by this call
   |
   = note: expected function signature `fn(String) -> _`
              found function signature `for<'a, 'b> fn(&'a &'b str) -> _`
note: required by a bound in `Option::<T>::and_then`
  --> $SRC_DIR/core/src/option.rs:LL:COL

error[E0277]: expected a `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
  --> $DIR/suggest-option-asderef-unfixable.rs:26:40
   |
LL |     let _ = produces_string().and_then(takes_str_but_wrong_abi);
   |                               -------- ^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
   |                               |
   |                               required by a bound introduced by this call
   |
   = help: the trait `FnOnce<(String,)>` is not implemented for fn item `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
note: required by a bound in `Option::<T>::and_then`
  --> $SRC_DIR/core/src/option.rs:LL:COL

error[E0277]: expected a `FnOnce<(String,)>` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
  --> $DIR/suggest-option-asderef-unfixable.rs:28:40
   |
LL |     let _ = produces_string().and_then(takes_str_but_unsafe);
   |                               -------- ^^^^^^^^^^^^^^^^^^^^ call the function in a closure: `|| unsafe { /* code */ }`
   |                               |
   |                               required by a bound introduced by this call
   |
   = help: the trait `FnOnce<(String,)>` is not implemented for fn item `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
   = note: unsafe function cannot be called generically without an unsafe block
note: required by a bound in `Option::<T>::and_then`
  --> $SRC_DIR/core/src/option.rs:LL:COL

error[E0593]: function is expected to take 1 argument, but it takes 0 arguments
  --> $DIR/suggest-option-asderef-unfixable.rs:30:40
   |
LL | fn no_args() -> Option<()> {
   | -------------------------- takes 0 arguments
...
LL |     let _ = produces_string().and_then(no_args);
   |                               -------- ^^^^^^^ expected function that takes 1 argument
   |                               |
   |                               required by a bound introduced by this call
   |
note: required by a bound in `Option::<T>::and_then`
  --> $SRC_DIR/core/src/option.rs:LL:COL

error[E0631]: type mismatch in function arguments
  --> $DIR/suggest-option-asderef-unfixable.rs:32:45
   |
LL | fn takes_str_but_too_many_refs(_: &&str) -> Option<()> {
   | ------------------------------------------------------ found signature defined here
...
LL |     let _ = Some(TypeWithoutDeref).and_then(takes_str_but_too_many_refs);
   |                                    -------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected due to this
   |                                    |
   |                                    required by a bound introduced by this call
   |
   = note: expected function signature `fn(TypeWithoutDeref) -> _`
              found function signature `for<'a, 'b> fn(&'a &'b str) -> _`
note: required by a bound in `Option::<T>::and_then`
  --> $SRC_DIR/core/src/option.rs:LL:COL

error: aborting due to 5 previous errors

Some errors have detailed explanations: E0277, E0593, E0631.
For more information about an error, try `rustc --explain E0277`.