Provide better compiler output when using ? on Option in fn returning Result and vice-versa

Author: Duddino

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -321,15 +321,15 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             err.span_suggestion_verbose(
                                 span.shrink_to_lo(),
                                 "consider converting the `Option<T>` into a `Result<T, _>` using `Option::ok_or` or `Option::ok_or_else`",
-                                ".ok_or_else(|_| /* error value */)".to_string(),
+                                ".ok_or_else(|| /* error value */)".to_string(),
                                 Applicability::HasPlaceholders,
                             );
                         } else if is_try && is_from && should_convert_result_to_option {
                             err.span_suggestion_verbose(
                                 span.shrink_to_lo(),
                                 "consider converting the `Result<T, _>` into an `Option<T>` using `Result::ok`",
                                 ".ok()".to_string(),
-                                Applicability::HasPlaceholders,
+                                Applicability::MachineApplicable,
                             );
                         }
 

src/test/ui/option-to-result.stderr

@@ -8,8 +8,8 @@ LL |     a?;
    = note: required by `std::convert::From::from`
 help: consider converting the `Option<T>` into a `Result<T, _>` using `Option::ok_or` or `Option::ok_or_else`
    |
-LL |     a.ok_or_else(|_| /* error value */)?;
-   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     a.ok_or_else(|| /* error value */)?;
+   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0277]: `?` couldn't convert the error to `std::option::NoneError`
   --> $DIR/option-to-result.rs:11:6

src/test/ui/try-on-option.stderr

@@ -8,8 +8,8 @@ LL |     x?;
    = note: required by `std::convert::From::from`
 help: consider converting the `Option<T>` into a `Result<T, _>` using `Option::ok_or` or `Option::ok_or_else`
    |
-LL |     x.ok_or_else(|_| /* error value */)?;
-   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     x.ok_or_else(|| /* error value */)?;
+   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option.rs:13:5