replace span_lint with span_lint_and_sugg along with error message

clippy_lints/src/casts/unnecessary_cast.rs

@@ -7,7 +7,7 @@ use rustc_middle::ty::{self, FloatTy, InferTy, Ty};
 
 use if_chain::if_chain;
 
-use crate::utils::{numeric_literal::NumericLiteral, snippet_opt, span_lint, span_lint_and_sugg};
+use crate::utils::{numeric_literal::NumericLiteral, snippet_opt, span_lint_and_sugg};
 
 use super::UNNECESSARY_CAST;
 
@@ -46,7 +46,7 @@ pub(super) fn check(
             LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
             _ => {
                 if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
-                    span_lint(
+                    span_lint_and_sugg(
                         cx,
                         UNNECESSARY_CAST,
                         expr.span,
@@ -54,6 +54,9 @@ pub(super) fn check(
                             "casting to the same type is unnecessary (`{}` -> `{}`)",
                             cast_from, cast_to
                         ),
+                        "try",
+                        literal_str,
+                        Applicability::MachineApplicable,
                     );
                     return true;
                 }

tests/ui/unnecessary_cast.stderr

@@ -2,7 +2,7 @@ error: casting to the same type is unnecessary (`i32` -> `i32`)
   --> $DIR/unnecessary_cast.rs:6:5
    |
 LL |     1i32 as i32;
-   |     ^^^^^^^^^^^
+   |     ^^^^^^^^^^^ help: try: `1i32`
    |
    = note: `-D clippy::unnecessary-cast` implied by `-D warnings`
 
@@ -10,13 +10,13 @@ error: casting to the same type is unnecessary (`f32` -> `f32`)
   --> $DIR/unnecessary_cast.rs:7:5
    |
 LL |     1f32 as f32;
-   |     ^^^^^^^^^^^
+   |     ^^^^^^^^^^^ help: try: `1f32`
 
 error: casting to the same type is unnecessary (`bool` -> `bool`)
   --> $DIR/unnecessary_cast.rs:8:5
    |
 LL |     false as bool;
-   |     ^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^ help: try: `false`
 
 error: aborting due to 3 previous errors