Add a help message

Author: botahamec

clippy_lints/src/unnecessary_box_returns.rs

@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::diagnostics::span_lint_and_then;
 use rustc_errors::Applicability;
 use rustc_hir::{def_id::LocalDefId, FnDecl, FnRetTy, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind};
 use rustc_hir_analysis::hir_ty_to_ty;
@@ -66,15 +66,22 @@ impl UnnecessaryBoxReturns {
 
         // it's sometimes useful to return Box<T> if T is unsized, so don't lint those
         if boxed_ty.is_sized(cx.tcx, cx.param_env) {
-            span_lint_and_sugg(
+            span_lint_and_then(
                 cx,
                 UNNECESSARY_BOX_RETURNS,
                 return_ty_hir.span,
                 format!("boxed return of the sized type `{boxed_ty}`").as_str(),
-                "try",
-                boxed_ty.to_string(),
-                // the return value and function callers also needs to be changed, so this can't be MachineApplicable
-                Applicability::Unspecified,
+                |diagnostic| {
+                    diagnostic.span_suggestion(
+                        return_ty_hir.span,
+                        "try",
+                        boxed_ty.to_string(),
+                        // the return value and function callers also needs to
+                        // be changed, so this can't be MachineApplicable
+                        Applicability::Unspecified,
+                    );
+                    diagnostic.help("Changing this also requires a change to the return expressions in this function");
+                },
             );
         }
     }

tests/ui/unnecessary_box_returns.stderr

@@ -4,25 +4,32 @@ error: boxed return of the sized type `usize`
 LL |     fn baz(&self) -> Box<usize>;
    |                      ^^^^^^^^^^ help: try: `usize`
    |
+   = help: Changing this also requires a change to the return expressions in this function
    = note: `-D clippy::unnecessary-box-returns` implied by `-D warnings`
 
 error: boxed return of the sized type `usize`
   --> $DIR/unnecessary_box_returns.rs:18:22
    |
 LL |     fn baz(&self) -> Box<usize> {
    |                      ^^^^^^^^^^ help: try: `usize`
+   |
+   = help: Changing this also requires a change to the return expressions in this function
 
 error: boxed return of the sized type `usize`
   --> $DIR/unnecessary_box_returns.rs:24:21
    |
 LL | fn boxed_usize() -> Box<usize> {
    |                     ^^^^^^^^^^ help: try: `usize`
+   |
+   = help: Changing this also requires a change to the return expressions in this function
 
 error: boxed return of the sized type `Foo`
   --> $DIR/unnecessary_box_returns.rs:29:20
    |
 LL | fn _boxed_foo() -> Box<Foo> {
    |                    ^^^^^^^^ help: try: `Foo`
+   |
+   = help: Changing this also requires a change to the return expressions in this function
 
 error: aborting due to 4 previous errors