Address review comments

clippy_lints/src/format_args.rs

@@ -153,14 +153,12 @@ fn check_to_string_in_format_args<'tcx>(cx: &LateContext<'tcx>, name: Symbol, ar
         if let Some(display_trait_id) = cx.tcx.get_diagnostic_item(sym::Display);
         if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
         then {
-            let (n_overloaded_derefs, target) = count_overloaded_derefs(
-                0,
-                0,
+            let (n_needed_derefs, target) = count_needed_derefs(
                 receiver_ty,
-                &mut cx.typeck_results().expr_adjustments(receiver).iter(),
+                cx.typeck_results().expr_adjustments(receiver).iter(),
             );
             if implements_trait(cx, target, display_trait_id, &[]) {
-                if n_overloaded_derefs == 0 {
+                if n_needed_derefs == 0 {
                     span_lint_and_sugg(
                         cx,
                         TO_STRING_IN_FORMAT_ARGS,
@@ -177,7 +175,7 @@ fn check_to_string_in_format_args<'tcx>(cx: &LateContext<'tcx>, name: Symbol, ar
                         value.span,
                         &format!("`to_string` applied to a type that implements `Display` in `{}!` args", name),
                         "use this",
-                        format!("{:*>width$}{}", "", receiver_snippet, width = n_overloaded_derefs),
+                        format!("{:*>width$}{}", "", receiver_snippet, width = n_needed_derefs),
                         Applicability::MachineApplicable,
                     );
                 }
@@ -201,31 +199,25 @@ fn trim_semicolon(cx: &LateContext<'_>, span: Span) -> Span {
     })
 }
 
-fn count_overloaded_derefs<'tcx, I>(
-    n_total: usize,
-    n_overloaded: usize,
-    ty: Ty<'tcx>,
-    iter: &mut I,
-) -> (usize, Ty<'tcx>)
+fn count_needed_derefs<'tcx, I>(mut ty: Ty<'tcx>, mut iter: I) -> (usize, Ty<'tcx>)
 where
     I: Iterator<Item = &'tcx Adjustment<'tcx>>,
 {
-    if let Some(Adjustment {
-        kind: Adjust::Deref(overloaded_deref),
-        target,
-    }) = iter.next()
-    {
-        count_overloaded_derefs(
-            n_total + 1,
-            if overloaded_deref.is_some() {
-                n_total + 1
-            } else {
-                n_overloaded
-            },
+    let mut n_total = 0;
+    let mut n_needed = 0;
+    loop {
+        if let Some(Adjustment {
+            kind: Adjust::Deref(overloaded_deref),
             target,
-            iter,
-        )
-    } else {
-        (n_overloaded, ty)
+        }) = iter.next()
+        {
+            n_total += 1;
+            if overloaded_deref.is_some() {
+                n_needed = n_total;
+            }
+            ty = target;
+        } else {
+            return (n_needed, ty);
+        }
     }
 }

tests/ui/format_args.fixed

@@ -69,7 +69,7 @@ macro_rules! my_other_macro {
 }
 
 fn main() {
-    let x = 'x';
+    let x = &X(1);
     let x_ref = &x;
 
     let _ = format!("error: something failed at {}", Location::caller());
@@ -95,7 +95,8 @@ fn main() {
     println!("{}", *X(1));
     println!("{}", ***Y(&X(1)));
     println!("{}", Z(1));
-    println!("{}", x_ref);
+    println!("{}", **x);
+    println!("{}", ***x_ref);
 
     println!("error: something failed at {}", Somewhere.to_string());
     println!("{} and again {0}", x.to_string());

tests/ui/format_args.rs

@@ -69,7 +69,7 @@ macro_rules! my_other_macro {
 }
 
 fn main() {
-    let x = 'x';
+    let x = &X(1);
     let x_ref = &x;
 
     let _ = format!("error: something failed at {}", Location::caller().to_string());
@@ -95,6 +95,7 @@ fn main() {
     println!("{}", X(1).to_string());
     println!("{}", Y(&X(1)).to_string());
     println!("{}", Z(1).to_string());
+    println!("{}", x.to_string());
     println!("{}", x_ref.to_string());
 
     println!("error: something failed at {}", Somewhere.to_string());

tests/ui/format_args.stderr

@@ -91,10 +91,16 @@ LL |     println!("{}", Z(1).to_string());
    |                        ^^^^^^^^^^^^ help: remove this
 
 error: `to_string` applied to a type that implements `Display` in `println!` args
-  --> $DIR/format_args.rs:98:25
+  --> $DIR/format_args.rs:98:20
+   |
+LL |     println!("{}", x.to_string());
+   |                    ^^^^^^^^^^^^^ help: use this: `**x`
+
+error: `to_string` applied to a type that implements `Display` in `println!` args
+  --> $DIR/format_args.rs:99:20
    |
 LL |     println!("{}", x_ref.to_string());
-   |                         ^^^^^^^^^^^^ help: remove this
+   |                    ^^^^^^^^^^^^^^^^^ help: use this: `***x_ref`
 
-error: aborting due to 16 previous errors
+error: aborting due to 17 previous errors