Auto merge of rust-lang#9870 - koka831:unformat-unused-rounding, r=Jarcho

Keep original literal notation in suggestion

While I did some investigation of rust-lang/rust-clippy#9866 (I couldn't reproduce it though) I found that `unused_rounding` formats as follows:

```rust
3.0_f64.round() // => 3.0f64
```

This PR makes them preserve as the original notation.

```rust
3.0_f64.round() // => 3.0_f64
```

changelog: Suggestion Enhancement: [`unused_rounding`]: The suggestion now preserves the original float literal notation

Author: bors

clippy_lints/src/unused_rounding.rs

@@ -1,5 +1,5 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use rustc_ast::ast::{Expr, ExprKind, LitFloatType, LitKind};
+use clippy_utils::{diagnostics::span_lint_and_sugg, source::snippet};
+use rustc_ast::ast::{Expr, ExprKind, LitKind};
 use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -29,19 +29,15 @@ declare_clippy_lint! {
 }
 declare_lint_pass!(UnusedRounding => [UNUSED_ROUNDING]);
 
-fn is_useless_rounding(expr: &Expr) -> Option<(&str, String)> {
+fn is_useless_rounding<'a>(cx: &EarlyContext<'a>, expr: &'a Expr) -> Option<(&'a str, String)> {
     if let ExprKind::MethodCall(name_ident, receiver, _, _) = &expr.kind
         && let method_name = name_ident.ident.name.as_str()
         && (method_name == "ceil" || method_name == "round" || method_name == "floor")
         && let ExprKind::Lit(spanned) = &receiver.kind
-        && let LitKind::Float(symbol, ty) = spanned.kind {
+        && let LitKind::Float(symbol, _) = spanned.kind {
             let f = symbol.as_str().parse::<f64>().unwrap();
-            let f_str = symbol.to_string() + if let LitFloatType::Suffixed(ty) = ty {
-                ty.name_str()
-            } else {
-                ""
-            };
             if f.fract() == 0.0 {
+                let f_str = snippet(cx, receiver.span, "..").to_string();
                 Some((method_name, f_str))
             } else {
                 None
@@ -53,7 +49,7 @@ fn is_useless_rounding(expr: &Expr) -> Option<(&str, String)> {
 
 impl EarlyLintPass for UnusedRounding {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
-        if let Some((method_name, float)) = is_useless_rounding(expr) {
+        if let Some((method_name, float)) = is_useless_rounding(cx, expr) {
             span_lint_and_sugg(
                 cx,
                 UNUSED_ROUNDING,

tests/ui/unused_rounding.fixed

@@ -6,4 +6,9 @@ fn main() {
     let _ = 1.0f64;
     let _ = 1.00f32;
     let _ = 2e-54f64.floor();
+
+    // issue9866
+    let _ = 3.3_f32.round();
+    let _ = 3.3_f64.round();
+    let _ = 3.0_f32;
 }

tests/ui/unused_rounding.rs

@@ -6,4 +6,9 @@ fn main() {
     let _ = 1.0f64.floor();
     let _ = 1.00f32.round();
     let _ = 2e-54f64.floor();
+
+    // issue9866
+    let _ = 3.3_f32.round();
+    let _ = 3.3_f64.round();
+    let _ = 3.0_f32.round();
 }

tests/ui/unused_rounding.stderr

@@ -18,5 +18,11 @@ error: used the `round` method with a whole number float
 LL |     let _ = 1.00f32.round();
    |             ^^^^^^^^^^^^^^^ help: remove the `round` method call: `1.00f32`
 
-error: aborting due to 3 previous errors
+error: used the `round` method with a whole number float
+  --> $DIR/unused_rounding.rs:13:13
+   |
+LL |     let _ = 3.0_f32.round();
+   |             ^^^^^^^^^^^^^^^ help: remove the `round` method call: `3.0_f32`
+
+error: aborting due to 4 previous errors