Addressed review

Author: teofr

clippy_lints/src/approx_const.rs

@@ -92,9 +92,9 @@ impl LateLintPass<'_> for ApproxConstant {
 impl ApproxConstant {
     fn check_known_consts(&self, cx: &LateContext<'_>, span: Span, s: symbol::Symbol, module: &str) {
         let s = s.as_str();
-        if let Ok(s_value) = s.parse::<f64>() {
+        if let Ok(maybe_constant) = s.parse::<f64>() {
             for &(constant, name, min_digits, msrv) in &KNOWN_CONSTS {
-                if is_approx_const(constant, s, s_value, min_digits)
+                if is_approx_const(constant, s, maybe_constant, min_digits)
                     && msrv.is_none_or(|msrv| self.msrv.meets(cx, msrv))
                 {
                     span_lint_and_help(
@@ -134,10 +134,14 @@ fn is_approx_const(constant: f64, value: &str, f_value: f64, min_digits: usize)
         true
     } else {
         // The value is a truncated constant
+
+        // Print constant with numeric formatting (`0`), with the length of `value` as minimum width
+        // (`value_len$`), and with the same precision as `value` (`.value_prec$`).
+        // See https://doc.rust-lang.org/std/fmt/index.html.
         let round_const = format!(
-            "{constant:0value_len$.*}",
-            count_digits_after_dot(value),
-            value_len = value.len()
+            "{constant:0value_len$.value_prec$}",
+            value_len = value.len(),
+            value_prec = count_digits_after_dot(value)
         );
         value == round_const
     }