Refine suggestion

Author: Centri3

clippy_lints/src/methods/inefficient_pow.rs

@@ -1,4 +1,6 @@
-use clippy_utils::{diagnostics::span_lint_and_sugg, is_from_proc_macro, source::snippet_opt};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_from_proc_macro;
+use clippy_utils::source::snippet_opt;
 use rustc_ast::{LitIntType, LitKind};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
@@ -29,14 +31,20 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, recv:
             LitIntType::Unsigned(int) => int.name_str(),
             LitIntType::Unsuffixed => "",
         };
+        // `lhs * 1` is useless
+        let rhs = if power_used == 1 {
+            arg_snippet.to_string()
+        } else {
+            format!("({arg_snippet} * {power_used})")
+        };
 
         span_lint_and_sugg(
             cx,
             INEFFICIENT_POW,
             expr.span,
             "inefficient `.pow()`",
             "use `<<` instead",
-            format!("1{suffix} << ({arg_snippet} * {power_used})"),
+            format!("1{suffix} << {rhs}"),
             Applicability::MaybeIncorrect,
         );
     }

tests/ui/inefficient_pow.fixed

@@ -13,10 +13,10 @@
 extern crate proc_macros;
 
 fn main() {
-    _ = 1i32 << (1 * 1);
-    _ = 1i32 << (0 * 1);
-    _ = 1i32 << (3 * 1);
-    _ = 1i32 << (100 * 1);
+    _ = 1i32 << 1;
+    _ = 1i32 << 0;
+    _ = 1i32 << 3;
+    _ = 1i32 << 100;
     _ = 1i32 << (3 * 2);
     _ = 1i32 << (3 * 5);
     _ = 1i32 << (3 * 6);

tests/ui/inefficient_pow.stderr

@@ -2,27 +2,27 @@ error: inefficient `.pow()`
   --> $DIR/inefficient_pow.rs:16:9
    |
 LL |     _ = 2i32.pow(1);
-   |         ^^^^^^^^^^^ help: use `<<` instead: `1i32 << (1 * 1)`
+   |         ^^^^^^^^^^^ help: use `<<` instead: `1i32 << 1`
    |
    = note: `-D clippy::inefficient-pow` implied by `-D warnings`
 
 error: inefficient `.pow()`
   --> $DIR/inefficient_pow.rs:17:9
    |
 LL |     _ = 2i32.pow(0);
-   |         ^^^^^^^^^^^ help: use `<<` instead: `1i32 << (0 * 1)`
+   |         ^^^^^^^^^^^ help: use `<<` instead: `1i32 << 0`
 
 error: inefficient `.pow()`
   --> $DIR/inefficient_pow.rs:18:9
    |
 LL |     _ = 2i32.pow(3);
-   |         ^^^^^^^^^^^ help: use `<<` instead: `1i32 << (3 * 1)`
+   |         ^^^^^^^^^^^ help: use `<<` instead: `1i32 << 3`
 
 error: inefficient `.pow()`
   --> $DIR/inefficient_pow.rs:19:9
    |
 LL |     _ = 2i32.pow(100);
-   |         ^^^^^^^^^^^^^ help: use `<<` instead: `1i32 << (100 * 1)`
+   |         ^^^^^^^^^^^^^ help: use `<<` instead: `1i32 << 100`
 
 error: inefficient `.pow()`
   --> $DIR/inefficient_pow.rs:20:9