[aritmetic_side_effects] Fix #11266

Author: c410-f3r

clippy_lints/src/operators/arithmetic_side_effects.rs

@@ -132,6 +132,16 @@ impl ArithmeticSideEffects {
         false
     }
 
+    /// For example, `fn foo<const N: usize>() -> i32 { N + 1 }`.
+    fn is_const_param(expr: &hir::Expr<'_>) -> bool {
+        if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
+            && let hir::def::Res::Def(hir::def::DefKind::ConstParam, _) = path.res
+        {
+            return true;
+        }
+        false
+    }
+
     // For example, 8i32 or &i64::MAX.
     fn is_integral(ty: Ty<'_>) -> bool {
         ty.peel_refs().is_integral()
@@ -197,6 +207,9 @@ impl ArithmeticSideEffects {
         lhs: &'tcx hir::Expr<'_>,
         rhs: &'tcx hir::Expr<'_>,
     ) {
+        if Self::is_const_param(lhs) || Self::is_const_param(rhs) {
+            return;
+        }
         if constant_simple(cx, cx.typeck_results(), expr).is_some() {
             return;
         }

tests/ui/arithmetic_side_effects.rs

@@ -521,6 +521,10 @@ pub fn issue_11393() {
     example_rem(x, maybe_zero);
 }
 
+pub fn issue_11266<const N: usize>() {
+    let _ = N + 1;
+}
+
 pub fn issue_12318() {
     use core::ops::{AddAssign, DivAssign, MulAssign, RemAssign, SubAssign};
     let mut one: i32 = 1;

tests/ui/arithmetic_side_effects.stderr

@@ -716,13 +716,13 @@ LL |         x % maybe_zero
    |         ^^^^^^^^^^^^^^
 
 error: arithmetic operation that can potentially result in unexpected side-effects
-  --> tests/ui/arithmetic_side_effects.rs:527:5
+  --> tests/ui/arithmetic_side_effects.rs:531:5
    |
 LL |     one.add_assign(1);
    |     ^^^^^^^^^^^^^^^^^
 
 error: arithmetic operation that can potentially result in unexpected side-effects
-  --> tests/ui/arithmetic_side_effects.rs:531:5
+  --> tests/ui/arithmetic_side_effects.rs:535:5
    |
 LL |     one.sub_assign(1);
    |     ^^^^^^^^^^^^^^^^^