[arithmetic_side_effects] Fix #11266

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()
@@ -233,24 +243,34 @@ impl ArithmeticSideEffects {
                 Self::literal_integer(cx, actual_lhs),
                 Self::literal_integer(cx, actual_rhs),
             ) {
-                (None, None) => false,
-                (None, Some(n)) => match (&op, n) {
-                    // Division and module are always valid if applied to non-zero integers
-                    (hir::BinOpKind::Div | hir::BinOpKind::Rem, local_n) if local_n != 0 => true,
-                    // Adding or subtracting zeros is always a no-op
-                    (hir::BinOpKind::Add | hir::BinOpKind::Sub, 0)
-                    // Multiplication by 1 or 0 will never overflow
-                    | (hir::BinOpKind::Mul, 0 | 1)
-                    => true,
-                    _ => false,
+                (None, None) => Self::is_const_param(lhs) && Self::is_const_param(rhs),
+                (None, Some(n)) => {
+                    if Self::is_const_param(lhs) {
+                        return;
+                    }
+                    match (&op, n) {
+                        // Division and module are always valid if applied to non-zero integers
+                        (hir::BinOpKind::Div | hir::BinOpKind::Rem, local_n) if local_n != 0 => true,
+                        // Adding or subtracting zeros is always a no-op
+                        (hir::BinOpKind::Add | hir::BinOpKind::Sub, 0)
+                        // Multiplication by 1 or 0 will never overflow
+                        | (hir::BinOpKind::Mul, 0 | 1)
+                        => true,
+                        _ => false,
+                    }
                 },
-                (Some(n), None) => match (&op, n) {
-                    // Adding or subtracting zeros is always a no-op
-                    (hir::BinOpKind::Add | hir::BinOpKind::Sub, 0)
-                    // Multiplication by 1 or 0 will never overflow
-                    | (hir::BinOpKind::Mul, 0 | 1)
-                    => true,
-                    _ => false,
+                (Some(n), None) => {
+                    if Self::is_const_param(rhs) {
+                        return;
+                    }
+                    match (&op, n) {
+                        // Adding or subtracting zeros is always a no-op
+                        (hir::BinOpKind::Add | hir::BinOpKind::Sub, 0)
+                        // Multiplication by 1 or 0 will never overflow
+                        | (hir::BinOpKind::Mul, 0 | 1)
+                        => true,
+                        _ => false,
+                    }
                 },
                 (Some(_), Some(_)) => {
                     matches!((lhs_ref_counter, rhs_ref_counter), (0, 0))

tests/ui/arithmetic_side_effects.rs

@@ -521,6 +521,19 @@ pub fn issue_11393() {
     example_rem(x, maybe_zero);
 }
 
+pub fn issue_11266_literal<const N: usize>() {
+    let _ = N + 1;
+    let _ = 1 + N;
+    let _ = N + N;
+}
+
+pub fn issue_11266_runtime<const N: usize>() {
+    fn runtime_number() -> usize {
+        1
+    }
+    let _ = N + runtime_number();
+}
+
 pub fn issue_12318() {
     use core::ops::{AddAssign, DivAssign, MulAssign, RemAssign, SubAssign};
     let mut one: i32 = 1;

tests/ui/arithmetic_side_effects.stderr

@@ -716,16 +716,22 @@ 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:534:13
+   |
+LL |     let _ = N + runtime_number();
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: arithmetic operation that can potentially result in unexpected side-effects
+  --> tests/ui/arithmetic_side_effects.rs:540:5
    |
 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:544:5
    |
 LL |     one.sub_assign(1);
    |     ^^^^^^^^^^^^^^^^^
 
-error: aborting due to 121 previous errors
+error: aborting due to 122 previous errors