Auto merge of rust-lang#10309 - c410-f3r:arith, r=giraffate

[arithmetic_side_effects] Fix rust-lang#10252

Fix rust-lang#10252

At least for integers, shifts are already handled by the compiler.

----

changelog: [`arithmetic_side_effects`]: No longer lints on right or left shifts with constant integers, as the compiler warns about them.
[rust-lang#10309](rust-lang/rust-clippy#10309)
<!-- changelog_checked-->

Author: bors

clippy_lints/src/operators/arithmetic_side_effects.rs

@@ -143,6 +143,10 @@ impl ArithmeticSideEffects {
             return;
         }
         let has_valid_op = if Self::is_integral(lhs_ty) && Self::is_integral(rhs_ty) {
+            if let hir::BinOpKind::Shl | hir::BinOpKind::Shr = op.node {
+                // At least for integers, shifts are already handled by the CTFE
+                return;
+            }
             let (actual_lhs, lhs_ref_counter) = peel_hir_expr_refs(lhs);
             let (actual_rhs, rhs_ref_counter) = peel_hir_expr_refs(rhs);
             match (
@@ -151,10 +155,13 @@ impl ArithmeticSideEffects {
             ) {
                 (None, None) => false,
                 (None, Some(n)) | (Some(n), None) => match (&op.node, n) {
-                    (hir::BinOpKind::Div | hir::BinOpKind::Rem, 0) => false,
+                    // 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,
+                    // Addition or subtracting zeros is always a no-op
                     (hir::BinOpKind::Add | hir::BinOpKind::Sub, 0)
-                    | (hir::BinOpKind::Div | hir::BinOpKind::Rem, _)
-                    | (hir::BinOpKind::Mul, 0 | 1) => true,
+                    // Multiplication by 1 or 0 will never overflow
+                    | (hir::BinOpKind::Mul, 0 | 1)
+                    => true,
                     _ => false,
                 },
                 (Some(_), Some(_)) => {

tests/ui/arithmetic_side_effects.rs

@@ -45,24 +45,32 @@ impl_arith!(
     Div, Custom, Custom, div;
     Mul, Custom, Custom, mul;
     Rem, Custom, Custom, rem;
+    Shl, Custom, Custom, shl;
+    Shr, Custom, Custom, shr;
     Sub, Custom, Custom, sub;
 
     Add, Custom, &Custom, add;
     Div, Custom, &Custom, div;
     Mul, Custom, &Custom, mul;
     Rem, Custom, &Custom, rem;
+    Shl, Custom, &Custom, shl;
+    Shr, Custom, &Custom, shr;
     Sub, Custom, &Custom, sub;
 
     Add, &Custom, Custom, add;
     Div, &Custom, Custom, div;
     Mul, &Custom, Custom, mul;
     Rem, &Custom, Custom, rem;
+    Shl, &Custom, Custom, shl;
+    Shr, &Custom, Custom, shr;
     Sub, &Custom, Custom, sub;
 
     Add, &Custom, &Custom, add;
     Div, &Custom, &Custom, div;
     Mul, &Custom, &Custom, mul;
     Rem, &Custom, &Custom, rem;
+    Shl, &Custom, &Custom, shl;
+    Shr, &Custom, &Custom, shr;
     Sub, &Custom, &Custom, sub;
 );
 
@@ -71,24 +79,32 @@ impl_assign_arith!(
     DivAssign, Custom, Custom, div_assign;
     MulAssign, Custom, Custom, mul_assign;
     RemAssign, Custom, Custom, rem_assign;
+    ShlAssign, Custom, Custom, shl_assign;
+    ShrAssign, Custom, Custom, shr_assign;
     SubAssign, Custom, Custom, sub_assign;
 
     AddAssign, Custom, &Custom, add_assign;
     DivAssign, Custom, &Custom, div_assign;
     MulAssign, Custom, &Custom, mul_assign;
     RemAssign, Custom, &Custom, rem_assign;
+    ShlAssign, Custom, &Custom, shl_assign;
+    ShrAssign, Custom, &Custom, shr_assign;
     SubAssign, Custom, &Custom, sub_assign;
 
     AddAssign, &Custom, Custom, add_assign;
     DivAssign, &Custom, Custom, div_assign;
     MulAssign, &Custom, Custom, mul_assign;
     RemAssign, &Custom, Custom, rem_assign;
+    ShlAssign, &Custom, Custom, shl_assign;
+    ShrAssign, &Custom, Custom, shr_assign;
     SubAssign, &Custom, Custom, sub_assign;
 
     AddAssign, &Custom, &Custom, add_assign;
     DivAssign, &Custom, &Custom, div_assign;
     MulAssign, &Custom, &Custom, mul_assign;
     RemAssign, &Custom, &Custom, rem_assign;
+    ShlAssign, &Custom, &Custom, shl_assign;
+    ShrAssign, &Custom, &Custom, shr_assign;
     SubAssign, &Custom, &Custom, sub_assign;
 );
 
@@ -297,6 +313,10 @@ pub fn unknown_ops_or_runtime_ops_that_can_overflow() {
     _custom %= &Custom;
     _custom *= Custom;
     _custom *= &Custom;
+    _custom >>= Custom;
+    _custom >>= &Custom;
+    _custom <<= Custom;
+    _custom <<= &Custom;
     _custom += -Custom;
     _custom += &-Custom;
     _custom -= -Custom;
@@ -307,6 +327,10 @@ pub fn unknown_ops_or_runtime_ops_that_can_overflow() {
     _custom %= &-Custom;
     _custom *= -Custom;
     _custom *= &-Custom;
+    _custom >>= -Custom;
+    _custom >>= &-Custom;
+    _custom <<= -Custom;
+    _custom <<= &-Custom;
 
     // Binary
     _n = _n + 1;
@@ -347,6 +371,10 @@ pub fn unknown_ops_or_runtime_ops_that_can_overflow() {
     _custom = Custom + &Custom;
     _custom = &Custom + Custom;
     _custom = &Custom + &Custom;
+    _custom = _custom >> _custom;
+    _custom = _custom >> &_custom;
+    _custom = Custom << _custom;
+    _custom = &Custom << _custom;
 
     // Unary
     _n = -_n;