New lint: manual_is_multiple_of

Author: samueltardieu

CHANGELOG.md

@@ -5803,6 +5803,7 @@ Released 2018-09-13
 [`manual_is_ascii_check`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_ascii_check
 [`manual_is_finite`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_finite
 [`manual_is_infinite`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_infinite
+[`manual_is_multiple_of`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_multiple_of
 [`manual_is_power_of_two`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_power_of_two
 [`manual_is_variant_and`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_variant_and
 [`manual_let_else`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_let_else
@@ -6372,6 +6373,7 @@ Released 2018-09-13
 [`max-struct-bools`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-struct-bools
 [`max-suggested-slice-pattern-length`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-suggested-slice-pattern-length
 [`max-trait-bounds`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-trait-bounds
+[`min-and-mask-size`]: https://doc.rust-lang.org/clippy/lint_configuration.html#min-and-mask-size
 [`min-ident-chars-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#min-ident-chars-threshold
 [`missing-docs-in-crate-items`]: https://doc.rust-lang.org/clippy/lint_configuration.html#missing-docs-in-crate-items
 [`module-item-order-groupings`]: https://doc.rust-lang.org/clippy/lint_configuration.html#module-item-order-groupings

book/src/lint_configuration.md

@@ -724,6 +724,16 @@ The maximum number of bounds a trait can have to be linted
 * [`type_repetition_in_bounds`](https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds)
 
 
+## `min-and-mask-size`
+The smallest number of bits masked with `&` which will be replaced by `.is_multiple_of()`.
+
+**Default Value:** `3`
+
+---
+**Affected lints:**
+* [`manual_is_multiple_of`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_multiple_of)
+
+
 ## `min-ident-chars-threshold`
 Minimum chars an ident can have, anything below or equal to this will be linted.
 

clippy_config/src/conf.rs

@@ -603,6 +603,9 @@ define_Conf! {
     /// The maximum number of bounds a trait can have to be linted
     #[lints(type_repetition_in_bounds)]
     max_trait_bounds: u64 = 3,
+    /// The smallest number of bits masked with `&` which will be replaced by `.is_multiple_of()`.
+    #[lints(manual_is_multiple_of)]
+    min_and_mask_size: u8 = 3,
     /// Minimum chars an ident can have, anything below or equal to this will be linted.
     #[lints(min_ident_chars)]
     min_ident_chars_threshold: u64 = 1,

clippy_lints/src/casts/cast_sign_loss.rs

@@ -167,7 +167,7 @@ fn pow_call_result_sign(cx: &LateContext<'_>, base: &Expr<'_>, exponent: &Expr<'
 
     // Rust's integer pow() functions take an unsigned exponent.
     let exponent_val = get_const_unsigned_int_eval(cx, exponent, None);
-    let exponent_is_even = exponent_val.map(|val| val % 2 == 0);
+    let exponent_is_even = exponent_val.map(|val| val.is_multiple_of(2));
 
     match (base_sign, exponent_is_even) {
         // Non-negative bases always return non-negative results, ignoring overflow.

clippy_lints/src/declared_lints.rs

@@ -610,6 +610,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::operators::IMPOSSIBLE_COMPARISONS_INFO,
     crate::operators::INEFFECTIVE_BIT_MASK_INFO,
     crate::operators::INTEGER_DIVISION_INFO,
+    crate::operators::MANUAL_IS_MULTIPLE_OF_INFO,
     crate::operators::MANUAL_MIDPOINT_INFO,
     crate::operators::MISREFACTORED_ASSIGN_OP_INFO,
     crate::operators::MODULO_ARITHMETIC_INFO,

clippy_lints/src/operators/manual_is_multiple_of.rs

@@ -0,0 +1,120 @@
+use clippy_utils::consts::{integer_const, is_zero_integer_const};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::msrvs::{self, Msrv};
+use clippy_utils::source::SpanRangeExt;
+use clippy_utils::sugg::Sugg;
+use rustc_ast::BinOpKind;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+
+use super::MANUAL_IS_MULTIPLE_OF;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &Expr<'_>,
+    op: BinOpKind,
+    lhs: &'tcx Expr<'tcx>,
+    rhs: &'tcx Expr<'tcx>,
+    min_and_mask_size: u8,
+    msrv: Msrv,
+) {
+    if msrv.meets(cx, msrvs::UNSIGNED_IS_MULTIPLE_OF)
+        && let Some(operand) = uint_compare_to_zero(cx, op, lhs, rhs)
+        && let ExprKind::Binary(lhs_op, lhs_left, lhs_right) = operand.kind
+    {
+        let mut app = Applicability::MachineApplicable;
+        let (dividend, divisor) = if lhs_op.node == BinOpKind::Rem {
+            (
+                lhs_left,
+                Sugg::hir_with_applicability(cx, lhs_right, "_", &mut app).into_string(),
+            )
+        } else if lhs_op.node == BinOpKind::BitAnd {
+            let min_divisor = 1u128 << min_and_mask_size;
+            if let Some(divisor) = is_all_ones(cx, lhs_right, min_divisor, &mut app) {
+                (lhs_left, divisor)
+            } else if let Some(divisor) = is_all_ones(cx, lhs_left, min_divisor, &mut app) {
+                (lhs_right, divisor)
+            } else {
+                return;
+            }
+        } else {
+            return;
+        };
+        span_lint_and_sugg(
+            cx,
+            MANUAL_IS_MULTIPLE_OF,
+            expr.span,
+            "manual implementation of `.is_multiple_of()`",
+            "replace with",
+            format!(
+                "{}{}.is_multiple_of({divisor})",
+                if op == BinOpKind::Eq { "" } else { "!" },
+                Sugg::hir_with_applicability(cx, dividend, "_", &mut app).maybe_paren()
+            ),
+            app,
+        );
+    }
+}
+
+// If we have a `x == 0`, `x != 0` or `x > 0` (or the reverted ones), return the non-zero operand
+fn uint_compare_to_zero<'tcx>(
+    cx: &LateContext<'tcx>,
+    op: BinOpKind,
+    lhs: &'tcx Expr<'tcx>,
+    rhs: &'tcx Expr<'tcx>,
+) -> Option<&'tcx Expr<'tcx>> {
+    let operand = if matches!(lhs.kind, ExprKind::Binary(..))
+        && matches!(op, BinOpKind::Eq | BinOpKind::Ne | BinOpKind::Gt)
+        && is_zero_integer_const(cx, rhs)
+    {
+        lhs
+    } else if matches!(rhs.kind, ExprKind::Binary(..))
+        && matches!(op, BinOpKind::Eq | BinOpKind::Ne | BinOpKind::Lt)
+        && is_zero_integer_const(cx, lhs)
+    {
+        rhs
+    } else {
+        return None;
+    };
+
+    matches!(cx.typeck_results().expr_ty_adjusted(operand).kind(), ty::Uint(_)).then_some(operand)
+}
+
+/// If `expr` is provably made of all ones, return the representation of `expr+1` if it is no
+/// smaller than `min_divisor`. This will catch expressions of the following forms:
+/// - `(1 << A) - 1` where `A` is a constant
+/// - integer literals — if it uses hexadecimal, the return value will as well
+///
+/// The function will not attempt to evaluate non-literal constant expressions, as those may depend
+/// on conditional compilation.
+fn is_all_ones<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'tcx>,
+    min_divisor: u128,
+    app: &mut Applicability,
+) -> Option<String> {
+    if let ExprKind::Binary(op, lhs, rhs) = expr.kind
+        && op.node == BinOpKind::Sub
+        && let ExprKind::Binary(op, lhs_left, lhs_right) = lhs.kind
+        && op.node == BinOpKind::Shl
+        && let Some(1) = integer_const(cx, lhs_left)
+        && let Some(1) = integer_const(cx, rhs)
+        && integer_const(cx, lhs_right).is_none_or(|v| 1 << v >= min_divisor)
+    {
+        Some(Sugg::hir_with_applicability(cx, lhs, "_", app).to_string())
+    } else if let Some(value) = integer_const(cx, expr)
+        && let Some(inc_value) = value.checked_add(1)
+        && inc_value.is_power_of_two()
+    {
+        let repr = if expr.span.check_source_text(cx, |s| s.starts_with("0x")) {
+            format!("{inc_value:#x}")
+        } else {
+            inc_value.to_string()
+        };
+        (inc_value >= min_divisor).then_some(repr)
+    } else {
+        None
+    }
+}

clippy_lints/src/operators/mod.rs

@@ -11,6 +11,7 @@ mod float_cmp;
 mod float_equality_without_abs;
 mod identity_op;
 mod integer_division;
+mod manual_is_multiple_of;
 mod manual_midpoint;
 mod misrefactored_assign_op;
 mod modulo_arithmetic;
@@ -830,18 +831,56 @@ declare_clippy_lint! {
     "manual implementation of `midpoint` which can overflow"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for manual implementation of `.is_multiple_of()` on
+    /// unsigned integer types.
+    ///
+    /// ### Why is this bad?
+    /// `a.is_multiple_of(b)` is a clearer way to check for divisibility
+    /// of `a` by `b`. This expression can never panic.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// # let (a, b) = (3u64, 4u64);
+    /// if a % b == 0 {
+    ///     println!("{a} is divisible by {b}");
+    /// }
+    /// if a & 3 != 0 {
+    ///     println!("{a} is not properly aligned");
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// # let (a, b) = (3u64, 4u64);
+    /// if a.is_multiple_of(b) {
+    ///     println!("{a} is divisible by {b}");
+    /// }
+    /// if !a.is_multiple_of(4) {
+    ///     println!("{a} is not properly aligned");
+    /// }
+    /// ```
+    #[clippy::version = "1.87.0"]
+    pub MANUAL_IS_MULTIPLE_OF,
+    complexity,
+    "manual implementation of `.is_multiple_of()`"
+}
+
 pub struct Operators {
     arithmetic_context: numeric_arithmetic::Context,
     verbose_bit_mask_threshold: u64,
     modulo_arithmetic_allow_comparison_to_zero: bool,
+    min_and_mask_size: u8,
     msrv: Msrv,
 }
+
 impl Operators {
     pub fn new(conf: &'static Conf) -> Self {
         Self {
             arithmetic_context: numeric_arithmetic::Context::default(),
             verbose_bit_mask_threshold: conf.verbose_bit_mask_threshold,
             modulo_arithmetic_allow_comparison_to_zero: conf.allow_comparison_to_zero,
+            min_and_mask_size: conf.min_and_mask_size,
             msrv: conf.msrv,
         }
     }
@@ -874,6 +913,7 @@ impl_lint_pass!(Operators => [
     NEEDLESS_BITWISE_BOOL,
     SELF_ASSIGNMENT,
     MANUAL_MIDPOINT,
+    MANUAL_IS_MULTIPLE_OF,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Operators {
@@ -891,6 +931,7 @@ impl<'tcx> LateLintPass<'tcx> for Operators {
                     identity_op::check(cx, e, op.node, lhs, rhs);
                     needless_bitwise_bool::check(cx, e, op.node, lhs, rhs);
                     manual_midpoint::check(cx, e, op.node, lhs, rhs, self.msrv);
+                    manual_is_multiple_of::check(cx, e, op.node, lhs, rhs, self.min_and_mask_size, self.msrv);
                 }
                 self.arithmetic_context.check_binary(cx, e, op.node, lhs, rhs);
                 bit_mask::check(cx, e, op.node, lhs, rhs);

clippy_utils/src/msrvs.rs

@@ -22,7 +22,7 @@ macro_rules! msrv_aliases {
 
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
-    1,87,0 { OS_STR_DISPLAY, INT_MIDPOINT }
+    1,87,0 { OS_STR_DISPLAY, INT_MIDPOINT, UNSIGNED_IS_MULTIPLE_OF }
     1,85,0 { UINT_FLOAT_MIDPOINT }
     1,84,0 { CONST_OPTION_AS_SLICE }
     1,83,0 { CONST_EXTERN_FN, CONST_FLOAT_BITS_CONV, CONST_FLOAT_CLASSIFY, CONST_MUT_REFS, CONST_UNWRAP }

tests/ui-toml/manual_is_multiple_of/greater-than-8-bits/clippy.toml

@@ -0,0 +1 @@
+min-and-mask-size = 9

tests/ui-toml/manual_is_multiple_of/greater-than-8-bits/manual_is_multiple_of.fixed

@@ -0,0 +1,8 @@
+#![warn(clippy::manual_is_multiple_of)]
+
+fn main() {}
+
+fn f(a: u64, b: u64) {
+    let _ = a & 0xff == 0;
+    let _ = a.is_multiple_of(0x200); //~ manual_is_multiple_of
+}