New lint: manual_midpoint

Author: samueltardieu

CHANGELOG.md

@@ -5718,6 +5718,7 @@ Released 2018-09-13
 [`manual_main_separator_str`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_main_separator_str
 [`manual_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_map
 [`manual_memcpy`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_memcpy
+[`manual_midpoint`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_midpoint
 [`manual_next_back`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_next_back
 [`manual_non_exhaustive`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive
 [`manual_ok_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_ok_or

clippy_lints/src/declared_lints.rs

@@ -593,6 +593,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::operators::IMPOSSIBLE_COMPARISONS_INFO,
     crate::operators::INEFFECTIVE_BIT_MASK_INFO,
     crate::operators::INTEGER_DIVISION_INFO,
+    crate::operators::MANUAL_MIDPOINT_INFO,
     crate::operators::MISREFACTORED_ASSIGN_OP_INFO,
     crate::operators::MODULO_ARITHMETIC_INFO,
     crate::operators::MODULO_ONE_INFO,

clippy_lints/src/operators/manual_midpoint.rs

@@ -0,0 +1,45 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::msrvs::{self, Msrv};
+use clippy_utils::sugg::Sugg;
+use clippy_utils::{is_floating_point_integer_literal, is_integer_literal};
+use rustc_ast::BinOpKind;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+
+use super::MANUAL_MIDPOINT;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    op: BinOpKind,
+    left: &'tcx Expr<'_>,
+    right: &'tcx Expr<'_>,
+    msrv: &Msrv,
+) {
+    if msrv.meets(msrvs::UINT_FLOAT_MIDPOINT)
+        && op == BinOpKind::Div
+        && (is_integer_literal(right, 2) || is_floating_point_integer_literal(right, 2))
+        && let ExprKind::Binary(left_op, ll_expr, lr_expr) = left.kind
+        && left_op.node == BinOpKind::Add
+        && let left_ty = cx.typeck_results().expr_ty_adjusted(ll_expr)
+        && let right_ty = cx.typeck_results().expr_ty_adjusted(lr_expr)
+        && left_ty == right_ty
+        && matches!(left_ty.kind(), ty::Uint(_) | ty::Float(_))
+    {
+        let mut app = Applicability::MachineApplicable;
+        let left_sugg = Sugg::hir_with_applicability(cx, ll_expr, "..", &mut app);
+        let right_sugg = Sugg::hir_with_applicability(cx, lr_expr, "..", &mut app);
+        let sugg = format!("{left_ty}::midpoint({left_sugg}, {right_sugg})");
+        span_lint_and_sugg(
+            cx,
+            MANUAL_MIDPOINT,
+            expr.span,
+            "manual implementation of `midpoint`",
+            "use instead",
+            sugg,
+            app,
+        );
+    }
+}

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_midpoint;
 mod misrefactored_assign_op;
 mod modulo_arithmetic;
 mod modulo_one;
@@ -24,6 +25,7 @@ mod verbose_bit_mask;
 pub(crate) mod arithmetic_side_effects;
 
 use clippy_config::Conf;
+use clippy_utils::msrvs::Msrv;
 use rustc_hir::{Body, Expr, ExprKind, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::impl_lint_pass;
@@ -837,17 +839,43 @@ declare_clippy_lint! {
     "explicit self-assignment"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for manual implementation of `midpoint`.
+    ///
+    /// ### Why is this bad?
+    /// Using `(x + y) / 2` might cause an overflow on the intermediate
+    /// addition result.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// # let a: u32 = 0;
+    /// let c = (a + 10) / 2;
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// # let a: u32 = 0;
+    /// let c = u32::midpoint(a, 10);
+    /// ```
+    #[clippy::version = "1.85.0"]
+    pub MANUAL_MIDPOINT,
+    correctness,
+    "manual implementation of `midpoint`"
+}
+
 pub struct Operators {
     arithmetic_context: numeric_arithmetic::Context,
     verbose_bit_mask_threshold: u64,
     modulo_arithmetic_allow_comparison_to_zero: bool,
+    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,
+            msrv: conf.msrv.clone(),
         }
     }
 }
@@ -879,6 +907,7 @@ impl_lint_pass!(Operators => [
     NEEDLESS_BITWISE_BOOL,
     PTR_EQ,
     SELF_ASSIGNMENT,
+    MANUAL_MIDPOINT,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Operators {
@@ -896,6 +925,7 @@ 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);
                     ptr_eq::check(cx, e, op.node, lhs, rhs);
+                    manual_midpoint::check(cx, e, op.node, lhs, rhs, &self.msrv);
                 }
                 self.arithmetic_context.check_binary(cx, e, op.node, lhs, rhs);
                 bit_mask::check(cx, e, op.node, lhs, rhs);
@@ -946,6 +976,8 @@ impl<'tcx> LateLintPass<'tcx> for Operators {
     fn check_body_post(&mut self, cx: &LateContext<'tcx>, b: &Body<'_>) {
         self.arithmetic_context.body_post(cx, b);
     }
+
+    extract_msrv_attr!(LateContext);
 }
 
 fn macro_with_not_op(e: &Expr<'_>) -> bool {

clippy_utils/src/msrvs.rs

@@ -18,6 +18,7 @@ macro_rules! msrv_aliases {
 
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
+    1,85,0 { UINT_FLOAT_MIDPOINT }
     1,83,0 { CONST_EXTERN_FN, CONST_FLOAT_BITS_CONV, CONST_FLOAT_CLASSIFY }
     1,82,0 { IS_NONE_OR, REPEAT_N, RAW_REF_OP }
     1,81,0 { LINT_REASONS_STABILIZATION, ERROR_IN_CORE }

tests/ui/manual_midpoint.fixed

@@ -0,0 +1,23 @@
+#![warn(clippy::manual_midpoint)]
+
+macro_rules! mac {
+    ($a: expr, $b: expr) => {{ ($a + $b) / 2 }};
+}
+
+fn main() {
+    let a: u32 = 10;
+    let _ = u32::midpoint(a, 5); //~ ERROR: manual implementation of `midpoint`
+
+    let f: f32 = 10.0;
+    let _ = f32::midpoint(f, 5.0); //~ ERROR: manual implementation of `midpoint`
+
+    // Do not lint if a literal is not present
+    let _ = (f + 5.0) / (1.0 + 1.0);
+
+    // Do not lint on signed integer types
+    let i: i32 = 10;
+    let _ = (i + 5) / 2;
+
+    // Do not lint
+    let _ = mac!(10, 20);
+}

tests/ui/manual_midpoint.rs

@@ -0,0 +1,23 @@
+#![warn(clippy::manual_midpoint)]
+
+macro_rules! mac {
+    ($a: expr, $b: expr) => {{ ($a + $b) / 2 }};
+}
+
+fn main() {
+    let a: u32 = 10;
+    let _ = (a + 5) / 2; //~ ERROR: manual implementation of `midpoint`
+
+    let f: f32 = 10.0;
+    let _ = (f + 5.0) / 2.0; //~ ERROR: manual implementation of `midpoint`
+
+    // Do not lint if a literal is not present
+    let _ = (f + 5.0) / (1.0 + 1.0);
+
+    // Do not lint on signed integer types
+    let i: i32 = 10;
+    let _ = (i + 5) / 2;
+
+    // Do not lint
+    let _ = mac!(10, 20);
+}

tests/ui/manual_midpoint.stderr

@@ -0,0 +1,17 @@
+error: manual implementation of `midpoint`
+  --> tests/ui/manual_midpoint.rs:9:13
+   |
+LL |     let _ = (a + 5) / 2;
+   |             ^^^^^^^^^^^ help: use instead: `u32::midpoint(a, 5)`
+   |
+   = note: `-D clippy::manual-midpoint` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::manual_midpoint)]`
+
+error: manual implementation of `midpoint`
+  --> tests/ui/manual_midpoint.rs:12:13
+   |
+LL |     let _ = (f + 5.0) / 2.0;
+   |             ^^^^^^^^^^^^^^^ help: use instead: `f32::midpoint(f, 5.0)`
+
+error: aborting due to 2 previous errors
+

tests/ui/option_if_let_else.fixed

@@ -4,6 +4,7 @@
     clippy::equatable_if_let,
     clippy::let_unit_value,
     clippy::redundant_locals,
+    clippy::manual_midpoint,
     clippy::manual_unwrap_or_default,
     clippy::manual_unwrap_or
 )]

tests/ui/option_if_let_else.rs

@@ -4,6 +4,7 @@
     clippy::equatable_if_let,
     clippy::let_unit_value,
     clippy::redundant_locals,
+    clippy::manual_midpoint,
     clippy::manual_unwrap_or_default,
     clippy::manual_unwrap_or
 )]