1 use clippy_utils::diagnostics::span_lint_and_help;
2 use if_chain::if_chain;
3 use rustc_hir as hir;
4 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
6
7 declare_clippy_lint! {
8 /// ### What it does
9 /// Checks for division of integers
10 ///
11 /// ### Why is this bad?
12 /// When outside of some very specific algorithms,
13 /// integer division is very often a mistake because it discards the
14 /// remainder.
15 ///
16 /// ### Example
17 /// ```rust
18 /// // Bad
19 /// let x = 3 / 2;
20 /// println!("{}", x);
21 ///
22 /// // Good
23 /// let x = 3f32 / 2f32;
24 /// println!("{}", x);
25 /// ```
26 pub INTEGER_DIVISION,
27 restriction,
28 "integer division may cause loss of precision"
29 }
30
31 declare_lint_pass!(IntegerDivision => [INTEGER_DIVISION]);
32
33 impl<'tcx> LateLintPass<'tcx> for IntegerDivision {
check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>)34 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
35 if is_integer_division(cx, expr) {
36 span_lint_and_help(
37 cx,
38 INTEGER_DIVISION,
39 expr.span,
40 "integer division",
41 None,
42 "division of integers may cause loss of precision. consider using floats",
43 );
44 }
45 }
46 }
47
is_integer_division<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) -> bool48 fn is_integer_division<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) -> bool {
49 if_chain! {
50 if let hir::ExprKind::Binary(binop, left, right) = &expr.kind;
51 if binop.node == hir::BinOpKind::Div;
52 then {
53 let (left_ty, right_ty) = (cx.typeck_results().expr_ty(left), cx.typeck_results().expr_ty(right));
54 return left_ty.is_integral() && right_ty.is_integral();
55 }
56 }
57
58 false
59 }
60