clippy_lints/src/zero_div_zero.rs

   1 use crate::consts::{constant_simple, Constant};
   2 use crate::utils::span_lint_and_help;
   3 use if_chain::if_chain;
   4 use rustc_hir::{BinOpKind, Expr, ExprKind};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for `0.0 / 0.0`.
  10     ///
  11     /// **Why is this bad?** It's less readable than `f32::NAN` or `f64::NAN`.
  12     ///
  13     /// **Known problems:** None.
  14     ///
  15     /// **Example:**
  16     /// ```rust
  17     /// 0.0f32 / 0.0;
  18     /// ```
  19     pub ZERO_DIVIDED_BY_ZERO,
  20     complexity,
  21     "usage of `0.0 / 0.0` to obtain NaN instead of `f32::NAN` or `f64::NAN`"
  22 }
  23
  24 declare_lint_pass!(ZeroDiv => [ZERO_DIVIDED_BY_ZERO]);
  25
  26 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ZeroDiv {
  27     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  28         // check for instances of 0.0/0.0
  29         if_chain! {
  30             if let ExprKind::Binary(ref op, ref left, ref right) = expr.kind;
  31             if let BinOpKind::Div = op.node;
  32             // TODO - constant_simple does not fold many operations involving floats.
  33             // That's probably fine for this lint - it's pretty unlikely that someone would
  34             // do something like 0.0/(2.0 - 2.0), but it would be nice to warn on that case too.
  35             if let Some(lhs_value) = constant_simple(cx, cx.tables, left);
  36             if let Some(rhs_value) = constant_simple(cx, cx.tables, right);
  37             if Constant::F32(0.0) == lhs_value || Constant::F64(0.0) == lhs_value;
  38             if Constant::F32(0.0) == rhs_value || Constant::F64(0.0) == rhs_value;
  39             then {
  40                 // since we're about to suggest a use of f32::NAN or f64::NAN,
  41                 // match the precision of the literals that are given.
  42                 let float_type = match (lhs_value, rhs_value) {
  43                     (Constant::F64(_), _)
  44                     | (_, Constant::F64(_)) => "f64",
  45                     _ => "f32"
  46                 };
  47                 span_lint_and_help(
  48                     cx,
  49                     ZERO_DIVIDED_BY_ZERO,
  50                     expr.span,
  51                     "constant division of `0.0` with `0.0` will always result in NaN",
  52                     &format!(
  53                         "Consider using `{}::NAN` if you would like a constant representing NaN",
  54                         float_type,
  55                     ),
  56                 );
  57             }
  58         }
  59     }
  60 }