src/tools/clippy/clippy_lints/src/zero_div_zero.rs

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