clippy_lints/src/zero_div_zero.rs

   1 use consts::{constant_simple, Constant, 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_chain! {
  35             if let ExprBinary(ref op, ref left, ref right) = expr.node;
  36             if 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             if let Some(Constant::Float(ref lhs_value, lhs_width)) = constant_simple(cx, left);
  41             if let Some(Constant::Float(ref rhs_value, rhs_width)) = constant_simple(cx, right);
  42             if Ok(0.0) == lhs_value.parse();
  43             if Ok(0.0) == rhs_value.parse();
  44             then {
  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(
  53                     cx,
  54                     ZERO_DIVIDED_BY_ZERO,
  55                     expr.span,
  56                     "constant division of 0.0 with 0.0 will always result in NaN",
  57                     &format!(
  58                         "Consider using `std::{}::NAN` if you would like a constant representing NaN",
  59                         float_type,
  60                     ),
  61                 );
  62             }
  63         }
  64     }
  65 }