clippy_lints/src/zero_div_zero.rs

   1 use crate::consts::{constant_simple, Constant};
   2 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use rustc::{declare_lint, lint_array};
   4 use if_chain::if_chain;
   5 use rustc::hir::*;
   6 use crate::utils::span_help_and_lint;
   7
   8 /// **What it does:** Checks for `0.0 / 0.0`.
   9 ///
  10 /// **Why is this bad?** It's less readable than `std::f32::NAN` or
  11 /// `std::f64::NAN`.
  12 ///
  13 /// **Known problems:** None.
  14 ///
  15 /// **Example:**
  16 /// ```rust
  17 /// 0.0f32 / 0.0
  18 /// ```
  19 declare_clippy_lint! {
  20     pub ZERO_DIVIDED_BY_ZERO,
  21     complexity,
  22     "usage of `0.0 / 0.0` to obtain NaN instead of std::f32::NaN or std::f64::NaN"
  23 }
  24
  25 pub struct Pass;
  26
  27 impl LintPass for Pass {
  28     fn get_lints(&self) -> LintArray {
  29         lint_array!(ZERO_DIVIDED_BY_ZERO)
  30     }
  31 }
  32
  33 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  34     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  35         // check for instances of 0.0/0.0
  36         if_chain! {
  37             if let ExprKind::Binary(ref op, ref left, ref right) = expr.node;
  38             if let BinOpKind::Div = op.node;
  39             // TODO - constant_simple does not fold many operations involving floats.
  40             // That's probably fine for this lint - it's pretty unlikely that someone would
  41             // do something like 0.0/(2.0 - 2.0), but it would be nice to warn on that case too.
  42             if let Some(lhs_value) = constant_simple(cx, cx.tables, left);
  43             if let Some(rhs_value) = constant_simple(cx, cx.tables, right);
  44             if Constant::F32(0.0) == lhs_value || Constant::F64(0.0) == lhs_value;
  45             if Constant::F32(0.0) == rhs_value || Constant::F64(0.0) == rhs_value;
  46             then {
  47                 // since we're about to suggest a use of std::f32::NaN or std::f64::NaN,
  48                 // match the precision of the literals that are given.
  49                 let float_type = match (lhs_value, rhs_value) {
  50                     (Constant::F64(_), _)
  51                     | (_, Constant::F64(_)) => "f64",
  52                     _ => "f32"
  53                 };
  54                 span_help_and_lint(
  55                     cx,
  56                     ZERO_DIVIDED_BY_ZERO,
  57                     expr.span,
  58                     "constant division of 0.0 with 0.0 will always result in NaN",
  59                     &format!(
  60                         "Consider using `std::{}::NAN` if you would like a constant representing NaN",
  61                         float_type,
  62                     ),
  63                 );
  64             }
  65         }
  66     }
  67 }