clippy_lints/src/zero_div_zero.rs

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