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

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