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use clippy_utils::consts::{constant_simple, Constant};
use clippy_utils::diagnostics::span_lint_and_help;
use if_chain::if_chain;
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for `0.0 / 0.0`.
///
/// ### Why is this bad?
/// It's less readable than `f32::NAN` or `f64::NAN`.
///
/// ### Example
/// ```rust
/// let nan = 0.0f32 / 0.0;
/// ```
///
/// Use instead:
/// ```rust
/// let nan = f32::NAN;
/// ```
#[clippy::version = "pre 1.29.0"]
pub ZERO_DIVIDED_BY_ZERO,
complexity,
"usage of `0.0 / 0.0` to obtain NaN instead of `f32::NAN` or `f64::NAN`"
}
declare_lint_pass!(ZeroDiv => [ZERO_DIVIDED_BY_ZERO]);
impl<'tcx> LateLintPass<'tcx> for ZeroDiv {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
// check for instances of 0.0/0.0
if_chain! {
if let ExprKind::Binary(ref op, left, right) = expr.kind;
if op.node == BinOpKind::Div;
// TODO - constant_simple does not fold many operations involving floats.
// That's probably fine for this lint - it's pretty unlikely that someone would
// do something like 0.0/(2.0 - 2.0), but it would be nice to warn on that case too.
if let Some(lhs_value) = constant_simple(cx, cx.typeck_results(), left);
if let Some(rhs_value) = constant_simple(cx, cx.typeck_results(), right);
if Constant::F32(0.0) == lhs_value || Constant::F64(0.0) == lhs_value;
if Constant::F32(0.0) == rhs_value || Constant::F64(0.0) == rhs_value;
then {
// since we're about to suggest a use of f32::NAN or f64::NAN,
// match the precision of the literals that are given.
let float_type = match (lhs_value, rhs_value) {
(Constant::F64(_), _)
| (_, Constant::F64(_)) => "f64",
_ => "f32"
};
span_lint_and_help(
cx,
ZERO_DIVIDED_BY_ZERO,
expr.span,
"constant division of `0.0` with `0.0` will always result in NaN",
None,
&format!(
"consider using `{}::NAN` if you would like a constant representing NaN",
float_type,
),
);
}
}
}
}
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