59 lines
2.4 KiB
Rust
59 lines
2.4 KiB
Rust
use consts::{Constant, constant_simple, FloatWidth};
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use rustc::lint::*;
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use rustc_front::hir::*;
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use utils::span_help_and_lint;
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/// `ZeroDivZeroPass` is a pass that checks for a binary expression that consists
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/// `of 0.0/0.0`, which is always `NaN`. It is more clear to replace instances of
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/// `0.0/0.0` with `std::f32::NaN` or `std::f64::NaN`, depending on the precision.
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pub struct ZeroDivZeroPass;
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/// **What it does:** This lint checks for `0.0 / 0.0`.
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///
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/// **Why is this bad?** It's less readable than `std::f32::NAN` or `std::f64::NAN`
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///
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/// **Known problems:** None
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///
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/// **Example** `0.0f32 / 0.0`
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declare_lint! {
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pub ZERO_DIVIDED_BY_ZERO,
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Warn,
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"usage of `0.0 / 0.0` to obtain NaN instead of std::f32::NaN or std::f64::NaN"
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}
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impl LintPass for ZeroDivZeroPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(ZERO_DIVIDED_BY_ZERO)
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}
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}
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impl LateLintPass for ZeroDivZeroPass {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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// check for instances of 0.0/0.0
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if_let_chain! {
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[
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let ExprBinary(ref op, ref left, ref right) = expr.node,
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let BinOp_::BiDiv = op.node,
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// TODO - constant_simple does not fold many operations involving floats.
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// That's probably fine for this lint - it's pretty unlikely that someone would
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// do something like 0.0/(2.0 - 2.0), but it would be nice to warn on that case too.
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let Some(Constant::Float(ref lhs_value, lhs_width)) = constant_simple(left),
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let Some(Constant::Float(ref rhs_value, rhs_width)) = constant_simple(right),
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let Some(0.0) = lhs_value.parse().ok(),
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let Some(0.0) = rhs_value.parse().ok()
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],
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{
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// since we're about to suggest a use of std::f32::NaN or std::f64::NaN,
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// match the precision of the literals that are given.
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let float_type = match (lhs_width, rhs_width) {
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(FloatWidth::F64, _)
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| (_, FloatWidth::F64) => "f64",
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_ => "f32"
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};
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span_help_and_lint(cx, ZERO_DIVIDED_BY_ZERO, expr.span,
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"constant division of 0.0 with 0.0 will always result in NaN",
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&format!("Consider using `std::{}::NAN` if you would like a constant representing NaN", float_type));
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}
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}
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}
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}
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