rust-clippy/src/approx_const.rs

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use rustc::lint::*;
use rustc_front::hir::*;
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use utils::span_lint;
use syntax::ast::Lit_::*;
use syntax::ast::Lit;
use syntax::ast::FloatTy::*;
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declare_lint! {
pub APPROX_CONSTANT,
Warn,
"the approximate of a known float constant (in `std::f64::consts` or `std::f32::consts`) \
is found; suggests to use the constant"
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}
// Tuples are of the form (name, lower_bound, upper_bound)
#[allow(approx_constant)]
const KNOWN_CONSTS : &'static [(&'static str, f64, f64)] = &[
("E", 2.7101, 2.7200),
("FRAC_1_PI", 0.31829, 0.31840),
("FRAC_1_SQRT_2", 0.7071, 0.7072),
("FRAC_2_PI", 0.6366, 0.6370),
("FRAC_2_SQRT_PI", 1.1283, 1.1284),
("FRAC_PI_2", 1.5707, 1.5708),
("FRAC_PI_3", 1.0471, 1.0472),
("FRAC_PI_4", 0.7853, 0.7854),
("FRAC_PI_6", 0.5235, 0.5236),
("FRAC_PI_8", 0.3926, 0.3927),
("LN_10", 2.302, 2.303),
("LN_2", 0.6931, 0.6932),
("LOG10_E", 0.4342, 0.4343),
("LOG2_E", 1.4426, 1.4427),
("PI", 3.140, 3.142),
("SQRT_2", 1.4142, 1.4143),
];
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#[derive(Copy,Clone)]
pub struct ApproxConstant;
impl LintPass for ApproxConstant {
fn get_lints(&self) -> LintArray {
lint_array!(APPROX_CONSTANT)
}
}
impl LateLintPass for ApproxConstant {
fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
if let &ExprLit(ref lit) = &e.node {
check_lit(cx, lit, e);
}
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}
}
fn check_lit(cx: &LateContext, lit: &Lit, e: &Expr) {
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match lit.node {
LitFloat(ref str, TyF32) => check_known_consts(cx, e, str, "f32"),
LitFloat(ref str, TyF64) => check_known_consts(cx, e, str, "f64"),
LitFloatUnsuffixed(ref str) =>
check_known_consts(cx, e, str, "f{32, 64}"),
_ => ()
}
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}
fn check_known_consts(cx: &LateContext, e: &Expr, s: &str, module: &str) {
if let Ok(value) = s.parse::<f64>() {
for &(name, lower_bound, upper_bound) in KNOWN_CONSTS {
if (value >= lower_bound) && (value < upper_bound) {
span_lint(cx, APPROX_CONSTANT, e.span, &format!(
"approximate value of `{}::{}` found. \
Consider using it directly", module, &name));
}
}
}
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}