rust-clippy/clippy_lints/src/approx_const.rs

114 lines
4.7 KiB
Rust
Raw Normal View History

2015-05-04 10:01:34 +00:00
use rustc::lint::*;
use rustc::hir::*;
use std::f64::consts as f64;
2016-02-12 17:35:44 +00:00
use syntax::ast::{Lit, LitKind, FloatTy};
use syntax::symbol;
2016-02-24 16:38:57 +00:00
use utils::span_lint;
2015-05-04 10:01:34 +00:00
/// **What it does:** Checks for floating point literals that approximate
/// constants which are defined in
/// [`std::f32::consts`](https://doc.rust-lang.org/stable/std/f32/consts/#constants)
/// or
/// [`std::f64::consts`](https://doc.rust-lang.org/stable/std/f64/consts/#constants),
/// respectively, suggesting to use the predefined constant.
///
/// **Why is this bad?** Usually, the definition in the standard library is more
/// precise than what people come up with. If you find that your definition is
/// actually more precise, please [file a Rust
/// issue](https://github.com/rust-lang/rust/issues).
///
/// **Known problems:** If you happen to have a value that is within 1/8192 of a
/// known constant, but is not *and should not* be the same, this lint will
/// report your value anyway. We have not yet noticed any false positives in
/// code we tested clippy with (this includes servo), but YMMV.
///
2016-07-15 22:25:44 +00:00
/// **Example:**
/// ```rust
/// let x = 3.14;
/// ```
2015-05-04 10:01:34 +00:00
declare_lint! {
pub APPROX_CONSTANT,
Warn,
"the approximate of a known float constant (in `std::fXX::consts`)"
2015-05-04 10:01:34 +00:00
}
// Tuples are of the form (constant, name, min_digits)
2016-01-04 04:26:12 +00:00
const KNOWN_CONSTS: &'static [(f64, &'static str, usize)] = &[(f64::E, "E", 4),
(f64::FRAC_1_PI, "FRAC_1_PI", 4),
(f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2", 5),
(f64::FRAC_2_PI, "FRAC_2_PI", 5),
(f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI", 5),
(f64::FRAC_PI_2, "FRAC_PI_2", 5),
(f64::FRAC_PI_3, "FRAC_PI_3", 5),
(f64::FRAC_PI_4, "FRAC_PI_4", 5),
(f64::FRAC_PI_6, "FRAC_PI_6", 5),
(f64::FRAC_PI_8, "FRAC_PI_8", 5),
(f64::LN_10, "LN_10", 5),
(f64::LN_2, "LN_2", 5),
(f64::LOG10_E, "LOG10_E", 5),
(f64::LOG2_E, "LOG2_E", 5),
(f64::PI, "PI", 3),
(f64::SQRT_2, "SQRT_2", 5)];
2015-05-04 10:01:34 +00:00
#[derive(Copy,Clone)]
2016-06-10 14:17:20 +00:00
pub struct Pass;
2015-05-04 10:01:34 +00:00
2016-06-10 14:17:20 +00:00
impl LintPass for Pass {
2015-05-04 10:01:34 +00:00
fn get_lints(&self) -> LintArray {
lint_array!(APPROX_CONSTANT)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
2015-11-24 17:44:40 +00:00
if let ExprLit(ref lit) = e.node {
check_lit(cx, lit, e);
}
2015-05-04 10:01:34 +00:00
}
}
fn check_lit(cx: &LateContext, lit: &Lit, e: &Expr) {
2015-08-21 18:44:48 +00:00
match lit.node {
2016-02-12 17:35:44 +00:00
LitKind::Float(ref s, FloatTy::F32) => check_known_consts(cx, e, s, "f32"),
LitKind::Float(ref s, FloatTy::F64) => check_known_consts(cx, e, s, "f64"),
LitKind::FloatUnsuffixed(ref s) => check_known_consts(cx, e, s, "f{32, 64}"),
2016-01-04 04:26:12 +00:00
_ => (),
}
2015-05-04 10:01:34 +00:00
}
fn check_known_consts(cx: &LateContext, e: &Expr, s: &symbol::Symbol, module: &str) {
let s = s.as_str();
if s.parse::<f64>().is_ok() {
for &(constant, name, min_digits) in KNOWN_CONSTS {
if is_approx_const(constant, &s, min_digits) {
2016-01-04 04:26:12 +00:00
span_lint(cx,
APPROX_CONSTANT,
e.span,
&format!("approximate value of `{}::consts::{}` found. \
2016-12-21 08:45:24 +00:00
Consider using it directly",
module,
&name));
return;
}
}
}
2015-05-04 10:01:34 +00:00
}
/// Returns false if the number of significant figures in `value` are
/// less than `min_digits`; otherwise, returns true if `value` is equal
/// to `constant`, rounded to the number of digits present in `value`.
fn is_approx_const(constant: f64, value: &str, min_digits: usize) -> bool {
if value.len() <= min_digits {
false
} else {
let round_const = format!("{:.*}", value.len() - 2, constant);
let mut trunc_const = constant.to_string();
if trunc_const.len() > value.len() {
trunc_const.truncate(value.len());
}
(value == round_const) || (value == trunc_const)
}
}