rust-clippy/src/approx_const.rs

65 lines
2.1 KiB
Rust
Raw Normal View History

2015-05-04 10:01:34 +00:00
use rustc::plugin::Registry;
use rustc::lint::*;
use rustc::middle::const_eval::lookup_const_by_id;
use rustc::middle::def::*;
use syntax::ast::*;
use syntax::ast_util::{is_comparison_binop, binop_to_string};
use syntax::ptr::P;
use syntax::codemap::Span;
use std::f64::consts as f64;
2015-07-26 14:53:11 +00:00
use utils::span_lint;
2015-05-04 10:01:34 +00:00
declare_lint! {
pub APPROX_CONSTANT,
Warn,
"Warn if a user writes an approximate known constant in their code"
}
const KNOWN_CONSTS : &'static [(f64, &'static str)] = &[(f64::E, "E"), (f64::FRAC_1_PI, "FRAC_1_PI"),
(f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2"), (f64::FRAC_2_PI, "FRAC_2_PI"),
(f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI"), (f64::FRAC_PI_2, "FRAC_PI_2"), (f64::FRAC_PI_3, "FRAC_PI_3"),
(f64::FRAC_PI_4, "FRAC_PI_4"), (f64::FRAC_PI_6, "FRAC_PI_6"), (f64::FRAC_PI_8, "FRAC_PI_8"),
(f64::LN_10, "LN_10"), (f64::LN_2, "LN_2"), (f64::LOG10_E, "LOG10_E"), (f64::LOG2_E, "LOG2_E"),
(f64::PI, "PI"), (f64::SQRT_2, "SQRT_2")];
const EPSILON_DIVISOR : f64 = 8192f64; //TODO: test to find a good value
#[derive(Copy,Clone)]
pub struct ApproxConstant;
impl LintPass for ApproxConstant {
fn get_lints(&self) -> LintArray {
lint_array!(APPROX_CONSTANT)
}
fn check_expr(&mut self, cx: &Context, e: &Expr) {
if let &ExprLit(ref lit) = &e.node {
check_lit(cx, lit, e.span);
}
}
}
fn check_lit(cx: &Context, lit: &Lit, span: Span) {
match &lit.node {
&LitFloat(ref str, TyF32) => check_known_consts(cx, span, str, "f32"),
&LitFloat(ref str, TyF64) => check_known_consts(cx, span, str, "f64"),
&LitFloatUnsuffixed(ref str) => check_known_consts(cx, span, str, "f{32, 64}"),
_ => ()
}
}
fn check_known_consts(cx: &Context, span: Span, str: &str, module: &str) {
if let Ok(value) = str.parse::<f64>() {
for &(constant, name) in KNOWN_CONSTS {
if within_epsilon(constant, value) {
2015-07-26 14:53:11 +00:00
span_lint(cx, APPROX_CONSTANT, span, &format!(
2015-05-04 10:01:34 +00:00
"Approximate value of {}::{} found, consider using it directly.", module, &name));
}
}
}
}
fn within_epsilon(target: f64, value: f64) -> bool {
f64::abs(value - target) < f64::abs((if target > value { target } else { value })) / EPSILON_DIVISOR
}