| use crate::utils::span_lint; |
| use rustc::hir::*; |
| use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| use rustc::{declare_tool_lint, lint_array}; |
| use std::f64::consts as f64; |
| use syntax::ast::{FloatTy, Lit, LitKind}; |
| use syntax::symbol; |
| |
| declare_clippy_lint! { |
| /// **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. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// let x = 3.14; |
| /// ``` |
| pub APPROX_CONSTANT, |
| correctness, |
| "the approximate of a known float constant (in `std::fXX::consts`)" |
| } |
| |
| // Tuples are of the form (constant, name, min_digits) |
| const KNOWN_CONSTS: &[(f64, &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), |
| ]; |
| |
| #[derive(Copy, Clone)] |
| pub struct Pass; |
| |
| impl LintPass for Pass { |
| fn get_lints(&self) -> LintArray { |
| lint_array!(APPROX_CONSTANT) |
| } |
| |
| fn name(&self) -> &'static str { |
| "ApproxConstant" |
| } |
| } |
| |
| impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { |
| fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) { |
| if let ExprKind::Lit(lit) = &e.node { |
| check_lit(cx, lit, e); |
| } |
| } |
| } |
| |
| fn check_lit(cx: &LateContext<'_, '_>, lit: &Lit, e: &Expr) { |
| match lit.node { |
| LitKind::Float(s, FloatTy::F32) => check_known_consts(cx, e, s, "f32"), |
| LitKind::Float(s, FloatTy::F64) => check_known_consts(cx, e, s, "f64"), |
| LitKind::FloatUnsuffixed(s) => check_known_consts(cx, e, s, "f{32, 64}"), |
| _ => (), |
| } |
| } |
| |
| 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) { |
| span_lint( |
| cx, |
| APPROX_CONSTANT, |
| e.span, |
| &format!( |
| "approximate value of `{}::consts::{}` found. \ |
| Consider using it directly", |
| module, &name |
| ), |
| ); |
| return; |
| } |
| } |
| } |
| } |
| |
| /// 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) |
| } |
| } |