| use crate::utils::span_lint; |
| use rustc_ast::ast::{FloatTy, LitFloatType, LitKind}; |
| use rustc_hir::{Expr, ExprKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::symbol; |
| use std::f64::consts as f64; |
| |
| 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:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// let x = 3.14; |
| /// let y = 1_f64 / x; |
| /// ``` |
| /// Use predefined constants instead: |
| /// ```rust |
| /// let x = std::f32::consts::PI; |
| /// let y = std::f64::consts::FRAC_1_PI; |
| /// ``` |
| 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); 18] = [ |
| (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::LOG2_10, "LOG2_10", 5), |
| (f64::LOG10_2, "LOG10_2", 5), |
| (f64::PI, "PI", 3), |
| (f64::SQRT_2, "SQRT_2", 5), |
| ]; |
| |
| declare_lint_pass!(ApproxConstant => [APPROX_CONSTANT]); |
| |
| impl<'tcx> LateLintPass<'tcx> for ApproxConstant { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) { |
| if let ExprKind::Lit(lit) = &e.kind { |
| check_lit(cx, &lit.node, e); |
| } |
| } |
| } |
| |
| fn check_lit(cx: &LateContext<'_>, lit: &LitKind, e: &Expr<'_>) { |
| match *lit { |
| LitKind::Float(s, LitFloatType::Suffixed(fty)) => match fty { |
| FloatTy::F32 => check_known_consts(cx, e, s, "f32"), |
| FloatTy::F64 => check_known_consts(cx, e, s, "f64"), |
| }, |
| LitKind::Float(s, LitFloatType::Unsuffixed) => 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`. |
| #[must_use] |
| fn is_approx_const(constant: f64, value: &str, min_digits: usize) -> bool { |
| if value.len() <= min_digits { |
| false |
| } else if constant.to_string().starts_with(value) { |
| // The value is a truncated constant |
| true |
| } else { |
| let round_const = format!("{:.*}", value.len() - 2, constant); |
| value == round_const |
| } |
| } |