mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-05 02:50:32 +00:00
132 lines
4.6 KiB
Rust
132 lines
4.6 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::msrvs::{self, Msrv};
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use rustc_ast::ast::{FloatTy, LitFloatType, LitKind};
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use rustc_hir::{Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_semver::RustcVersion;
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::symbol;
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use std::f64::consts as f64;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for floating point literals that approximate
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/// constants which are defined in
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/// [`std::f32::consts`](https://doc.rust-lang.org/stable/std/f32/consts/#constants)
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/// or
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/// [`std::f64::consts`](https://doc.rust-lang.org/stable/std/f64/consts/#constants),
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/// respectively, suggesting to use the predefined constant.
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///
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/// ### Why is this bad?
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/// Usually, the definition in the standard library is more
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/// precise than what people come up with. If you find that your definition is
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/// actually more precise, please [file a Rust
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/// issue](https://github.com/rust-lang/rust/issues).
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///
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/// ### Example
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/// ```rust
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/// let x = 3.14;
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/// let y = 1_f64 / x;
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/// ```
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/// Use instead:
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/// ```rust
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/// let x = std::f32::consts::PI;
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/// let y = std::f64::consts::FRAC_1_PI;
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub APPROX_CONSTANT,
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correctness,
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"the approximate of a known float constant (in `std::fXX::consts`)"
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}
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// Tuples are of the form (constant, name, min_digits, msrv)
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const KNOWN_CONSTS: [(f64, &str, usize, Option<RustcVersion>); 19] = [
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(f64::E, "E", 4, None),
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(f64::FRAC_1_PI, "FRAC_1_PI", 4, None),
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(f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2", 5, None),
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(f64::FRAC_2_PI, "FRAC_2_PI", 5, None),
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(f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI", 5, None),
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(f64::FRAC_PI_2, "FRAC_PI_2", 5, None),
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(f64::FRAC_PI_3, "FRAC_PI_3", 5, None),
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(f64::FRAC_PI_4, "FRAC_PI_4", 5, None),
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(f64::FRAC_PI_6, "FRAC_PI_6", 5, None),
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(f64::FRAC_PI_8, "FRAC_PI_8", 5, None),
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(f64::LN_2, "LN_2", 5, None),
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(f64::LN_10, "LN_10", 5, None),
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(f64::LOG2_10, "LOG2_10", 5, Some(msrvs::LOG2_10)),
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(f64::LOG2_E, "LOG2_E", 5, None),
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(f64::LOG10_2, "LOG10_2", 5, Some(msrvs::LOG10_2)),
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(f64::LOG10_E, "LOG10_E", 5, None),
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(f64::PI, "PI", 3, None),
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(f64::SQRT_2, "SQRT_2", 5, None),
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(f64::TAU, "TAU", 3, Some(msrvs::TAU)),
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];
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pub struct ApproxConstant {
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msrv: Msrv,
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}
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impl ApproxConstant {
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#[must_use]
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pub fn new(msrv: Msrv) -> Self {
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Self { msrv }
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}
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fn check_lit(&self, cx: &LateContext<'_>, lit: &LitKind, e: &Expr<'_>) {
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match *lit {
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LitKind::Float(s, LitFloatType::Suffixed(fty)) => match fty {
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FloatTy::F32 => self.check_known_consts(cx, e, s, "f32"),
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FloatTy::F64 => self.check_known_consts(cx, e, s, "f64"),
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},
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LitKind::Float(s, LitFloatType::Unsuffixed) => self.check_known_consts(cx, e, s, "f{32, 64}"),
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_ => (),
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}
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}
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fn check_known_consts(&self, cx: &LateContext<'_>, e: &Expr<'_>, s: symbol::Symbol, module: &str) {
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let s = s.as_str();
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if s.parse::<f64>().is_ok() {
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for &(constant, name, min_digits, msrv) in &KNOWN_CONSTS {
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if is_approx_const(constant, s, min_digits) && msrv.map_or(true, |msrv| self.msrv.meets(msrv)) {
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span_lint_and_help(
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cx,
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APPROX_CONSTANT,
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e.span,
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&format!("approximate value of `{module}::consts::{}` found", &name),
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None,
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"consider using the constant directly",
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);
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return;
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}
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}
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}
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}
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}
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impl_lint_pass!(ApproxConstant => [APPROX_CONSTANT]);
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impl<'tcx> LateLintPass<'tcx> for ApproxConstant {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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if let ExprKind::Lit(lit) = &e.kind {
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self.check_lit(cx, &lit.node, e);
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}
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}
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extract_msrv_attr!(LateContext);
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}
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/// Returns `false` if the number of significant figures in `value` are
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/// less than `min_digits`; otherwise, returns true if `value` is equal
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/// to `constant`, rounded to the number of digits present in `value`.
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#[must_use]
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fn is_approx_const(constant: f64, value: &str, min_digits: usize) -> bool {
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if value.len() <= min_digits {
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false
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} else if constant.to_string().starts_with(value) {
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// The value is a truncated constant
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true
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} else {
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let round_const = format!("{constant:.*}", value.len() - 2);
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value == round_const
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}
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}
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