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| 1 | +use rustc::hir; |
| 2 | +use rustc::lint::*; |
| 3 | +use rustc::ty::TypeVariants; |
| 4 | +use std::f32; |
| 5 | +use std::f64; |
| 6 | +use std::fmt; |
| 7 | +use syntax::ast::*; |
| 8 | +use syntax_pos::symbol::Symbol; |
| 9 | +use utils::span_lint_and_sugg; |
| 10 | + |
| 11 | +/// **What it does:** Checks for float literals with a precision greater |
| 12 | +/// than that supported by the underlying type |
| 13 | +/// |
| 14 | +/// **Why is this bad?** Rust will truncate the literal silently. |
| 15 | +/// |
| 16 | +/// **Known problems:** None. |
| 17 | +/// |
| 18 | +/// **Example:** |
| 19 | +/// |
| 20 | +/// ```rust |
| 21 | +/// // Bad |
| 22 | +/// Insert a short example of code that triggers the lint |
| 23 | +/// let v: f32 = 0.123_456_789_9; |
| 24 | +/// println!("{}", v); // 0.123_456_789 |
| 25 | +/// |
| 26 | +/// // Good |
| 27 | +/// Insert a short example of improved code that doesn't trigger the lint |
| 28 | +/// let v: f64 = 0.123_456_789_9; |
| 29 | +/// println!("{}", v); // 0.123_456_789_9 |
| 30 | +/// ``` |
| 31 | +declare_clippy_lint! { |
| 32 | + pub EXCESSIVE_PRECISION, |
| 33 | + style, |
| 34 | + "excessive precision for float literal" |
| 35 | +} |
| 36 | + |
| 37 | +pub struct ExcessivePrecision; |
| 38 | + |
| 39 | +impl LintPass for ExcessivePrecision { |
| 40 | + fn get_lints(&self) -> LintArray { |
| 41 | + lint_array!(EXCESSIVE_PRECISION) |
| 42 | + } |
| 43 | +} |
| 44 | + |
| 45 | +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExcessivePrecision { |
| 46 | + fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) { |
| 47 | + if_chain! { |
| 48 | + let ty = cx.tables.expr_ty(expr); |
| 49 | + if let TypeVariants::TyFloat(ref fty) = ty.sty; |
| 50 | + if let hir::ExprLit(ref lit) = expr.node; |
| 51 | + if let LitKind::Float(ref sym, _) | LitKind::FloatUnsuffixed(ref sym) = lit.node; |
| 52 | + if let Some(sugg) = self.check(sym, fty); |
| 53 | + then { |
| 54 | + span_lint_and_sugg( |
| 55 | + cx, |
| 56 | + EXCESSIVE_PRECISION, |
| 57 | + expr.span, |
| 58 | + "float has excessive precision", |
| 59 | + "consider changing the type or truncating it to", |
| 60 | + sugg, |
| 61 | + ); |
| 62 | + } |
| 63 | + } |
| 64 | + } |
| 65 | +} |
| 66 | + |
| 67 | +impl ExcessivePrecision { |
| 68 | + // None if nothing to lint, Some(suggestion) if lint neccessary |
| 69 | + fn check(&self, sym: &Symbol, fty: &FloatTy) -> Option<String> { |
| 70 | + let max = max_digits(fty); |
| 71 | + let sym_str = sym.as_str(); |
| 72 | + let formatter = FloatFormat::new(&sym_str); |
| 73 | + let digits = count_digits(&sym_str); |
| 74 | + // Try to bail out if the float is for sure fine. |
| 75 | + // If its within the 2 decimal digits of being out of precision we |
| 76 | + // check if the parsed representation is the same as the string |
| 77 | + // since we'll need the truncated string anyway. |
| 78 | + if digits > max as usize { |
| 79 | + let sr = match *fty { |
| 80 | + FloatTy::F32 => sym_str.parse::<f32>().map(|f| formatter.format(f)), |
| 81 | + FloatTy::F64 => sym_str.parse::<f64>().map(|f| formatter.format(f)), |
| 82 | + }; |
| 83 | + // We know this will parse since we are in LatePass |
| 84 | + let s = sr.unwrap(); |
| 85 | + |
| 86 | + if sym_str == s { |
| 87 | + None |
| 88 | + } else { |
| 89 | + Some(s) |
| 90 | + } |
| 91 | + } else { |
| 92 | + None |
| 93 | + } |
| 94 | + } |
| 95 | +} |
| 96 | + |
| 97 | +fn max_digits(fty: &FloatTy) -> u32 { |
| 98 | + match fty { |
| 99 | + FloatTy::F32 => f32::DIGITS, |
| 100 | + FloatTy::F64 => f64::DIGITS, |
| 101 | + } |
| 102 | +} |
| 103 | + |
| 104 | +fn count_digits(s: &str) -> usize { |
| 105 | + s.chars() |
| 106 | + .filter(|c| *c != '-' || *c != '.') |
| 107 | + .take_while(|c| *c != 'e' || *c != 'E') |
| 108 | + .fold(0, |count, c| { |
| 109 | + // leading zeros |
| 110 | + if c == '0' && count == 0 { |
| 111 | + count |
| 112 | + } else { |
| 113 | + count + 1 |
| 114 | + } |
| 115 | + }) |
| 116 | +} |
| 117 | + |
| 118 | +enum FloatFormat { |
| 119 | + LowerExp, |
| 120 | + UpperExp, |
| 121 | + Normal, |
| 122 | +} |
| 123 | +impl FloatFormat { |
| 124 | + fn new(s: &str) -> Self { |
| 125 | + s.chars() |
| 126 | + .find_map(|x| match x { |
| 127 | + 'e' => Some(FloatFormat::LowerExp), |
| 128 | + 'E' => Some(FloatFormat::UpperExp), |
| 129 | + _ => None, |
| 130 | + }) |
| 131 | + .unwrap_or(FloatFormat::Normal) |
| 132 | + } |
| 133 | + fn format<T>(&self, f: T) -> String |
| 134 | + where T: fmt::UpperExp + fmt::LowerExp + fmt::Display { |
| 135 | + match self { |
| 136 | + FloatFormat::LowerExp => format!("{:e}", f), |
| 137 | + FloatFormat::UpperExp => format!("{:E}", f), |
| 138 | + FloatFormat::Normal => format!("{}", f), |
| 139 | + } |
| 140 | + } |
| 141 | +} |
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