1 use crate::utils::span_lint_and_sugg;
2 use crate::utils::sugg::format_numeric_literal;
3 use if_chain::if_chain;
5 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
7 use rustc::{declare_lint_pass, declare_tool_lint};
8 use rustc_errors::Applicability;
13 use syntax_pos::symbol::Symbol;
15 declare_clippy_lint! {
16 /// **What it does:** Checks for float literals with a precision greater
17 /// than that supported by the underlying type
19 /// **Why is this bad?** Rust will truncate the literal silently.
21 /// **Known problems:** None.
27 /// let v: f32 = 0.123_456_789_9;
28 /// println!("{}", v); // 0.123_456_789
31 /// let v: f64 = 0.123_456_789_9;
32 /// println!("{}", v); // 0.123_456_789_9
34 pub EXCESSIVE_PRECISION,
36 "excessive precision for float literal"
39 declare_lint_pass!(ExcessivePrecision => [EXCESSIVE_PRECISION]);
41 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExcessivePrecision {
42 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
44 let ty = cx.tables.expr_ty(expr);
45 if let ty::Float(fty) = ty.kind;
46 if let hir::ExprKind::Lit(ref lit) = expr.kind;
47 if let LitKind::Float(sym, _) = lit.node;
48 if let Some(sugg) = Self::check(sym, fty);
54 "float has excessive precision",
55 "consider changing the type or truncating it to",
57 Applicability::MachineApplicable,
64 impl ExcessivePrecision {
65 // None if nothing to lint, Some(suggestion) if lint necessary
67 fn check(sym: Symbol, fty: FloatTy) -> Option<String> {
68 let max = max_digits(fty);
69 let sym_str = sym.as_str();
70 if dot_zero_exclusion(&sym_str) {
73 // Try to bail out if the float is for sure fine.
74 // If its within the 2 decimal digits of being out of precision we
75 // check if the parsed representation is the same as the string
76 // since we'll need the truncated string anyway.
77 let digits = count_digits(&sym_str);
78 if digits > max as usize {
79 let formatter = FloatFormat::new(&sym_str);
81 FloatTy::F32 => sym_str.parse::<f32>().map(|f| formatter.format(f)),
82 FloatTy::F64 => sym_str.parse::<f64>().map(|f| formatter.format(f)),
84 // We know this will parse since we are in LatePass
90 Some(format_numeric_literal(&s, None, true))
98 /// Should we exclude the float because it has a `.0` or `.` suffix
99 /// Ex `1_000_000_000.0`
100 /// Ex `1_000_000_000.`
102 fn dot_zero_exclusion(s: &str) -> bool {
103 s.split('.').nth(1).map_or(false, |after_dec| {
104 let mut decpart = after_dec.chars().take_while(|c| *c != 'e' || *c != 'E');
106 match decpart.next() {
107 Some('0') => decpart.count() == 0,
115 fn max_digits(fty: FloatTy) -> u32 {
117 FloatTy::F32 => f32::DIGITS,
118 FloatTy::F64 => f64::DIGITS,
122 /// Counts the digits excluding leading zeros
124 fn count_digits(s: &str) -> usize {
125 // Note that s does not contain the f32/64 suffix, and underscores have been stripped
127 .filter(|c| *c != '-' && *c != '.')
128 .take_while(|c| *c != 'e' && *c != 'E')
129 .fold(0, |count, c| {
131 if c == '0' && count == 0 {
146 fn new(s: &str) -> Self {
148 .find_map(|x| match x {
149 'e' => Some(Self::LowerExp),
150 'E' => Some(Self::UpperExp),
153 .unwrap_or(Self::Normal)
155 fn format<T>(&self, f: T) -> String
157 T: fmt::UpperExp + fmt::LowerExp + fmt::Display,
160 Self::LowerExp => format!("{:e}", f),
161 Self::UpperExp => format!("{:E}", f),
162 Self::Normal => format!("{}", f),