diff --git a/clippy_lints/src/excessive_precision.rs b/clippy_lints/src/excessive_precision.rs index 2b63d5e9088e..70b44dee6619 100644 --- a/clippy_lints/src/excessive_precision.rs +++ b/clippy_lints/src/excessive_precision.rs @@ -6,17 +6,15 @@ use rustc_errors::Applicability; use rustc_hir as hir; use rustc_lint::{LateContext, LateLintPass}; use rustc_session::{declare_lint_pass, declare_tool_lint}; -use rustc_span::symbol::Symbol; -use std::f32; -use std::f64; -use std::fmt; +use std::{f32, f64, fmt}; use syntax::ast::*; declare_clippy_lint! { /// **What it does:** Checks for float literals with a precision greater - /// than that supported by the underlying type + /// than that supported by the underlying type. /// - /// **Why is this bad?** Rust will truncate the literal silently. + /// **Why is this bad?** Rust will silently lose precision during conversion + /// to a float. /// /// **Known problems:** None. /// @@ -44,71 +42,62 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExcessivePrecision { let ty = cx.tables.expr_ty(expr); if let ty::Float(fty) = ty.kind; if let hir::ExprKind::Lit(ref lit) = expr.kind; - if let LitKind::Float(sym, _) = lit.node; - if let Some(sugg) = Self::check(sym, fty); + if let LitKind::Float(sym, lit_float_ty) = lit.node; then { - span_lint_and_sugg( - cx, - EXCESSIVE_PRECISION, - expr.span, - "float has excessive precision", - "consider changing the type or truncating it to", - sugg, - Applicability::MachineApplicable, - ); + let sym_str = sym.as_str(); + let formatter = FloatFormat::new(&sym_str); + // Try to bail out if the float is for sure fine. + // If its within the 2 decimal digits of being out of precision we + // check if the parsed representation is the same as the string + // since we'll need the truncated string anyway. + let digits = count_digits(&sym_str); + let max = max_digits(fty); + let float_str = match fty { + FloatTy::F32 => sym_str.parse::().map(|f| formatter.format(f)), + FloatTy::F64 => sym_str.parse::().map(|f| formatter.format(f)), + }.unwrap(); + let type_suffix = match lit_float_ty { + LitFloatType::Suffixed(FloatTy::F32) => Some("f32"), + LitFloatType::Suffixed(FloatTy::F64) => Some("f64"), + _ => None + }; + + if is_whole_number(&sym_str, fty) { + // Normalize the literal by stripping the fractional portion + if sym_str.split('.').next().unwrap() != float_str { + span_lint_and_sugg( + cx, + EXCESSIVE_PRECISION, + expr.span, + "literal cannot be represented as the underlying type without loss of precision", + "consider changing the type or replacing it with", + format_numeric_literal(format!("{}.0", float_str).as_str(), type_suffix, true), + Applicability::MachineApplicable, + ); + } + } else if digits > max as usize && sym_str != float_str { + span_lint_and_sugg( + cx, + EXCESSIVE_PRECISION, + expr.span, + "float has excessive precision", + "consider changing the type or truncating it to", + format_numeric_literal(&float_str, type_suffix, true), + Applicability::MachineApplicable, + ); + } } } } } -impl ExcessivePrecision { - // None if nothing to lint, Some(suggestion) if lint necessary - #[must_use] - fn check(sym: Symbol, fty: FloatTy) -> Option { - let max = max_digits(fty); - let sym_str = sym.as_str(); - if dot_zero_exclusion(&sym_str) { - return None; - } - // Try to bail out if the float is for sure fine. - // If its within the 2 decimal digits of being out of precision we - // check if the parsed representation is the same as the string - // since we'll need the truncated string anyway. - let digits = count_digits(&sym_str); - if digits > max as usize { - let formatter = FloatFormat::new(&sym_str); - let sr = match fty { - FloatTy::F32 => sym_str.parse::().map(|f| formatter.format(f)), - FloatTy::F64 => sym_str.parse::().map(|f| formatter.format(f)), - }; - // We know this will parse since we are in LatePass - let s = sr.unwrap(); - - if sym_str == s { - None - } else { - Some(format_numeric_literal(&s, None, true)) - } - } else { - None - } - } -} - -/// Should we exclude the float because it has a `.0` or `.` suffix -/// Ex `1_000_000_000.0` -/// Ex `1_000_000_000.` +// Checks whether a float literal is a whole number #[must_use] -fn dot_zero_exclusion(s: &str) -> bool { - s.split('.').nth(1).map_or(false, |after_dec| { - let mut decpart = after_dec.chars().take_while(|c| *c != 'e' || *c != 'E'); - - match decpart.next() { - Some('0') => decpart.count() == 0, - Some(_) => false, - None => true, - } - }) +fn is_whole_number(sym_str: &str, fty: FloatTy) -> bool { + match fty { + FloatTy::F32 => sym_str.parse::().unwrap().fract() == 0.0, + FloatTy::F64 => sym_str.parse::().unwrap().fract() == 0.0, + } } #[must_use]