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Auto merge of #5185 - krishna-veerareddy:issue-5160-lossy-float-literal, r=flip1995

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Lint lossy whole number float literals

changelog: Extend `excessive_precision` to lint lossy whole number float literals

Fixes #5160
This commit is contained in:
bors 2020-02-17 09:18:25 +00:00
commit 74f5e348fa
6 changed files with 181 additions and 82 deletions
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127
clippy_lints/src/excessive_precision.rs
View file

@ -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.
///
@ -24,15 +22,15 @@ declare_clippy_lint! {
///
/// ```rust
/// // Bad
/// let v: f32 = 0.123_456_789_9;
/// println!("{}", v); // 0.123_456_789
/// let a: f32 = 0.123_456_789_9; // 0.123_456_789
/// let b: f32 = 16_777_217.0; // 16_777_216.0
///
/// // Good
/// let v: f64 = 0.123_456_789_9;
/// println!("{}", v); // 0.123_456_789_9
/// let a: f64 = 0.123_456_789_9;
/// let b: f64 = 16_777_216.0;
/// ```
pub EXCESSIVE_PRECISION,
style,
correctness,
"excessive precision for float literal"
}
@ -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::<f32>().map(|f| formatter.format(f)),
FloatTy::F64 => sym_str.parse::<f64>().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<String> {
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::<f32>().map(|f| formatter.format(f)),
FloatTy::F64 => sym_str.parse::<f64>().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::<f32>().unwrap().fract() == 0.0,
FloatTy::F64 => sym_str.parse::<f64>().unwrap().fract() == 0.0,
}
}
#[must_use]

2
clippy_lints/src/lib.rs
View file

@ -1386,7 +1386,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&enum_variants::MODULE_INCEPTION),
LintId::of(&eq_op::OP_REF),
LintId::of(&eta_reduction::REDUNDANT_CLOSURE),
LintId::of(&excessive_precision::EXCESSIVE_PRECISION),
LintId::of(&formatting::SUSPICIOUS_ASSIGNMENT_FORMATTING),
LintId::of(&formatting::SUSPICIOUS_ELSE_FORMATTING),
LintId::of(&formatting::SUSPICIOUS_UNARY_OP_FORMATTING),
@ -1567,6 +1566,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&enum_clike::ENUM_CLIKE_UNPORTABLE_VARIANT),
LintId::of(&eq_op::EQ_OP),
LintId::of(&erasing_op::ERASING_OP),
LintId::of(&excessive_precision::EXCESSIVE_PRECISION),
LintId::of(&formatting::POSSIBLE_MISSING_COMMA),
LintId::of(&functions::NOT_UNSAFE_PTR_ARG_DEREF),
LintId::of(&indexing_slicing::OUT_OF_BOUNDS_INDEXING),

2
src/lintlist/mod.rs
View file

@ -492,7 +492,7 @@ pub const ALL_LINTS: [Lint; 355] = [
},
Lint {
name: "excessive_precision",
group: "style",
group: "correctness",
desc: "excessive precision for float literal",
deprecation: None,
module: "excessive_precision",

32
tests/ui/excessive_precision.fixed
View file

@ -12,12 +12,12 @@ fn main() {
const GOOD64_SM: f32 = 0.000_000_000_000_000_1;
const GOOD64_DOT: f32 = 10_000_000_000_000_000.0;
const BAD32_1: f32 = 0.123_456_79;
const BAD32_1: f32 = 0.123_456_79_f32;
const BAD32_2: f32 = 0.123_456_79;
const BAD32_3: f32 = 0.1;
const BAD32_EDGE: f32 = 1.000_001;
const BAD64_1: f64 = 0.123_456_789_012_345_66;
const BAD64_1: f64 = 0.123_456_789_012_345_66_f64;
const BAD64_2: f64 = 0.123_456_789_012_345_66;
const BAD64_3: f64 = 0.1;
@ -34,11 +34,11 @@ fn main() {
let good64_inf = 0.123_456_789_012;
let bad32: f32 = 1.123_456_8;
let bad32_suf: f32 = 1.123_456_8;
let bad32_inf = 1.123_456_8;
let bad32_suf: f32 = 1.123_456_8_f32;
let bad32_inf = 1.123_456_8_f32;
let bad64: f64 = 0.123_456_789_012_345_66;
let bad64_suf: f64 = 0.123_456_789_012_345_66;
let bad64_suf: f64 = 0.123_456_789_012_345_66_f64;
let bad64_inf = 0.123_456_789_012_345_66;
// Vectors
@ -60,4 +60,26 @@ fn main() {
// issue #2840
let num = 0.000_000_000_01e-10f64;
// Lossy whole-number float literals
let _: f32 = 16_777_216.0;
let _: f32 = 16_777_220.0;
let _: f32 = 16_777_220.0;
let _: f32 = 16_777_220.0;
let _ = 16_777_220.0_f32;
let _: f32 = -16_777_220.0;
let _: f64 = 9_007_199_254_740_992.0;
let _: f64 = 9_007_199_254_740_992.0;
let _: f64 = 9_007_199_254_740_992.0;
let _ = 9_007_199_254_740_992.0_f64;
let _: f64 = -9_007_199_254_740_992.0;
// Lossless whole number float literals
let _: f32 = 16_777_216.0;
let _: f32 = 16_777_218.0;
let _: f32 = 16_777_220.0;
let _: f32 = -16_777_216.0;
let _: f32 = -16_777_220.0;
let _: f64 = 9_007_199_254_740_992.0;
let _: f64 = -9_007_199_254_740_992.0;
}

22
tests/ui/excessive_precision.rs
View file

@ -60,4 +60,26 @@ fn main() {
// issue #2840
let num = 0.000_000_000_01e-10f64;
// Lossy whole-number float literals
let _: f32 = 16_777_217.0;
let _: f32 = 16_777_219.0;
let _: f32 = 16_777_219.;
let _: f32 = 16_777_219.000;
let _ = 16_777_219f32;
let _: f32 = -16_777_219.0;
let _: f64 = 9_007_199_254_740_993.0;
let _: f64 = 9_007_199_254_740_993.;
let _: f64 = 9_007_199_254_740_993.000;
let _ = 9_007_199_254_740_993f64;
let _: f64 = -9_007_199_254_740_993.0;
// Lossless whole number float literals
let _: f32 = 16_777_216.0;
let _: f32 = 16_777_218.0;
let _: f32 = 16_777_220.0;
let _: f32 = -16_777_216.0;
let _: f32 = -16_777_220.0;
let _: f64 = 9_007_199_254_740_992.0;
let _: f64 = -9_007_199_254_740_992.0;
}

78
tests/ui/excessive_precision.stderr
View file

@ -2,7 +2,7 @@ error: float has excessive precision
--> $DIR/excessive_precision.rs:15:26
|
LL | const BAD32_1: f32 = 0.123_456_789_f32;
| ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_79`
| ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_79_f32`
|
= note: `-D clippy::excessive-precision` implied by `-D warnings`
@ -28,7 +28,7 @@ error: float has excessive precision
--> $DIR/excessive_precision.rs:20:26
|
LL | const BAD64_1: f64 = 0.123_456_789_012_345_67f64;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66_f64`
error: float has excessive precision
--> $DIR/excessive_precision.rs:21:26
@ -58,13 +58,13 @@ error: float has excessive precision
--> $DIR/excessive_precision.rs:37:26
|
LL | let bad32_suf: f32 = 1.123_456_789_f32;
| ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8`
| ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8_f32`
error: float has excessive precision
--> $DIR/excessive_precision.rs:38:21
|
LL | let bad32_inf = 1.123_456_789_f32;
| ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8`
| ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8_f32`
error: float has excessive precision
--> $DIR/excessive_precision.rs:40:22
@ -76,7 +76,7 @@ error: float has excessive precision
--> $DIR/excessive_precision.rs:41:26
|
LL | let bad64_suf: f64 = 0.123_456_789_012_345_67f64;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66_f64`
error: float has excessive precision
--> $DIR/excessive_precision.rs:42:21
@ -108,5 +108,71 @@ error: float has excessive precision
LL | let bad_bige32: f32 = 1.123_456_788_888E-10;
| ^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8E-10`
error: aborting due to 18 previous errors
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:65:18
|
LL | let _: f32 = 16_777_217.0;
| ^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_216.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:66:18
|
LL | let _: f32 = 16_777_219.0;
| ^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:67:18
|
LL | let _: f32 = 16_777_219.;
| ^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:68:18
|
LL | let _: f32 = 16_777_219.000;
| ^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:69:13
|
LL | let _ = 16_777_219f32;
| ^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0_f32`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:70:19
|
LL | let _: f32 = -16_777_219.0;
| ^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:71:18
|
LL | let _: f64 = 9_007_199_254_740_993.0;
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:72:18
|
LL | let _: f64 = 9_007_199_254_740_993.;
| ^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:73:18
|
LL | let _: f64 = 9_007_199_254_740_993.000;
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:74:13
|
LL | let _ = 9_007_199_254_740_993f64;
| ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0_f64`
error: literal cannot be represented as the underlying type without loss of precision
--> $DIR/excessive_precision.rs:75:19
|
LL | let _: f64 = -9_007_199_254_740_993.0;
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
error: aborting due to 29 previous errors