rust-clippy/clippy_lints/src/literal_representation.rs
Andre Bogus cc622608db new lints around #[must_use] fns
`must_use_unit` lints unit-returning functions with a `#[must_use]`
attribute, suggesting to remove it.

`double_must_use` lints functions with a plain `#[must_use]`
attribute, but which return a type which is already `#[must_use]`,
so the attribute has no benefit.

`must_use_candidate` is a pedantic lint that lints functions and
methods that return some non-unit type that is not already
`#[must_use]` and suggests to add the annotation.
2019-10-14 12:09:04 +02:00

603 lines
22 KiB
Rust

//! Lints concerned with the grouping of digits with underscores in integral or
//! floating-point literal expressions.
use crate::utils::{in_macro, snippet_opt, span_lint_and_sugg};
use if_chain::if_chain;
use rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintContext, LintPass};
use rustc::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
use rustc_errors::Applicability;
use syntax::ast::*;
use syntax_pos;
declare_clippy_lint! {
/// **What it does:** Warns if a long integral or floating-point constant does
/// not contain underscores.
///
/// **Why is this bad?** Reading long numbers is difficult without separators.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let x: u64 = 61864918973511;
/// ```
pub UNREADABLE_LITERAL,
style,
"long integer literal without underscores"
}
declare_clippy_lint! {
/// **What it does:** Warns for mistyped suffix in literals
///
/// **Why is this bad?** This is most probably a typo
///
/// **Known problems:**
/// - Recommends a signed suffix, even though the number might be too big and an unsigned
/// suffix is required
/// - Does not match on `_128` since that is a valid grouping for decimal and octal numbers
///
/// **Example:**
///
/// ```rust
/// 2_32;
/// ```
pub MISTYPED_LITERAL_SUFFIXES,
correctness,
"mistyped literal suffix"
}
declare_clippy_lint! {
/// **What it does:** Warns if an integral or floating-point constant is
/// grouped inconsistently with underscores.
///
/// **Why is this bad?** Readers may incorrectly interpret inconsistently
/// grouped digits.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let x: u64 = 618_64_9189_73_511;
/// ```
pub INCONSISTENT_DIGIT_GROUPING,
style,
"integer literals with digits grouped inconsistently"
}
declare_clippy_lint! {
/// **What it does:** Warns if the digits of an integral or floating-point
/// constant are grouped into groups that
/// are too large.
///
/// **Why is this bad?** Negatively impacts readability.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let x: u64 = 6186491_8973511;
/// ```
pub LARGE_DIGIT_GROUPS,
pedantic,
"grouping digits into groups that are too large"
}
declare_clippy_lint! {
/// **What it does:** Warns if there is a better representation for a numeric literal.
///
/// **Why is this bad?** Especially for big powers of 2 a hexadecimal representation is more
/// readable than a decimal representation.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// `255` => `0xFF`
/// `65_535` => `0xFFFF`
/// `4_042_322_160` => `0xF0F0_F0F0`
pub DECIMAL_LITERAL_REPRESENTATION,
restriction,
"using decimal representation when hexadecimal would be better"
}
#[derive(Debug, PartialEq)]
pub(super) enum Radix {
Binary,
Octal,
Decimal,
Hexadecimal,
}
impl Radix {
/// Returns a reasonable digit group size for this radix.
#[must_use]
crate fn suggest_grouping(&self) -> usize {
match *self {
Self::Binary | Self::Hexadecimal => 4,
Self::Octal | Self::Decimal => 3,
}
}
}
#[derive(Debug)]
pub(super) struct DigitInfo<'a> {
/// Characters of a literal between the radix prefix and type suffix.
crate digits: &'a str,
/// Which radix the literal was represented in.
crate radix: Radix,
/// The radix prefix, if present.
crate prefix: Option<&'a str>,
/// The type suffix, including preceding underscore if present.
crate suffix: Option<&'a str>,
/// True for floating-point literals.
crate float: bool,
}
impl<'a> DigitInfo<'a> {
#[must_use]
crate fn new(lit: &'a str, float: bool) -> Self {
// Determine delimiter for radix prefix, if present, and radix.
let radix = if lit.starts_with("0x") {
Radix::Hexadecimal
} else if lit.starts_with("0b") {
Radix::Binary
} else if lit.starts_with("0o") {
Radix::Octal
} else {
Radix::Decimal
};
// Grab part of the literal after prefix, if present.
let (prefix, sans_prefix) = if let Radix::Decimal = radix {
(None, lit)
} else {
let (p, s) = lit.split_at(2);
(Some(p), s)
};
let len = sans_prefix.len();
let mut last_d = '\0';
for (d_idx, d) in sans_prefix.char_indices() {
let suffix_start = if last_d == '_' { d_idx - 1 } else { d_idx };
if float
&& (d == 'f'
|| is_possible_float_suffix_index(&sans_prefix, suffix_start, len)
|| ((d == 'E' || d == 'e') && !has_possible_float_suffix(&sans_prefix)))
|| !float && (d == 'i' || d == 'u' || is_possible_suffix_index(&sans_prefix, suffix_start, len))
{
let (digits, suffix) = sans_prefix.split_at(suffix_start);
return Self {
digits,
radix,
prefix,
suffix: Some(suffix),
float,
};
}
last_d = d
}
// No suffix found
Self {
digits: sans_prefix,
radix,
prefix,
suffix: None,
float,
}
}
/// Returns literal formatted in a sensible way.
crate fn grouping_hint(&self) -> String {
let group_size = self.radix.suggest_grouping();
if self.digits.contains('.') {
let mut parts = self.digits.split('.');
let int_part_hint = parts
.next()
.expect("split always returns at least one element")
.chars()
.rev()
.filter(|&c| c != '_')
.collect::<Vec<_>>()
.chunks(group_size)
.map(|chunk| chunk.iter().rev().collect())
.rev()
.collect::<Vec<String>>()
.join("_");
let frac_part_hint = parts
.next()
.expect("already checked that there is a `.`")
.chars()
.filter(|&c| c != '_')
.collect::<Vec<_>>()
.chunks(group_size)
.map(|chunk| chunk.iter().collect())
.collect::<Vec<String>>()
.join("_");
let suffix_hint = match self.suffix {
Some(suffix) if is_mistyped_float_suffix(suffix) => format!("_f{}", &suffix[1..]),
Some(suffix) => suffix.to_string(),
None => String::new(),
};
format!("{}.{}{}", int_part_hint, frac_part_hint, suffix_hint)
} else if self.float && (self.digits.contains('E') || self.digits.contains('e')) {
let which_e = if self.digits.contains('E') { 'E' } else { 'e' };
let parts: Vec<&str> = self.digits.split(which_e).collect();
let filtered_digits_vec_0 = parts[0].chars().filter(|&c| c != '_').rev().collect::<Vec<_>>();
let filtered_digits_vec_1 = parts[1].chars().filter(|&c| c != '_').rev().collect::<Vec<_>>();
let before_e_hint = filtered_digits_vec_0
.chunks(group_size)
.map(|chunk| chunk.iter().rev().collect())
.rev()
.collect::<Vec<String>>()
.join("_");
let after_e_hint = filtered_digits_vec_1
.chunks(group_size)
.map(|chunk| chunk.iter().rev().collect())
.rev()
.collect::<Vec<String>>()
.join("_");
let suffix_hint = match self.suffix {
Some(suffix) if is_mistyped_float_suffix(suffix) => format!("_f{}", &suffix[1..]),
Some(suffix) => suffix.to_string(),
None => String::new(),
};
format!(
"{}{}{}{}{}",
self.prefix.unwrap_or(""),
before_e_hint,
which_e,
after_e_hint,
suffix_hint
)
} else {
let filtered_digits_vec = self.digits.chars().filter(|&c| c != '_').rev().collect::<Vec<_>>();
let mut hint = filtered_digits_vec
.chunks(group_size)
.map(|chunk| chunk.iter().rev().collect())
.rev()
.collect::<Vec<String>>()
.join("_");
// Forces hexadecimal values to be grouped by 4 being filled with zeroes (e.g 0x00ab_cdef)
let nb_digits_to_fill = filtered_digits_vec.len() % 4;
if self.radix == Radix::Hexadecimal && nb_digits_to_fill != 0 {
hint = format!("{:0>4}{}", &hint[..nb_digits_to_fill], &hint[nb_digits_to_fill..]);
}
let suffix_hint = match self.suffix {
Some(suffix) if is_mistyped_suffix(suffix) => format!("_i{}", &suffix[1..]),
Some(suffix) => suffix.to_string(),
None => String::new(),
};
format!("{}{}{}", self.prefix.unwrap_or(""), hint, suffix_hint)
}
}
}
enum WarningType {
UnreadableLiteral,
InconsistentDigitGrouping,
LargeDigitGroups,
DecimalRepresentation,
MistypedLiteralSuffix,
}
impl WarningType {
crate fn display(&self, grouping_hint: &str, cx: &EarlyContext<'_>, span: syntax_pos::Span) {
match self {
Self::MistypedLiteralSuffix => span_lint_and_sugg(
cx,
MISTYPED_LITERAL_SUFFIXES,
span,
"mistyped literal suffix",
"did you mean to write",
grouping_hint.to_string(),
Applicability::MaybeIncorrect,
),
Self::UnreadableLiteral => span_lint_and_sugg(
cx,
UNREADABLE_LITERAL,
span,
"long literal lacking separators",
"consider",
grouping_hint.to_owned(),
Applicability::MachineApplicable,
),
Self::LargeDigitGroups => span_lint_and_sugg(
cx,
LARGE_DIGIT_GROUPS,
span,
"digit groups should be smaller",
"consider",
grouping_hint.to_owned(),
Applicability::MachineApplicable,
),
Self::InconsistentDigitGrouping => span_lint_and_sugg(
cx,
INCONSISTENT_DIGIT_GROUPING,
span,
"digits grouped inconsistently by underscores",
"consider",
grouping_hint.to_owned(),
Applicability::MachineApplicable,
),
Self::DecimalRepresentation => span_lint_and_sugg(
cx,
DECIMAL_LITERAL_REPRESENTATION,
span,
"integer literal has a better hexadecimal representation",
"consider",
grouping_hint.to_owned(),
Applicability::MachineApplicable,
),
};
}
}
declare_lint_pass!(LiteralDigitGrouping => [
UNREADABLE_LITERAL,
INCONSISTENT_DIGIT_GROUPING,
LARGE_DIGIT_GROUPS,
MISTYPED_LITERAL_SUFFIXES,
]);
impl EarlyLintPass for LiteralDigitGrouping {
fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
if in_external_macro(cx.sess(), expr.span) {
return;
}
if let ExprKind::Lit(ref lit) = expr.kind {
self.check_lit(cx, lit)
}
}
}
impl LiteralDigitGrouping {
fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
let in_macro = in_macro(lit.span);
match lit.kind {
LitKind::Int(..) => {
// Lint integral literals.
if_chain! {
if let Some(src) = snippet_opt(cx, lit.span);
if let Some(firstch) = src.chars().next();
if char::to_digit(firstch, 10).is_some();
then {
let digit_info = DigitInfo::new(&src, false);
let _ = Self::do_lint(digit_info.digits, digit_info.suffix, in_macro).map_err(|warning_type| {
warning_type.display(&digit_info.grouping_hint(), cx, lit.span)
});
}
}
},
LitKind::Float(..) | LitKind::FloatUnsuffixed(..) => {
// Lint floating-point literals.
if_chain! {
if let Some(src) = snippet_opt(cx, lit.span);
if let Some(firstch) = src.chars().next();
if char::to_digit(firstch, 10).is_some();
then {
let digit_info = DigitInfo::new(&src, true);
// Separate digits into integral and fractional parts.
let parts: Vec<&str> = digit_info
.digits
.split_terminator('.')
.collect();
// Lint integral and fractional parts separately, and then check consistency of digit
// groups if both pass.
let _ = Self::do_lint(parts[0], digit_info.suffix, in_macro)
.map(|integral_group_size| {
if parts.len() > 1 {
// Lint the fractional part of literal just like integral part, but reversed.
let fractional_part = &parts[1].chars().rev().collect::<String>();
let _ = Self::do_lint(fractional_part, None, in_macro)
.map(|fractional_group_size| {
let consistent = Self::parts_consistent(integral_group_size,
fractional_group_size,
parts[0].len(),
parts[1].len());
if !consistent {
WarningType::InconsistentDigitGrouping.display(
&digit_info.grouping_hint(),
cx,
lit.span,
);
}
})
.map_err(|warning_type| warning_type.display(&digit_info.grouping_hint(),
cx,
lit.span));
}
})
.map_err(|warning_type| warning_type.display(&digit_info.grouping_hint(), cx, lit.span));
}
}
},
_ => (),
}
}
/// Given the sizes of the digit groups of both integral and fractional
/// parts, and the length
/// of both parts, determine if the digits have been grouped consistently.
#[must_use]
fn parts_consistent(int_group_size: usize, frac_group_size: usize, int_size: usize, frac_size: usize) -> bool {
match (int_group_size, frac_group_size) {
// No groups on either side of decimal point - trivially consistent.
(0, 0) => true,
// Integral part has grouped digits, fractional part does not.
(_, 0) => frac_size <= int_group_size,
// Fractional part has grouped digits, integral part does not.
(0, _) => int_size <= frac_group_size,
// Both parts have grouped digits. Groups should be the same size.
(_, _) => int_group_size == frac_group_size,
}
}
/// Performs lint on `digits` (no decimal point) and returns the group
/// size on success or `WarningType` when emitting a warning.
fn do_lint(digits: &str, suffix: Option<&str>, in_macro: bool) -> Result<usize, WarningType> {
if let Some(suffix) = suffix {
if is_mistyped_suffix(suffix) {
return Err(WarningType::MistypedLiteralSuffix);
}
}
// Grab underscore indices with respect to the units digit.
let underscore_positions: Vec<usize> = digits
.chars()
.rev()
.enumerate()
.filter_map(|(idx, digit)| if digit == '_' { Some(idx) } else { None })
.collect();
if underscore_positions.is_empty() {
// Check if literal needs underscores.
if !in_macro && digits.len() > 5 {
Err(WarningType::UnreadableLiteral)
} else {
Ok(0)
}
} else {
// Check consistency and the sizes of the groups.
let group_size = underscore_positions[0];
let consistent = underscore_positions
.windows(2)
.all(|ps| ps[1] - ps[0] == group_size + 1)
// number of digits to the left of the last group cannot be bigger than group size.
&& (digits.len() - underscore_positions.last()
.expect("there's at least one element") <= group_size + 1);
if !consistent {
return Err(WarningType::InconsistentDigitGrouping);
} else if group_size > 4 {
return Err(WarningType::LargeDigitGroups);
}
Ok(group_size)
}
}
}
#[allow(clippy::module_name_repetitions)]
#[derive(Copy, Clone)]
pub struct DecimalLiteralRepresentation {
threshold: u64,
}
impl_lint_pass!(DecimalLiteralRepresentation => [DECIMAL_LITERAL_REPRESENTATION]);
impl EarlyLintPass for DecimalLiteralRepresentation {
fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
if in_external_macro(cx.sess(), expr.span) {
return;
}
if let ExprKind::Lit(ref lit) = expr.kind {
self.check_lit(cx, lit)
}
}
}
impl DecimalLiteralRepresentation {
#[must_use]
pub fn new(threshold: u64) -> Self {
Self { threshold }
}
fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
// Lint integral literals.
if_chain! {
if let LitKind::Int(..) = lit.kind;
if let Some(src) = snippet_opt(cx, lit.span);
if let Some(firstch) = src.chars().next();
if char::to_digit(firstch, 10).is_some();
let digit_info = DigitInfo::new(&src, false);
if digit_info.radix == Radix::Decimal;
if let Ok(val) = digit_info.digits
.chars()
.filter(|&c| c != '_')
.collect::<String>()
.parse::<u128>();
if val >= u128::from(self.threshold);
then {
let hex = format!("{:#X}", val);
let digit_info = DigitInfo::new(&hex, false);
let _ = Self::do_lint(digit_info.digits).map_err(|warning_type| {
warning_type.display(&digit_info.grouping_hint(), cx, lit.span)
});
}
}
}
fn do_lint(digits: &str) -> Result<(), WarningType> {
if digits.len() == 1 {
// Lint for 1 digit literals, if someone really sets the threshold that low
if digits == "1"
|| digits == "2"
|| digits == "4"
|| digits == "8"
|| digits == "3"
|| digits == "7"
|| digits == "F"
{
return Err(WarningType::DecimalRepresentation);
}
} else if digits.len() < 4 {
// Lint for Literals with a hex-representation of 2 or 3 digits
let f = &digits[0..1]; // first digit
let s = &digits[1..]; // suffix
// Powers of 2
if ((f.eq("1") || f.eq("2") || f.eq("4") || f.eq("8")) && s.chars().all(|c| c == '0'))
// Powers of 2 minus 1
|| ((f.eq("1") || f.eq("3") || f.eq("7") || f.eq("F")) && s.chars().all(|c| c == 'F'))
{
return Err(WarningType::DecimalRepresentation);
}
} else {
// Lint for Literals with a hex-representation of 4 digits or more
let f = &digits[0..1]; // first digit
let m = &digits[1..digits.len() - 1]; // middle digits, except last
let s = &digits[1..]; // suffix
// Powers of 2 with a margin of +15/-16
if ((f.eq("1") || f.eq("2") || f.eq("4") || f.eq("8")) && m.chars().all(|c| c == '0'))
|| ((f.eq("1") || f.eq("3") || f.eq("7") || f.eq("F")) && m.chars().all(|c| c == 'F'))
// Lint for representations with only 0s and Fs, while allowing 7 as the first
// digit
|| ((f.eq("7") || f.eq("F")) && s.chars().all(|c| c == '0' || c == 'F'))
{
return Err(WarningType::DecimalRepresentation);
}
}
Ok(())
}
}
#[must_use]
fn is_mistyped_suffix(suffix: &str) -> bool {
["_8", "_16", "_32", "_64"].contains(&suffix)
}
#[must_use]
fn is_possible_suffix_index(lit: &str, idx: usize, len: usize) -> bool {
((len > 3 && idx == len - 3) || (len > 2 && idx == len - 2)) && is_mistyped_suffix(lit.split_at(idx).1)
}
#[must_use]
fn is_mistyped_float_suffix(suffix: &str) -> bool {
["_32", "_64"].contains(&suffix)
}
#[must_use]
fn is_possible_float_suffix_index(lit: &str, idx: usize, len: usize) -> bool {
(len > 3 && idx == len - 3) && is_mistyped_float_suffix(lit.split_at(idx).1)
}
#[must_use]
fn has_possible_float_suffix(lit: &str) -> bool {
lit.ends_with("_32") || lit.ends_with("_64")
}