clippy_lints/src/literal_representation.rs

   1 //! Lints concerned with the grouping of digits with underscores in integral or
   2 //! floating-point literal expressions.
   3
   4 use rustc::lint::*;
   5 use syntax::ast::*;
   6 use syntax_pos;
   7 use utils::{in_external_macro, snippet_opt, span_lint_and_sugg};
   8
   9 /// **What it does:** Warns if a long integral or floating-point constant does
  10 /// not contain underscores.
  11 ///
  12 /// **Why is this bad?** Reading long numbers is difficult without separators.
  13 ///
  14 /// **Known problems:** None.
  15 ///
  16 /// **Example:**
  17 ///
  18 /// ```rust
  19 /// 61864918973511
  20 /// ```
  21 declare_clippy_lint! {
  22     pub UNREADABLE_LITERAL,
  23     style,
  24     "long integer literal without underscores"
  25 }
  26
  27 /// **What it does:** Warns if an integral or floating-point constant is
  28 /// grouped inconsistently with underscores.
  29 ///
  30 /// **Why is this bad?** Readers may incorrectly interpret inconsistently
  31 /// grouped digits.
  32 ///
  33 /// **Known problems:** None.
  34 ///
  35 /// **Example:**
  36 ///
  37 /// ```rust
  38 /// 618_64_9189_73_511
  39 /// ```
  40 declare_clippy_lint! {
  41     pub INCONSISTENT_DIGIT_GROUPING,
  42     style,
  43     "integer literals with digits grouped inconsistently"
  44 }
  45
  46 /// **What it does:** Warns if the digits of an integral or floating-point
  47 /// constant are grouped into groups that
  48 /// are too large.
  49 ///
  50 /// **Why is this bad?** Negatively impacts readability.
  51 ///
  52 /// **Known problems:** None.
  53 ///
  54 /// **Example:**
  55 ///
  56 /// ```rust
  57 /// 6186491_8973511
  58 /// ```
  59 declare_clippy_lint! {
  60     pub LARGE_DIGIT_GROUPS,
  61     style,
  62     "grouping digits into groups that are too large"
  63 }
  64
  65 /// **What it does:** Warns if there is a better representation for a numeric literal.
  66 ///
  67 /// **Why is this bad?** Especially for big powers of 2 a hexadecimal representation is more
  68 /// readable than a decimal representation.
  69 ///
  70 /// **Known problems:** None.
  71 ///
  72 /// **Example:**
  73 ///
  74 /// `255` => `0xFF`
  75 /// `65_535` => `0xFFFF`
  76 /// `4_042_322_160` => `0xF0F0_F0F0`
  77 declare_clippy_lint! {
  78     pub DECIMAL_LITERAL_REPRESENTATION,
  79     restriction,
  80     "using decimal representation when hexadecimal would be better"
  81 }
  82
  83 #[derive(Debug, PartialEq)]
  84 enum Radix {
  85     Binary,
  86     Octal,
  87     Decimal,
  88     Hexadecimal,
  89 }
  90
  91 impl Radix {
  92     /// Return a reasonable digit group size for this radix.
  93     pub fn suggest_grouping(&self) -> usize {
  94         match *self {
  95             Radix::Binary | Radix::Hexadecimal => 4,
  96             Radix::Octal | Radix::Decimal => 3,
  97         }
  98     }
  99 }
 100
 101 #[derive(Debug)]
 102 struct DigitInfo<'a> {
 103     /// Characters of a literal between the radix prefix and type suffix.
 104     pub digits: &'a str,
 105     /// Which radix the literal was represented in.
 106     pub radix: Radix,
 107     /// The radix prefix, if present.
 108     pub prefix: Option<&'a str>,
 109     /// The type suffix, including preceding underscore if present.
 110     pub suffix: Option<&'a str>,
 111     /// True for floating-point literals.
 112     pub float: bool,
 113 }
 114
 115 impl<'a> DigitInfo<'a> {
 116     pub fn new(lit: &'a str, float: bool) -> Self {
 117         // Determine delimiter for radix prefix, if present, and radix.
 118         let radix = if lit.starts_with("0x") {
 119             Radix::Hexadecimal
 120         } else if lit.starts_with("0b") {
 121             Radix::Binary
 122         } else if lit.starts_with("0o") {
 123             Radix::Octal
 124         } else {
 125             Radix::Decimal
 126         };
 127
 128         // Grab part of the literal after prefix, if present.
 129         let (prefix, sans_prefix) = if let Radix::Decimal = radix {
 130             (None, lit)
 131         } else {
 132             let (p, s) = lit.split_at(2);
 133             (Some(p), s)
 134         };
 135
 136         let mut last_d = '\0';
 137         for (d_idx, d) in sans_prefix.char_indices() {
 138             if !float && (d == 'i' || d == 'u') || float && (d == 'f' || d == 'e' || d == 'E') {
 139                 let suffix_start = if last_d == '_' { d_idx - 1 } else { d_idx };
 140                 let (digits, suffix) = sans_prefix.split_at(suffix_start);
 141                 return Self {
 142                     digits,
 143                     radix,
 144                     prefix,
 145                     suffix: Some(suffix),
 146                     float,
 147                 };
 148             }
 149             last_d = d
 150         }
 151
 152         // No suffix found
 153         Self {
 154             digits: sans_prefix,
 155             radix,
 156             prefix,
 157             suffix: None,
 158             float,
 159         }
 160     }
 161
 162     /// Returns digits grouped in a sensible way.
 163     fn grouping_hint(&self) -> String {
 164         let group_size = self.radix.suggest_grouping();
 165         if self.digits.contains('.') {
 166             let mut parts = self.digits.split('.');
 167             let int_part_hint = parts
 168                 .next()
 169                 .expect("split always returns at least one element")
 170                 .chars()
 171                 .rev()
 172                 .filter(|&c| c != '_')
 173                 .collect::<Vec<_>>()
 174                 .chunks(group_size)
 175                 .map(|chunk| chunk.into_iter().rev().collect())
 176                 .rev()
 177                 .collect::<Vec<String>>()
 178                 .join("_");
 179             let frac_part_hint = parts
 180                 .next()
 181                 .expect("already checked that there is a `.`")
 182                 .chars()
 183                 .filter(|&c| c != '_')
 184                 .collect::<Vec<_>>()
 185                 .chunks(group_size)
 186                 .map(|chunk| chunk.into_iter().collect())
 187                 .collect::<Vec<String>>()
 188                 .join("_");
 189             format!(
 190                 "{}.{}{}",
 191                 int_part_hint,
 192                 frac_part_hint,
 193                 self.suffix.unwrap_or("")
 194             )
 195         } else {
 196             let hint = self.digits
 197                 .chars()
 198                 .rev()
 199                 .filter(|&c| c != '_')
 200                 .collect::<Vec<_>>()
 201                 .chunks(group_size)
 202                 .map(|chunk| chunk.into_iter().rev().collect())
 203                 .rev()
 204                 .collect::<Vec<String>>()
 205                 .join("_");
 206             format!(
 207                 "{}{}{}",
 208                 self.prefix.unwrap_or(""),
 209                 hint,
 210                 self.suffix.unwrap_or("")
 211             )
 212         }
 213     }
 214 }
 215
 216 enum WarningType {
 217     UnreadableLiteral,
 218     InconsistentDigitGrouping,
 219     LargeDigitGroups,
 220     DecimalRepresentation,
 221 }
 222
 223 impl WarningType {
 224     pub fn display(&self, grouping_hint: &str, cx: &EarlyContext, span: &syntax_pos::Span) {
 225         match *self {
 226             WarningType::UnreadableLiteral => span_lint_and_sugg(
 227                 cx,
 228                 UNREADABLE_LITERAL,
 229                 *span,
 230                 "long literal lacking separators",
 231                 "consider",
 232                 grouping_hint.to_owned(),
 233             ),
 234             WarningType::LargeDigitGroups => span_lint_and_sugg(
 235                 cx,
 236                 LARGE_DIGIT_GROUPS,
 237                 *span,
 238                 "digit groups should be smaller",
 239                 "consider",
 240                 grouping_hint.to_owned(),
 241             ),
 242             WarningType::InconsistentDigitGrouping => span_lint_and_sugg(
 243                 cx,
 244                 INCONSISTENT_DIGIT_GROUPING,
 245                 *span,
 246                 "digits grouped inconsistently by underscores",
 247                 "consider",
 248                 grouping_hint.to_owned(),
 249             ),
 250             WarningType::DecimalRepresentation => span_lint_and_sugg(
 251                 cx,
 252                 DECIMAL_LITERAL_REPRESENTATION,
 253                 *span,
 254                 "integer literal has a better hexadecimal representation",
 255                 "consider",
 256                 grouping_hint.to_owned(),
 257             ),
 258         };
 259     }
 260 }
 261
 262 #[derive(Copy, Clone)]
 263 pub struct LiteralDigitGrouping;
 264
 265 impl LintPass for LiteralDigitGrouping {
 266     fn get_lints(&self) -> LintArray {
 267         lint_array!(
 268             UNREADABLE_LITERAL,
 269             INCONSISTENT_DIGIT_GROUPING,
 270             LARGE_DIGIT_GROUPS
 271         )
 272     }
 273 }
 274
 275 impl EarlyLintPass for LiteralDigitGrouping {
 276     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 277         if in_external_macro(cx, expr.span) {
 278             return;
 279         }
 280
 281         if let ExprKind::Lit(ref lit) = expr.node {
 282             self.check_lit(cx, lit)
 283         }
 284     }
 285 }
 286
 287 impl LiteralDigitGrouping {
 288     fn check_lit(&self, cx: &EarlyContext, lit: &Lit) {
 289         match lit.node {
 290             LitKind::Int(..) => {
 291                 // Lint integral literals.
 292                 if_chain! {
 293                     if let Some(src) = snippet_opt(cx, lit.span);
 294                     if let Some(firstch) = src.chars().next();
 295                     if char::to_digit(firstch, 10).is_some();
 296                     then {
 297                         let digit_info = DigitInfo::new(&src, false);
 298                         let _ = Self::do_lint(digit_info.digits).map_err(|warning_type| {
 299                             warning_type.display(&digit_info.grouping_hint(), cx, &lit.span)
 300                         });
 301                     }
 302                 }
 303             },
 304             LitKind::Float(..) | LitKind::FloatUnsuffixed(..) => {
 305                 // Lint floating-point literals.
 306                 if_chain! {
 307                     if let Some(src) = snippet_opt(cx, lit.span);
 308                     if let Some(firstch) = src.chars().next();
 309                     if char::to_digit(firstch, 10).is_some();
 310                     then {
 311                         let digit_info = DigitInfo::new(&src, true);
 312                         // Separate digits into integral and fractional parts.
 313                         let parts: Vec<&str> = digit_info
 314                             .digits
 315                             .split_terminator('.')
 316                             .collect();
 317
 318                         // Lint integral and fractional parts separately, and then check consistency of digit
 319                         // groups if both pass.
 320                         let _ = Self::do_lint(parts[0])
 321                             .map(|integral_group_size| {
 322                                 if parts.len() > 1 {
 323                                     // Lint the fractional part of literal just like integral part, but reversed.
 324                                     let fractional_part = &parts[1].chars().rev().collect::<String>();
 325                                     let _ = Self::do_lint(fractional_part)
 326                                         .map(|fractional_group_size| {
 327                                             let consistent = Self::parts_consistent(integral_group_size,
 328                                                                                     fractional_group_size,
 329                                                                                     parts[0].len(),
 330                                                                                     parts[1].len());
 331                                             if !consistent {
 332                                                 WarningType::InconsistentDigitGrouping.display(&digit_info.grouping_hint(),
 333                                                 cx,
 334                                                 &lit.span);
 335                                             }
 336                                         })
 337                                     .map_err(|warning_type| warning_type.display(&digit_info.grouping_hint(),
 338                                     cx,
 339                                     &lit.span));
 340                                 }
 341                             })
 342                         .map_err(|warning_type| warning_type.display(&digit_info.grouping_hint(), cx, &lit.span));
 343                     }
 344                 }
 345             },
 346             _ => (),
 347         }
 348     }
 349
 350     /// Given the sizes of the digit groups of both integral and fractional
 351     /// parts, and the length
 352     /// of both parts, determine if the digits have been grouped consistently.
 353     fn parts_consistent(int_group_size: usize, frac_group_size: usize, int_size: usize, frac_size: usize) -> bool {
 354         match (int_group_size, frac_group_size) {
 355             // No groups on either side of decimal point - trivially consistent.
 356             (0, 0) => true,
 357             // Integral part has grouped digits, fractional part does not.
 358             (_, 0) => frac_size <= int_group_size,
 359             // Fractional part has grouped digits, integral part does not.
 360             (0, _) => int_size <= frac_group_size,
 361             // Both parts have grouped digits. Groups should be the same size.
 362             (_, _) => int_group_size == frac_group_size,
 363         }
 364     }
 365
 366     /// Performs lint on `digits` (no decimal point) and returns the group
 367     /// size on success or `WarningType` when emitting a warning.
 368     fn do_lint(digits: &str) -> Result<usize, WarningType> {
 369         // Grab underscore indices with respect to the units digit.
 370         let underscore_positions: Vec<usize> = digits
 371             .chars()
 372             .rev()
 373             .enumerate()
 374             .filter_map(|(idx, digit)| if digit == '_' { Some(idx) } else { None })
 375             .collect();
 376
 377         if underscore_positions.is_empty() {
 378             // Check if literal needs underscores.
 379             if digits.len() > 5 {
 380                 Err(WarningType::UnreadableLiteral)
 381             } else {
 382                 Ok(0)
 383             }
 384         } else {
 385             // Check consistency and the sizes of the groups.
 386             let group_size = underscore_positions[0];
 387             let consistent = underscore_positions
 388                 .windows(2)
 389                 .all(|ps| ps[1] - ps[0] == group_size + 1)
 390                 // number of digits to the left of the last group cannot be bigger than group size.
 391                 && (digits.len() - underscore_positions.last()
 392                                                        .expect("there's at least one element") <= group_size + 1);
 393
 394             if !consistent {
 395                 return Err(WarningType::InconsistentDigitGrouping);
 396             } else if group_size > 4 {
 397                 return Err(WarningType::LargeDigitGroups);
 398             }
 399             Ok(group_size)
 400         }
 401     }
 402 }
 403
 404 #[derive(Copy, Clone)]
 405 pub struct LiteralRepresentation {
 406     threshold: u64,
 407 }
 408
 409 impl LintPass for LiteralRepresentation {
 410     fn get_lints(&self) -> LintArray {
 411         lint_array!(DECIMAL_LITERAL_REPRESENTATION)
 412     }
 413 }
 414
 415 impl EarlyLintPass for LiteralRepresentation {
 416     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 417         if in_external_macro(cx, expr.span) {
 418             return;
 419         }
 420
 421         if let ExprKind::Lit(ref lit) = expr.node {
 422             self.check_lit(cx, lit)
 423         }
 424     }
 425 }
 426
 427 impl LiteralRepresentation {
 428     pub fn new(threshold: u64) -> Self {
 429         Self {
 430             threshold,
 431         }
 432     }
 433     fn check_lit(&self, cx: &EarlyContext, lit: &Lit) {
 434         // Lint integral literals.
 435         if_chain! {
 436             if let LitKind::Int(..) = lit.node;
 437             if let Some(src) = snippet_opt(cx, lit.span);
 438             if let Some(firstch) = src.chars().next();
 439             if char::to_digit(firstch, 10).is_some();
 440             then {
 441                 let digit_info = DigitInfo::new(&src, false);
 442                 if digit_info.radix == Radix::Decimal {
 443                     let val = digit_info.digits
 444                         .chars()
 445                         .filter(|&c| c != '_')
 446                         .collect::<String>()
 447                         .parse::<u128>().unwrap();
 448                     if val < u128::from(self.threshold) {
 449                         return
 450                     }
 451                     let hex = format!("{:#X}", val);
 452                     let digit_info = DigitInfo::new(&hex[..], false);
 453                     let _ = Self::do_lint(digit_info.digits).map_err(|warning_type| {
 454                         warning_type.display(&digit_info.grouping_hint(), cx, &lit.span)
 455                     });
 456                 }
 457             }
 458         }
 459     }
 460
 461     fn do_lint(digits: &str) -> Result<(), WarningType> {
 462         if digits.len() == 1 {
 463             // Lint for 1 digit literals, if someone really sets the threshold that low
 464             if digits == "1" || digits == "2" || digits == "4" || digits == "8" || digits == "3" || digits == "7"
 465                 || digits == "F"
 466             {
 467                 return Err(WarningType::DecimalRepresentation);
 468             }
 469         } else if digits.len() < 4 {
 470             // Lint for Literals with a hex-representation of 2 or 3 digits
 471             let f = &digits[0..1]; // first digit
 472             let s = &digits[1..]; // suffix
 473             // Powers of 2
 474             if ((f.eq("1") || f.eq("2") || f.eq("4") || f.eq("8")) && s.chars().all(|c| c == '0'))
 475                 // Powers of 2 minus 1
 476                 || ((f.eq("1") || f.eq("3") || f.eq("7") || f.eq("F")) && s.chars().all(|c| c == 'F'))
 477             {
 478                 return Err(WarningType::DecimalRepresentation);
 479             }
 480         } else {
 481             // Lint for Literals with a hex-representation of 4 digits or more
 482             let f = &digits[0..1]; // first digit
 483             let m = &digits[1..digits.len() - 1]; // middle digits, except last
 484             let s = &digits[1..]; // suffix
 485             // Powers of 2 with a margin of +15/-16
 486             if ((f.eq("1") || f.eq("2") || f.eq("4") || f.eq("8")) && m.chars().all(|c| c == '0'))
 487                 || ((f.eq("1") || f.eq("3") || f.eq("7") || f.eq("F")) && m.chars().all(|c| c == 'F'))
 488                 // Lint for representations with only 0s and Fs, while allowing 7 as the first
 489                 // digit
 490                 || ((f.eq("7") || f.eq("F")) && s.chars().all(|c| c == '0' || c == 'F'))
 491             {
 492                 return Err(WarningType::DecimalRepresentation);
 493             }
 494         }
 495
 496         Ok(())
 497     }
 498 }