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