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_help_and_lint};
   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_lint! {
  78     pub BAD_LITERAL_REPRESENTATION,
  79     Warn,
  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' {
 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: digits,
 143                     radix: radix,
 144                     prefix: prefix,
 145                     suffix: Some(suffix),
 146                     float: float,
 147                 };
 148             }
 149             last_d = d
 150         }
 151
 152         // No suffix found
 153         Self {
 154             digits: sans_prefix,
 155             radix: radix,
 156             prefix: prefix,
 157             suffix: None,
 158             float: 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     BadRepresentation,
 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_help_and_lint(
 227                 cx,
 228                 UNREADABLE_LITERAL,
 229                 *span,
 230                 "long literal lacking separators",
 231                 &format!("consider: {}", grouping_hint),
 232             ),
 233             WarningType::LargeDigitGroups => span_help_and_lint(
 234                 cx,
 235                 LARGE_DIGIT_GROUPS,
 236                 *span,
 237                 "digit groups should be smaller",
 238                 &format!("consider: {}", grouping_hint),
 239             ),
 240             WarningType::InconsistentDigitGrouping => span_help_and_lint(
 241                 cx,
 242                 INCONSISTENT_DIGIT_GROUPING,
 243                 *span,
 244                 "digits grouped inconsistently by underscores",
 245                 &format!("consider: {}", grouping_hint),
 246             ),
 247             WarningType::BadRepresentation => span_help_and_lint(
 248                 cx,
 249                 BAD_LITERAL_REPRESENTATION,
 250                 *span,
 251                 "bad representation of integer literal",
 252                 &format!("consider: {}", grouping_hint),
 253             ),
 254         };
 255     }
 256 }
 257
 258 #[derive(Copy, Clone)]
 259 pub struct LiteralDigitGrouping;
 260
 261 impl LintPass for LiteralDigitGrouping {
 262     fn get_lints(&self) -> LintArray {
 263         lint_array!(
 264             UNREADABLE_LITERAL,
 265             INCONSISTENT_DIGIT_GROUPING,
 266             LARGE_DIGIT_GROUPS
 267         )
 268     }
 269 }
 270
 271 impl EarlyLintPass for LiteralDigitGrouping {
 272     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 273         if in_external_macro(cx, expr.span) {
 274             return;
 275         }
 276
 277         if let ExprKind::Lit(ref lit) = expr.node {
 278             self.check_lit(cx, lit)
 279         }
 280     }
 281 }
 282
 283 impl LiteralDigitGrouping {
 284     fn check_lit(&self, cx: &EarlyContext, lit: &Lit) {
 285         // Lint integral literals.
 286         if_chain! {
 287             if let LitKind::Int(..) = lit.node;
 288             if let Some(src) = snippet_opt(cx, lit.span);
 289             if let Some(firstch) = src.chars().next();
 290             if char::to_digit(firstch, 10).is_some();
 291             then {
 292                 let digit_info = DigitInfo::new(&src, false);
 293                 let _ = Self::do_lint(digit_info.digits).map_err(|warning_type| {
 294                     warning_type.display(&digit_info.grouping_hint(), cx, &lit.span)
 295                 });
 296             }
 297         }
 298
 299         // Lint floating-point literals.
 300         if_chain! {
 301             if let LitKind::Float(..) = lit.node;
 302             if let Some(src) = snippet_opt(cx, lit.span);
 303             if let Some(firstch) = src.chars().next();
 304             if char::to_digit(firstch, 10).is_some();
 305             then {
 306                 let digit_info = DigitInfo::new(&src, true);
 307                 // Separate digits into integral and fractional parts.
 308                 let parts: Vec<&str> = digit_info
 309                     .digits
 310                     .split_terminator('.')
 311                     .collect();
 312
 313                 // Lint integral and fractional parts separately, and then check consistency of digit
 314                 // groups if both pass.
 315                 let _ = Self::do_lint(parts[0])
 316                     .map(|integral_group_size| {
 317                         if parts.len() > 1 {
 318                             // Lint the fractional part of literal just like integral part, but reversed.
 319                             let fractional_part = &parts[1].chars().rev().collect::<String>();
 320                             let _ = Self::do_lint(fractional_part)
 321                                 .map(|fractional_group_size| {
 322                                     let consistent = Self::parts_consistent(integral_group_size,
 323                                                                             fractional_group_size,
 324                                                                             parts[0].len(),
 325                                                                             parts[1].len());
 326                                     if !consistent {
 327                                         WarningType::InconsistentDigitGrouping.display(&digit_info.grouping_hint(),
 328                                                                                        cx,
 329                                                                                        &lit.span);
 330                                     }
 331                                 })
 332                                 .map_err(|warning_type| warning_type.display(&digit_info.grouping_hint(),
 333                                                                              cx,
 334                                                                              &lit.span));
 335                         }
 336                     })
 337                     .map_err(|warning_type| warning_type.display(&digit_info.grouping_hint(), cx, &lit.span));
 338             }
 339         }
 340     }
 341
 342     /// Given the sizes of the digit groups of both integral and fractional
 343     /// parts, and the length
 344     /// of both parts, determine if the digits have been grouped consistently.
 345     fn parts_consistent(int_group_size: usize, frac_group_size: usize, int_size: usize, frac_size: usize) -> bool {
 346         match (int_group_size, frac_group_size) {
 347             // No groups on either side of decimal point - trivially consistent.
 348             (0, 0) => true,
 349             // Integral part has grouped digits, fractional part does not.
 350             (_, 0) => frac_size <= int_group_size,
 351             // Fractional part has grouped digits, integral part does not.
 352             (0, _) => int_size <= frac_group_size,
 353             // Both parts have grouped digits. Groups should be the same size.
 354             (_, _) => int_group_size == frac_group_size,
 355         }
 356     }
 357
 358     /// Performs lint on `digits` (no decimal point) and returns the group
 359     /// size on success or `WarningType` when emitting a warning.
 360     fn do_lint(digits: &str) -> Result<usize, WarningType> {
 361         // Grab underscore indices with respect to the units digit.
 362         let underscore_positions: Vec<usize> = digits
 363             .chars()
 364             .rev()
 365             .enumerate()
 366             .filter_map(|(idx, digit)| if digit == '_' { Some(idx) } else { None })
 367             .collect();
 368
 369         if underscore_positions.is_empty() {
 370             // Check if literal needs underscores.
 371             if digits.len() > 4 {
 372                 Err(WarningType::UnreadableLiteral)
 373             } else {
 374                 Ok(0)
 375             }
 376         } else {
 377             // Check consistency and the sizes of the groups.
 378             let group_size = underscore_positions[0];
 379             let consistent = underscore_positions
 380                 .windows(2)
 381                 .all(|ps| ps[1] - ps[0] == group_size + 1)
 382                 // number of digits to the left of the last group cannot be bigger than group size.
 383                 && (digits.len() - underscore_positions.last()
 384                                                        .expect("there's at least one element") <= group_size + 1);
 385
 386             if !consistent {
 387                 return Err(WarningType::InconsistentDigitGrouping);
 388             } else if group_size > 4 {
 389                 return Err(WarningType::LargeDigitGroups);
 390             }
 391             Ok(group_size)
 392         }
 393     }
 394 }
 395
 396 #[derive(Copy, Clone)]
 397 pub struct LiteralRepresentation;
 398
 399 impl LintPass for LiteralRepresentation {
 400     fn get_lints(&self) -> LintArray {
 401         lint_array!(BAD_LITERAL_REPRESENTATION)
 402     }
 403 }
 404
 405 impl EarlyLintPass for LiteralRepresentation {
 406     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 407         if in_external_macro(cx, expr.span) {
 408             return;
 409         }
 410
 411         if let ExprKind::Lit(ref lit) = expr.node {
 412             self.check_lit(cx, lit)
 413         }
 414     }
 415 }
 416
 417 impl LiteralRepresentation {
 418     fn check_lit(&self, cx: &EarlyContext, lit: &Lit) {
 419         // Lint integral literals.
 420         if_chain! {
 421             if let LitKind::Int(..) = lit.node;
 422             if let Some(src) = snippet_opt(cx, lit.span);
 423             if let Some(firstch) = src.chars().next();
 424             if char::to_digit(firstch, 10).is_some();
 425             then {
 426                 let digit_info = DigitInfo::new(&src, false);
 427                 if digit_info.radix == Radix::Decimal {
 428                     let hex = format!("{:#X}", digit_info.digits
 429                                                             .chars()
 430                                                             .filter(|&c| c != '_')
 431                                                             .collect::<String>()
 432                                                             .parse::<u128>().unwrap());
 433                     let digit_info = DigitInfo::new(&hex[..], false);
 434                     let _ = Self::do_lint(digit_info.digits).map_err(|warning_type| {
 435                         warning_type.display(&digit_info.grouping_hint(), cx, &lit.span)
 436                     });
 437                 }
 438             }
 439         }
 440     }
 441
 442     fn do_lint(digits: &str) -> Result<(), WarningType> {
 443         if digits.len() == 2 && digits == "FF" {
 444             return Err(WarningType::BadRepresentation);
 445         } else if digits.len() == 3 {
 446             // Lint for Literals with a hex-representation of 3 digits
 447             let f = &digits[0..1]; // first digit
 448             let s = &digits[1..]; // suffix
 449                                   // Powers of 2 minus 1
 450             if (f.eq("1") || f.eq("3") || f.eq("7") || f.eq("F")) && s.eq("FF") {
 451                 return Err(WarningType::BadRepresentation);
 452             }
 453         } else if digits.len() > 3 {
 454             // Lint for Literals with a hex-representation of 4 digits or more
 455             let f = &digits[0..1]; // first digit
 456             let m = &digits[1..digits.len() - 1]; // middle digits, except last
 457             let s = &digits[1..]; // suffix
 458                                   // Powers of 2 with a margin of +15/-16
 459             if ((f.eq("1") || f.eq("2") || f.eq("4") || f.eq("8")) && m.chars().all(|c| c == '0'))
 460                 || ((f.eq("1") || f.eq("3") || f.eq("7") || f.eq("F")) && m.chars().all(|c| c == 'F'))
 461                 // Lint for representations with only 0s and Fs, while allowing 7 as the first
 462                 // digit
 463                 || ((f.eq("7") || f.eq("F")) && s.chars().all(|c| c == '0' || c == 'F'))
 464             {
 465                 return Err(WarningType::BadRepresentation);
 466             }
 467         }
 468
 469         Ok(())
 470     }
 471 }