compiler/rustc_parse/src/lexer/mod.rs

   1 use crate::lexer::unicode_chars::UNICODE_ARRAY;
   2 use rustc_ast::ast::{self, AttrStyle};
   3 use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
   4 use rustc_ast::tokenstream::{Spacing, TokenStream};
   5 use rustc_ast::util::unicode::contains_text_flow_control_chars;
   6 use rustc_errors::{error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
   7 use rustc_lexer::unescape::{self, Mode};
   8 use rustc_lexer::{Base, DocStyle, RawStrError};
   9 use rustc_session::lint::builtin::{
  10     RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX, TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
  11 };
  12 use rustc_session::lint::BuiltinLintDiagnostics;
  13 use rustc_session::parse::ParseSess;
  14 use rustc_span::symbol::{sym, Symbol};
  15 use rustc_span::{edition::Edition, BytePos, Pos, Span};
  16
  17 use tracing::debug;
  18
  19 mod tokentrees;
  20 mod unescape_error_reporting;
  21 mod unicode_chars;
  22
  23 use unescape_error_reporting::{emit_unescape_error, escaped_char};
  24
  25 #[derive(Clone, Debug)]
  26 pub struct UnmatchedBrace {
  27     pub expected_delim: Delimiter,
  28     pub found_delim: Option<Delimiter>,
  29     pub found_span: Span,
  30     pub unclosed_span: Option<Span>,
  31     pub candidate_span: Option<Span>,
  32 }
  33
  34 crate fn parse_token_trees<'a>(
  35     sess: &'a ParseSess,
  36     src: &'a str,
  37     start_pos: BytePos,
  38     override_span: Option<Span>,
  39 ) -> (PResult<'a, TokenStream>, Vec<UnmatchedBrace>) {
  40     StringReader { sess, start_pos, pos: start_pos, end_src_index: src.len(), src, override_span }
  41         .into_token_trees()
  42 }
  43
  44 struct StringReader<'a> {
  45     sess: &'a ParseSess,
  46     /// Initial position, read-only.
  47     start_pos: BytePos,
  48     /// The absolute offset within the source_map of the current character.
  49     pos: BytePos,
  50     /// Stop reading src at this index.
  51     end_src_index: usize,
  52     /// Source text to tokenize.
  53     src: &'a str,
  54     override_span: Option<Span>,
  55 }
  56
  57 impl<'a> StringReader<'a> {
  58     fn mk_sp(&self, lo: BytePos, hi: BytePos) -> Span {
  59         self.override_span.unwrap_or_else(|| Span::with_root_ctxt(lo, hi))
  60     }
  61
  62     /// Returns the next token, and info about preceding whitespace, if any.
  63     fn next_token(&mut self) -> (Spacing, Token) {
  64         let mut spacing = Spacing::Joint;
  65
  66         // Skip `#!` at the start of the file
  67         let start_src_index = self.src_index(self.pos);
  68         let text: &str = &self.src[start_src_index..self.end_src_index];
  69         let is_beginning_of_file = self.pos == self.start_pos;
  70         if is_beginning_of_file {
  71             if let Some(shebang_len) = rustc_lexer::strip_shebang(text) {
  72                 self.pos = self.pos + BytePos::from_usize(shebang_len);
  73                 spacing = Spacing::Alone;
  74             }
  75         }
  76
  77         // Skip trivial (whitespace & comments) tokens
  78         loop {
  79             let start_src_index = self.src_index(self.pos);
  80             let text: &str = &self.src[start_src_index..self.end_src_index];
  81
  82             if text.is_empty() {
  83                 let span = self.mk_sp(self.pos, self.pos);
  84                 return (spacing, Token::new(token::Eof, span));
  85             }
  86
  87             let token = rustc_lexer::first_token(text);
  88
  89             let start = self.pos;
  90             self.pos = self.pos + BytePos::from_usize(token.len);
  91
  92             debug!("next_token: {:?}({:?})", token.kind, self.str_from(start));
  93
  94             match self.cook_lexer_token(token.kind, start) {
  95                 Some(kind) => {
  96                     let span = self.mk_sp(start, self.pos);
  97                     return (spacing, Token::new(kind, span));
  98                 }
  99                 None => spacing = Spacing::Alone,
 100             }
 101         }
 102     }
 103
 104     /// Report a fatal lexical error with a given span.
 105     fn fatal_span(&self, sp: Span, m: &str) -> ! {
 106         self.sess.span_diagnostic.span_fatal(sp, m)
 107     }
 108
 109     /// Report a lexical error with a given span.
 110     fn err_span(&self, sp: Span, m: &str) {
 111         self.sess.span_diagnostic.struct_span_err(sp, m).emit();
 112     }
 113
 114     /// Report a fatal error spanning [`from_pos`, `to_pos`).
 115     fn fatal_span_(&self, from_pos: BytePos, to_pos: BytePos, m: &str) -> ! {
 116         self.fatal_span(self.mk_sp(from_pos, to_pos), m)
 117     }
 118
 119     /// Report a lexical error spanning [`from_pos`, `to_pos`).
 120     fn err_span_(&self, from_pos: BytePos, to_pos: BytePos, m: &str) {
 121         self.err_span(self.mk_sp(from_pos, to_pos), m)
 122     }
 123
 124     fn struct_fatal_span_char(
 125         &self,
 126         from_pos: BytePos,
 127         to_pos: BytePos,
 128         m: &str,
 129         c: char,
 130     ) -> DiagnosticBuilder<'a, !> {
 131         self.sess
 132             .span_diagnostic
 133             .struct_span_fatal(self.mk_sp(from_pos, to_pos), &format!("{}: {}", m, escaped_char(c)))
 134     }
 135
 136     fn struct_err_span_char(
 137         &self,
 138         from_pos: BytePos,
 139         to_pos: BytePos,
 140         m: &str,
 141         c: char,
 142     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 143         self.sess
 144             .span_diagnostic
 145             .struct_span_err(self.mk_sp(from_pos, to_pos), &format!("{}: {}", m, escaped_char(c)))
 146     }
 147
 148     /// Detect usages of Unicode codepoints changing the direction of the text on screen and loudly
 149     /// complain about it.
 150     fn lint_unicode_text_flow(&self, start: BytePos) {
 151         // Opening delimiter of the length 2 is not included into the comment text.
 152         let content_start = start + BytePos(2);
 153         let content = self.str_from(content_start);
 154         if contains_text_flow_control_chars(content) {
 155             let span = self.mk_sp(start, self.pos);
 156             self.sess.buffer_lint_with_diagnostic(
 157                 &TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
 158                 span,
 159                 ast::CRATE_NODE_ID,
 160                 "unicode codepoint changing visible direction of text present in comment",
 161                 BuiltinLintDiagnostics::UnicodeTextFlow(span, content.to_string()),
 162             );
 163         }
 164     }
 165
 166     /// Turns simple `rustc_lexer::TokenKind` enum into a rich
 167     /// `rustc_ast::TokenKind`. This turns strings into interned
 168     /// symbols and runs additional validation.
 169     fn cook_lexer_token(&self, token: rustc_lexer::TokenKind, start: BytePos) -> Option<TokenKind> {
 170         Some(match token {
 171             rustc_lexer::TokenKind::LineComment { doc_style } => {
 172                 // Skip non-doc comments
 173                 let Some(doc_style) = doc_style else {
 174                     self.lint_unicode_text_flow(start);
 175                     return None;
 176                 };
 177
 178                 // Opening delimiter of the length 3 is not included into the symbol.
 179                 let content_start = start + BytePos(3);
 180                 let content = self.str_from(content_start);
 181                 self.cook_doc_comment(content_start, content, CommentKind::Line, doc_style)
 182             }
 183             rustc_lexer::TokenKind::BlockComment { doc_style, terminated } => {
 184                 if !terminated {
 185                     self.report_unterminated_block_comment(start, doc_style);
 186                 }
 187
 188                 // Skip non-doc comments
 189                 let Some(doc_style) = doc_style else {
 190                     self.lint_unicode_text_flow(start);
 191                     return None;
 192                 };
 193
 194                 // Opening delimiter of the length 3 and closing delimiter of the length 2
 195                 // are not included into the symbol.
 196                 let content_start = start + BytePos(3);
 197                 let content_end = self.pos - BytePos(if terminated { 2 } else { 0 });
 198                 let content = self.str_from_to(content_start, content_end);
 199                 self.cook_doc_comment(content_start, content, CommentKind::Block, doc_style)
 200             }
 201             rustc_lexer::TokenKind::Whitespace => return None,
 202             rustc_lexer::TokenKind::Ident
 203             | rustc_lexer::TokenKind::RawIdent
 204             | rustc_lexer::TokenKind::UnknownPrefix => {
 205                 let is_raw_ident = token == rustc_lexer::TokenKind::RawIdent;
 206                 let is_unknown_prefix = token == rustc_lexer::TokenKind::UnknownPrefix;
 207                 let mut ident_start = start;
 208                 if is_raw_ident {
 209                     ident_start = ident_start + BytePos(2);
 210                 }
 211                 if is_unknown_prefix {
 212                     self.report_unknown_prefix(start);
 213                 }
 214                 let sym = nfc_normalize(self.str_from(ident_start));
 215                 let span = self.mk_sp(start, self.pos);
 216                 self.sess.symbol_gallery.insert(sym, span);
 217                 if is_raw_ident {
 218                     if !sym.can_be_raw() {
 219                         self.err_span(span, &format!("`{}` cannot be a raw identifier", sym));
 220                     }
 221                     self.sess.raw_identifier_spans.borrow_mut().push(span);
 222                 }
 223                 token::Ident(sym, is_raw_ident)
 224             }
 225             rustc_lexer::TokenKind::InvalidIdent
 226                 // Do not recover an identifier with emoji if the codepoint is a confusable
 227                 // with a recoverable substitution token, like `➖`.
 228                 if !UNICODE_ARRAY
 229                     .iter()
 230                     .any(|&(c, _, _)| {
 231                         let sym = self.str_from(start);
 232                         sym.chars().count() == 1 && c == sym.chars().next().unwrap()
 233                     })
 234                      =>
 235             {
 236                 let sym = nfc_normalize(self.str_from(start));
 237                 let span = self.mk_sp(start, self.pos);
 238                 self.sess.bad_unicode_identifiers.borrow_mut().entry(sym).or_default().push(span);
 239                 token::Ident(sym, false)
 240             }
 241             rustc_lexer::TokenKind::Literal { kind, suffix_start } => {
 242                 let suffix_start = start + BytePos(suffix_start as u32);
 243                 let (kind, symbol) = self.cook_lexer_literal(start, suffix_start, kind);
 244                 let suffix = if suffix_start < self.pos {
 245                     let string = self.str_from(suffix_start);
 246                     if string == "_" {
 247                         self.sess
 248                             .span_diagnostic
 249                             .struct_span_warn(
 250                                 self.mk_sp(suffix_start, self.pos),
 251                                 "underscore literal suffix is not allowed",
 252                             )
 253                             .warn(
 254                                 "this was previously accepted by the compiler but is \
 255                                    being phased out; it will become a hard error in \
 256                                    a future release!",
 257                             )
 258                             .note(
 259                                 "see issue #42326 \
 260                                  <https://github.com/rust-lang/rust/issues/42326> \
 261                                  for more information",
 262                             )
 263                             .emit();
 264                         None
 265                     } else {
 266                         Some(Symbol::intern(string))
 267                     }
 268                 } else {
 269                     None
 270                 };
 271                 token::Literal(token::Lit { kind, symbol, suffix })
 272             }
 273             rustc_lexer::TokenKind::Lifetime { starts_with_number } => {
 274                 // Include the leading `'` in the real identifier, for macro
 275                 // expansion purposes. See #12512 for the gory details of why
 276                 // this is necessary.
 277                 let lifetime_name = self.str_from(start);
 278                 if starts_with_number {
 279                     self.err_span_(start, self.pos, "lifetimes cannot start with a number");
 280                 }
 281                 let ident = Symbol::intern(lifetime_name);
 282                 token::Lifetime(ident)
 283             }
 284             rustc_lexer::TokenKind::Semi => token::Semi,
 285             rustc_lexer::TokenKind::Comma => token::Comma,
 286             rustc_lexer::TokenKind::Dot => token::Dot,
 287             rustc_lexer::TokenKind::OpenParen => token::OpenDelim(Delimiter::Parenthesis),
 288             rustc_lexer::TokenKind::CloseParen => token::CloseDelim(Delimiter::Parenthesis),
 289             rustc_lexer::TokenKind::OpenBrace => token::OpenDelim(Delimiter::Brace),
 290             rustc_lexer::TokenKind::CloseBrace => token::CloseDelim(Delimiter::Brace),
 291             rustc_lexer::TokenKind::OpenBracket => token::OpenDelim(Delimiter::Bracket),
 292             rustc_lexer::TokenKind::CloseBracket => token::CloseDelim(Delimiter::Bracket),
 293             rustc_lexer::TokenKind::At => token::At,
 294             rustc_lexer::TokenKind::Pound => token::Pound,
 295             rustc_lexer::TokenKind::Tilde => token::Tilde,
 296             rustc_lexer::TokenKind::Question => token::Question,
 297             rustc_lexer::TokenKind::Colon => token::Colon,
 298             rustc_lexer::TokenKind::Dollar => token::Dollar,
 299             rustc_lexer::TokenKind::Eq => token::Eq,
 300             rustc_lexer::TokenKind::Bang => token::Not,
 301             rustc_lexer::TokenKind::Lt => token::Lt,
 302             rustc_lexer::TokenKind::Gt => token::Gt,
 303             rustc_lexer::TokenKind::Minus => token::BinOp(token::Minus),
 304             rustc_lexer::TokenKind::And => token::BinOp(token::And),
 305             rustc_lexer::TokenKind::Or => token::BinOp(token::Or),
 306             rustc_lexer::TokenKind::Plus => token::BinOp(token::Plus),
 307             rustc_lexer::TokenKind::Star => token::BinOp(token::Star),
 308             rustc_lexer::TokenKind::Slash => token::BinOp(token::Slash),
 309             rustc_lexer::TokenKind::Caret => token::BinOp(token::Caret),
 310             rustc_lexer::TokenKind::Percent => token::BinOp(token::Percent),
 311
 312             rustc_lexer::TokenKind::Unknown | rustc_lexer::TokenKind::InvalidIdent => {
 313                 let c = self.str_from(start).chars().next().unwrap();
 314                 let mut err =
 315                     self.struct_err_span_char(start, self.pos, "unknown start of token", c);
 316                 // FIXME: the lexer could be used to turn the ASCII version of unicode homoglyphs,
 317                 // instead of keeping a table in `check_for_substitution`into the token. Ideally,
 318                 // this should be inside `rustc_lexer`. However, we should first remove compound
 319                 // tokens like `<<` from `rustc_lexer`, and then add fancier error recovery to it,
 320                 // as there will be less overall work to do this way.
 321                 let token = unicode_chars::check_for_substitution(self, start, c, &mut err);
 322                 if c == '\x00' {
 323                     err.help("source files must contain UTF-8 encoded text, unexpected null bytes might occur when a different encoding is used");
 324                 }
 325                 err.emit();
 326                 token?
 327             }
 328         })
 329     }
 330
 331     fn cook_doc_comment(
 332         &self,
 333         content_start: BytePos,
 334         content: &str,
 335         comment_kind: CommentKind,
 336         doc_style: DocStyle,
 337     ) -> TokenKind {
 338         if content.contains('\r') {
 339             for (idx, _) in content.char_indices().filter(|&(_, c)| c == '\r') {
 340                 self.err_span_(
 341                     content_start + BytePos(idx as u32),
 342                     content_start + BytePos(idx as u32 + 1),
 343                     match comment_kind {
 344                         CommentKind::Line => "bare CR not allowed in doc-comment",
 345                         CommentKind::Block => "bare CR not allowed in block doc-comment",
 346                     },
 347                 );
 348             }
 349         }
 350
 351         let attr_style = match doc_style {
 352             DocStyle::Outer => AttrStyle::Outer,
 353             DocStyle::Inner => AttrStyle::Inner,
 354         };
 355
 356         token::DocComment(comment_kind, attr_style, Symbol::intern(content))
 357     }
 358
 359     fn cook_lexer_literal(
 360         &self,
 361         start: BytePos,
 362         suffix_start: BytePos,
 363         kind: rustc_lexer::LiteralKind,
 364     ) -> (token::LitKind, Symbol) {
 365         // prefix means `"` or `br"` or `r###"`, ...
 366         let (lit_kind, mode, prefix_len, postfix_len) = match kind {
 367             rustc_lexer::LiteralKind::Char { terminated } => {
 368                 if !terminated {
 369                     self.sess.span_diagnostic.span_fatal_with_code(
 370                         self.mk_sp(start, suffix_start),
 371                         "unterminated character literal",
 372                         error_code!(E0762),
 373                     )
 374                 }
 375                 (token::Char, Mode::Char, 1, 1) // ' '
 376             }
 377             rustc_lexer::LiteralKind::Byte { terminated } => {
 378                 if !terminated {
 379                     self.sess.span_diagnostic.span_fatal_with_code(
 380                         self.mk_sp(start + BytePos(1), suffix_start),
 381                         "unterminated byte constant",
 382                         error_code!(E0763),
 383                     )
 384                 }
 385                 (token::Byte, Mode::Byte, 2, 1) // b' '
 386             }
 387             rustc_lexer::LiteralKind::Str { terminated } => {
 388                 if !terminated {
 389                     self.sess.span_diagnostic.span_fatal_with_code(
 390                         self.mk_sp(start, suffix_start),
 391                         "unterminated double quote string",
 392                         error_code!(E0765),
 393                     )
 394                 }
 395                 (token::Str, Mode::Str, 1, 1) // " "
 396             }
 397             rustc_lexer::LiteralKind::ByteStr { terminated } => {
 398                 if !terminated {
 399                     self.sess.span_diagnostic.span_fatal_with_code(
 400                         self.mk_sp(start + BytePos(1), suffix_start),
 401                         "unterminated double quote byte string",
 402                         error_code!(E0766),
 403                     )
 404                 }
 405                 (token::ByteStr, Mode::ByteStr, 2, 1) // b" "
 406             }
 407             rustc_lexer::LiteralKind::RawStr { n_hashes, err } => {
 408                 self.report_raw_str_error(start, err);
 409                 let n = u32::from(n_hashes);
 410                 (token::StrRaw(n_hashes), Mode::RawStr, 2 + n, 1 + n) // r##" "##
 411             }
 412             rustc_lexer::LiteralKind::RawByteStr { n_hashes, err } => {
 413                 self.report_raw_str_error(start, err);
 414                 let n = u32::from(n_hashes);
 415                 (token::ByteStrRaw(n_hashes), Mode::RawByteStr, 3 + n, 1 + n) // br##" "##
 416             }
 417             rustc_lexer::LiteralKind::Int { base, empty_int } => {
 418                 return if empty_int {
 419                     self.sess
 420                         .span_diagnostic
 421                         .struct_span_err_with_code(
 422                             self.mk_sp(start, suffix_start),
 423                             "no valid digits found for number",
 424                             error_code!(E0768),
 425                         )
 426                         .emit();
 427                     (token::Integer, sym::integer(0))
 428                 } else {
 429                     self.validate_int_literal(base, start, suffix_start);
 430                     (token::Integer, self.symbol_from_to(start, suffix_start))
 431                 };
 432             }
 433             rustc_lexer::LiteralKind::Float { base, empty_exponent } => {
 434                 if empty_exponent {
 435                     self.err_span_(start, self.pos, "expected at least one digit in exponent");
 436                 }
 437
 438                 match base {
 439                     Base::Hexadecimal => self.err_span_(
 440                         start,
 441                         suffix_start,
 442                         "hexadecimal float literal is not supported",
 443                     ),
 444                     Base::Octal => {
 445                         self.err_span_(start, suffix_start, "octal float literal is not supported")
 446                     }
 447                     Base::Binary => {
 448                         self.err_span_(start, suffix_start, "binary float literal is not supported")
 449                     }
 450                     _ => (),
 451                 }
 452
 453                 let id = self.symbol_from_to(start, suffix_start);
 454                 return (token::Float, id);
 455             }
 456         };
 457         let content_start = start + BytePos(prefix_len);
 458         let content_end = suffix_start - BytePos(postfix_len);
 459         let id = self.symbol_from_to(content_start, content_end);
 460         self.validate_literal_escape(mode, content_start, content_end, prefix_len, postfix_len);
 461         (lit_kind, id)
 462     }
 463
 464     #[inline]
 465     fn src_index(&self, pos: BytePos) -> usize {
 466         (pos - self.start_pos).to_usize()
 467     }
 468
 469     /// Slice of the source text from `start` up to but excluding `self.pos`,
 470     /// meaning the slice does not include the character `self.ch`.
 471     fn str_from(&self, start: BytePos) -> &str {
 472         self.str_from_to(start, self.pos)
 473     }
 474
 475     /// As symbol_from, with an explicit endpoint.
 476     fn symbol_from_to(&self, start: BytePos, end: BytePos) -> Symbol {
 477         debug!("taking an ident from {:?} to {:?}", start, end);
 478         Symbol::intern(self.str_from_to(start, end))
 479     }
 480
 481     /// Slice of the source text spanning from `start` up to but excluding `end`.
 482     fn str_from_to(&self, start: BytePos, end: BytePos) -> &str {
 483         &self.src[self.src_index(start)..self.src_index(end)]
 484     }
 485
 486     fn report_raw_str_error(&self, start: BytePos, opt_err: Option<RawStrError>) {
 487         match opt_err {
 488             Some(RawStrError::InvalidStarter { bad_char }) => {
 489                 self.report_non_started_raw_string(start, bad_char)
 490             }
 491             Some(RawStrError::NoTerminator { expected, found, possible_terminator_offset }) => self
 492                 .report_unterminated_raw_string(start, expected, possible_terminator_offset, found),
 493             Some(RawStrError::TooManyDelimiters { found }) => {
 494                 self.report_too_many_hashes(start, found)
 495             }
 496             None => (),
 497         }
 498     }
 499
 500     fn report_non_started_raw_string(&self, start: BytePos, bad_char: char) -> ! {
 501         self.struct_fatal_span_char(
 502             start,
 503             self.pos,
 504             "found invalid character; only `#` is allowed in raw string delimitation",
 505             bad_char,
 506         )
 507         .emit()
 508     }
 509
 510     fn report_unterminated_raw_string(
 511         &self,
 512         start: BytePos,
 513         n_hashes: usize,
 514         possible_offset: Option<usize>,
 515         found_terminators: usize,
 516     ) -> ! {
 517         let mut err = self.sess.span_diagnostic.struct_span_fatal_with_code(
 518             self.mk_sp(start, start),
 519             "unterminated raw string",
 520             error_code!(E0748),
 521         );
 522
 523         err.span_label(self.mk_sp(start, start), "unterminated raw string");
 524
 525         if n_hashes > 0 {
 526             err.note(&format!(
 527                 "this raw string should be terminated with `\"{}`",
 528                 "#".repeat(n_hashes)
 529             ));
 530         }
 531
 532         if let Some(possible_offset) = possible_offset {
 533             let lo = start + BytePos(possible_offset as u32);
 534             let hi = lo + BytePos(found_terminators as u32);
 535             let span = self.mk_sp(lo, hi);
 536             err.span_suggestion(
 537                 span,
 538                 "consider terminating the string here",
 539                 "#".repeat(n_hashes),
 540                 Applicability::MaybeIncorrect,
 541             );
 542         }
 543
 544         err.emit()
 545     }
 546
 547     fn report_unterminated_block_comment(&self, start: BytePos, doc_style: Option<DocStyle>) {
 548         let msg = match doc_style {
 549             Some(_) => "unterminated block doc-comment",
 550             None => "unterminated block comment",
 551         };
 552         let last_bpos = self.pos;
 553         let mut err = self.sess.span_diagnostic.struct_span_fatal_with_code(
 554             self.mk_sp(start, last_bpos),
 555             msg,
 556             error_code!(E0758),
 557         );
 558         let mut nested_block_comment_open_idxs = vec![];
 559         let mut last_nested_block_comment_idxs = None;
 560         let mut content_chars = self.str_from(start).char_indices().peekable();
 561
 562         while let Some((idx, current_char)) = content_chars.next() {
 563             match content_chars.peek() {
 564                 Some((_, '*')) if current_char == '/' => {
 565                     nested_block_comment_open_idxs.push(idx);
 566                 }
 567                 Some((_, '/')) if current_char == '*' => {
 568                     last_nested_block_comment_idxs =
 569                         nested_block_comment_open_idxs.pop().map(|open_idx| (open_idx, idx));
 570                 }
 571                 _ => {}
 572             };
 573         }
 574
 575         if let Some((nested_open_idx, nested_close_idx)) = last_nested_block_comment_idxs {
 576             err.span_label(self.mk_sp(start, start + BytePos(2)), msg)
 577                 .span_label(
 578                     self.mk_sp(
 579                         start + BytePos(nested_open_idx as u32),
 580                         start + BytePos(nested_open_idx as u32 + 2),
 581                     ),
 582                     "...as last nested comment starts here, maybe you want to close this instead?",
 583                 )
 584                 .span_label(
 585                     self.mk_sp(
 586                         start + BytePos(nested_close_idx as u32),
 587                         start + BytePos(nested_close_idx as u32 + 2),
 588                     ),
 589                     "...and last nested comment terminates here.",
 590                 );
 591         }
 592
 593         err.emit();
 594     }
 595
 596     // RFC 3101 introduced the idea of (reserved) prefixes. As of Rust 2021,
 597     // using a (unknown) prefix is an error. In earlier editions, however, they
 598     // only result in a (allowed by default) lint, and are treated as regular
 599     // identifier tokens.
 600     fn report_unknown_prefix(&self, start: BytePos) {
 601         let prefix_span = self.mk_sp(start, self.pos);
 602         let prefix_str = self.str_from_to(start, self.pos);
 603         let msg = format!("prefix `{}` is unknown", prefix_str);
 604
 605         let expn_data = prefix_span.ctxt().outer_expn_data();
 606
 607         if expn_data.edition >= Edition::Edition2021 {
 608             // In Rust 2021, this is a hard error.
 609             let mut err = self.sess.span_diagnostic.struct_span_err(prefix_span, &msg);
 610             err.span_label(prefix_span, "unknown prefix");
 611             if prefix_str == "rb" {
 612                 err.span_suggestion_verbose(
 613                     prefix_span,
 614                     "use `br` for a raw byte string",
 615                     "br",
 616                     Applicability::MaybeIncorrect,
 617                 );
 618             } else if expn_data.is_root() {
 619                 err.span_suggestion_verbose(
 620                     prefix_span.shrink_to_hi(),
 621                     "consider inserting whitespace here",
 622                     " ",
 623                     Applicability::MaybeIncorrect,
 624                 );
 625             }
 626             err.note("prefixed identifiers and literals are reserved since Rust 2021");
 627             err.emit();
 628         } else {
 629             // Before Rust 2021, only emit a lint for migration.
 630             self.sess.buffer_lint_with_diagnostic(
 631                 &RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
 632                 prefix_span,
 633                 ast::CRATE_NODE_ID,
 634                 &msg,
 635                 BuiltinLintDiagnostics::ReservedPrefix(prefix_span),
 636             );
 637         }
 638     }
 639
 640     fn report_too_many_hashes(&self, start: BytePos, found: usize) -> ! {
 641         self.fatal_span_(
 642             start,
 643             self.pos,
 644             &format!(
 645                 "too many `#` symbols: raw strings may be delimited \
 646                 by up to 255 `#` symbols, but found {}",
 647                 found
 648             ),
 649         )
 650     }
 651
 652     fn validate_literal_escape(
 653         &self,
 654         mode: Mode,
 655         content_start: BytePos,
 656         content_end: BytePos,
 657         prefix_len: u32,
 658         postfix_len: u32,
 659     ) {
 660         let lit_content = self.str_from_to(content_start, content_end);
 661         unescape::unescape_literal(lit_content, mode, &mut |range, result| {
 662             // Here we only check for errors. The actual unescaping is done later.
 663             if let Err(err) = result {
 664                 let span_with_quotes = self
 665                     .mk_sp(content_start - BytePos(prefix_len), content_end + BytePos(postfix_len));
 666                 let (start, end) = (range.start as u32, range.end as u32);
 667                 let lo = content_start + BytePos(start);
 668                 let hi = lo + BytePos(end - start);
 669                 let span = self.mk_sp(lo, hi);
 670                 emit_unescape_error(
 671                     &self.sess.span_diagnostic,
 672                     lit_content,
 673                     span_with_quotes,
 674                     span,
 675                     mode,
 676                     range,
 677                     err,
 678                 );
 679             }
 680         });
 681     }
 682
 683     fn validate_int_literal(&self, base: Base, content_start: BytePos, content_end: BytePos) {
 684         let base = match base {
 685             Base::Binary => 2,
 686             Base::Octal => 8,
 687             _ => return,
 688         };
 689         let s = self.str_from_to(content_start + BytePos(2), content_end);
 690         for (idx, c) in s.char_indices() {
 691             let idx = idx as u32;
 692             if c != '_' && c.to_digit(base).is_none() {
 693                 let lo = content_start + BytePos(2 + idx);
 694                 let hi = content_start + BytePos(2 + idx + c.len_utf8() as u32);
 695                 self.err_span_(lo, hi, &format!("invalid digit for a base {} literal", base));
 696             }
 697         }
 698     }
 699 }
 700
 701 pub fn nfc_normalize(string: &str) -> Symbol {
 702     use unicode_normalization::{is_nfc_quick, IsNormalized, UnicodeNormalization};
 703     match is_nfc_quick(string.chars()) {
 704         IsNormalized::Yes => Symbol::intern(string),
 705         _ => {
 706             let normalized_str: String = string.chars().nfc().collect();
 707             Symbol::intern(&normalized_str)
 708         }
 709     }
 710 }