compiler/rustc_parse/src/parser/stmt.rs

   1 use super::attr::DEFAULT_INNER_ATTR_FORBIDDEN;
   2 use super::diagnostics::{AttemptLocalParseRecovery, Error};
   3 use super::expr::LhsExpr;
   4 use super::pat::{GateOr, RecoverComma};
   5 use super::path::PathStyle;
   6 use super::TrailingToken;
   7 use super::{AttrWrapper, BlockMode, ForceCollect, Parser, Restrictions, SemiColonMode};
   8 use crate::maybe_whole;
   9
  10 use rustc_ast as ast;
  11 use rustc_ast::ptr::P;
  12 use rustc_ast::token::{self, TokenKind};
  13 use rustc_ast::util::classify;
  14 use rustc_ast::AstLike;
  15 use rustc_ast::{AttrStyle, AttrVec, Attribute, MacCall, MacCallStmt, MacStmtStyle};
  16 use rustc_ast::{Block, BlockCheckMode, Expr, ExprKind, Local, Stmt};
  17 use rustc_ast::{StmtKind, DUMMY_NODE_ID};
  18 use rustc_errors::{Applicability, PResult};
  19 use rustc_span::source_map::{BytePos, Span};
  20 use rustc_span::symbol::{kw, sym};
  21
  22 use std::mem;
  23
  24 impl<'a> Parser<'a> {
  25     /// Parses a statement. This stops just before trailing semicolons on everything but items.
  26     /// e.g., a `StmtKind::Semi` parses to a `StmtKind::Expr`, leaving the trailing `;` unconsumed.
  27     // Public for rustfmt usage.
  28     pub fn parse_stmt(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<Stmt>> {
  29         Ok(self.parse_stmt_without_recovery(false, force_collect).unwrap_or_else(|mut e| {
  30             e.emit();
  31             self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
  32             None
  33         }))
  34     }
  35
  36     /// If `force_capture` is true, forces collection of tokens regardless of whether
  37     /// or not we have attributes
  38     crate fn parse_stmt_without_recovery(
  39         &mut self,
  40         capture_semi: bool,
  41         force_collect: ForceCollect,
  42     ) -> PResult<'a, Option<Stmt>> {
  43         let attrs = self.parse_outer_attributes()?;
  44         let lo = self.token.span;
  45
  46         // Don't use `maybe_whole` so that we have precise control
  47         // over when we bump the parser
  48         if let token::Interpolated(nt) = &self.token.kind {
  49             if let token::NtStmt(stmt) = &**nt {
  50                 let mut stmt = stmt.clone();
  51                 return self.collect_tokens_trailing_token(
  52                     attrs,
  53                     force_collect,
  54                     |this, mut attrs| {
  55                         stmt.visit_attrs(|stmt_attrs| {
  56                             mem::swap(stmt_attrs, &mut attrs);
  57                             stmt_attrs.extend(attrs);
  58                         });
  59                         // Make sure we capture the token::Interpolated
  60                         this.bump();
  61                         Ok((Some(stmt), TrailingToken::None))
  62                     },
  63                 );
  64             }
  65         }
  66
  67         Ok(Some(if self.token.is_keyword(kw::Let) {
  68             self.parse_local_mk(lo, attrs, capture_semi, force_collect)?
  69         } else if self.is_kw_followed_by_ident(kw::Mut) {
  70             self.recover_stmt_local(
  71                 lo,
  72                 attrs.take_for_recovery().into(),
  73                 "missing keyword",
  74                 "let mut",
  75             )?
  76         } else if self.is_kw_followed_by_ident(kw::Auto) {
  77             self.bump(); // `auto`
  78             let msg = "write `let` instead of `auto` to introduce a new variable";
  79             self.recover_stmt_local(lo, attrs.take_for_recovery().into(), msg, "let")?
  80         } else if self.is_kw_followed_by_ident(sym::var) {
  81             self.bump(); // `var`
  82             let msg = "write `let` instead of `var` to introduce a new variable";
  83             self.recover_stmt_local(lo, attrs.take_for_recovery().into(), msg, "let")?
  84         } else if self.check_path() && !self.token.is_qpath_start() && !self.is_path_start_item() {
  85             // We have avoided contextual keywords like `union`, items with `crate` visibility,
  86             // or `auto trait` items. We aim to parse an arbitrary path `a::b` but not something
  87             // that starts like a path (1 token), but it fact not a path.
  88             // Also, we avoid stealing syntax from `parse_item_`.
  89             self.parse_stmt_path_start(lo, attrs, force_collect)?
  90         } else if let Some(item) =
  91             self.parse_item_common(attrs.clone(), false, true, |_| true, force_collect)?
  92         {
  93             // FIXME: Bad copy of attrs
  94             self.mk_stmt(lo.to(item.span), StmtKind::Item(P(item)))
  95         } else if self.eat(&token::Semi) {
  96             // Do not attempt to parse an expression if we're done here.
  97             self.error_outer_attrs(&attrs.take_for_recovery());
  98             self.mk_stmt(lo, StmtKind::Empty)
  99         } else if self.token != token::CloseDelim(token::Brace) {
 100             // Remainder are line-expr stmts.
 101             let e = self.parse_expr_res(Restrictions::STMT_EXPR, Some(attrs))?;
 102             self.mk_stmt(lo.to(e.span), StmtKind::Expr(e))
 103         } else {
 104             self.error_outer_attrs(&attrs.take_for_recovery());
 105             return Ok(None);
 106         }))
 107     }
 108
 109     fn parse_stmt_path_start(
 110         &mut self,
 111         lo: Span,
 112         attrs: AttrWrapper,
 113         force_collect: ForceCollect,
 114     ) -> PResult<'a, Stmt> {
 115         self.collect_tokens_trailing_token(attrs, force_collect, |this, attrs| {
 116             let path = this.parse_path(PathStyle::Expr)?;
 117
 118             if this.eat(&token::Not) {
 119                 let stmt_mac = this.parse_stmt_mac(lo, attrs.into(), path)?;
 120                 if this.token == token::Semi {
 121                     return Ok((stmt_mac, TrailingToken::Semi));
 122                 } else {
 123                     return Ok((stmt_mac, TrailingToken::None));
 124                 }
 125             }
 126
 127             let expr = if this.eat(&token::OpenDelim(token::Brace)) {
 128                 this.parse_struct_expr(path, AttrVec::new(), true)?
 129             } else {
 130                 let hi = this.prev_token.span;
 131                 this.mk_expr(lo.to(hi), ExprKind::Path(None, path), AttrVec::new())
 132             };
 133
 134             let expr = this.with_res(Restrictions::STMT_EXPR, |this| {
 135                 let expr = this.parse_dot_or_call_expr_with(expr, lo, attrs)?;
 136                 this.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(expr))
 137             })?;
 138             Ok((
 139                 this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Expr(expr)),
 140                 TrailingToken::None,
 141             ))
 142         })
 143     }
 144
 145     /// Parses a statement macro `mac!(args)` provided a `path` representing `mac`.
 146     /// At this point, the `!` token after the path has already been eaten.
 147     fn parse_stmt_mac(&mut self, lo: Span, attrs: AttrVec, path: ast::Path) -> PResult<'a, Stmt> {
 148         let args = self.parse_mac_args()?;
 149         let delim = args.delim();
 150         let hi = self.prev_token.span;
 151
 152         let style =
 153             if delim == token::Brace { MacStmtStyle::Braces } else { MacStmtStyle::NoBraces };
 154
 155         let mac = MacCall { path, args, prior_type_ascription: self.last_type_ascription };
 156
 157         let kind = if delim == token::Brace || self.token == token::Semi || self.token == token::Eof
 158         {
 159             StmtKind::MacCall(P(MacCallStmt { mac, style, attrs, tokens: None }))
 160         } else {
 161             // Since none of the above applied, this is an expression statement macro.
 162             let e = self.mk_expr(lo.to(hi), ExprKind::MacCall(mac), AttrVec::new());
 163             let e = self.maybe_recover_from_bad_qpath(e, true)?;
 164             let e = self.parse_dot_or_call_expr_with(e, lo, attrs.into())?;
 165             let e = self.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(e))?;
 166             StmtKind::Expr(e)
 167         };
 168         Ok(self.mk_stmt(lo.to(hi), kind))
 169     }
 170
 171     /// Error on outer attributes in this context.
 172     /// Also error if the previous token was a doc comment.
 173     fn error_outer_attrs(&self, attrs: &[Attribute]) {
 174         if let [.., last] = attrs {
 175             if last.is_doc_comment() {
 176                 self.span_fatal_err(last.span, Error::UselessDocComment).emit();
 177             } else if attrs.iter().any(|a| a.style == AttrStyle::Outer) {
 178                 self.struct_span_err(last.span, "expected statement after outer attribute").emit();
 179             }
 180         }
 181     }
 182
 183     fn recover_stmt_local(
 184         &mut self,
 185         lo: Span,
 186         attrs: AttrVec,
 187         msg: &str,
 188         sugg: &str,
 189     ) -> PResult<'a, Stmt> {
 190         let stmt = self.recover_local_after_let(lo, attrs)?;
 191         self.struct_span_err(lo, "invalid variable declaration")
 192             .span_suggestion(lo, msg, sugg.to_string(), Applicability::MachineApplicable)
 193             .emit();
 194         Ok(stmt)
 195     }
 196
 197     fn parse_local_mk(
 198         &mut self,
 199         lo: Span,
 200         attrs: AttrWrapper,
 201         capture_semi: bool,
 202         force_collect: ForceCollect,
 203     ) -> PResult<'a, Stmt> {
 204         self.collect_tokens_trailing_token(attrs, force_collect, |this, attrs| {
 205             this.expect_keyword(kw::Let)?;
 206             let local = this.parse_local(attrs.into())?;
 207             let trailing = if capture_semi && this.token.kind == token::Semi {
 208                 TrailingToken::Semi
 209             } else {
 210                 TrailingToken::None
 211             };
 212             Ok((this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Local(local)), trailing))
 213         })
 214     }
 215
 216     fn recover_local_after_let(&mut self, lo: Span, attrs: AttrVec) -> PResult<'a, Stmt> {
 217         let local = self.parse_local(attrs)?;
 218         Ok(self.mk_stmt(lo.to(self.prev_token.span), StmtKind::Local(local)))
 219     }
 220
 221     /// Parses a local variable declaration.
 222     fn parse_local(&mut self, attrs: AttrVec) -> PResult<'a, P<Local>> {
 223         let lo = self.prev_token.span;
 224         let (pat, colon) =
 225             self.parse_pat_before_ty(None, GateOr::Yes, RecoverComma::Yes, "`let` bindings")?;
 226
 227         let (err, ty) = if colon {
 228             // Save the state of the parser before parsing type normally, in case there is a `:`
 229             // instead of an `=` typo.
 230             let parser_snapshot_before_type = self.clone();
 231             let colon_sp = self.prev_token.span;
 232             match self.parse_ty() {
 233                 Ok(ty) => (None, Some(ty)),
 234                 Err(mut err) => {
 235                     if let Ok(snip) = self.span_to_snippet(pat.span) {
 236                         err.span_label(pat.span, format!("while parsing the type for `{}`", snip));
 237                     }
 238                     let err = if self.check(&token::Eq) {
 239                         err.emit();
 240                         None
 241                     } else {
 242                         // Rewind to before attempting to parse the type and continue parsing.
 243                         let parser_snapshot_after_type =
 244                             mem::replace(self, parser_snapshot_before_type);
 245                         Some((parser_snapshot_after_type, colon_sp, err))
 246                     };
 247                     (err, None)
 248                 }
 249             }
 250         } else {
 251             (None, None)
 252         };
 253         let init = match (self.parse_initializer(err.is_some()), err) {
 254             (Ok(init), None) => {
 255                 // init parsed, ty parsed
 256                 init
 257             }
 258             (Ok(init), Some((_, colon_sp, mut err))) => {
 259                 // init parsed, ty error
 260                 // Could parse the type as if it were the initializer, it is likely there was a
 261                 // typo in the code: `:` instead of `=`. Add suggestion and emit the error.
 262                 err.span_suggestion_short(
 263                     colon_sp,
 264                     "use `=` if you meant to assign",
 265                     " =".to_string(),
 266                     Applicability::MachineApplicable,
 267                 );
 268                 err.emit();
 269                 // As this was parsed successfully, continue as if the code has been fixed for the
 270                 // rest of the file. It will still fail due to the emitted error, but we avoid
 271                 // extra noise.
 272                 init
 273             }
 274             (Err(mut init_err), Some((snapshot, _, ty_err))) => {
 275                 // init error, ty error
 276                 init_err.cancel();
 277                 // Couldn't parse the type nor the initializer, only raise the type error and
 278                 // return to the parser state before parsing the type as the initializer.
 279                 // let x: <parse_error>;
 280                 *self = snapshot;
 281                 return Err(ty_err);
 282             }
 283             (Err(err), None) => {
 284                 // init error, ty parsed
 285                 // Couldn't parse the initializer and we're not attempting to recover a failed
 286                 // parse of the type, return the error.
 287                 return Err(err);
 288             }
 289         };
 290         let hi = if self.token == token::Semi { self.token.span } else { self.prev_token.span };
 291         Ok(P(ast::Local { ty, pat, init, id: DUMMY_NODE_ID, span: lo.to(hi), attrs, tokens: None }))
 292     }
 293
 294     /// Parses the RHS of a local variable declaration (e.g., `= 14;`).
 295     fn parse_initializer(&mut self, eq_optional: bool) -> PResult<'a, Option<P<Expr>>> {
 296         let eq_consumed = match self.token.kind {
 297             token::BinOpEq(..) => {
 298                 // Recover `let x <op>= 1` as `let x = 1`
 299                 self.struct_span_err(
 300                     self.token.span,
 301                     "can't reassign to an uninitialized variable",
 302                 )
 303                 .span_suggestion_short(
 304                     self.token.span,
 305                     "initialize the variable",
 306                     "=".to_string(),
 307                     Applicability::MaybeIncorrect,
 308                 )
 309                 .help("if you meant to overwrite, remove the `let` binding")
 310                 .emit();
 311                 self.bump();
 312                 true
 313             }
 314             _ => self.eat(&token::Eq),
 315         };
 316
 317         Ok(if eq_consumed || eq_optional { Some(self.parse_expr()?) } else { None })
 318     }
 319
 320     /// Parses a block. No inner attributes are allowed.
 321     pub(super) fn parse_block(&mut self) -> PResult<'a, P<Block>> {
 322         let (attrs, block) = self.parse_inner_attrs_and_block()?;
 323         if let [.., last] = &*attrs {
 324             self.error_on_forbidden_inner_attr(last.span, DEFAULT_INNER_ATTR_FORBIDDEN);
 325         }
 326         Ok(block)
 327     }
 328
 329     fn error_block_no_opening_brace<T>(&mut self) -> PResult<'a, T> {
 330         let sp = self.token.span;
 331         let tok = super::token_descr(&self.token);
 332         let mut e = self.struct_span_err(sp, &format!("expected `{{`, found {}", tok));
 333         let do_not_suggest_help = self.token.is_keyword(kw::In) || self.token == token::Colon;
 334
 335         // Check to see if the user has written something like
 336         //
 337         //    if (cond)
 338         //      bar;
 339         //
 340         // which is valid in other languages, but not Rust.
 341         match self.parse_stmt_without_recovery(false, ForceCollect::No) {
 342             // If the next token is an open brace (e.g., `if a b {`), the place-
 343             // inside-a-block suggestion would be more likely wrong than right.
 344             Ok(Some(_))
 345                 if self.look_ahead(1, |t| t == &token::OpenDelim(token::Brace))
 346                     || do_not_suggest_help => {}
 347             Ok(Some(stmt)) => {
 348                 let stmt_own_line = self.sess.source_map().is_line_before_span_empty(sp);
 349                 let stmt_span = if stmt_own_line && self.eat(&token::Semi) {
 350                     // Expand the span to include the semicolon.
 351                     stmt.span.with_hi(self.prev_token.span.hi())
 352                 } else {
 353                     stmt.span
 354                 };
 355                 if let Ok(snippet) = self.span_to_snippet(stmt_span) {
 356                     e.span_suggestion(
 357                         stmt_span,
 358                         "try placing this code inside a block",
 359                         format!("{{ {} }}", snippet),
 360                         // Speculative; has been misleading in the past (#46836).
 361                         Applicability::MaybeIncorrect,
 362                     );
 363                 }
 364             }
 365             Err(mut e) => {
 366                 self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
 367                 e.cancel();
 368             }
 369             _ => {}
 370         }
 371         e.span_label(sp, "expected `{`");
 372         Err(e)
 373     }
 374
 375     /// Parses a block. Inner attributes are allowed.
 376     pub(super) fn parse_inner_attrs_and_block(
 377         &mut self,
 378     ) -> PResult<'a, (Vec<Attribute>, P<Block>)> {
 379         self.parse_block_common(self.token.span, BlockCheckMode::Default)
 380     }
 381
 382     /// Parses a block. Inner attributes are allowed.
 383     pub(super) fn parse_block_common(
 384         &mut self,
 385         lo: Span,
 386         blk_mode: BlockCheckMode,
 387     ) -> PResult<'a, (Vec<Attribute>, P<Block>)> {
 388         maybe_whole!(self, NtBlock, |x| (Vec::new(), x));
 389
 390         if !self.eat(&token::OpenDelim(token::Brace)) {
 391             return self.error_block_no_opening_brace();
 392         }
 393
 394         let attrs = self.parse_inner_attributes()?;
 395         let tail = if let Some(tail) = self.maybe_suggest_struct_literal(lo, blk_mode) {
 396             tail?
 397         } else {
 398             self.parse_block_tail(lo, blk_mode, AttemptLocalParseRecovery::Yes)?
 399         };
 400         Ok((attrs, tail))
 401     }
 402
 403     /// Parses the rest of a block expression or function body.
 404     /// Precondition: already parsed the '{'.
 405     crate fn parse_block_tail(
 406         &mut self,
 407         lo: Span,
 408         s: BlockCheckMode,
 409         recover: AttemptLocalParseRecovery,
 410     ) -> PResult<'a, P<Block>> {
 411         let mut stmts = vec![];
 412         while !self.eat(&token::CloseDelim(token::Brace)) {
 413             if self.token == token::Eof {
 414                 break;
 415             }
 416             let stmt = match self.parse_full_stmt(recover) {
 417                 Err(mut err) if recover.yes() => {
 418                     self.maybe_annotate_with_ascription(&mut err, false);
 419                     err.emit();
 420                     self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
 421                     Some(self.mk_stmt_err(self.token.span))
 422                 }
 423                 Ok(stmt) => stmt,
 424                 Err(err) => return Err(err),
 425             };
 426             if let Some(stmt) = stmt {
 427                 stmts.push(stmt);
 428             } else {
 429                 // Found only `;` or `}`.
 430                 continue;
 431             };
 432         }
 433         Ok(self.mk_block(stmts, s, lo.to(self.prev_token.span)))
 434     }
 435
 436     /// Parses a statement, including the trailing semicolon.
 437     pub fn parse_full_stmt(
 438         &mut self,
 439         recover: AttemptLocalParseRecovery,
 440     ) -> PResult<'a, Option<Stmt>> {
 441         // Skip looking for a trailing semicolon when we have an interpolated statement.
 442         maybe_whole!(self, NtStmt, |x| Some(x));
 443
 444         let mut stmt = match self.parse_stmt_without_recovery(true, ForceCollect::No)? {
 445             Some(stmt) => stmt,
 446             None => return Ok(None),
 447         };
 448
 449         let mut eat_semi = true;
 450         match stmt.kind {
 451             // Expression without semicolon.
 452             StmtKind::Expr(ref mut expr)
 453                 if self.token != token::Eof && classify::expr_requires_semi_to_be_stmt(expr) =>
 454             {
 455                 // Just check for errors and recover; do not eat semicolon yet.
 456                 if let Err(mut e) =
 457                     self.expect_one_of(&[], &[token::Semi, token::CloseDelim(token::Brace)])
 458                 {
 459                     if let TokenKind::DocComment(..) = self.token.kind {
 460                         if let Ok(snippet) = self.span_to_snippet(self.token.span) {
 461                             let sp = self.token.span;
 462                             let marker = &snippet[..3];
 463                             let (comment_marker, doc_comment_marker) = marker.split_at(2);
 464
 465                             e.span_suggestion(
 466                                 sp.with_hi(sp.lo() + BytePos(marker.len() as u32)),
 467                                 &format!(
 468                                     "add a space before `{}` to use a regular comment",
 469                                     doc_comment_marker,
 470                                 ),
 471                                 format!("{} {}", comment_marker, doc_comment_marker),
 472                                 Applicability::MaybeIncorrect,
 473                             );
 474                         }
 475                     }
 476                     if let Err(mut e) =
 477                         self.check_mistyped_turbofish_with_multiple_type_params(e, expr)
 478                     {
 479                         if recover.no() {
 480                             return Err(e);
 481                         }
 482                         e.emit();
 483                         self.recover_stmt();
 484                     }
 485                     // Don't complain about type errors in body tail after parse error (#57383).
 486                     let sp = expr.span.to(self.prev_token.span);
 487                     *expr = self.mk_expr_err(sp);
 488                 }
 489             }
 490             StmtKind::Expr(_) | StmtKind::MacCall(_) => {}
 491             StmtKind::Local(ref mut local) => {
 492                 if let Err(e) = self.expect_semi() {
 493                     // We might be at the `,` in `let x = foo<bar, baz>;`. Try to recover.
 494                     match &mut local.init {
 495                         Some(ref mut expr) => {
 496                             self.check_mistyped_turbofish_with_multiple_type_params(e, expr)?;
 497                             // We found `foo<bar, baz>`, have we fully recovered?
 498                             self.expect_semi()?;
 499                         }
 500                         None => return Err(e),
 501                     }
 502                 }
 503                 eat_semi = false;
 504             }
 505             StmtKind::Empty | StmtKind::Item(_) | StmtKind::Semi(_) => eat_semi = false,
 506         }
 507
 508         if eat_semi && self.eat(&token::Semi) {
 509             stmt = stmt.add_trailing_semicolon();
 510         }
 511         stmt.span = stmt.span.to(self.prev_token.span);
 512         Ok(Some(stmt))
 513     }
 514
 515     pub(super) fn mk_block(&self, stmts: Vec<Stmt>, rules: BlockCheckMode, span: Span) -> P<Block> {
 516         P(Block { stmts, id: DUMMY_NODE_ID, rules, span, tokens: None })
 517     }
 518
 519     pub(super) fn mk_stmt(&self, span: Span, kind: StmtKind) -> Stmt {
 520         Stmt { id: DUMMY_NODE_ID, kind, span }
 521     }
 522
 523     pub(super) fn mk_stmt_err(&self, span: Span) -> Stmt {
 524         self.mk_stmt(span, StmtKind::Expr(self.mk_expr_err(span)))
 525     }
 526
 527     pub(super) fn mk_block_err(&self, span: Span) -> P<Block> {
 528         self.mk_block(vec![self.mk_stmt_err(span)], BlockCheckMode::Default, span)
 529     }
 530 }