src/libsyntax/parse/parser/stmt.rs

   1 use super::{Parser, PResult, Restrictions, PrevTokenKind, SemiColonMode, BlockMode};
   2 use super::expr::LhsExpr;
   3 use super::path::PathStyle;
   4
   5 use crate::ptr::P;
   6 use crate::{maybe_whole, ThinVec};
   7 use crate::ast::{self, Stmt, StmtKind, Local, Block, BlockCheckMode, Expr, ExprKind};
   8 use crate::ast::{Attribute, AttrStyle, VisibilityKind, MacStmtStyle, Mac_, MacDelimiter};
   9 use crate::ext::base::DummyResult;
  10 use crate::parse::{classify, DirectoryOwnership};
  11 use crate::parse::diagnostics::Error;
  12 use crate::parse::token::{self};
  13 use crate::source_map::{respan, Span};
  14 use crate::symbol::{kw, sym};
  15
  16 use std::mem;
  17 use errors::Applicability;
  18
  19 impl<'a> Parser<'a> {
  20     /// Parse a statement. This stops just before trailing semicolons on everything but items.
  21     /// e.g., a `StmtKind::Semi` parses to a `StmtKind::Expr`, leaving the trailing `;` unconsumed.
  22     pub fn parse_stmt(&mut self) -> PResult<'a, Option<Stmt>> {
  23         Ok(self.parse_stmt_(true))
  24     }
  25
  26     fn parse_stmt_(&mut self, macro_legacy_warnings: bool) -> Option<Stmt> {
  27         self.parse_stmt_without_recovery(macro_legacy_warnings).unwrap_or_else(|mut e| {
  28             e.emit();
  29             self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
  30             None
  31         })
  32     }
  33
  34     fn parse_stmt_without_recovery(
  35         &mut self,
  36         macro_legacy_warnings: bool,
  37     ) -> PResult<'a, Option<Stmt>> {
  38         maybe_whole!(self, NtStmt, |x| Some(x));
  39
  40         let attrs = self.parse_outer_attributes()?;
  41         let lo = self.token.span;
  42
  43         Ok(Some(if self.eat_keyword(kw::Let) {
  44             Stmt {
  45                 id: ast::DUMMY_NODE_ID,
  46                 node: StmtKind::Local(self.parse_local(attrs.into())?),
  47                 span: lo.to(self.prev_span),
  48             }
  49         } else if let Some(macro_def) = self.eat_macro_def(
  50             &attrs,
  51             &respan(lo, VisibilityKind::Inherited),
  52             lo,
  53         )? {
  54             Stmt {
  55                 id: ast::DUMMY_NODE_ID,
  56                 node: StmtKind::Item(macro_def),
  57                 span: lo.to(self.prev_span),
  58             }
  59         // Starts like a simple path, being careful to avoid contextual keywords
  60         // such as a union items, item with `crate` visibility or auto trait items.
  61         // Our goal here is to parse an arbitrary path `a::b::c` but not something that starts
  62         // like a path (1 token), but it fact not a path.
  63         // `union::b::c` - path, `union U { ... }` - not a path.
  64         // `crate::b::c` - path, `crate struct S;` - not a path.
  65         } else if self.token.is_path_start() &&
  66                   !self.token.is_qpath_start() &&
  67                   !self.is_union_item() &&
  68                   !self.is_crate_vis() &&
  69                   !self.is_auto_trait_item() &&
  70                   !self.is_async_fn() {
  71             let path = self.parse_path(PathStyle::Expr)?;
  72
  73             if !self.eat(&token::Not) {
  74                 let expr = if self.check(&token::OpenDelim(token::Brace)) {
  75                     self.parse_struct_expr(lo, path, ThinVec::new())?
  76                 } else {
  77                     let hi = self.prev_span;
  78                     self.mk_expr(lo.to(hi), ExprKind::Path(None, path), ThinVec::new())
  79                 };
  80
  81                 let expr = self.with_res(Restrictions::STMT_EXPR, |this| {
  82                     let expr = this.parse_dot_or_call_expr_with(expr, lo, attrs.into())?;
  83                     this.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(expr))
  84                 })?;
  85
  86                 return Ok(Some(Stmt {
  87                     id: ast::DUMMY_NODE_ID,
  88                     node: StmtKind::Expr(expr),
  89                     span: lo.to(self.prev_span),
  90                 }));
  91             }
  92
  93             let (delim, tts) = self.expect_delimited_token_tree()?;
  94             let hi = self.prev_span;
  95
  96             let style = if delim == MacDelimiter::Brace {
  97                 MacStmtStyle::Braces
  98             } else {
  99                 MacStmtStyle::NoBraces
 100             };
 101
 102             let mac = respan(lo.to(hi), Mac_ {
 103                 path,
 104                 tts,
 105                 delim,
 106                 prior_type_ascription: self.last_type_ascription,
 107             });
 108             let node = if delim == MacDelimiter::Brace ||
 109                           self.token == token::Semi || self.token == token::Eof {
 110                 StmtKind::Mac(P((mac, style, attrs.into())))
 111             }
 112             // We used to incorrectly stop parsing macro-expanded statements here.
 113             // If the next token will be an error anyway but could have parsed with the
 114             // earlier behavior, stop parsing here and emit a warning to avoid breakage.
 115             else if macro_legacy_warnings &&
 116                     self.token.can_begin_expr() &&
 117                     match self.token.kind {
 118                 // These can continue an expression, so we can't stop parsing and warn.
 119                 token::OpenDelim(token::Paren) | token::OpenDelim(token::Bracket) |
 120                 token::BinOp(token::Minus) | token::BinOp(token::Star) |
 121                 token::BinOp(token::And) | token::BinOp(token::Or) |
 122                 token::AndAnd | token::OrOr |
 123                 token::DotDot | token::DotDotDot | token::DotDotEq => false,
 124                 _ => true,
 125             } {
 126                 self.warn_missing_semicolon();
 127                 StmtKind::Mac(P((mac, style, attrs.into())))
 128             } else {
 129                 let e = self.mk_expr(mac.span, ExprKind::Mac(mac), ThinVec::new());
 130                 let e = self.maybe_recover_from_bad_qpath(e, true)?;
 131                 let e = self.parse_dot_or_call_expr_with(e, lo, attrs.into())?;
 132                 let e = self.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(e))?;
 133                 StmtKind::Expr(e)
 134             };
 135             Stmt {
 136                 id: ast::DUMMY_NODE_ID,
 137                 span: lo.to(hi),
 138                 node,
 139             }
 140         } else {
 141             // FIXME: Bad copy of attrs
 142             let old_directory_ownership =
 143                 mem::replace(&mut self.directory.ownership, DirectoryOwnership::UnownedViaBlock);
 144             let item = self.parse_item_(attrs.clone(), false, true)?;
 145             self.directory.ownership = old_directory_ownership;
 146
 147             match item {
 148                 Some(i) => Stmt {
 149                     id: ast::DUMMY_NODE_ID,
 150                     span: lo.to(i.span),
 151                     node: StmtKind::Item(i),
 152                 },
 153                 None => {
 154                     let unused_attrs = |attrs: &[Attribute], s: &mut Self| {
 155                         if !attrs.is_empty() {
 156                             if s.prev_token_kind == PrevTokenKind::DocComment {
 157                                 s.span_fatal_err(s.prev_span, Error::UselessDocComment).emit();
 158                             } else if attrs.iter().any(|a| a.style == AttrStyle::Outer) {
 159                                 s.span_err(
 160                                     s.token.span, "expected statement after outer attribute"
 161                                 );
 162                             }
 163                         }
 164                     };
 165
 166                     // Do not attempt to parse an expression if we're done here.
 167                     if self.token == token::Semi {
 168                         unused_attrs(&attrs, self);
 169                         self.bump();
 170                         return Ok(None);
 171                     }
 172
 173                     if self.token == token::CloseDelim(token::Brace) {
 174                         unused_attrs(&attrs, self);
 175                         return Ok(None);
 176                     }
 177
 178                     // Remainder are line-expr stmts.
 179                     let e = self.parse_expr_res(
 180                         Restrictions::STMT_EXPR, Some(attrs.into()))?;
 181                     Stmt {
 182                         id: ast::DUMMY_NODE_ID,
 183                         span: lo.to(e.span),
 184                         node: StmtKind::Expr(e),
 185                     }
 186                 }
 187             }
 188         }))
 189     }
 190
 191     /// Parses a local variable declaration.
 192     fn parse_local(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Local>> {
 193         let lo = self.prev_span;
 194         let pat = self.parse_top_level_pat()?;
 195
 196         let (err, ty) = if self.eat(&token::Colon) {
 197             // Save the state of the parser before parsing type normally, in case there is a `:`
 198             // instead of an `=` typo.
 199             let parser_snapshot_before_type = self.clone();
 200             let colon_sp = self.prev_span;
 201             match self.parse_ty() {
 202                 Ok(ty) => (None, Some(ty)),
 203                 Err(mut err) => {
 204                     // Rewind to before attempting to parse the type and continue parsing
 205                     let parser_snapshot_after_type = self.clone();
 206                     mem::replace(self, parser_snapshot_before_type);
 207
 208                     let snippet = self.span_to_snippet(pat.span).unwrap();
 209                     err.span_label(pat.span, format!("while parsing the type for `{}`", snippet));
 210                     (Some((parser_snapshot_after_type, colon_sp, err)), None)
 211                 }
 212             }
 213         } else {
 214             (None, None)
 215         };
 216         let init = match (self.parse_initializer(err.is_some()), err) {
 217             (Ok(init), None) => {  // init parsed, ty parsed
 218                 init
 219             }
 220             (Ok(init), Some((_, colon_sp, mut err))) => {  // init parsed, ty error
 221                 // Could parse the type as if it were the initializer, it is likely there was a
 222                 // typo in the code: `:` instead of `=`. Add suggestion and emit the error.
 223                 err.span_suggestion_short(
 224                     colon_sp,
 225                     "use `=` if you meant to assign",
 226                     "=".to_string(),
 227                     Applicability::MachineApplicable
 228                 );
 229                 err.emit();
 230                 // As this was parsed successfully, continue as if the code has been fixed for the
 231                 // rest of the file. It will still fail due to the emitted error, but we avoid
 232                 // extra noise.
 233                 init
 234             }
 235             (Err(mut init_err), Some((snapshot, _, ty_err))) => {  // init error, ty error
 236                 init_err.cancel();
 237                 // Couldn't parse the type nor the initializer, only raise the type error and
 238                 // return to the parser state before parsing the type as the initializer.
 239                 // let x: <parse_error>;
 240                 mem::replace(self, snapshot);
 241                 return Err(ty_err);
 242             }
 243             (Err(err), None) => {  // init error, ty parsed
 244                 // Couldn't parse the initializer and we're not attempting to recover a failed
 245                 // parse of the type, return the error.
 246                 return Err(err);
 247             }
 248         };
 249         let hi = if self.token == token::Semi {
 250             self.token.span
 251         } else {
 252             self.prev_span
 253         };
 254         Ok(P(ast::Local {
 255             ty,
 256             pat,
 257             init,
 258             id: ast::DUMMY_NODE_ID,
 259             span: lo.to(hi),
 260             attrs,
 261         }))
 262     }
 263
 264     /// Parses the RHS of a local variable declaration (e.g., '= 14;').
 265     fn parse_initializer(&mut self, skip_eq: bool) -> PResult<'a, Option<P<Expr>>> {
 266         if self.eat(&token::Eq) {
 267             Ok(Some(self.parse_expr()?))
 268         } else if skip_eq {
 269             Ok(Some(self.parse_expr()?))
 270         } else {
 271             Ok(None)
 272         }
 273     }
 274
 275     fn is_auto_trait_item(&self) -> bool {
 276         // auto trait
 277         (self.token.is_keyword(kw::Auto) &&
 278             self.is_keyword_ahead(1, &[kw::Trait]))
 279         || // unsafe auto trait
 280         (self.token.is_keyword(kw::Unsafe) &&
 281          self.is_keyword_ahead(1, &[kw::Auto]) &&
 282          self.is_keyword_ahead(2, &[kw::Trait]))
 283     }
 284
 285     /// Parses a block. No inner attributes are allowed.
 286     pub fn parse_block(&mut self) -> PResult<'a, P<Block>> {
 287         maybe_whole!(self, NtBlock, |x| x);
 288
 289         let lo = self.token.span;
 290
 291         if !self.eat(&token::OpenDelim(token::Brace)) {
 292             let sp = self.token.span;
 293             let tok = self.this_token_descr();
 294             let mut e = self.span_fatal(sp, &format!("expected `{{`, found {}", tok));
 295             let do_not_suggest_help =
 296                 self.token.is_keyword(kw::In) || self.token == token::Colon;
 297
 298             if self.token.is_ident_named(sym::and) {
 299                 e.span_suggestion_short(
 300                     self.token.span,
 301                     "use `&&` instead of `and` for the boolean operator",
 302                     "&&".to_string(),
 303                     Applicability::MaybeIncorrect,
 304                 );
 305             }
 306             if self.token.is_ident_named(sym::or) {
 307                 e.span_suggestion_short(
 308                     self.token.span,
 309                     "use `||` instead of `or` for the boolean operator",
 310                     "||".to_string(),
 311                     Applicability::MaybeIncorrect,
 312                 );
 313             }
 314
 315             // Check to see if the user has written something like
 316             //
 317             //    if (cond)
 318             //      bar;
 319             //
 320             // Which is valid in other languages, but not Rust.
 321             match self.parse_stmt_without_recovery(false) {
 322                 Ok(Some(stmt)) => {
 323                     if self.look_ahead(1, |t| t == &token::OpenDelim(token::Brace))
 324                         || do_not_suggest_help {
 325                         // if the next token is an open brace (e.g., `if a b {`), the place-
 326                         // inside-a-block suggestion would be more likely wrong than right
 327                         e.span_label(sp, "expected `{`");
 328                         return Err(e);
 329                     }
 330                     let mut stmt_span = stmt.span;
 331                     // expand the span to include the semicolon, if it exists
 332                     if self.eat(&token::Semi) {
 333                         stmt_span = stmt_span.with_hi(self.prev_span.hi());
 334                     }
 335                     if let Ok(snippet) = self.span_to_snippet(stmt_span) {
 336                         e.span_suggestion(
 337                             stmt_span,
 338                             "try placing this code inside a block",
 339                             format!("{{ {} }}", snippet),
 340                             // speculative, has been misleading in the past (#46836)
 341                             Applicability::MaybeIncorrect,
 342                         );
 343                     }
 344                 }
 345                 Err(mut e) => {
 346                     self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
 347                     self.cancel(&mut e);
 348                 }
 349                 _ => ()
 350             }
 351             e.span_label(sp, "expected `{`");
 352             return Err(e);
 353         }
 354
 355         self.parse_block_tail(lo, BlockCheckMode::Default)
 356     }
 357
 358     /// Parses a block. Inner attributes are allowed.
 359     crate fn parse_inner_attrs_and_block(&mut self) -> PResult<'a, (Vec<Attribute>, P<Block>)> {
 360         maybe_whole!(self, NtBlock, |x| (Vec::new(), x));
 361
 362         let lo = self.token.span;
 363         self.expect(&token::OpenDelim(token::Brace))?;
 364         Ok((self.parse_inner_attributes()?,
 365             self.parse_block_tail(lo, BlockCheckMode::Default)?))
 366     }
 367
 368     /// Parses the rest of a block expression or function body.
 369     /// Precondition: already parsed the '{'.
 370     pub(super) fn parse_block_tail(
 371         &mut self,
 372         lo: Span,
 373         s: BlockCheckMode
 374     ) -> PResult<'a, P<Block>> {
 375         let mut stmts = vec![];
 376         while !self.eat(&token::CloseDelim(token::Brace)) {
 377             if self.token == token::Eof {
 378                 break;
 379             }
 380             let stmt = match self.parse_full_stmt(false) {
 381                 Err(mut err) => {
 382                     err.emit();
 383                     self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
 384                     Some(Stmt {
 385                         id: ast::DUMMY_NODE_ID,
 386                         node: StmtKind::Expr(DummyResult::raw_expr(self.token.span, true)),
 387                         span: self.token.span,
 388                     })
 389                 }
 390                 Ok(stmt) => stmt,
 391             };
 392             if let Some(stmt) = stmt {
 393                 stmts.push(stmt);
 394             } else {
 395                 // Found only `;` or `}`.
 396                 continue;
 397             };
 398         }
 399         Ok(P(ast::Block {
 400             stmts,
 401             id: ast::DUMMY_NODE_ID,
 402             rules: s,
 403             span: lo.to(self.prev_span),
 404         }))
 405     }
 406
 407     /// Parses a statement, including the trailing semicolon.
 408     crate fn parse_full_stmt(&mut self, macro_legacy_warnings: bool) -> PResult<'a, Option<Stmt>> {
 409         // skip looking for a trailing semicolon when we have an interpolated statement
 410         maybe_whole!(self, NtStmt, |x| Some(x));
 411
 412         let mut stmt = match self.parse_stmt_without_recovery(macro_legacy_warnings)? {
 413             Some(stmt) => stmt,
 414             None => return Ok(None),
 415         };
 416
 417         match stmt.node {
 418             StmtKind::Expr(ref expr) if self.token != token::Eof => {
 419                 // expression without semicolon
 420                 if classify::expr_requires_semi_to_be_stmt(expr) {
 421                     // Just check for errors and recover; do not eat semicolon yet.
 422                     if let Err(mut e) =
 423                         self.expect_one_of(&[], &[token::Semi, token::CloseDelim(token::Brace)])
 424                     {
 425                         e.emit();
 426                         self.recover_stmt();
 427                         // Don't complain about type errors in body tail after parse error (#57383).
 428                         let sp = expr.span.to(self.prev_span);
 429                         stmt.node = StmtKind::Expr(DummyResult::raw_expr(sp, true));
 430                     }
 431                 }
 432             }
 433             StmtKind::Local(..) => {
 434                 // We used to incorrectly allow a macro-expanded let statement to lack a semicolon.
 435                 if macro_legacy_warnings && self.token != token::Semi {
 436                     self.warn_missing_semicolon();
 437                 } else {
 438                     self.expect_one_of(&[], &[token::Semi])?;
 439                 }
 440             }
 441             _ => {}
 442         }
 443
 444         if self.eat(&token::Semi) {
 445             stmt = stmt.add_trailing_semicolon();
 446         }
 447         stmt.span = stmt.span.to(self.prev_span);
 448         Ok(Some(stmt))
 449     }
 450
 451     fn warn_missing_semicolon(&self) {
 452         self.diagnostic().struct_span_warn(self.token.span, {
 453             &format!("expected `;`, found {}", self.this_token_descr())
 454         }).note({
 455             "This was erroneously allowed and will become a hard error in a future release"
 456         }).emit();
 457     }
 458 }