compiler/rustc_parse/src/parser/stmt.rs

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