From 81e6b5094eb1c2fbf5184b6952a1a3ddf647bf7a Mon Sep 17 00:00:00 2001 From: Mazdak Farrokhzad Date: Sun, 11 Aug 2019 13:14:30 +0200 Subject: parser: split into expr.rs --- src/libsyntax/parse/parser/expr.rs | 1703 ++++++++++++++++++++++++++++++++++++ 1 file changed, 1703 insertions(+) create mode 100644 src/libsyntax/parse/parser/expr.rs (limited to 'src/libsyntax/parse/parser') diff --git a/src/libsyntax/parse/parser/expr.rs b/src/libsyntax/parse/parser/expr.rs new file mode 100644 index 00000000000..88e534394fe --- /dev/null +++ b/src/libsyntax/parse/parser/expr.rs @@ -0,0 +1,1703 @@ +use super::{Parser, PResult, Restrictions, PrevTokenKind, TokenType, PathStyle}; +use super::{BlockCheckMode, BlockMode, SemiColonMode}; +use super::SeqSep; + +use crate::{maybe_recover_from_interpolated_ty_qpath}; + +use crate::ptr::P; +use crate::ast; +use crate::ast::{Attribute, AttrStyle}; +use crate::ast::{Ident, CaptureBy}; +use crate::ast::{Expr, ExprKind, RangeLimits, Label, Movability, IsAsync, Arm}; +use crate::ast::{Ty, TyKind, FunctionRetTy}; +use crate::ast::{BinOpKind, BinOp, UnOp}; +use crate::ast::{Mac_, AnonConst, Field}; + +use crate::parse::classify; +use crate::parse::token::{self, Token}; +use crate::parse::diagnostics::{Error}; +use crate::print::pprust; +use crate::source_map::{self, respan, Span}; +use crate::symbol::{kw, sym}; +use crate::util::parser::{AssocOp, Fixity, prec_let_scrutinee_needs_par}; + +use std::mem; + +use errors::{Applicability}; + +use rustc_data_structures::thin_vec::ThinVec; + +/// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression +/// dropped into the token stream, which happens while parsing the result of +/// macro expansion). Placement of these is not as complex as I feared it would +/// be. The important thing is to make sure that lookahead doesn't balk at +/// `token::Interpolated` tokens. +macro_rules! maybe_whole_expr { + ($p:expr) => { + if let token::Interpolated(nt) = &$p.token.kind { + match &**nt { + token::NtExpr(e) | token::NtLiteral(e) => { + let e = e.clone(); + $p.bump(); + return Ok(e); + } + token::NtPath(path) => { + let path = path.clone(); + $p.bump(); + return Ok($p.mk_expr( + $p.token.span, ExprKind::Path(None, path), ThinVec::new() + )); + } + token::NtBlock(block) => { + let block = block.clone(); + $p.bump(); + return Ok($p.mk_expr( + $p.token.span, ExprKind::Block(block, None), ThinVec::new() + )); + } + // N.B: `NtIdent(ident)` is normalized to `Ident` in `fn bump`. + _ => {}, + }; + } + } +} + +#[derive(Debug)] +pub(super) enum LhsExpr { + NotYetParsed, + AttributesParsed(ThinVec), + AlreadyParsed(P), +} + +impl From>> for LhsExpr { + fn from(o: Option>) -> Self { + if let Some(attrs) = o { + LhsExpr::AttributesParsed(attrs) + } else { + LhsExpr::NotYetParsed + } + } +} + +impl From> for LhsExpr { + fn from(expr: P) -> Self { + LhsExpr::AlreadyParsed(expr) + } +} + +impl<'a> Parser<'a> { + /// Parses an expression. + #[inline] + pub fn parse_expr(&mut self) -> PResult<'a, P> { + self.parse_expr_res(Restrictions::empty(), None) + } + + fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec>> { + self.parse_paren_comma_seq(|p| { + match p.parse_expr() { + Ok(expr) => Ok(expr), + Err(mut err) => match p.token.kind { + token::Ident(name, false) + if name == kw::Underscore && p.look_ahead(1, |t| { + t == &token::Comma + }) => { + // Special-case handling of `foo(_, _, _)` + err.emit(); + let sp = p.token.span; + p.bump(); + Ok(p.mk_expr(sp, ExprKind::Err, ThinVec::new())) + } + _ => Err(err), + }, + } + }).map(|(r, _)| r) + } + + /// Parses an expression, subject to the given restrictions. + #[inline] + pub(super) fn parse_expr_res( + &mut self, + r: Restrictions, + already_parsed_attrs: Option> + ) -> PResult<'a, P> { + self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs)) + } + + /// Parses an associative expression. + /// + /// This parses an expression accounting for associativity and precedence of the operators in + /// the expression. + #[inline] + fn parse_assoc_expr( + &mut self, + already_parsed_attrs: Option>, + ) -> PResult<'a, P> { + self.parse_assoc_expr_with(0, already_parsed_attrs.into()) + } + + /// Parses an associative expression with operators of at least `min_prec` precedence. + pub(super) fn parse_assoc_expr_with( + &mut self, + min_prec: usize, + lhs: LhsExpr, + ) -> PResult<'a, P> { + let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs { + expr + } else { + let attrs = match lhs { + LhsExpr::AttributesParsed(attrs) => Some(attrs), + _ => None, + }; + if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) { + return self.parse_prefix_range_expr(attrs); + } else { + self.parse_prefix_expr(attrs)? + } + }; + let last_type_ascription_set = self.last_type_ascription.is_some(); + + match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) { + (true, None) => { + self.last_type_ascription = None; + // Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071 + return Ok(lhs); + } + (false, _) => {} // continue parsing the expression + // An exhaustive check is done in the following block, but these are checked first + // because they *are* ambiguous but also reasonable looking incorrect syntax, so we + // want to keep their span info to improve diagnostics in these cases in a later stage. + (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3` + (true, Some(AssocOp::Subtract)) | // `{ 42 } -5` + (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475) + (true, Some(AssocOp::Add)) // `{ 42 } + 42 + // If the next token is a keyword, then the tokens above *are* unambiguously incorrect: + // `if x { a } else { b } && if y { c } else { d }` + if !self.look_ahead(1, |t| t.is_reserved_ident()) => { + self.last_type_ascription = None; + // These cases are ambiguous and can't be identified in the parser alone + let sp = self.sess.source_map().start_point(self.token.span); + self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span); + return Ok(lhs); + } + (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => { + self.last_type_ascription = None; + return Ok(lhs); + } + (true, Some(_)) => { + // We've found an expression that would be parsed as a statement, but the next + // token implies this should be parsed as an expression. + // For example: `if let Some(x) = x { x } else { 0 } / 2` + let mut err = self.struct_span_err(self.token.span, &format!( + "expected expression, found `{}`", + pprust::token_to_string(&self.token), + )); + err.span_label(self.token.span, "expected expression"); + self.sess.expr_parentheses_needed( + &mut err, + lhs.span, + Some(pprust::expr_to_string(&lhs), + )); + err.emit(); + } + } + self.expected_tokens.push(TokenType::Operator); + while let Some(op) = AssocOp::from_token(&self.token) { + + // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what + // it refers to. Interpolated identifiers are unwrapped early and never show up here + // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process + // it as "interpolated", it doesn't change the answer for non-interpolated idents. + let lhs_span = match (self.prev_token_kind, &lhs.node) { + (PrevTokenKind::Interpolated, _) => self.prev_span, + (PrevTokenKind::Ident, &ExprKind::Path(None, ref path)) + if path.segments.len() == 1 => self.prev_span, + _ => lhs.span, + }; + + let cur_op_span = self.token.span; + let restrictions = if op.is_assign_like() { + self.restrictions & Restrictions::NO_STRUCT_LITERAL + } else { + self.restrictions + }; + let prec = op.precedence(); + if prec < min_prec { + break; + } + // Check for deprecated `...` syntax + if self.token == token::DotDotDot && op == AssocOp::DotDotEq { + self.err_dotdotdot_syntax(self.token.span); + } + + self.bump(); + if op.is_comparison() { + self.check_no_chained_comparison(&lhs, &op); + } + // Special cases: + if op == AssocOp::As { + lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?; + continue + } else if op == AssocOp::Colon { + let maybe_path = self.could_ascription_be_path(&lhs.node); + self.last_type_ascription = Some((self.prev_span, maybe_path)); + + lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?; + continue + } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq { + // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to + // generalise it to the Fixity::None code. + // + // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other + // two variants are handled with `parse_prefix_range_expr` call above. + let rhs = if self.is_at_start_of_range_notation_rhs() { + Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?) + } else { + None + }; + let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs { + x.span + } else { + cur_op_span + }); + let limits = if op == AssocOp::DotDot { + RangeLimits::HalfOpen + } else { + RangeLimits::Closed + }; + + let r = self.mk_range(Some(lhs), rhs, limits)?; + lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new()); + break + } + + let fixity = op.fixity(); + let prec_adjustment = match fixity { + Fixity::Right => 0, + Fixity::Left => 1, + // We currently have no non-associative operators that are not handled above by + // the special cases. The code is here only for future convenience. + Fixity::None => 1, + }; + let rhs = self.with_res( + restrictions - Restrictions::STMT_EXPR, + |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed) + )?; + + // Make sure that the span of the parent node is larger than the span of lhs and rhs, + // including the attributes. + let lhs_span = lhs + .attrs + .iter() + .filter(|a| a.style == AttrStyle::Outer) + .next() + .map_or(lhs_span, |a| a.span); + let span = lhs_span.to(rhs.span); + lhs = match op { + AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide | + AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor | + AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight | + AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual | + AssocOp::Greater | AssocOp::GreaterEqual => { + let ast_op = op.to_ast_binop().unwrap(); + let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs); + self.mk_expr(span, binary, ThinVec::new()) + } + AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()), + AssocOp::AssignOp(k) => { + let aop = match k { + token::Plus => BinOpKind::Add, + token::Minus => BinOpKind::Sub, + token::Star => BinOpKind::Mul, + token::Slash => BinOpKind::Div, + token::Percent => BinOpKind::Rem, + token::Caret => BinOpKind::BitXor, + token::And => BinOpKind::BitAnd, + token::Or => BinOpKind::BitOr, + token::Shl => BinOpKind::Shl, + token::Shr => BinOpKind::Shr, + }; + let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs); + self.mk_expr(span, aopexpr, ThinVec::new()) + } + AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => { + self.bug("AssocOp should have been handled by special case") + } + }; + + if let Fixity::None = fixity { break } + } + if last_type_ascription_set { + self.last_type_ascription = None; + } + Ok(lhs) + } + + /// Checks if this expression is a successfully parsed statement. + fn expr_is_complete(&self, e: &Expr) -> bool { + self.restrictions.contains(Restrictions::STMT_EXPR) && + !classify::expr_requires_semi_to_be_stmt(e) + } + + fn is_at_start_of_range_notation_rhs(&self) -> bool { + if self.token.can_begin_expr() { + // parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`. + if self.token == token::OpenDelim(token::Brace) { + return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL); + } + true + } else { + false + } + } + + /// Parse prefix-forms of range notation: `..expr`, `..`, `..=expr` + fn parse_prefix_range_expr( + &mut self, + already_parsed_attrs: Option> + ) -> PResult<'a, P> { + // Check for deprecated `...` syntax + if self.token == token::DotDotDot { + self.err_dotdotdot_syntax(self.token.span); + } + + debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind), + "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq", + self.token); + let tok = self.token.clone(); + let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?; + let lo = self.token.span; + let mut hi = self.token.span; + self.bump(); + let opt_end = if self.is_at_start_of_range_notation_rhs() { + // RHS must be parsed with more associativity than the dots. + let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1; + Some(self.parse_assoc_expr_with(next_prec, LhsExpr::NotYetParsed) + .map(|x| { + hi = x.span; + x + })?) + } else { + None + }; + let limits = if tok == token::DotDot { + RangeLimits::HalfOpen + } else { + RangeLimits::Closed + }; + + let r = self.mk_range(None, opt_end, limits)?; + Ok(self.mk_expr(lo.to(hi), r, attrs)) + } + + /// Parse a prefix-unary-operator expr + fn parse_prefix_expr( + &mut self, + already_parsed_attrs: Option> + ) -> PResult<'a, P> { + let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?; + let lo = self.token.span; + // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr() + let (hi, ex) = match self.token.kind { + token::Not => { + self.bump(); + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + (lo.to(span), self.mk_unary(UnOp::Not, e)) + } + // Suggest `!` for bitwise negation when encountering a `~` + token::Tilde => { + self.bump(); + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + let span_of_tilde = lo; + self.struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator") + .span_suggestion_short( + span_of_tilde, + "use `!` to perform bitwise negation", + "!".to_owned(), + Applicability::MachineApplicable + ) + .emit(); + (lo.to(span), self.mk_unary(UnOp::Not, e)) + } + token::BinOp(token::Minus) => { + self.bump(); + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + (lo.to(span), self.mk_unary(UnOp::Neg, e)) + } + token::BinOp(token::Star) => { + self.bump(); + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + (lo.to(span), self.mk_unary(UnOp::Deref, e)) + } + token::BinOp(token::And) | token::AndAnd => { + self.expect_and()?; + let m = self.parse_mutability(); + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + (lo.to(span), ExprKind::AddrOf(m, e)) + } + token::Ident(..) if self.token.is_keyword(kw::Box) => { + self.bump(); + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + (lo.to(span), ExprKind::Box(e)) + } + token::Ident(..) if self.token.is_ident_named(sym::not) => { + // `not` is just an ordinary identifier in Rust-the-language, + // but as `rustc`-the-compiler, we can issue clever diagnostics + // for confused users who really want to say `!` + let token_cannot_continue_expr = |t: &Token| match t.kind { + // These tokens can start an expression after `!`, but + // can't continue an expression after an ident + token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw), + token::Literal(..) | token::Pound => true, + _ => t.is_whole_expr(), + }; + let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr); + if cannot_continue_expr { + self.bump(); + // Emit the error ... + self.struct_span_err( + self.token.span, + &format!("unexpected {} after identifier",self.this_token_descr()) + ) + .span_suggestion_short( + // Span the `not` plus trailing whitespace to avoid + // trailing whitespace after the `!` in our suggestion + self.sess.source_map() + .span_until_non_whitespace(lo.to(self.token.span)), + "use `!` to perform logical negation", + "!".to_owned(), + Applicability::MachineApplicable + ) + .emit(); + // —and recover! (just as if we were in the block + // for the `token::Not` arm) + let e = self.parse_prefix_expr(None); + let (span, e) = self.interpolated_or_expr_span(e)?; + (lo.to(span), self.mk_unary(UnOp::Not, e)) + } else { + return self.parse_dot_or_call_expr(Some(attrs)); + } + } + _ => { return self.parse_dot_or_call_expr(Some(attrs)); } + }; + return Ok(self.mk_expr(lo.to(hi), ex, attrs)); + } + + /// Returns the span of expr, if it was not interpolated or the span of the interpolated token. + fn interpolated_or_expr_span( + &self, + expr: PResult<'a, P>, + ) -> PResult<'a, (Span, P)> { + expr.map(|e| { + if self.prev_token_kind == PrevTokenKind::Interpolated { + (self.prev_span, e) + } else { + (e.span, e) + } + }) + } + + fn parse_assoc_op_cast(&mut self, lhs: P, lhs_span: Span, + expr_kind: fn(P, P) -> ExprKind) + -> PResult<'a, P> { + let mk_expr = |this: &mut Self, rhs: P| { + this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new()) + }; + + // Save the state of the parser before parsing type normally, in case there is a + // LessThan comparison after this cast. + let parser_snapshot_before_type = self.clone(); + match self.parse_ty_no_plus() { + Ok(rhs) => { + Ok(mk_expr(self, rhs)) + } + Err(mut type_err) => { + // Rewind to before attempting to parse the type with generics, to recover + // from situations like `x as usize < y` in which we first tried to parse + // `usize < y` as a type with generic arguments. + let parser_snapshot_after_type = self.clone(); + mem::replace(self, parser_snapshot_before_type); + + match self.parse_path(PathStyle::Expr) { + Ok(path) => { + let (op_noun, op_verb) = match self.token.kind { + token::Lt => ("comparison", "comparing"), + token::BinOp(token::Shl) => ("shift", "shifting"), + _ => { + // We can end up here even without `<` being the next token, for + // example because `parse_ty_no_plus` returns `Err` on keywords, + // but `parse_path` returns `Ok` on them due to error recovery. + // Return original error and parser state. + mem::replace(self, parser_snapshot_after_type); + return Err(type_err); + } + }; + + // Successfully parsed the type path leaving a `<` yet to parse. + type_err.cancel(); + + // Report non-fatal diagnostics, keep `x as usize` as an expression + // in AST and continue parsing. + let msg = format!("`<` is interpreted as a start of generic \ + arguments for `{}`, not a {}", path, op_noun); + let span_after_type = parser_snapshot_after_type.token.span; + let expr = mk_expr(self, P(Ty { + span: path.span, + node: TyKind::Path(None, path), + id: ast::DUMMY_NODE_ID + })); + + let expr_str = self.span_to_snippet(expr.span) + .unwrap_or_else(|_| pprust::expr_to_string(&expr)); + + self.struct_span_err(self.token.span, &msg) + .span_label( + self.look_ahead(1, |t| t.span).to(span_after_type), + "interpreted as generic arguments" + ) + .span_label(self.token.span, format!("not interpreted as {}", op_noun)) + .span_suggestion( + expr.span, + &format!("try {} the cast value", op_verb), + format!("({})", expr_str), + Applicability::MachineApplicable + ) + .emit(); + + Ok(expr) + } + Err(mut path_err) => { + // Couldn't parse as a path, return original error and parser state. + path_err.cancel(); + mem::replace(self, parser_snapshot_after_type); + Err(type_err) + } + } + } + } + } + + /// Parses `a.b` or `a(13)` or `a[4]` or just `a`. + fn parse_dot_or_call_expr( + &mut self, + already_parsed_attrs: Option>, + ) -> PResult<'a, P> { + let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?; + + let b = self.parse_bottom_expr(); + let (span, b) = self.interpolated_or_expr_span(b)?; + self.parse_dot_or_call_expr_with(b, span, attrs) + } + + pub(super) fn parse_dot_or_call_expr_with( + &mut self, + e0: P, + lo: Span, + mut attrs: ThinVec, + ) -> PResult<'a, P> { + // Stitch the list of outer attributes onto the return value. + // A little bit ugly, but the best way given the current code + // structure + self.parse_dot_or_call_expr_with_(e0, lo).map(|expr| + expr.map(|mut expr| { + attrs.extend::>(expr.attrs.into()); + expr.attrs = attrs; + match expr.node { + ExprKind::If(..) if !expr.attrs.is_empty() => { + // Just point to the first attribute in there... + let span = expr.attrs[0].span; + self.span_err(span, "attributes are not yet allowed on `if` expressions"); + } + _ => {} + } + expr + }) + ) + } + + fn parse_dot_or_call_expr_with_(&mut self, e0: P, lo: Span) -> PResult<'a, P> { + let mut e = e0; + let mut hi; + loop { + // expr? + while self.eat(&token::Question) { + let hi = self.prev_span; + e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new()); + } + + // expr.f + if self.eat(&token::Dot) { + match self.token.kind { + token::Ident(..) => { + e = self.parse_dot_suffix(e, lo)?; + } + token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => { + let span = self.token.span; + self.bump(); + let field = ExprKind::Field(e, Ident::new(symbol, span)); + e = self.mk_expr(lo.to(span), field, ThinVec::new()); + + self.expect_no_suffix(span, "a tuple index", suffix); + } + token::Literal(token::Lit { kind: token::Float, symbol, .. }) => { + self.bump(); + let fstr = symbol.as_str(); + let msg = format!("unexpected token: `{}`", symbol); + let mut err = self.diagnostic().struct_span_err(self.prev_span, &msg); + err.span_label(self.prev_span, "unexpected token"); + if fstr.chars().all(|x| "0123456789.".contains(x)) { + let float = match fstr.parse::().ok() { + Some(f) => f, + None => continue, + }; + let sugg = pprust::to_string(|s| { + s.popen(); + s.print_expr(&e); + s.s.word( "."); + s.print_usize(float.trunc() as usize); + s.pclose(); + s.s.word("."); + s.s.word(fstr.splitn(2, ".").last().unwrap().to_string()) + }); + err.span_suggestion( + lo.to(self.prev_span), + "try parenthesizing the first index", + sugg, + Applicability::MachineApplicable + ); + } + return Err(err); + + } + _ => { + // FIXME Could factor this out into non_fatal_unexpected or something. + let actual = self.this_token_to_string(); + self.span_err(self.token.span, &format!("unexpected token: `{}`", actual)); + } + } + continue; + } + if self.expr_is_complete(&e) { break; } + match self.token.kind { + // expr(...) + token::OpenDelim(token::Paren) => { + let seq = self.parse_paren_expr_seq().map(|es| { + let nd = self.mk_call(e, es); + let hi = self.prev_span; + self.mk_expr(lo.to(hi), nd, ThinVec::new()) + }); + e = self.recover_seq_parse_error(token::Paren, lo, seq); + } + + // expr[...] + // Could be either an index expression or a slicing expression. + token::OpenDelim(token::Bracket) => { + self.bump(); + let ix = self.parse_expr()?; + hi = self.token.span; + self.expect(&token::CloseDelim(token::Bracket))?; + let index = self.mk_index(e, ix); + e = self.mk_expr(lo.to(hi), index, ThinVec::new()) + } + _ => return Ok(e) + } + } + return Ok(e); + } + + /// Assuming we have just parsed `.`, continue parsing into an expression. + fn parse_dot_suffix(&mut self, self_arg: P, lo: Span) -> PResult<'a, P> { + if self.token.span.rust_2018() && self.eat_keyword(kw::Await) { + return self.mk_await_expr(self_arg, lo); + } + + let segment = self.parse_path_segment(PathStyle::Expr)?; + self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren)); + + Ok(match self.token.kind { + token::OpenDelim(token::Paren) => { + // Method call `expr.f()` + let mut args = self.parse_paren_expr_seq()?; + args.insert(0, self_arg); + + let span = lo.to(self.prev_span); + self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new()) + } + _ => { + // Field access `expr.f` + if let Some(args) = segment.args { + self.span_err(args.span(), + "field expressions may not have generic arguments"); + } + + let span = lo.to(self.prev_span); + self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new()) + } + }) + } + + + /// At the bottom (top?) of the precedence hierarchy, + /// Parses things like parenthesized exprs, macros, `return`, etc. + /// + /// N.B., this does not parse outer attributes, and is private because it only works + /// correctly if called from `parse_dot_or_call_expr()`. + fn parse_bottom_expr(&mut self) -> PResult<'a, P> { + maybe_recover_from_interpolated_ty_qpath!(self, true); + maybe_whole_expr!(self); + + // Outer attributes are already parsed and will be + // added to the return value after the fact. + // + // Therefore, prevent sub-parser from parsing + // attributes by giving them a empty "already parsed" list. + let mut attrs = ThinVec::new(); + + let lo = self.token.span; + let mut hi = self.token.span; + + let ex: ExprKind; + + macro_rules! parse_lit { + () => { + match self.parse_lit() { + Ok(literal) => { + hi = self.prev_span; + ex = ExprKind::Lit(literal); + } + Err(mut err) => { + self.cancel(&mut err); + return Err(self.expected_expression_found()); + } + } + } + } + + // Note: when adding new syntax here, don't forget to adjust TokenKind::can_begin_expr(). + match self.token.kind { + // This match arm is a special-case of the `_` match arm below and + // could be removed without changing functionality, but it's faster + // to have it here, especially for programs with large constants. + token::Literal(_) => { + parse_lit!() + } + token::OpenDelim(token::Paren) => { + self.bump(); + + attrs.extend(self.parse_inner_attributes()?); + + // (e) is parenthesized e + // (e,) is a tuple with only one field, e + let mut es = vec![]; + let mut trailing_comma = false; + let mut recovered = false; + while self.token != token::CloseDelim(token::Paren) { + es.push(match self.parse_expr() { + Ok(es) => es, + Err(mut err) => { + // recover from parse error in tuple list + match self.token.kind { + token::Ident(name, false) + if name == kw::Underscore && self.look_ahead(1, |t| { + t == &token::Comma + }) => { + // Special-case handling of `Foo<(_, _, _)>` + err.emit(); + let sp = self.token.span; + self.bump(); + self.mk_expr(sp, ExprKind::Err, ThinVec::new()) + } + _ => return Ok( + self.recover_seq_parse_error(token::Paren, lo, Err(err)), + ), + } + } + }); + recovered = self.expect_one_of( + &[], + &[token::Comma, token::CloseDelim(token::Paren)], + )?; + if self.eat(&token::Comma) { + trailing_comma = true; + } else { + trailing_comma = false; + break; + } + } + if !recovered { + self.bump(); + } + + hi = self.prev_span; + ex = if es.len() == 1 && !trailing_comma { + ExprKind::Paren(es.into_iter().nth(0).unwrap()) + } else { + ExprKind::Tup(es) + }; + } + token::OpenDelim(token::Brace) => { + return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs); + } + token::BinOp(token::Or) | token::OrOr => { + return self.parse_lambda_expr(attrs); + } + token::OpenDelim(token::Bracket) => { + self.bump(); + + attrs.extend(self.parse_inner_attributes()?); + + if self.eat(&token::CloseDelim(token::Bracket)) { + // Empty vector. + ex = ExprKind::Array(Vec::new()); + } else { + // Nonempty vector. + let first_expr = self.parse_expr()?; + if self.eat(&token::Semi) { + // Repeating array syntax: [ 0; 512 ] + let count = AnonConst { + id: ast::DUMMY_NODE_ID, + value: self.parse_expr()?, + }; + self.expect(&token::CloseDelim(token::Bracket))?; + ex = ExprKind::Repeat(first_expr, count); + } else if self.eat(&token::Comma) { + // Vector with two or more elements. + let remaining_exprs = self.parse_seq_to_end( + &token::CloseDelim(token::Bracket), + SeqSep::trailing_allowed(token::Comma), + |p| Ok(p.parse_expr()?) + )?; + let mut exprs = vec![first_expr]; + exprs.extend(remaining_exprs); + ex = ExprKind::Array(exprs); + } else { + // Vector with one element. + self.expect(&token::CloseDelim(token::Bracket))?; + ex = ExprKind::Array(vec![first_expr]); + } + } + hi = self.prev_span; + } + _ => { + if self.eat_lt() { + let (qself, path) = self.parse_qpath(PathStyle::Expr)?; + hi = path.span; + return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs)); + } + if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) { + return self.parse_lambda_expr(attrs); + } + if self.eat_keyword(kw::If) { + return self.parse_if_expr(attrs); + } + if self.eat_keyword(kw::For) { + let lo = self.prev_span; + return self.parse_for_expr(None, lo, attrs); + } + if self.eat_keyword(kw::While) { + let lo = self.prev_span; + return self.parse_while_expr(None, lo, attrs); + } + if let Some(label) = self.eat_label() { + let lo = label.ident.span; + self.expect(&token::Colon)?; + if self.eat_keyword(kw::While) { + return self.parse_while_expr(Some(label), lo, attrs) + } + if self.eat_keyword(kw::For) { + return self.parse_for_expr(Some(label), lo, attrs) + } + if self.eat_keyword(kw::Loop) { + return self.parse_loop_expr(Some(label), lo, attrs) + } + if self.token == token::OpenDelim(token::Brace) { + return self.parse_block_expr(Some(label), + lo, + BlockCheckMode::Default, + attrs); + } + let msg = "expected `while`, `for`, `loop` or `{` after a label"; + let mut err = self.fatal(msg); + err.span_label(self.token.span, msg); + return Err(err); + } + if self.eat_keyword(kw::Loop) { + let lo = self.prev_span; + return self.parse_loop_expr(None, lo, attrs); + } + if self.eat_keyword(kw::Continue) { + let label = self.eat_label(); + let ex = ExprKind::Continue(label); + let hi = self.prev_span; + return Ok(self.mk_expr(lo.to(hi), ex, attrs)); + } + if self.eat_keyword(kw::Match) { + let match_sp = self.prev_span; + return self.parse_match_expr(attrs).map_err(|mut err| { + err.span_label(match_sp, "while parsing this match expression"); + err + }); + } + if self.eat_keyword(kw::Unsafe) { + return self.parse_block_expr( + None, + lo, + BlockCheckMode::Unsafe(ast::UserProvided), + attrs); + } + if self.is_do_catch_block() { + let mut db = self.fatal("found removed `do catch` syntax"); + db.help("Following RFC #2388, the new non-placeholder syntax is `try`"); + return Err(db); + } + if self.is_try_block() { + let lo = self.token.span; + assert!(self.eat_keyword(kw::Try)); + return self.parse_try_block(lo, attrs); + } + + // Span::rust_2018() is somewhat expensive; don't get it repeatedly. + let is_span_rust_2018 = self.token.span.rust_2018(); + if is_span_rust_2018 && self.check_keyword(kw::Async) { + return if self.is_async_block() { // check for `async {` and `async move {` + self.parse_async_block(attrs) + } else { + self.parse_lambda_expr(attrs) + }; + } + if self.eat_keyword(kw::Return) { + if self.token.can_begin_expr() { + let e = self.parse_expr()?; + hi = e.span; + ex = ExprKind::Ret(Some(e)); + } else { + ex = ExprKind::Ret(None); + } + } else if self.eat_keyword(kw::Break) { + let label = self.eat_label(); + let e = if self.token.can_begin_expr() + && !(self.token == token::OpenDelim(token::Brace) + && self.restrictions.contains( + Restrictions::NO_STRUCT_LITERAL)) { + Some(self.parse_expr()?) + } else { + None + }; + ex = ExprKind::Break(label, e); + hi = self.prev_span; + } else if self.eat_keyword(kw::Yield) { + if self.token.can_begin_expr() { + let e = self.parse_expr()?; + hi = e.span; + ex = ExprKind::Yield(Some(e)); + } else { + ex = ExprKind::Yield(None); + } + } else if self.eat_keyword(kw::Let) { + return self.parse_let_expr(attrs); + } else if is_span_rust_2018 && self.eat_keyword(kw::Await) { + let (await_hi, e_kind) = self.parse_incorrect_await_syntax(lo, self.prev_span)?; + hi = await_hi; + ex = e_kind; + } else if self.token.is_path_start() { + let path = self.parse_path(PathStyle::Expr)?; + + // `!`, as an operator, is prefix, so we know this isn't that + if self.eat(&token::Not) { + // MACRO INVOCATION expression + let (delim, tts) = self.expect_delimited_token_tree()?; + hi = self.prev_span; + ex = ExprKind::Mac(respan(lo.to(hi), Mac_ { + path, + tts, + delim, + prior_type_ascription: self.last_type_ascription, + })); + } else if self.check(&token::OpenDelim(token::Brace)) { + if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) { + return expr; + } else { + hi = path.span; + ex = ExprKind::Path(None, path); + } + } else { + hi = path.span; + ex = ExprKind::Path(None, path); + } + } else { + if !self.unclosed_delims.is_empty() && self.check(&token::Semi) { + // Don't complain about bare semicolons after unclosed braces + // recovery in order to keep the error count down. Fixing the + // delimiters will possibly also fix the bare semicolon found in + // expression context. For example, silence the following error: + // ``` + // error: expected expression, found `;` + // --> file.rs:2:13 + // | + // 2 | foo(bar(; + // | ^ expected expression + // ``` + self.bump(); + return Ok(self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new())); + } + parse_lit!() + } + } + } + + let expr = self.mk_expr(lo.to(hi), ex, attrs); + self.maybe_recover_from_bad_qpath(expr, true) + } + + /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`). + crate fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P> { + maybe_whole_expr!(self); + + let minus_lo = self.token.span; + let minus_present = self.eat(&token::BinOp(token::Minus)); + let lo = self.token.span; + let literal = self.parse_lit()?; + let hi = self.prev_span; + let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new()); + + if minus_present { + let minus_hi = self.prev_span; + let unary = self.mk_unary(UnOp::Neg, expr); + Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new())) + } else { + Ok(expr) + } + } + + /// Parses a block or unsafe block. + crate fn parse_block_expr( + &mut self, + opt_label: Option