Move some parser recovery methods to diagnostics

Author: estebank

src/libsyntax/parse/diagnostics.rs

@@ -1,14 +1,16 @@
 use crate::ast;
 use crate::ast::{BlockCheckMode, Expr, ExprKind, Item, ItemKind, Pat, PatKind, QSelf, Ty, TyKind};
-use crate::parse::parser::PathStyle;
+use crate::parse::parser::{BlockMode, PathStyle, TokenType, SemiColonMode};
 use crate::parse::token;
 use crate::parse::PResult;
 use crate::parse::Parser;
 use crate::print::pprust;
 use crate::ptr::P;
+use crate::symbol::keywords;
 use crate::ThinVec;
-use errors::Applicability;
+use errors::{Applicability, DiagnosticBuilder};
 use syntax_pos::Span;
+use log::debug;
 
 pub trait RecoverQPath: Sized + 'static {
     const PATH_STYLE: PathStyle = PathStyle::Expr;
@@ -261,4 +263,266 @@ impl<'a> Parser<'a> {
             .emit();
         Ok((sp, ExprKind::Await(ast::AwaitOrigin::FieldLike, expr)))
     }
+
+    /// If encountering `future.await()`, consume and emit error.
+    crate fn recover_from_await_method_call(&mut self) {
+        if self.token == token::OpenDelim(token::Paren) &&
+            self.look_ahead(1, |t| t == &token::CloseDelim(token::Paren))
+        {
+            // future.await()
+            let lo = self.span;
+            self.bump(); // (
+            let sp = lo.to(self.span);
+            self.bump(); // )
+            let mut err = self.struct_span_err(sp, "incorrect use of `await`");
+            err.span_suggestion(
+                sp,
+                "`await` is not a method call, remove the parentheses",
+                String::new(),
+                Applicability::MachineApplicable,
+            );
+            err.emit()
+        }
+    }
+
+    crate fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
+        self.token.is_ident() &&
+            if let ast::ExprKind::Path(..) = node { true } else { false } &&
+            !self.token.is_reserved_ident() &&           // v `foo:bar(baz)`
+            self.look_ahead(1, |t| t == &token::OpenDelim(token::Paren)) ||
+            self.look_ahead(1, |t| t == &token::Lt) &&     // `foo:bar<baz`
+            self.look_ahead(2, |t| t.is_ident()) ||
+            self.look_ahead(1, |t| t == &token::Colon) &&  // `foo:bar:baz`
+            self.look_ahead(2, |t| t.is_ident()) ||
+            self.look_ahead(1, |t| t == &token::ModSep) &&  // `foo:bar::baz`
+            self.look_ahead(2, |t| t.is_ident())
+    }
+
+    crate fn bad_type_ascription(
+        &self,
+        err: &mut DiagnosticBuilder<'a>,
+        lhs_span: Span,
+        cur_op_span: Span,
+        next_sp: Span,
+        maybe_path: bool,
+    ) {
+        err.span_label(self.span, "expecting a type here because of type ascription");
+        let cm = self.sess.source_map();
+        let next_pos = cm.lookup_char_pos(next_sp.lo());
+        let op_pos = cm.lookup_char_pos(cur_op_span.hi());
+        if op_pos.line != next_pos.line {
+            err.span_suggestion(
+                cur_op_span,
+                "try using a semicolon",
+                ";".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        } else {
+            if maybe_path {
+                err.span_suggestion(
+                    cur_op_span,
+                    "maybe you meant to write a path separator here",
+                    "::".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            } else {
+                err.note("type ascription is a nightly-only feature that lets \
+                          you annotate an expression with a type: `<expr>: <type>`");
+                err.span_note(
+                    lhs_span,
+                    "this expression expects an ascribed type after the colon",
+                );
+                err.help("this might be indicative of a syntax error elsewhere");
+            }
+        }
+    }
+
+    crate fn recover_seq_parse_error(
+        &mut self,
+        delim: token::DelimToken,
+        lo: Span,
+        result: PResult<'a, P<Expr>>,
+    ) -> P<Expr> {
+        match result {
+            Ok(x) => x,
+            Err(mut err) => {
+                err.emit();
+                // recover from parse error
+                self.consume_block(delim);
+                self.mk_expr(lo.to(self.prev_span), ExprKind::Err, ThinVec::new())
+            }
+        }
+    }
+
+    crate fn recover_closing_delimiter(
+        &mut self,
+        tokens: &[token::Token],
+        mut err: DiagnosticBuilder<'a>,
+    ) -> PResult<'a, bool> {
+        let mut pos = None;
+        // we want to use the last closing delim that would apply
+        for (i, unmatched) in self.unclosed_delims.iter().enumerate().rev() {
+            if tokens.contains(&token::CloseDelim(unmatched.expected_delim))
+                && Some(self.span) > unmatched.unclosed_span
+            {
+                pos = Some(i);
+            }
+        }
+        match pos {
+            Some(pos) => {
+                // Recover and assume that the detected unclosed delimiter was meant for
+                // this location. Emit the diagnostic and act as if the delimiter was
+                // present for the parser's sake.
+
+                 // Don't attempt to recover from this unclosed delimiter more than once.
+                let unmatched = self.unclosed_delims.remove(pos);
+                let delim = TokenType::Token(token::CloseDelim(unmatched.expected_delim));
+
+                 // We want to suggest the inclusion of the closing delimiter where it makes
+                // the most sense, which is immediately after the last token:
+                //
+                //  {foo(bar {}}
+                //      -      ^
+                //      |      |
+                //      |      help: `)` may belong here (FIXME: #58270)
+                //      |
+                //      unclosed delimiter
+                if let Some(sp) = unmatched.unclosed_span {
+                    err.span_label(sp, "unclosed delimiter");
+                }
+                err.span_suggestion_short(
+                    self.sess.source_map().next_point(self.prev_span),
+                    &format!("{} may belong here", delim.to_string()),
+                    delim.to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+                err.emit();
+                self.expected_tokens.clear();  // reduce errors
+                Ok(true)
+            }
+            _ => Err(err),
+        }
+    }
+
+    /// Recover from `pub` keyword in places where it seems _reasonable_ but isn't valid.
+    crate fn eat_bad_pub(&mut self) {
+        if self.token.is_keyword(keywords::Pub) {
+            match self.parse_visibility(false) {
+                Ok(vis) => {
+                    let mut err = self.diagnostic()
+                        .struct_span_err(vis.span, "unnecessary visibility qualifier");
+                    err.span_label(vis.span, "`pub` not permitted here");
+                    err.emit();
+                }
+                Err(mut err) => err.emit(),
+            }
+        }
+    }
+
+    // Eat tokens until we can be relatively sure we reached the end of the
+    // statement. This is something of a best-effort heuristic.
+    //
+    // We terminate when we find an unmatched `}` (without consuming it).
+    crate fn recover_stmt(&mut self) {
+        self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore)
+    }
+
+    // If `break_on_semi` is `Break`, then we will stop consuming tokens after
+    // finding (and consuming) a `;` outside of `{}` or `[]` (note that this is
+    // approximate - it can mean we break too early due to macros, but that
+    // should only lead to sub-optimal recovery, not inaccurate parsing).
+    //
+    // If `break_on_block` is `Break`, then we will stop consuming tokens
+    // after finding (and consuming) a brace-delimited block.
+    crate fn recover_stmt_(&mut self, break_on_semi: SemiColonMode, break_on_block: BlockMode) {
+        let mut brace_depth = 0;
+        let mut bracket_depth = 0;
+        let mut in_block = false;
+        debug!("recover_stmt_ enter loop (semi={:?}, block={:?})",
+               break_on_semi, break_on_block);
+        loop {
+            debug!("recover_stmt_ loop {:?}", self.token);
+            match self.token {
+                token::OpenDelim(token::DelimToken::Brace) => {
+                    brace_depth += 1;
+                    self.bump();
+                    if break_on_block == BlockMode::Break &&
+                       brace_depth == 1 &&
+                       bracket_depth == 0 {
+                        in_block = true;
+                    }
+                }
+                token::OpenDelim(token::DelimToken::Bracket) => {
+                    bracket_depth += 1;
+                    self.bump();
+                }
+                token::CloseDelim(token::DelimToken::Brace) => {
+                    if brace_depth == 0 {
+                        debug!("recover_stmt_ return - close delim {:?}", self.token);
+                        break;
+                    }
+                    brace_depth -= 1;
+                    self.bump();
+                    if in_block && bracket_depth == 0 && brace_depth == 0 {
+                        debug!("recover_stmt_ return - block end {:?}", self.token);
+                        break;
+                    }
+                }
+                token::CloseDelim(token::DelimToken::Bracket) => {
+                    bracket_depth -= 1;
+                    if bracket_depth < 0 {
+                        bracket_depth = 0;
+                    }
+                    self.bump();
+                }
+                token::Eof => {
+                    debug!("recover_stmt_ return - Eof");
+                    break;
+                }
+                token::Semi => {
+                    self.bump();
+                    if break_on_semi == SemiColonMode::Break &&
+                       brace_depth == 0 &&
+                       bracket_depth == 0 {
+                        debug!("recover_stmt_ return - Semi");
+                        break;
+                    }
+                }
+                token::Comma => {
+                    if break_on_semi == SemiColonMode::Comma &&
+                       brace_depth == 0 &&
+                       bracket_depth == 0 {
+                        debug!("recover_stmt_ return - Semi");
+                        break;
+                    } else {
+                        self.bump();
+                    }
+                }
+                _ => {
+                    self.bump()
+                }
+            }
+        }
+    }
+
+    crate fn consume_block(&mut self, delim: token::DelimToken) {
+        let mut brace_depth = 0;
+        loop {
+            if self.eat(&token::OpenDelim(delim)) {
+                brace_depth += 1;
+            } else if self.eat(&token::CloseDelim(delim)) {
+                if brace_depth == 0 {
+                    return;
+                } else {
+                    brace_depth -= 1;
+                    continue;
+                }
+            } else if self.token == token::Eof || self.eat(&token::CloseDelim(token::NoDelim)) {
+                return;
+            } else {
+                self.bump();
+            }
+        }
+    }
+
 }