Rollup merge of rust-lang#60348 - agnxy:refactor-parser, r=petrochenkov

move some functions from parser.rs to diagostics.rs

Starting with a few functions mentioned in rust-lang#60015 (comment). We might refactor parser.rs further in subsequent changes.
r? @petrochenkov

src/libsyntax/parse/diagnostics.rs

@@ -0,0 +1,226 @@
+use crate::ast;
+use crate::ast::{Expr, ExprKind, Item, ItemKind, Pat, PatKind, QSelf, Ty, TyKind};
+use crate::parse::parser::PathStyle;
+use crate::parse::token;
+use crate::parse::PResult;
+use crate::parse::Parser;
+use crate::print::pprust;
+use crate::ptr::P;
+use crate::ThinVec;
+use errors::Applicability;
+use syntax_pos::Span;
+
+pub trait RecoverQPath: Sized + 'static {
+    const PATH_STYLE: PathStyle = PathStyle::Expr;
+    fn to_ty(&self) -> Option<P<Ty>>;
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self;
+}
+
+impl RecoverQPath for Ty {
+    const PATH_STYLE: PathStyle = PathStyle::Type;
+    fn to_ty(&self) -> Option<P<Ty>> {
+        Some(P(self.clone()))
+    }
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            node: TyKind::Path(qself, path),
+            id: ast::DUMMY_NODE_ID,
+        }
+    }
+}
+
+impl RecoverQPath for Pat {
+    fn to_ty(&self) -> Option<P<Ty>> {
+        self.to_ty()
+    }
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            node: PatKind::Path(qself, path),
+            id: ast::DUMMY_NODE_ID,
+        }
+    }
+}
+
+impl RecoverQPath for Expr {
+    fn to_ty(&self) -> Option<P<Ty>> {
+        self.to_ty()
+    }
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            node: ExprKind::Path(qself, path),
+            attrs: ThinVec::new(),
+            id: ast::DUMMY_NODE_ID,
+        }
+    }
+}
+
+impl<'a> Parser<'a> {
+    crate fn maybe_report_ambiguous_plus(
+        &mut self,
+        allow_plus: bool,
+        impl_dyn_multi: bool,
+        ty: &Ty,
+    ) {
+        if !allow_plus && impl_dyn_multi {
+            let sum_with_parens = format!("({})", pprust::ty_to_string(&ty));
+            self.struct_span_err(ty.span, "ambiguous `+` in a type")
+                .span_suggestion(
+                    ty.span,
+                    "use parentheses to disambiguate",
+                    sum_with_parens,
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+        }
+    }
+
+    crate fn maybe_recover_from_bad_type_plus(
+        &mut self,
+        allow_plus: bool,
+        ty: &Ty,
+    ) -> PResult<'a, ()> {
+        // Do not add `+` to expected tokens.
+        if !allow_plus || !self.token.is_like_plus() {
+            return Ok(());
+        }
+
+        self.bump(); // `+`
+        let bounds = self.parse_generic_bounds(None)?;
+        let sum_span = ty.span.to(self.prev_span);
+
+        let mut err = struct_span_err!(
+            self.sess.span_diagnostic,
+            sum_span,
+            E0178,
+            "expected a path on the left-hand side of `+`, not `{}`",
+            pprust::ty_to_string(ty)
+        );
+
+        match ty.node {
+            TyKind::Rptr(ref lifetime, ref mut_ty) => {
+                let sum_with_parens = pprust::to_string(|s| {
+                    use crate::print::pprust::PrintState;
+
+                    s.s.word("&")?;
+                    s.print_opt_lifetime(lifetime)?;
+                    s.print_mutability(mut_ty.mutbl)?;
+                    s.popen()?;
+                    s.print_type(&mut_ty.ty)?;
+                    s.print_type_bounds(" +", &bounds)?;
+                    s.pclose()
+                });
+                err.span_suggestion(
+                    sum_span,
+                    "try adding parentheses",
+                    sum_with_parens,
+                    Applicability::MachineApplicable,
+                );
+            }
+            TyKind::Ptr(..) | TyKind::BareFn(..) => {
+                err.span_label(sum_span, "perhaps you forgot parentheses?");
+            }
+            _ => {
+                err.span_label(sum_span, "expected a path");
+            }
+        }
+        err.emit();
+        Ok(())
+    }
+
+    /// Try to recover from associated item paths like `[T]::AssocItem`/`(T, U)::AssocItem`.
+    /// Attempt to convert the base expression/pattern/type into a type, parse the `::AssocItem`
+    /// tail, and combine them into a `<Ty>::AssocItem` expression/pattern/type.
+    crate fn maybe_recover_from_bad_qpath<T: RecoverQPath>(
+        &mut self,
+        base: P<T>,
+        allow_recovery: bool,
+    ) -> PResult<'a, P<T>> {
+        // Do not add `::` to expected tokens.
+        if allow_recovery && self.token == token::ModSep {
+            if let Some(ty) = base.to_ty() {
+                return self.maybe_recover_from_bad_qpath_stage_2(ty.span, ty);
+            }
+        }
+        Ok(base)
+    }
+
+    /// Given an already parsed `Ty` parse the `::AssocItem` tail and
+    /// combine them into a `<Ty>::AssocItem` expression/pattern/type.
+    crate fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
+        &mut self,
+        ty_span: Span,
+        ty: P<Ty>,
+    ) -> PResult<'a, P<T>> {
+        self.expect(&token::ModSep)?;
+
+        let mut path = ast::Path {
+            segments: Vec::new(),
+            span: syntax_pos::DUMMY_SP,
+        };
+        self.parse_path_segments(&mut path.segments, T::PATH_STYLE)?;
+        path.span = ty_span.to(self.prev_span);
+
+        let ty_str = self
+            .sess
+            .source_map()
+            .span_to_snippet(ty_span)
+            .unwrap_or_else(|_| pprust::ty_to_string(&ty));
+        self.diagnostic()
+            .struct_span_err(path.span, "missing angle brackets in associated item path")
+            .span_suggestion(
+                // this is a best-effort recovery
+                path.span,
+                "try",
+                format!("<{}>::{}", ty_str, path),
+                Applicability::MaybeIncorrect,
+            )
+            .emit();
+
+        let path_span = ty_span.shrink_to_hi(); // use an empty path since `position` == 0
+        Ok(P(T::recovered(
+            Some(QSelf {
+                ty,
+                path_span,
+                position: 0,
+            }),
+            path,
+        )))
+    }
+
+    crate fn maybe_consume_incorrect_semicolon(&mut self, items: &[P<Item>]) -> bool {
+        if self.eat(&token::Semi) {
+            let mut err = self.struct_span_err(self.prev_span, "expected item, found `;`");
+            err.span_suggestion_short(
+                self.prev_span,
+                "remove this semicolon",
+                String::new(),
+                Applicability::MachineApplicable,
+            );
+            if !items.is_empty() {
+                let previous_item = &items[items.len() - 1];
+                let previous_item_kind_name = match previous_item.node {
+                    // say "braced struct" because tuple-structs and
+                    // braceless-empty-struct declarations do take a semicolon
+                    ItemKind::Struct(..) => Some("braced struct"),
+                    ItemKind::Enum(..) => Some("enum"),
+                    ItemKind::Trait(..) => Some("trait"),
+                    ItemKind::Union(..) => Some("union"),
+                    _ => None,
+                };
+                if let Some(name) = previous_item_kind_name {
+                    err.help(&format!(
+                        "{} declarations are not followed by a semicolon",
+                        name
+                    ));
+                }
+            }
+            err.emit();
+            true
+        } else {
+            false
+        }
+    }
+}

src/libsyntax/parse/mod.rs

@@ -30,6 +30,7 @@ pub mod parser;
 pub mod lexer;
 pub mod token;
 pub mod attr;
+pub mod diagnostics;
 
 pub mod classify;