Detect blocks that could be struct expr bodies

compiler/rustc_expand/src/expand.rs

@@ -20,7 +20,7 @@ use rustc_data_structures::map_in_place::MapInPlace;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{struct_span_err, Applicability, PResult};
 use rustc_feature::Features;
-use rustc_parse::parser::Parser;
+use rustc_parse::parser::{AttemptLocalParseRecovery, Parser};
 use rustc_parse::validate_attr;
 use rustc_session::lint::builtin::UNUSED_DOC_COMMENTS;
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -921,7 +921,7 @@ pub fn parse_ast_fragment<'a>(
             let mut stmts = SmallVec::new();
             // Won't make progress on a `}`.
             while this.token != token::Eof && this.token != token::CloseDelim(token::Brace) {
-                if let Some(stmt) = this.parse_full_stmt()? {
+                if let Some(stmt) = this.parse_full_stmt(AttemptLocalParseRecovery::Yes)? {
                     stmts.push(stmt);
                 }
             }

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -5,8 +5,9 @@ use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Lit, LitKind, TokenKind};
 use rustc_ast::util::parser::AssocOp;
 use rustc_ast::{
-    self as ast, AngleBracketedArgs, AttrVec, BinOpKind, BindingMode, BlockCheckMode, Expr,
-    ExprKind, Item, ItemKind, Mutability, Param, Pat, PatKind, PathSegment, QSelf, Ty, TyKind,
+    self as ast, AngleBracketedArgs, AttrVec, BinOpKind, BindingMode, Block, BlockCheckMode, Expr,
+    ExprKind, Item, ItemKind, Mutability, Param, Pat, PatKind, Path, PathSegment, QSelf, Ty,
+    TyKind,
 };
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
@@ -119,6 +120,28 @@ crate enum ConsumeClosingDelim {
     No,
 }
 
+#[derive(Clone, Copy)]
+pub enum AttemptLocalParseRecovery {
+    Yes,
+    No,
+}
+
+impl AttemptLocalParseRecovery {
+    pub fn yes(&self) -> bool {
+        match self {
+            AttemptLocalParseRecovery::Yes => true,
+            AttemptLocalParseRecovery::No => false,
+        }
+    }
+
+    pub fn no(&self) -> bool {
+        match self {
+            AttemptLocalParseRecovery::Yes => false,
+            AttemptLocalParseRecovery::No => true,
+        }
+    }
+}
+
 impl<'a> Parser<'a> {
     pub(super) fn span_fatal_err<S: Into<MultiSpan>>(
         &self,
@@ -321,6 +344,66 @@ impl<'a> Parser<'a> {
         }
     }
 
+    pub fn maybe_suggest_struct_literal(
+        &mut self,
+        lo: Span,
+        s: BlockCheckMode,
+    ) -> Option<PResult<'a, P<Block>>> {
+        if self.token.is_ident() && self.look_ahead(1, |t| t == &token::Colon) {
+            // We might be having a struct literal where people forgot to include the path:
+            // fn foo() -> Foo {
+            //     field: value,
+            // }
+            let mut snapshot = self.clone();
+            let path =
+                Path { segments: vec![], span: self.prev_token.span.shrink_to_lo(), tokens: None };
+            let struct_expr = snapshot.parse_struct_expr(path, AttrVec::new(), false);
+            let block_tail = self.parse_block_tail(lo, s, AttemptLocalParseRecovery::No);
+            return Some(match (struct_expr, block_tail) {
+                (Ok(expr), Err(mut err)) => {
+                    // We have encountered the following:
+                    // fn foo() -> Foo {
+                    //     field: value,
+                    // }
+                    // Suggest:
+                    // fn foo() -> Foo { Path {
+                    //     field: value,
+                    // } }
+                    err.delay_as_bug();
+                    self.struct_span_err(expr.span, "struct literal body without path")
+                        .multipart_suggestion(
+                            "you might have forgotten to add the struct literal inside the block",
+                            vec![
+                                (expr.span.shrink_to_lo(), "{ SomeStruct ".to_string()),
+                                (expr.span.shrink_to_hi(), " }".to_string()),
+                            ],
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                    *self = snapshot;
+                    Ok(self.mk_block(
+                        vec![self.mk_stmt_err(expr.span)],
+                        s,
+                        lo.to(self.prev_token.span),
+                    ))
+                }
+                (Err(mut err), Ok(tail)) => {
+                    // We have a block tail that contains a somehow valid type ascription expr.
+                    err.cancel();
+                    Ok(tail)
+                }
+                (Err(mut snapshot_err), Err(err)) => {
+                    // We don't know what went wrong, emit the normal error.
+                    snapshot_err.cancel();
+                    self.consume_block(token::Brace, ConsumeClosingDelim::Yes);
+                    Err(err)
+                }
+                (Ok(_), Ok(tail)) => Ok(tail),
+            });
+        }
+        None
+    }
+
     pub fn maybe_annotate_with_ascription(
         &mut self,
         err: &mut DiagnosticBuilder<'_>,

compiler/rustc_parse/src/parser/expr.rs

@@ -2015,9 +2015,12 @@ impl<'a> Parser<'a> {
     ) -> Option<PResult<'a, P<Expr>>> {
         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
         if struct_allowed || self.is_certainly_not_a_block() {
-            // This is a struct literal, but we don't can't accept them here.
-            let expr = self.parse_struct_expr(path.clone(), attrs.clone());
+            if let Err(err) = self.expect(&token::OpenDelim(token::Brace)) {
+                return Some(Err(err));
+            }
+            let expr = self.parse_struct_expr(path.clone(), attrs.clone(), true);
             if let (Ok(expr), false) = (&expr, struct_allowed) {
+                // This is a struct literal, but we don't can't accept them here.
                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
             }
             return Some(expr);
@@ -2035,12 +2038,13 @@ impl<'a> Parser<'a> {
             .emit();
     }
 
+    /// Precondition: already parsed the '{'.
     pub(super) fn parse_struct_expr(
         &mut self,
         pth: ast::Path,
         mut attrs: AttrVec,
+        recover: bool,
     ) -> PResult<'a, P<Expr>> {
-        self.bump();
         let mut fields = Vec::new();
         let mut base = None;
         let mut recover_async = false;
@@ -2059,10 +2063,11 @@ impl<'a> Parser<'a> {
                 let exp_span = self.prev_token.span;
                 match self.parse_expr() {
                     Ok(e) => base = Some(e),
-                    Err(mut e) => {
+                    Err(mut e) if recover => {
                         e.emit();
                         self.recover_stmt();
                     }
+                    Err(e) => return Err(e),
                 }
                 self.recover_struct_comma_after_dotdot(exp_span);
                 break;
@@ -2114,6 +2119,9 @@ impl<'a> Parser<'a> {
                             );
                         }
                     }
+                    if !recover {
+                        return Err(e);
+                    }
                     e.emit();
                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
                     self.eat(&token::Comma);

compiler/rustc_parse/src/parser/mod.rs

@@ -10,6 +10,7 @@ mod stmt;
 mod ty;
 
 use crate::lexer::UnmatchedBrace;
+pub use diagnostics::AttemptLocalParseRecovery;
 use diagnostics::Error;
 pub use path::PathStyle;
 

compiler/rustc_parse/src/parser/stmt.rs

@@ -1,5 +1,5 @@
 use super::attr::DEFAULT_INNER_ATTR_FORBIDDEN;
-use super::diagnostics::Error;
+use super::diagnostics::{AttemptLocalParseRecovery, Error};
 use super::expr::LhsExpr;
 use super::pat::GateOr;
 use super::path::PathStyle;
@@ -79,8 +79,8 @@ impl<'a> Parser<'a> {
             return self.parse_stmt_mac(lo, attrs.into(), path);
         }
 
-        let expr = if self.check(&token::OpenDelim(token::Brace)) {
-            self.parse_struct_expr(path, AttrVec::new())?
+        let expr = if self.eat(&token::OpenDelim(token::Brace)) {
+            self.parse_struct_expr(path, AttrVec::new(), true)?
         } else {
             let hi = self.prev_token.span;
             self.mk_expr(lo.to(hi), ExprKind::Path(None, path), AttrVec::new())
@@ -321,25 +321,37 @@ impl<'a> Parser<'a> {
             return self.error_block_no_opening_brace();
         }
 
-        Ok((self.parse_inner_attributes()?, self.parse_block_tail(lo, blk_mode)?))
+        let attrs = self.parse_inner_attributes()?;
+        let tail = if let Some(tail) = self.maybe_suggest_struct_literal(lo, blk_mode) {
+            tail?
+        } else {
+            self.parse_block_tail(lo, blk_mode, AttemptLocalParseRecovery::Yes)?
+        };
+        Ok((attrs, tail))
     }
 
     /// Parses the rest of a block expression or function body.
     /// Precondition: already parsed the '{'.
-    fn parse_block_tail(&mut self, lo: Span, s: BlockCheckMode) -> PResult<'a, P<Block>> {
+    crate fn parse_block_tail(
+        &mut self,
+        lo: Span,
+        s: BlockCheckMode,
+        recover: AttemptLocalParseRecovery,
+    ) -> PResult<'a, P<Block>> {
         let mut stmts = vec![];
         while !self.eat(&token::CloseDelim(token::Brace)) {
             if self.token == token::Eof {
                 break;
             }
-            let stmt = match self.parse_full_stmt() {
-                Err(mut err) => {
+            let stmt = match self.parse_full_stmt(recover) {
+                Err(mut err) if recover.yes() => {
                     self.maybe_annotate_with_ascription(&mut err, false);
                     err.emit();
                     self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
                     Some(self.mk_stmt_err(self.token.span))
                 }
                 Ok(stmt) => stmt,
+                Err(err) => return Err(err),
             };
             if let Some(stmt) = stmt {
                 stmts.push(stmt);
@@ -352,7 +364,10 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a statement, including the trailing semicolon.
-    pub fn parse_full_stmt(&mut self) -> PResult<'a, Option<Stmt>> {
+    pub fn parse_full_stmt(
+        &mut self,
+        recover: AttemptLocalParseRecovery,
+    ) -> PResult<'a, Option<Stmt>> {
         // Skip looking for a trailing semicolon when we have an interpolated statement.
         maybe_whole!(self, NtStmt, |x| Some(x));
 
@@ -391,6 +406,9 @@ impl<'a> Parser<'a> {
                     if let Err(mut e) =
                         self.check_mistyped_turbofish_with_multiple_type_params(e, expr)
                     {
+                        if recover.no() {
+                            return Err(e);
+                        }
                         e.emit();
                         self.recover_stmt();
                     }
@@ -432,7 +450,7 @@ impl<'a> Parser<'a> {
         Stmt { id: DUMMY_NODE_ID, kind, span, tokens: None }
     }
 
-    fn mk_stmt_err(&self, span: Span) -> Stmt {
+    pub(super) fn mk_stmt_err(&self, span: Span) -> Stmt {
         self.mk_stmt(span, StmtKind::Expr(self.mk_expr_err(span)))
     }
 

src/test/ui/parser/bare-struct-body.rs

@@ -0,0 +1,15 @@
+struct Foo {
+    val: (),
+}
+
+fn foo() -> Foo { //~ ERROR struct literal body without path
+    val: (),
+}
+
+fn main() {
+    let x = foo();
+    x.val == 42; //~ ERROR mismatched types
+    let x = { //~ ERROR struct literal body without path
+        val: (),
+    };
+}

src/test/ui/parser/bare-struct-body.stderr

@@ -0,0 +1,41 @@
+error: struct literal body without path
+  --> $DIR/bare-struct-body.rs:5:17
+   |
+LL |   fn foo() -> Foo {
+   |  _________________^
+LL | |     val: (),
+LL | | }
+   | |_^
+   |
+help: you might have forgotten to add the struct literal inside the block
+   |
+LL | fn foo() -> Foo { SomeStruct {
+LL |     val: (),
+LL | } }
+   |
+
+error: struct literal body without path
+  --> $DIR/bare-struct-body.rs:12:13
+   |
+LL |       let x = {
+   |  _____________^
+LL | |         val: (),
+LL | |     };
+   | |_____^
+   |
+help: you might have forgotten to add the struct literal inside the block
+   |
+LL |     let x = { SomeStruct {
+LL |         val: (),
+LL |     } };
+   |
+
+error[E0308]: mismatched types
+  --> $DIR/bare-struct-body.rs:11:14
+   |
+LL |     x.val == 42;
+   |              ^^ expected `()`, found integer
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.