Throw errors when doc comments are added where they're unused

src/libsyntax/parse/parser.rs

@@ -2131,14 +2131,14 @@ impl<'a> Parser<'a> {
                 } else {
                     Ok(self.mk_expr(span, ExprKind::Tup(es), attrs))
                 }
-            },
+            }
             token::OpenDelim(token::Brace) => {
                 return self.parse_block_expr(lo, BlockCheckMode::Default, attrs);
-            },
-            token::BinOp(token::Or) |  token::OrOr => {
+            }
+            token::BinOp(token::Or) | token::OrOr => {
                 let lo = self.span;
                 return self.parse_lambda_expr(lo, CaptureBy::Ref, attrs);
-            },
+            }
             token::OpenDelim(token::Bracket) => {
                 self.bump();
 
@@ -2387,7 +2387,6 @@ impl<'a> Parser<'a> {
     pub fn parse_block_expr(&mut self, lo: Span, blk_mode: BlockCheckMode,
                             outer_attrs: ThinVec<Attribute>)
                             -> PResult<'a, P<Expr>> {
-
         self.expect(&token::OpenDelim(token::Brace))?;
 
         let mut attrs = outer_attrs;
@@ -2421,6 +2420,12 @@ impl<'a> Parser<'a> {
             expr.map(|mut expr| {
                 attrs.extend::<Vec<_>>(expr.attrs.into());
                 expr.attrs = attrs;
+                if if let Some(ref doc) = expr.attrs.iter().find(|x| x.is_sugared_doc) {
+                    self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+                    true
+                } else { false } {
+                    return expr;
+                }
                 match expr.node {
                     ExprKind::If(..) | ExprKind::IfLet(..) => {
                         if !expr.attrs.is_empty() {
@@ -3105,6 +3110,9 @@ impl<'a> Parser<'a> {
 
     // `else` token already eaten
     pub fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
+        if self.prev_token_kind == PrevTokenKind::DocComment {
+            return Err(self.span_fatal_err(self.span, Error::UselessDocComment));
+        }
         if self.eat_keyword(keywords::If) {
             return self.parse_if_expr(ThinVec::new());
         } else {
@@ -3118,6 +3126,9 @@ impl<'a> Parser<'a> {
                           span_lo: Span,
                           mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
         // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
 
         let pat = self.parse_pat()?;
         self.expect_keyword(keywords::In)?;
@@ -3133,6 +3144,9 @@ impl<'a> Parser<'a> {
     pub fn parse_while_expr(&mut self, opt_ident: Option<ast::SpannedIdent>,
                             span_lo: Span,
                             mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
         if self.token.is_keyword(keywords::Let) {
             return self.parse_while_let_expr(opt_ident, span_lo, attrs);
         }
@@ -3161,6 +3175,9 @@ impl<'a> Parser<'a> {
     pub fn parse_loop_expr(&mut self, opt_ident: Option<ast::SpannedIdent>,
                            span_lo: Span,
                            mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
         attrs.extend(iattrs);
         let span = span_lo.to(body.span);
@@ -3171,6 +3188,9 @@ impl<'a> Parser<'a> {
     pub fn parse_catch_expr(&mut self, span_lo: Span, mut attrs: ThinVec<Attribute>)
         -> PResult<'a, P<Expr>>
     {
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
         attrs.extend(iattrs);
         Ok(self.mk_expr(span_lo.to(body.span), ExprKind::Catch(body), attrs))
@@ -3178,6 +3198,9 @@ impl<'a> Parser<'a> {
 
     // `match` token already eaten
     fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
         let match_span = self.prev_span;
         let lo = self.prev_span;
         let discriminant = self.parse_expr_res(RESTRICTION_NO_STRUCT_LITERAL,
@@ -3215,6 +3238,9 @@ impl<'a> Parser<'a> {
         maybe_whole!(self, NtArm, |x| x);
 
         let attrs = self.parse_outer_attributes()?;
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
         let pats = self.parse_pats()?;
         let guard = if self.eat_keyword(keywords::If) {
             Some(self.parse_expr()?)
@@ -3669,6 +3695,9 @@ impl<'a> Parser<'a> {
 
     /// Parse a local variable declaration
     fn parse_local(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Local>> {
+        if let Some(doc) = attrs.iter().find(|x| x.is_sugared_doc) {
+            self.span_fatal_err(doc.span, Error::UselessDocComment).emit();
+        }
         let lo = self.span;
         let pat = self.parse_pat()?;
 
@@ -4158,6 +4187,8 @@ impl<'a> Parser<'a> {
                 stmts.push(stmt);
             } else if self.token == token::Eof {
                 break;
+            } else if let token::DocComment(_) = self.token {
+                return Err(self.span_fatal_err(self.span, Error::UselessDocComment));
             } else {
                 // Found only `;` or `}`.
                 continue;