syntax: extract parse_cfg_attr

src/libsyntax/parse/parser/attr.rs

@@ -260,6 +260,27 @@ impl<'a> Parser<'a> {
         Ok(lit)
     }
 
+    /// Parses `cfg_attr(pred, attr_item_list)` where `attr_item_list` is comma-delimited.
+    crate fn parse_cfg_attr(&mut self) -> PResult<'a, (ast::MetaItem, Vec<(ast::AttrItem, Span)>)> {
+        self.expect(&token::OpenDelim(token::Paren))?;
+
+        let cfg_predicate = self.parse_meta_item()?;
+        self.expect(&token::Comma)?;
+
+        // Presumably, the majority of the time there will only be one attr.
+        let mut expanded_attrs = Vec::with_capacity(1);
+
+        while !self.check(&token::CloseDelim(token::Paren)) {
+            let lo = self.token.span.lo();
+            let item = self.parse_attr_item()?;
+            expanded_attrs.push((item, self.prev_span.with_lo(lo)));
+            self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Paren)])?;
+        }
+
+        self.expect(&token::CloseDelim(token::Paren))?;
+        Ok((cfg_predicate, expanded_attrs))
+    }
+
     /// Matches the following grammar (per RFC 1559).
     ///
     ///     meta_item : PATH ( '=' UNSUFFIXED_LIT | '(' meta_item_inner? ')' )? ;