Implement RFC 1925

src/libsyntax/parse/parser.rs

@@ -3155,6 +3155,12 @@ impl<'a> Parser<'a> {
         maybe_whole!(self, NtArm, |x| x);
 
         let attrs = self.parse_outer_attributes()?;
+        // Allow a '|' before the pats (RFC 1925)
+        let beginning_vert = if self.eat(&token::BinOp(token::Or)) {
+            Some(self.prev_span)
+        } else {
+            None
+        };
         let pats = self.parse_pats()?;
         let guard = if self.eat_keyword(keywords::If) {
             Some(self.parse_expr()?)
@@ -3178,6 +3184,7 @@ impl<'a> Parser<'a> {
             pats,
             guard,
             body: expr,
+            beginning_vert,
         })
     }