Merge #19

19: Add YieldExpr r=lnicola a=sasurau4

Adding YieldExpr

Part of #7209
ref: https://doc.rust-lang.org/beta/unstable-book/language-features/generators.html

Co-authored-by: Daiki Ihara <sasurau4@gmail.com>

Author: bors[bot]

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "ungrammar"
 description = "A DSL for describing concrete syntax trees"
-version = "1.6.0"
+version = "1.7.0"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/matklad/ungrammar"
 authors = ["Aleksey Kladov <aleksey.kladov@gmail.com>"]

rust.ungram

@@ -351,6 +351,7 @@ Expr =
 | TryExpr
 | TupleExpr
 | WhileExpr
+| YieldExpr
 
 Literal =
   Attr* value:(
@@ -491,6 +492,9 @@ MatchGuard =
 ReturnExpr =
   Attr* 'return' Expr?
 
+YieldExpr =
+  Attr* 'yield' Expr?
+
 AwaitExpr =
   Attr* Expr '.' 'await'