Add syntax elements for if let match guards

Author: jonas-schievink

src/tools/rust-analyzer/lib/ungrammar/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "ungrammar"
 description = "A DSL for describing concrete syntax trees"
-version = "1.14.2"
+version = "1.14.3"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/matklad/ungrammar"
 authors = ["Aleksey Kladov <aleksey.kladov@gmail.com>"]

src/tools/rust-analyzer/lib/ungrammar/rust.ungram

@@ -488,7 +488,7 @@ MatchArm =
   Attr* Pat guard:MatchGuard? '=>' Expr ','?
 
 MatchGuard =
-  'if' Expr
+  'if' ('let' Pat '=')? Expr
 
 ReturnExpr =
   Attr* 'return' Expr?