Add type annotation pattern

Author: tathanhdinh

src/lib.rs

@@ -152,6 +152,10 @@ macro_rules! __if_chain {
             $($pat)|+ => __if_chain! { @expand $other $($tt)+ }
         }
     };
+    (@expand $other:block let $ident:ident:$ty:ty = $expr:expr; $($tt:tt)+) => {
+        let $ident:$ty = $expr;
+        __if_chain! { @expand $other $($tt)+ }
+    };
     (@expand $other:block if let $($pat:pat)|+ = $expr:expr; $($tt:tt)+) => {
         match $expr {
             $($pat)|+ => __if_chain! { @expand $other $($tt)+ },
@@ -236,4 +240,17 @@ mod tests {
             else { panic!(); }
         }
     }
+
+    #[test]
+    fn let_type_annotation_patterns() {
+        let mut x: u32 = 1;
+        if_chain! {
+            if x > 0;
+            let y: u32 = 2;
+
+            then { x += y; }
+            else { x += 1; }
+        };
+        assert_eq!(x, 3);
+    }
 }