Fix scope of else clause, and avoid duplication

src/lib.rs

@@ -164,7 +164,10 @@ macro_rules! if_chain {
 macro_rules! __if_chain {
     // Expand with both a successful case and a fallback
     (@init ($($tt:tt)*) then { $($then:tt)* } else { $($other:tt)* }) => {
-        __if_chain! { @expand { $($other)* } $($tt)* then { $($then)* } }
+        match __if_chain! { @expand { None } $($tt)* then { Some({ $($then)* })} } {
+            Some(__if_chain_y) => __if_chain_y,
+            None => { $($other)* },
+        }
     };
     // Expand with no fallback
     (@init ($($tt:tt)*) then { $($then:tt)* }) => {
@@ -239,6 +242,10 @@ macro_rules! __if_chain {
 
 #[cfg(test)]
 mod tests {
+    #[derive(Debug,Copy,Clone,Eq,PartialEq)]
+    enum Got { Then(usize), Else(usize) }
+    use self::Got::*;
+
     #[test]
     fn simple() {
         let x: Option<Result<Option<String>, (u32, u32)>> = Some(Err((41, 42)));
@@ -311,4 +318,37 @@ mod tests {
         };
         assert_eq!(x, 3);
     }
+
+    #[test]
+    fn let_rebinding_values() {
+        #[allow(unused_variables)]
+        fn wat(seq: &[usize]) -> Got {
+            let mut seq = seq.iter();
+            let dunno  = 0;
+            if_chain! {
+                if let Some(&dunno) = seq.next(); // unused binding
+                if let Some(&dunno) = seq.next();
+                then { Then(dunno) }
+                else { Else(dunno) }
+            }
+        }
+
+        assert_eq!(Else(0), wat(&[         ]));
+        assert_eq!(Else(0), wat(&[ 1       ]));
+        assert_eq!(Then(2), wat(&[ 1, 2    ]));
+        assert_eq!(Then(2), wat(&[ 1, 2, 3 ]));
+    }
+
+    #[test]
+    fn let_rebinding() {
+        let v = Some(Some(Some('a')));
+        if_chain! {
+            if let Some(v) = v;
+            if let Some(v) = v;
+            if let Some(v) = v;
+            if true;
+            then { let _: char = v; }
+            else { let _: Option<Option<Option<char>>> = v; }
+        };
+    }
 }