gnu: Add rust-if-chain-1.

* gnu/packages/crates-io.scm (rust-if-chain-1): New variable.

gnu/packages/crates-io.scm

@@ -10470,6 +10470,25 @@ SystemTime}}.")
        (("rust-rustc-serialize" ,rust-rustc-serialize-0.3)
         ("rust-rustc-test" ,rust-rustc-test-0.3))))))
 
+(define-public rust-if-chain-1
+  (package
+    (name "rust-if-chain")
+    (version "1.0.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (crate-uri "if_chain" version))
+       (file-name (string-append name "-" version ".tar.gz"))
+       (sha256
+        (base32
+         "0zgcn31bahnsmsjc0cgk0cy38p8sfjs79yvi6rjs5zz5b5xhqdn3"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/lfairy/if_chain")
+    (synopsis "Macro for writing nested @code{if let} expressions")
+    (description "This package provides a macro for writing nested @code{if
+let} expressions.")
+    (license (list license:expat license:asl2.0))))
+
 (define-public rust-ignore-0.4
   (package
     (name "rust-ignore")