Fix offset for unary operations

Fixes https://github.com/nrc/rustfmt/issues/227.

src/expr.rs

@@ -1134,11 +1134,10 @@ fn rewrite_unary_op(context: &RewriteContext,
         ast::UnOp::UnNot => "!",
         ast::UnOp::UnNeg => "-",
     };
+    let operator_len = operator_str.len();
 
-    let subexpr =
-        try_opt!(expr.rewrite(context, try_opt!(width.checked_sub(operator_str.len())), offset));
-
-    Some(format!("{}{}", operator_str, subexpr))
+    expr.rewrite(context, try_opt!(width.checked_sub(operator_len)), offset + operator_len)
+        .map(|r| format!("{}{}", operator_str, r))
 }
 
 fn rewrite_assignment(context: &RewriteContext,

tests/source/expr.rs

@@ -105,3 +105,9 @@ fn qux() {
         // A block with a comment.
     }
 }
+
+fn issue227() {
+    {
+        let handler = box DocumentProgressHandler::new(addr, DocumentProgressTask::DOMContentLoaded);
+    }
+}

tests/target/expr.rs

@@ -139,3 +139,10 @@ fn qux() {
         // A block with a comment.
     }
 }
+
+fn issue227() {
+    {
+        let handler = box DocumentProgressHandler::new(addr,
+                                                       DocumentProgressTask::DOMContentLoaded);
+    }
+}