Revert "SERVER-8008: $unwind of scalar should return 1 doc with scalar"

This reverts commit 25feddadeef43fb0668350b40282fcdfbb1f2296.

1 files changed, 8 insertions, 12 deletions

diff --git a/src/mongo/db/pipeline/document_source_unwind.cpp b/src/mongo/db/pipeline/document_source_unwind.cpp
index 4aa33633ca8..11c8d0880ec 100644
--- a/src/mongo/db/pipeline/document_source_unwind.cpp
+++ b/src/mongo/db/pipeline/document_source_unwind.cpp
@@ -87,11 +87,17 @@ namespace mongo {
             return;
         }
 
+        // The target field must be an array to unwind.
+        uassert(15978, str::stream() << "Value at end of $unwind field path '"
+                << _unwindPath.getPath(true) << "' must be an Array, but is a "
+                << typeName(pathValue.getType()),
+                pathValue.getType() == Array);
+
         _inputArray = pathValue;
     }
 
     boost::optional<Document> DocumentSourceUnwind::Unwinder::getNext() {
-        if (_inputArray.missing())
+        if (_inputArray.missing() || _index == _inputArray.getArrayLength())
             return boost::none;
 
         // If needed, this will automatically clone all the documents along the
@@ -101,17 +107,7 @@ namespace mongo {
         // along the path leading to that will be replaced in order not to share
         // that change with any other clones (or the original).
 
-        if (_inputArray.getType() == Array) {
-            if (_index == _inputArray.getArrayLength())
-                return boost::none;
-            _output.setNestedField(_unwindPathFieldIndexes, _inputArray[_index]);
-        }
-        else if (_index > 0) {
-            return boost::none;
-        }
-        else {
-            _output.setNestedField(_unwindPathFieldIndexes, _inputArray);
-        }
+        _output.setNestedField(_unwindPathFieldIndexes, _inputArray[_index]);
         _index++;
         return _output.peek();
     }