SERVER-33323 Fix pushBack, remove const from size_t, and fix s390x

Check if the pipeline is empty before setting the new stage to point to
the last one in Pipeline::pushBack().

Remove unnecessary const qualifier from std::size_t return types.

Work around a compiler bug on s390x by allowing a CursorResponse to be
copied.

9 files changed, 25 insertions, 8 deletions

diff --git a/src/mongo/db/pipeline/pipeline.cpp b/src/mongo/db/pipeline/pipeline.cpp
index 335ca4f5655..c784bdd624f 100644
--- a/src/mongo/db/pipeline/pipeline.cpp
+++ b/src/mongo/db/pipeline/pipeline.cpp
@@ -613,7 +613,9 @@ Status Pipeline::_pipelineCanRunOnMongoS() const {
 }
 
 void Pipeline::pushBack(boost::intrusive_ptr<DocumentSource> newStage) {
-    newStage->setSource(_sources.back().get());
+    if (!_sources.empty()) {
+        newStage->setSource(_sources.back().get());
+    }
     _sources.push_back(std::move(newStage));
 }
 
diff --git a/src/mongo/db/query/cursor_response.h b/src/mongo/db/query/cursor_response.h
index b2dd828f4c2..091b64e0c73 100644
--- a/src/mongo/db/query/cursor_response.h
+++ b/src/mongo/db/query/cursor_response.h
@@ -132,7 +132,13 @@ void appendGetMoreResponseObject(long long cursorId,
                                  BSONObjBuilder* builder);
 
 class CursorResponse {
+// In order to work around a bug in the compiler on the s390x platform, the IDL needs to invoke the
+// copy constructor on that platform.
+// TODO SERVER-32467 Remove this ifndef once the compiler has been fixed and the workaround has been
+// removed.
+#ifndef __s390x__
     MONGO_DISALLOW_COPYING(CursorResponse);
+#endif
 
 public:
     enum class ResponseType {
@@ -170,6 +176,15 @@ public:
     CursorResponse(CursorResponse&& other) = default;
     CursorResponse& operator=(CursorResponse&& other) = default;
 
+// In order to work around a bug in the compiler on the s390x platform, the IDL needs to invoke the
+// copy constructor on that platform.
+// TODO SERVER-32467 Remove this ifndef once the compiler has been fixed and the workaround has been
+// removed.
+#ifdef __s390x__
+    CursorResponse(const CursorResponse& other) = default;
+    CursorResponse& operator=(const CursorResponse& other) = default;
+#endif
+
     //
     // Accessors.
     //
diff --git a/src/mongo/s/query/cluster_client_cursor.h b/src/mongo/s/query/cluster_client_cursor.h
index 9c01c013ce6..1afb5ae1b38 100644
--- a/src/mongo/s/query/cluster_client_cursor.h
+++ b/src/mongo/s/query/cluster_client_cursor.h
@@ -113,7 +113,7 @@ public:
     /**
      * Returns a reference to the vector of remote hosts involved in this operation.
      */
-    virtual const std::size_t getNumRemotes() const = 0;
+    virtual std::size_t getNumRemotes() const = 0;
 
     /**
      * Returns the number of result documents returned so far by this cursor via the next() method.
diff --git a/src/mongo/s/query/cluster_client_cursor_impl.cpp b/src/mongo/s/query/cluster_client_cursor_impl.cpp
index 1a4be45f1be..e5348f3d86f 100644
--- a/src/mongo/s/query/cluster_client_cursor_impl.cpp
+++ b/src/mongo/s/query/cluster_client_cursor_impl.cpp
@@ -147,7 +147,7 @@ BSONObj ClusterClientCursorImpl::getOriginatingCommand() const {
     return _params.originatingCommandObj;
 }
 
-const std::size_t ClusterClientCursorImpl::getNumRemotes() const {
+std::size_t ClusterClientCursorImpl::getNumRemotes() const {
     return _root->getNumRemotes();
 }
 
diff --git a/src/mongo/s/query/cluster_client_cursor_impl.h b/src/mongo/s/query/cluster_client_cursor_impl.h
index d3c9349233b..34fa7d16c61 100644
--- a/src/mongo/s/query/cluster_client_cursor_impl.h
+++ b/src/mongo/s/query/cluster_client_cursor_impl.h
@@ -105,7 +105,7 @@ public:
 
     BSONObj getOriginatingCommand() const final;
 
-    const std::size_t getNumRemotes() const final;
+    std::size_t getNumRemotes() const final;
 
     long long getNumReturnedSoFar() const final;
 
diff --git a/src/mongo/s/query/cluster_client_cursor_mock.cpp b/src/mongo/s/query/cluster_client_cursor_mock.cpp
index 6e624f36b84..b248b35f77e 100644
--- a/src/mongo/s/query/cluster_client_cursor_mock.cpp
+++ b/src/mongo/s/query/cluster_client_cursor_mock.cpp
@@ -68,7 +68,7 @@ BSONObj ClusterClientCursorMock::getOriginatingCommand() const {
     return _originatingCommand;
 }
 
-const std::size_t ClusterClientCursorMock::getNumRemotes() const {
+std::size_t ClusterClientCursorMock::getNumRemotes() const {
     MONGO_UNREACHABLE;
 }
 
diff --git a/src/mongo/s/query/cluster_client_cursor_mock.h b/src/mongo/s/query/cluster_client_cursor_mock.h
index 1c50403c3ae..beb49735a8d 100644
--- a/src/mongo/s/query/cluster_client_cursor_mock.h
+++ b/src/mongo/s/query/cluster_client_cursor_mock.h
@@ -69,7 +69,7 @@ public:
 
     BSONObj getOriginatingCommand() const final;
 
-    const std::size_t getNumRemotes() const final;
+    std::size_t getNumRemotes() const final;
 
     long long getNumReturnedSoFar() const final;
 
diff --git a/src/mongo/s/query/cluster_cursor_manager.cpp b/src/mongo/s/query/cluster_cursor_manager.cpp
index ca66ee04e08..44cd6333f19 100644
--- a/src/mongo/s/query/cluster_cursor_manager.cpp
+++ b/src/mongo/s/query/cluster_cursor_manager.cpp
@@ -147,7 +147,7 @@ BSONObj ClusterCursorManager::PinnedCursor::getOriginatingCommand() const {
     return _cursor->getOriginatingCommand();
 }
 
-const std::size_t ClusterCursorManager::PinnedCursor::getNumRemotes() const {
+std::size_t ClusterCursorManager::PinnedCursor::getNumRemotes() const {
     invariant(_cursor);
     return _cursor->getNumRemotes();
 }
diff --git a/src/mongo/s/query/cluster_cursor_manager.h b/src/mongo/s/query/cluster_cursor_manager.h
index cf6dc54f21e..e8ab24cfa36 100644
--- a/src/mongo/s/query/cluster_cursor_manager.h
+++ b/src/mongo/s/query/cluster_cursor_manager.h
@@ -198,7 +198,7 @@ public:
         /**
          * Returns a reference to the vector of remote hosts involved in this operation.
          */
-        const std::size_t getNumRemotes() const;
+        std::size_t getNumRemotes() const;
 
         /**
          * Returns the cursor id for the underlying cursor, or zero if no cursor is owned.