SERVER-22569 Change findParentEqualityElement() to return by value.

MSVC 2013 doesn't support thread-safe initialization of function-local
static-duration objects, so it's possible to return a reference to
'eooElement' prior to the value being fully initialized.

(cherry picked from commit 4f1cc51f3e21e4ff76c68e86ecae4e5d138de0aa)

3 files changed, 9 insertions, 10 deletions

diff --git a/src/mongo/db/ops/path_support.cpp b/src/mongo/db/ops/path_support.cpp
index 894b0117393..0523ef6acbb 100644
--- a/src/mongo/db/ops/path_support.cpp
+++ b/src/mongo/db/ops/path_support.cpp
@@ -287,9 +287,9 @@ Status setElementAtPath(const FieldRef& path,
     }
 }
 
-const BSONElement& findParentEqualityElement(const EqualityMatches& equalities,
-                                             const FieldRef& path,
-                                             int* parentPathParts) {
+BSONElement findParentEqualityElement(const EqualityMatches& equalities,
+                                      const FieldRef& path,
+                                      int* parentPathParts) {
     // We may have an equality match to an object at a higher point in the pattern path, check
     // all path prefixes for equality matches
     // ex: path: 'a.b', query : { 'a' : { b : <value> } }
@@ -309,8 +309,7 @@ const BSONElement& findParentEqualityElement(const EqualityMatches& equalities,
     }
 
     *parentPathParts = -1;
-    static const BSONElement eooElement;
-    return eooElement;
+    return BSONElement();
 }
 
 /**
@@ -318,7 +317,7 @@ const BSONElement& findParentEqualityElement(const EqualityMatches& equalities,
  */
 static Status checkEqualityConflicts(const EqualityMatches& equalities, const FieldRef& path) {
     int parentPathPart = -1;
-    const BSONElement& parentEl = findParentEqualityElement(equalities, path, &parentPathPart);
+    const BSONElement parentEl = findParentEqualityElement(equalities, path, &parentPathPart);
 
     if (parentEl.eoo())
         return Status::OK();
diff --git a/src/mongo/db/ops/path_support.h b/src/mongo/db/ops/path_support.h
index 6e01c03390e..6fbd95ec0a9 100644
--- a/src/mongo/db/ops/path_support.h
+++ b/src/mongo/db/ops/path_support.h
@@ -170,9 +170,9 @@ Status extractFullEqualityMatches(const MatchExpression& root,
  *   Path 'a.b.c' has an eqmatch parent of 'a.b' : 1
  *
  */
-const BSONElement& findParentEqualityElement(const EqualityMatches& equalities,
-                                             const FieldRef& path,
-                                             int* parentPathParts);
+BSONElement findParentEqualityElement(const EqualityMatches& equalities,
+                                      const FieldRef& path,
+                                      int* parentPathParts);
 
 /**
  * Adds the BSON values from equality matches into the given document at the equality match
diff --git a/src/mongo/s/shard_key_pattern.cpp b/src/mongo/s/shard_key_pattern.cpp
index 67d2743ac22..5a30cff8fb3 100644
--- a/src/mongo/s/shard_key_pattern.cpp
+++ b/src/mongo/s/shard_key_pattern.cpp
@@ -247,7 +247,7 @@ BSONObj ShardKeyPattern::extractShardKeyFromDoc(const BSONObj& doc) const {
 
 static BSONElement findEqualityElement(const EqualityMatches& equalities, const FieldRef& path) {
     int parentPathPart;
-    const BSONElement& parentEl =
+    const BSONElement parentEl =
         pathsupport::findParentEqualityElement(equalities, path, &parentPathPart);
 
     if (parentPathPart == static_cast<int>(path.numParts()))