SERVER-19510 Refactor WhereMatchExpression/WhereNoOpMatchExpression

- Moves ExtensionsCallbackReal and ExtensionsCallbackNoop to their own
  files, and introduces a new library 'expressions_mongod_only' in
  db/matcher/.
- Introduces a common base class for WhereMatchExpression and
  WhereNoOpMatchExpression.
- Introduces a protected method extractWhereMatchExpressionParams() on
  ExtensionsCallback.

41 files changed, 680 insertions, 241 deletions

diff --git a/src/mongo/db/SConscript b/src/mongo/db/SConscript
index 8b9d7a7854f..b52da371023 100644
--- a/src/mongo/db/SConscript
+++ b/src/mongo/db/SConscript
@@ -590,7 +590,6 @@ serverOnlyFiles = [
     "index_rebuilder.cpp",
     "instance.cpp",
     "introspect.cpp",
-    "matcher/expression_where.cpp",
     "op_observer.cpp",
     "operation_context_impl.cpp",
     "ops/delete.cpp",
@@ -668,6 +667,7 @@ serveronlyLibdeps = [
     "ftdc/ftdc_mongod",
     "global_timestamp",
     "index/index_descriptor",
+    "matcher/expressions_mongod_only",
     "ops/update_driver",
     "pipeline/document_source",
     "pipeline/pipeline",
diff --git a/src/mongo/db/commands/current_op.cpp b/src/mongo/db/commands/current_op.cpp
index 224105b4ce4..f15f60807e7 100644
--- a/src/mongo/db/commands/current_op.cpp
+++ b/src/mongo/db/commands/current_op.cpp
@@ -40,6 +40,7 @@
 #include "mongo/db/curop.h"
 #include "mongo/db/dbmessage.h"
 #include "mongo/db/jsobj.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/matcher/matcher.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/operation_context.h"
diff --git a/src/mongo/db/commands/find_cmd.cpp b/src/mongo/db/commands/find_cmd.cpp
index e0977c97845..853bdb3d850 100644
--- a/src/mongo/db/commands/find_cmd.cpp
+++ b/src/mongo/db/commands/find_cmd.cpp
@@ -42,6 +42,7 @@
 #include "mongo/db/db_raii.h"
 #include "mongo/db/exec/working_set_common.h"
 #include "mongo/db/service_context.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/repl/replication_coordinator.h"
 #include "mongo/db/query/cursor_response.h"
 #include "mongo/db/query/explain.h"
diff --git a/src/mongo/db/commands/geo_near_cmd.cpp b/src/mongo/db/commands/geo_near_cmd.cpp
index 91b01ac481b..f26d4e5e59e 100644
--- a/src/mongo/db/commands/geo_near_cmd.cpp
+++ b/src/mongo/db/commands/geo_near_cmd.cpp
@@ -46,6 +46,7 @@
 #include "mongo/db/index_names.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/db/matcher/expression_geo.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/query/explain.h"
 #include "mongo/db/query/get_executor.h"
 #include "mongo/db/range_preserver.h"
diff --git a/src/mongo/db/commands/index_filter_commands.cpp b/src/mongo/db/commands/index_filter_commands.cpp
index d9b5c8b20c0..a02ca782417 100644
--- a/src/mongo/db/commands/index_filter_commands.cpp
+++ b/src/mongo/db/commands/index_filter_commands.cpp
@@ -43,6 +43,7 @@
 #include "mongo/db/db_raii.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/db/matcher/expression_parser.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 
 
 namespace {
diff --git a/src/mongo/db/commands/mr.cpp b/src/mongo/db/commands/mr.cpp
index 57ec5779a55..1d9a52067fa 100644
--- a/src/mongo/db/commands/mr.cpp
+++ b/src/mongo/db/commands/mr.cpp
@@ -49,6 +49,7 @@
 #include "mongo/db/index/index_descriptor.h"
 #include "mongo/db/instance.h"
 #include "mongo/db/matcher/matcher.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/op_observer.h"
 #include "mongo/db/operation_context_impl.h"
diff --git a/src/mongo/db/commands/plan_cache_commands.cpp b/src/mongo/db/commands/plan_cache_commands.cpp
index b4d56421a33..8b5c94e74e7 100644
--- a/src/mongo/db/commands/plan_cache_commands.cpp
+++ b/src/mongo/db/commands/plan_cache_commands.cpp
@@ -42,6 +42,7 @@
 #include "mongo/db/commands/plan_cache_commands.h"
 #include "mongo/db/db_raii.h"
 #include "mongo/db/jsobj.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/query/explain.h"
 #include "mongo/db/query/plan_ranker.h"
 #include "mongo/util/log.h"
diff --git a/src/mongo/db/dbhelpers.cpp b/src/mongo/db/dbhelpers.cpp
index cbf7259d0f6..f0cc920452f 100644
--- a/src/mongo/db/dbhelpers.cpp
+++ b/src/mongo/db/dbhelpers.cpp
@@ -44,6 +44,7 @@
 #include "mongo/db/index/btree_access_method.h"
 #include "mongo/db/json.h"
 #include "mongo/db/keypattern.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/op_observer.h"
 #include "mongo/db/ops/delete.h"
 #include "mongo/db/ops/update.h"
diff --git a/src/mongo/db/exec/sort_key_generator.cpp b/src/mongo/db/exec/sort_key_generator.cpp
index 0287c2287f6..26e9d6886db 100644
--- a/src/mongo/db/exec/sort_key_generator.cpp
+++ b/src/mongo/db/exec/sort_key_generator.cpp
@@ -39,6 +39,7 @@
 #include "mongo/db/exec/working_set.h"
 #include "mongo/db/exec/working_set_common.h"
 #include "mongo/db/exec/working_set_computed_data.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/query/query_planner.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/log.h"
diff --git a/src/mongo/db/exec/stagedebug_cmd.cpp b/src/mongo/db/exec/stagedebug_cmd.cpp
index 6adae8898fc..261df368104 100644
--- a/src/mongo/db/exec/stagedebug_cmd.cpp
+++ b/src/mongo/db/exec/stagedebug_cmd.cpp
@@ -54,6 +54,7 @@
 #include "mongo/db/index/fts_access_method.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/db/matcher/expression_parser.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/query/plan_executor.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/log.h"
diff --git a/src/mongo/db/exec/subplan.cpp b/src/mongo/db/exec/subplan.cpp
index efed540c37d..c77b7d05454 100644
--- a/src/mongo/db/exec/subplan.cpp
+++ b/src/mongo/db/exec/subplan.cpp
@@ -35,6 +35,7 @@
 #include "mongo/client/dbclientinterface.h"
 #include "mongo/db/exec/multi_plan.h"
 #include "mongo/db/exec/scoped_timer.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/query/get_executor.h"
 #include "mongo/db/query/plan_executor.h"
 #include "mongo/db/query/planner_analysis.h"
diff --git a/src/mongo/db/matcher/SConscript b/src/mongo/db/matcher/SConscript
index f91ca8b2b34..b4b62c29b55 100644
--- a/src/mongo/db/matcher/SConscript
+++ b/src/mongo/db/matcher/SConscript
@@ -33,7 +33,9 @@ env.Library(
         'expression_parser.cpp',
         'expression_parser_tree.cpp',
         'expression_tree.cpp',
+        'expression_where_base.cpp',
         'expression_where_noop.cpp',
+        'extensions_callback_noop.cpp',
         'match_details.cpp',
         'matchable.cpp',
         "matcher.cpp",
@@ -137,3 +139,16 @@ env.CppUnitTest(
         'expressions_text',
     ],
 )
+
+env.Library(
+    target='expressions_mongod_only',
+    source=[
+        'extensions_callback_real.cpp',
+        'expression_where.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/db/auth/authorization_manager_global',
+        '$BUILD_DIR/mongo/scripting/scripting_server',
+        'expressions',
+    ],
+)
diff --git a/src/mongo/db/matcher/expression_parser.cpp b/src/mongo/db/matcher/expression_parser.cpp
index 818c92c6376..afbff931422 100644
--- a/src/mongo/db/matcher/expression_parser.cpp
+++ b/src/mongo/db/matcher/expression_parser.cpp
@@ -36,6 +36,7 @@
 #include "mongo/db/matcher/expression_array.h"
 #include "mongo/db/matcher/expression_leaf.h"
 #include "mongo/db/matcher/expression_tree.h"
+#include "mongo/db/namespace_string.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/mongoutils/str.h"
 
@@ -955,10 +956,35 @@ StatusWith<std::vector<uint32_t>> MatchExpressionParser::_parseBitPositionsArray
 }
 
 StatusWithMatchExpression MatchExpressionParser::ExtensionsCallback::parseWhere(
-    const BSONElement& where) const {
+    BSONElement where) const {
     return {Status(ErrorCodes::NoWhereParseContext, "no context for parsing $where")};
 }
 
+StatusWith<WhereMatchExpressionBase::WhereParams>
+MatchExpressionParser::ExtensionsCallback::extractWhereMatchExpressionParams(BSONElement where) {
+    WhereMatchExpressionBase::WhereParams params;
+
+    switch (where.type()) {
+        case mongo::String:
+        case mongo::Code:
+            params.code = where._asCode();
+            params.scope = BSONObj();
+            break;
+        case mongo::CodeWScope:
+            params.code = where._asCode();
+            params.scope = where.codeWScopeObject().getOwned();
+            break;
+        default:
+            return {ErrorCodes::BadValue, "$where got bad type"};
+    }
+
+    if (params.code.empty()) {
+        return {ErrorCodes::BadValue, "code for $where cannot be empty"};
+    }
+
+    return params;
+}
+
 // Geo
 StatusWithMatchExpression expressionParserGeoCallbackDefault(const char* name,
                                                              int type,
diff --git a/src/mongo/db/matcher/expression_parser.h b/src/mongo/db/matcher/expression_parser.h
index 1b8c71a3539..4b7bf4a751c 100644
--- a/src/mongo/db/matcher/expression_parser.h
+++ b/src/mongo/db/matcher/expression_parser.h
@@ -35,11 +35,11 @@
 #include "mongo/db/matcher/expression.h"
 #include "mongo/db/matcher/expression_leaf.h"
 #include "mongo/db/matcher/expression_tree.h"
+#include "mongo/db/matcher/expression_where_base.h"
 #include "mongo/stdx/functional.h"
 
 namespace mongo {
 
-class NamespaceString;
 class OperationContext;
 
 typedef StatusWith<std::unique_ptr<MatchExpression>> StatusWithMatchExpression;
@@ -56,9 +56,16 @@ public:
      */
     class ExtensionsCallback {
     public:
-        virtual StatusWithMatchExpression parseWhere(const BSONElement& where) const;
+        virtual StatusWithMatchExpression parseWhere(BSONElement where) const;
 
         virtual ~ExtensionsCallback() {}
+
+    protected:
+        /**
+         * Helper method which extracts parameters from the given $where element.
+         */
+        static StatusWith<WhereMatchExpressionBase::WhereParams> extractWhereMatchExpressionParams(
+            BSONElement where);
     };
 
     /**
@@ -168,38 +175,6 @@ private:
     const ExtensionsCallback* _extensionsCallback;
 };
 
-/**
- * This implementation is used for the server-side code.
- */
-class ExtensionsCallbackReal : public MatchExpressionParser::ExtensionsCallback {
-public:
-    /**
-     * Does not take ownership of 'nss' or 'txn'.
-     *
-     * 'nss' must outlive this object.  'txn' must outlive this object also; in addition, 'txn' must
-     * outlive any MatchExpression objects generated by these callbacks (as the generated objects
-     * are allowed to keep a reference to 'txn').
-     */
-    ExtensionsCallbackReal(OperationContext* txn, const NamespaceString* nss);
-
-    virtual StatusWithMatchExpression parseWhere(const BSONElement& where) const;
-
-private:
-    OperationContext* const _txn;
-    const NamespaceString* const _nss;
-};
-
-/**
- * This is just a pass-through implementation, used by sharding only.
- */
-class ExtensionsCallbackNoop : public MatchExpressionParser::ExtensionsCallback {
-public:
-    ExtensionsCallbackNoop();
-
-    virtual StatusWithMatchExpression parseWhere(const BSONElement& where) const;
-};
-
-
 typedef stdx::function<StatusWithMatchExpression(
     const char* name, int type, const BSONObj& section)> MatchExpressionParserGeoCallback;
 extern MatchExpressionParserGeoCallback expressionParserGeoCallback;
diff --git a/src/mongo/db/matcher/expression_where.cpp b/src/mongo/db/matcher/expression_where.cpp
index 09cdd3d6417..63b705f6127 100644
--- a/src/mongo/db/matcher/expression_where.cpp
+++ b/src/mongo/db/matcher/expression_where.cpp
@@ -30,6 +30,8 @@
 
 #include "mongo/platform/basic.h"
 
+#include "mongo/db/matcher/expression_where.h"
+
 #include "mongo/base/init.h"
 #include "mongo/db/auth/authorization_session.h"
 #include "mongo/db/namespace_string.h"
@@ -44,79 +46,34 @@
 namespace mongo {
 
 using std::unique_ptr;
-using std::endl;
 using std::string;
 using std::stringstream;
 using stdx::make_unique;
 
-class WhereMatchExpression : public MatchExpression {
-public:
-    WhereMatchExpression(OperationContext* txn) : MatchExpression(WHERE), _txn(txn) {
-        invariant(_txn != NULL);
-
-        _func = 0;
-    }
-
-    virtual ~WhereMatchExpression() {}
-
-    Status init(StringData dbName, StringData theCode, const BSONObj& scope);
-
-    virtual bool matches(const MatchableDocument* doc, MatchDetails* details = 0) const;
-
-    virtual bool matchesSingleElement(const BSONElement& e) const {
-        return false;
-    }
-
-    virtual unique_ptr<MatchExpression> shallowClone() const {
-        unique_ptr<WhereMatchExpression> e = make_unique<WhereMatchExpression>(_txn);
-        e->init(_dbName, _code, _userScope);
-        if (getTag()) {
-            e->setTag(getTag()->clone());
-        }
-        return std::move(e);
-    }
-
-    virtual void debugString(StringBuilder& debug, int level = 0) const;
-
-    virtual void toBSON(BSONObjBuilder* out) const;
+WhereMatchExpression::WhereMatchExpression(OperationContext* txn, WhereParams params)
+    : WhereMatchExpressionBase(std::move(params)), _txn(txn) {
+    invariant(_txn != NULL);
 
-    virtual bool equivalent(const MatchExpression* other) const;
+    _func = 0;
+}
 
-    virtual void resetTag() {
-        setTag(NULL);
+Status WhereMatchExpression::init(StringData dbName) {
+    if (!globalScriptEngine) {
+        return Status(ErrorCodes::BadValue, "no globalScriptEngine in $where parsing");
     }
 
-private:
-    string _dbName;
-    string _code;
-    BSONObj _userScope;
-
-    unique_ptr<Scope> _scope;
-    ScriptingFunction _func;
-
-    // Not owned. See comments insde ExtensionsCallbackReal for the lifetime of this pointer.
-    OperationContext* _txn;
-};
-
-Status WhereMatchExpression::init(StringData dbName, StringData theCode, const BSONObj& scope) {
     if (dbName.size() == 0) {
         return Status(ErrorCodes::BadValue, "ns for $where cannot be empty");
     }
 
-    if (theCode.size() == 0) {
-        return Status(ErrorCodes::BadValue, "code for $where cannot be empty");
-    }
-
     _dbName = dbName.toString();
-    _code = theCode.toString();
-    _userScope = scope.getOwned();
 
     const string userToken =
         AuthorizationSession::get(ClientBasic::getCurrent())->getAuthenticatedUserNamesToken();
 
     try {
         _scope = globalScriptEngine->getPooledScope(_txn, _dbName, "where" + userToken);
-        _func = _scope->createFunction(_code.c_str());
+        _func = _scope->createFunction(getCode().c_str());
     } catch (...) {
         return exceptionToStatus();
     }
@@ -131,8 +88,8 @@ bool WhereMatchExpression::matches(const MatchableDocument* doc, MatchDetails* d
     uassert(28692, "$where compile error", _func);
     BSONObj obj = doc->toBSON();
 
-    if (!_userScope.isEmpty()) {
-        _scope->init(&_userScope);
+    if (!getScope().isEmpty()) {
+        _scope->init(&getScope());
     }
 
     _scope->advanceGeneration();
@@ -151,56 +108,15 @@ bool WhereMatchExpression::matches(const MatchableDocument* doc, MatchDetails* d
     return _scope->getBoolean("__returnValue") != 0;
 }
 
-void WhereMatchExpression::debugString(StringBuilder& debug, int level) const {
-    _debugAddSpace(debug, level);
-    debug << "$where\n";
-
-    _debugAddSpace(debug, level + 1);
-    debug << "dbName: " << _dbName << "\n";
-
-    _debugAddSpace(debug, level + 1);
-    debug << "code: " << _code << "\n";
-
-    _debugAddSpace(debug, level + 1);
-    debug << "scope: " << _userScope << "\n";
-}
-
-void WhereMatchExpression::toBSON(BSONObjBuilder* out) const {
-    out->append("$where", _code);
-}
-
-bool WhereMatchExpression::equivalent(const MatchExpression* other) const {
-    if (matchType() != other->matchType())
-        return false;
-    const WhereMatchExpression* realOther = static_cast<const WhereMatchExpression*>(other);
-    return _dbName == realOther->_dbName && _code == realOther->_code &&
-        _userScope == realOther->_userScope;
-}
-
-ExtensionsCallbackReal::ExtensionsCallbackReal(OperationContext* txn, const NamespaceString* nss)
-    : _txn(txn), _nss(nss) {}
-
-StatusWithMatchExpression ExtensionsCallbackReal::parseWhere(const BSONElement& where) const {
-    if (!globalScriptEngine)
-        return StatusWithMatchExpression(ErrorCodes::BadValue,
-                                         "no globalScriptEngine in $where parsing");
-
-    unique_ptr<WhereMatchExpression> exp(new WhereMatchExpression(_txn));
-    if (where.type() == String || where.type() == Code) {
-        Status s = exp->init(_nss->db(), where.valuestr(), BSONObj());
-        if (!s.isOK())
-            return StatusWithMatchExpression(s);
-        return {std::move(exp)};
-    }
-
-    if (where.type() == CodeWScope) {
-        Status s = exp->init(
-            _nss->db(), where.codeWScopeCode(), BSONObj(where.codeWScopeScopeDataUnsafe()));
-        if (!s.isOK())
-            return StatusWithMatchExpression(s);
-        return {std::move(exp)};
+unique_ptr<MatchExpression> WhereMatchExpression::shallowClone() const {
+    WhereParams params;
+    params.code = getCode();
+    params.scope = getScope();
+    unique_ptr<WhereMatchExpression> e = make_unique<WhereMatchExpression>(_txn, std::move(params));
+    e->init(_dbName);
+    if (getTag()) {
+        e->setTag(getTag()->clone());
     }
-
-    return StatusWithMatchExpression(ErrorCodes::BadValue, "$where got bad type");
+    return std::move(e);
 }
 }
diff --git a/src/mongo/db/matcher/expression_where.h b/src/mongo/db/matcher/expression_where.h
new file mode 100644
index 00000000000..780c169b217
--- /dev/null
+++ b/src/mongo/db/matcher/expression_where.h
@@ -0,0 +1,57 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/matcher/expression_where_base.h"
+#include "mongo/scripting/engine.h"
+
+namespace mongo {
+
+class OperationContext;
+
+class WhereMatchExpression final : public WhereMatchExpressionBase {
+public:
+    WhereMatchExpression(OperationContext* txn, WhereParams params);
+
+    Status init(StringData dbName);
+
+    bool matches(const MatchableDocument* doc, MatchDetails* details = nullptr) const final;
+
+    std::unique_ptr<MatchExpression> shallowClone() const final;
+
+private:
+    std::string _dbName;
+
+    std::unique_ptr<Scope> _scope;
+    ScriptingFunction _func;
+
+    OperationContext* const _txn;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/expression_where_base.cpp b/src/mongo/db/matcher/expression_where_base.cpp
new file mode 100644
index 00000000000..1bd7c2bde22
--- /dev/null
+++ b/src/mongo/db/matcher/expression_where_base.cpp
@@ -0,0 +1,61 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/matcher/expression_where_base.h"
+
+namespace mongo {
+
+WhereMatchExpressionBase::WhereMatchExpressionBase(WhereParams params)
+    : MatchExpression(WHERE), _code(std::move(params.code)), _scope(std::move(params.scope)) {}
+
+void WhereMatchExpressionBase::debugString(StringBuilder& debug, int level) const {
+    _debugAddSpace(debug, level);
+    debug << "$where\n";
+
+    _debugAddSpace(debug, level + 1);
+    debug << "code: " << getCode() << "\n";
+
+    _debugAddSpace(debug, level + 1);
+    debug << "scope: " << getScope() << "\n";
+}
+
+void WhereMatchExpressionBase::toBSON(BSONObjBuilder* out) const {
+    out->appendCodeWScope("$where", getCode(), getScope());
+}
+
+bool WhereMatchExpressionBase::equivalent(const MatchExpression* other) const {
+    if (matchType() != other->matchType()) {
+        return false;
+    }
+    const WhereMatchExpressionBase* realOther = static_cast<const WhereMatchExpressionBase*>(other);
+    return getCode() == realOther->getCode() && getScope() == realOther->getScope();
+}
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/expression_where_base.h b/src/mongo/db/matcher/expression_where_base.h
new file mode 100644
index 00000000000..8aabbed669d
--- /dev/null
+++ b/src/mongo/db/matcher/expression_where_base.h
@@ -0,0 +1,75 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/matcher/expression.h"
+
+namespace mongo {
+
+/**
+ * Common base class for $where match expression implementations.
+ */
+class WhereMatchExpressionBase : public MatchExpression {
+public:
+    struct WhereParams {
+        std::string code;
+        BSONObj scope;  // Owned.
+    };
+
+    WhereMatchExpressionBase(WhereParams params);
+
+    //
+    // Methods inherited from MatchExpression.
+    //
+
+    bool matchesSingleElement(const BSONElement& e) const final {
+        return false;
+    }
+
+    void debugString(StringBuilder& debug, int level = 0) const final;
+
+    void toBSON(BSONObjBuilder* out) const final;
+
+    bool equivalent(const MatchExpression* other) const final;
+
+protected:
+    const std::string& getCode() const {
+        return _code;
+    }
+
+    const BSONObj& getScope() const {
+        return _scope;
+    }
+
+private:
+    const std::string _code;
+    const BSONObj _scope;  // Owned.
+};
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/expression_where_noop.cpp b/src/mongo/db/matcher/expression_where_noop.cpp
index ccb64190690..23bb7c287e5 100644
--- a/src/mongo/db/matcher/expression_where_noop.cpp
+++ b/src/mongo/db/matcher/expression_where_noop.cpp
@@ -29,110 +29,29 @@
  */
 
 #include "mongo/platform/basic.h"
-#include "mongo/base/init.h"
-#include "mongo/db/matcher/expression.h"
-#include "mongo/db/matcher/expression_parser.h"
-#include "mongo/stdx/memory.h"
-
-namespace mongo {
-
-using std::unique_ptr;
-using std::string;
-using stdx::make_unique;
-
-/**
- * Bogus no-op $where match expression to parse $where in mongos,
- * since mongos doesn't have script engine to compile JS functions.
- *
- * Linked into mongos, instead of the real WhereMatchExpression.
- */
-class WhereNoOpMatchExpression : public MatchExpression {
-public:
-    WhereNoOpMatchExpression() : MatchExpression(WHERE) {}
-    virtual ~WhereNoOpMatchExpression() {}
-
-    Status init(StringData theCode);
-
-    virtual bool matches(const MatchableDocument* doc, MatchDetails* details = 0) const {
-        return false;
-    }
-
-    virtual bool matchesSingleElement(const BSONElement& e) const {
-        return false;
-    }
-
-    virtual unique_ptr<MatchExpression> shallowClone() const {
-        unique_ptr<WhereNoOpMatchExpression> e = make_unique<WhereNoOpMatchExpression>();
-        e->init(_code);
-        if (getTag()) {
-            e->setTag(getTag()->clone());
-        }
-        return std::move(e);
-    }
-
-    virtual void debugString(StringBuilder& debug, int level = 0) const;
-
-    virtual void toBSON(BSONObjBuilder* out) const;
 
-    virtual bool equivalent(const MatchExpression* other) const;
+#include "mongo/db/matcher/expression_where_noop.h"
 
-    virtual void resetTag() {
-        setTag(NULL);
-    }
-
-private:
-    string _code;
-};
-
-Status WhereNoOpMatchExpression::init(StringData theCode) {
-    if (theCode.size() == 0)
-        return Status(ErrorCodes::BadValue, "code for $where cannot be empty");
-
-    _code = theCode.toString();
-
-    return Status::OK();
-}
-
-void WhereNoOpMatchExpression::debugString(StringBuilder& debug, int level) const {
-    _debugAddSpace(debug, level);
-    debug << "$where (only in mongos)\n";
+#include "mongo/stdx/memory.h"
 
-    _debugAddSpace(debug, level + 1);
-    debug << "code: " << _code << "\n";
-}
+namespace mongo {
 
-void WhereNoOpMatchExpression::toBSON(BSONObjBuilder* out) const {
-    out->append("$where", _code);
-}
+WhereNoOpMatchExpression::WhereNoOpMatchExpression(WhereParams params)
+    : WhereMatchExpressionBase(std::move(params)) {}
 
-bool WhereNoOpMatchExpression::equivalent(const MatchExpression* other) const {
-    if (matchType() != other->matchType())
-        return false;
-    const WhereNoOpMatchExpression* noopOther = static_cast<const WhereNoOpMatchExpression*>(other);
-    return _code == noopOther->_code;
+bool WhereNoOpMatchExpression::matches(const MatchableDocument* doc, MatchDetails* details) const {
+    return false;
 }
 
-
-// -----------------
-
-ExtensionsCallbackNoop::ExtensionsCallbackNoop() {}
-
-StatusWithMatchExpression ExtensionsCallbackNoop::parseWhere(const BSONElement& where) const {
-    unique_ptr<WhereNoOpMatchExpression> exp(new WhereNoOpMatchExpression());
-    if (where.type() == String || where.type() == Code) {
-        Status s = exp->init(where.valuestr());
-        if (!s.isOK())
-            return StatusWithMatchExpression(s);
-        return {std::move(exp)};
-    }
-
-    if (where.type() == CodeWScope) {
-        Status s = exp->init(where.codeWScopeCode());
-        if (!s.isOK())
-            return StatusWithMatchExpression(s);
-        return {std::move(exp)};
+std::unique_ptr<MatchExpression> WhereNoOpMatchExpression::shallowClone() const {
+    WhereParams params;
+    params.code = getCode();
+    params.scope = getScope();
+    std::unique_ptr<WhereNoOpMatchExpression> e =
+        stdx::make_unique<WhereNoOpMatchExpression>(std::move(params));
+    if (getTag()) {
+        e->setTag(getTag()->clone());
     }
-
-    return StatusWithMatchExpression(ErrorCodes::BadValue, "$where got bad type");
+    return std::move(e);
 }
 }
diff --git a/src/mongo/db/matcher/expression_where_noop.h b/src/mongo/db/matcher/expression_where_noop.h
new file mode 100644
index 00000000000..10235e3176f
--- /dev/null
+++ b/src/mongo/db/matcher/expression_where_noop.h
@@ -0,0 +1,50 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/matcher/expression_where_base.h"
+
+namespace mongo {
+
+/**
+ * Bogus no-op $where match expression to parse $where in mongos, since mongos doesn't have script
+ * engine to compile JS functions.
+ *
+ * Linked into mongos, instead of the real WhereMatchExpression.
+ */
+class WhereNoOpMatchExpression final : public WhereMatchExpressionBase {
+public:
+    WhereNoOpMatchExpression(WhereParams params);
+
+    bool matches(const MatchableDocument* doc, MatchDetails* details = nullptr) const final;
+
+    std::unique_ptr<MatchExpression> shallowClone() const final;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/extensions_callback_noop.cpp b/src/mongo/db/matcher/extensions_callback_noop.cpp
new file mode 100644
index 00000000000..ca51ae22b76
--- /dev/null
+++ b/src/mongo/db/matcher/extensions_callback_noop.cpp
@@ -0,0 +1,46 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/matcher/extensions_callback_noop.h"
+
+#include "mongo/db/matcher/expression_where_noop.h"
+
+namespace mongo {
+
+StatusWithMatchExpression ExtensionsCallbackNoop::parseWhere(BSONElement where) const {
+    auto whereParams = extractWhereMatchExpressionParams(where);
+    if (!whereParams.isOK()) {
+        return whereParams.getStatus();
+    }
+
+    return {stdx::make_unique<WhereNoOpMatchExpression>(std::move(whereParams.getValue()))};
+}
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/extensions_callback_noop.h b/src/mongo/db/matcher/extensions_callback_noop.h
new file mode 100644
index 00000000000..9ac019e3947
--- /dev/null
+++ b/src/mongo/db/matcher/extensions_callback_noop.h
@@ -0,0 +1,43 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/matcher/expression_parser.h"
+
+namespace mongo {
+
+/**
+ * This is just a pass-through implementation, used by sharding only.
+ */
+class ExtensionsCallbackNoop : public MatchExpressionParser::ExtensionsCallback {
+public:
+    StatusWithMatchExpression parseWhere(BSONElement where) const final;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/extensions_callback_real.cpp b/src/mongo/db/matcher/extensions_callback_real.cpp
new file mode 100644
index 00000000000..e07a098fc87
--- /dev/null
+++ b/src/mongo/db/matcher/extensions_callback_real.cpp
@@ -0,0 +1,55 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/matcher/extensions_callback_real.h"
+
+#include "mongo/db/matcher/expression_where.h"
+#include "mongo/db/namespace_string.h"
+
+namespace mongo {
+
+ExtensionsCallbackReal::ExtensionsCallbackReal(OperationContext* txn, const NamespaceString* nss)
+    : _txn(txn), _nss(nss) {}
+
+StatusWithMatchExpression ExtensionsCallbackReal::parseWhere(BSONElement where) const {
+    auto whereParams = extractWhereMatchExpressionParams(where);
+    if (!whereParams.isOK()) {
+        return whereParams.getStatus();
+    }
+
+    auto exp = stdx::make_unique<WhereMatchExpression>(_txn, std::move(whereParams.getValue()));
+    Status status = exp->init(_nss->db());
+    if (!status.isOK()) {
+        return status;
+    }
+    return {std::move(exp)};
+}
+
+}  // namespace mongo
diff --git a/src/mongo/db/matcher/extensions_callback_real.h b/src/mongo/db/matcher/extensions_callback_real.h
new file mode 100644
index 00000000000..b820a300dec
--- /dev/null
+++ b/src/mongo/db/matcher/extensions_callback_real.h
@@ -0,0 +1,58 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/matcher/expression_parser.h"
+
+namespace mongo {
+
+class NamespaceString;
+
+/**
+ * This implementation is used for the server-side code.
+ */
+class ExtensionsCallbackReal : public MatchExpressionParser::ExtensionsCallback {
+public:
+    /**
+     * Does not take ownership of 'nss' or 'txn'.
+     *
+     * 'nss' must outlive this object. 'txn' must outlive this object also; in addition, 'txn' must
+     * outlive any MatchExpression objects generated by these callbacks (as the generated objects
+     * are allowed to keep a reference to 'txn').
+     */
+    ExtensionsCallbackReal(OperationContext* txn, const NamespaceString* nss);
+
+    StatusWithMatchExpression parseWhere(BSONElement where) const final;
+
+private:
+    OperationContext* const _txn;
+    const NamespaceString* const _nss;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/db/ops/parsed_delete.cpp b/src/mongo/db/ops/parsed_delete.cpp
index 91031ab8ef3..1acc76dcb3e 100644
--- a/src/mongo/db/ops/parsed_delete.cpp
+++ b/src/mongo/db/ops/parsed_delete.cpp
@@ -36,6 +36,7 @@
 #include "mongo/db/catalog/database.h"
 #include "mongo/db/exec/delete.h"
 #include "mongo/db/ops/delete_request.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/db/query/get_executor.h"
 #include "mongo/db/query/query_planner_common.h"
diff --git a/src/mongo/db/ops/parsed_update.cpp b/src/mongo/db/ops/parsed_update.cpp
index c905e9b9c1e..d24a2aeef95 100644
--- a/src/mongo/db/ops/parsed_update.cpp
+++ b/src/mongo/db/ops/parsed_update.cpp
@@ -29,6 +29,8 @@
 #include "mongo/platform/basic.h"
 
 #include "mongo/db/ops/parsed_update.h"
+
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/ops/update_request.h"
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/db/query/query_planner_common.h"
diff --git a/src/mongo/db/ops/path_support_test.cpp b/src/mongo/db/ops/path_support_test.cpp
index bac517aec4b..8167504f4c0 100644
--- a/src/mongo/db/ops/path_support_test.cpp
+++ b/src/mongo/db/ops/path_support_test.cpp
@@ -44,6 +44,7 @@
 #include "mongo/db/matcher/expression.h"
 #include "mongo/db/matcher/expression_leaf.h"
 #include "mongo/db/matcher/expression_parser.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/unittest/unittest.h"
 #include "mongo/util/mongoutils/str.h"
 
@@ -490,8 +491,7 @@ TEST_F(ArrayDoc, NonNumericPathInArray) {
 //
 
 static MatchExpression* makeExpr(const BSONObj& exprBSON) {
-    static const ExtensionsCallbackNoop callbackNoop;
-    return MatchExpressionParser::parse(exprBSON, callbackNoop).getValue().release();
+    return MatchExpressionParser::parse(exprBSON, ExtensionsCallbackNoop()).getValue().release();
 }
 
 static void assertContains(const EqualityMatches& equalities, const BSONObj& wrapped) {
diff --git a/src/mongo/db/ops/update_driver.cpp b/src/mongo/db/ops/update_driver.cpp
index e66264e2027..251d2aabae4 100644
--- a/src/mongo/db/ops/update_driver.cpp
+++ b/src/mongo/db/ops/update_driver.cpp
@@ -35,6 +35,7 @@
 #include "mongo/bson/mutable/document.h"
 #include "mongo/db/field_ref.h"
 #include "mongo/db/matcher/expression_leaf.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/ops/log_builder.h"
 #include "mongo/db/ops/modifier_object_replace.h"
 #include "mongo/db/ops/modifier_table.h"
diff --git a/src/mongo/db/pipeline/pipeline_d.cpp b/src/mongo/db/pipeline/pipeline_d.cpp
index c52f3183ef7..06114c90404 100644
--- a/src/mongo/db/pipeline/pipeline_d.cpp
+++ b/src/mongo/db/pipeline/pipeline_d.cpp
@@ -45,6 +45,7 @@
 #include "mongo/db/db_raii.h"
 #include "mongo/db/dbdirectclient.h"
 #include "mongo/db/index/index_access_method.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/pipeline/document_source.h"
 #include "mongo/db/pipeline/pipeline.h"
 #include "mongo/db/query/get_executor.h"
diff --git a/src/mongo/db/query/find.cpp b/src/mongo/db/query/find.cpp
index c06ba454168..6423d965fc6 100644
--- a/src/mongo/db/query/find.cpp
+++ b/src/mongo/db/query/find.cpp
@@ -44,6 +44,7 @@
 #include "mongo/db/exec/working_set_common.h"
 #include "mongo/db/service_context.h"
 #include "mongo/db/keypattern.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/query/explain.h"
 #include "mongo/db/query/find_common.h"
 #include "mongo/db/query/get_executor.h"
diff --git a/src/mongo/db/query/get_executor.cpp b/src/mongo/db/query/get_executor.cpp
index a35e543733d..497f1221e57 100644
--- a/src/mongo/db/query/get_executor.cpp
+++ b/src/mongo/db/query/get_executor.cpp
@@ -53,6 +53,8 @@
 #include "mongo/db/exec/update.h"
 #include "mongo/db/index_names.h"
 #include "mongo/db/index/index_descriptor.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/ops/update_lifecycle.h"
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/db/query/explain.h"
diff --git a/src/mongo/db/query/query_planner_test_fixture.cpp b/src/mongo/db/query/query_planner_test_fixture.cpp
index 3042665fadd..8d559f24c7f 100644
--- a/src/mongo/db/query/query_planner_test_fixture.cpp
+++ b/src/mongo/db/query/query_planner_test_fixture.cpp
@@ -34,6 +34,7 @@
 
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/matcher/expression_parser.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/query/query_knobs.h"
 #include "mongo/db/query/query_planner.h"
 #include "mongo/db/query/query_planner_test_lib.h"
diff --git a/src/mongo/db/query/stage_builder.cpp b/src/mongo/db/query/stage_builder.cpp
index 06eab97b70e..d23c16ad38b 100644
--- a/src/mongo/db/query/stage_builder.cpp
+++ b/src/mongo/db/query/stage_builder.cpp
@@ -52,6 +52,7 @@
 #include "mongo/db/exec/skip.h"
 #include "mongo/db/exec/text.h"
 #include "mongo/db/index/fts_access_method.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/catalog/collection.h"
 #include "mongo/db/catalog/database.h"
 #include "mongo/db/s/sharding_state.h"
diff --git a/src/mongo/dbtests/SConscript b/src/mongo/dbtests/SConscript
index aaf6aa069c1..b353987ac96 100644
--- a/src/mongo/dbtests/SConscript
+++ b/src/mongo/dbtests/SConscript
@@ -69,6 +69,7 @@ dbtest = env.Program(
         'directclienttests.cpp',
         'documentsourcetests.cpp',
         'executor_registry.cpp',
+        'expression_where_test.cpp',
         'gle_test.cpp',
         'indexcatalogtests.cpp',
         'indexupdatetests.cpp',
diff --git a/src/mongo/dbtests/expression_where_test.cpp b/src/mongo/dbtests/expression_where_test.cpp
new file mode 100644
index 00000000000..047027022e0
--- /dev/null
+++ b/src/mongo/dbtests/expression_where_test.cpp
@@ -0,0 +1,116 @@
+/**
+ *    Copyright (C) 2015 10gen Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects
+ *    for all of the code used other than as permitted herein. If you modify
+ *    file(s) with this exception, you may extend this exception to your
+ *    version of the file(s), but you are not obligated to do so. If you do not
+ *    wish to do so, delete this exception statement from your version. If you
+ *    delete this exception statement from all source files in the program,
+ *    then also delete it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/json.h"
+#include "mongo/db/matcher/expression.h"
+#include "mongo/db/matcher/expression_parser.h"
+#include "mongo/db/matcher/expression_where.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
+#include "mongo/db/namespace_string.h"
+#include "mongo/db/operation_context_impl.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+const NamespaceString nss("unittests.expression_where_test");
+
+TEST(ExpressionWhere, WhereExpressionsWithSameScopeHaveSameBSONRepresentation) {
+    OperationContextImpl txn;
+    const char code[] = "function(){ return a; }";
+
+    BSONObj query1 = BSON("$where" << BSONCodeWScope(code, BSON("a" << true)));
+    auto expr1 = unittest::assertGet(
+        MatchExpressionParser::parse(query1, ExtensionsCallbackReal(&txn, &nss)));
+    BSONObjBuilder builder1;
+    expr1->toBSON(&builder1);
+
+    BSONObj query2 = BSON("$where" << BSONCodeWScope(code, BSON("a" << true)));
+    auto expr2 = unittest::assertGet(
+        MatchExpressionParser::parse(query2, ExtensionsCallbackReal(&txn, &nss)));
+    BSONObjBuilder builder2;
+    expr2->toBSON(&builder2);
+
+    ASSERT_EQ(builder1.obj(), builder2.obj());
+}
+
+TEST(ExpressionWhere, WhereExpressionsWithDifferentScopesHaveDifferentBSONRepresentations) {
+    OperationContextImpl txn;
+    const char code[] = "function(){ return a; }";
+
+    BSONObj query1 = BSON("$where" << BSONCodeWScope(code, BSON("a" << true)));
+    auto expr1 = unittest::assertGet(
+        MatchExpressionParser::parse(query1, ExtensionsCallbackReal(&txn, &nss)));
+    BSONObjBuilder builder1;
+    expr1->toBSON(&builder1);
+
+    BSONObj query2 = BSON("$where" << BSONCodeWScope(code, BSON("a" << false)));
+    auto expr2 = unittest::assertGet(
+        MatchExpressionParser::parse(query2, ExtensionsCallbackReal(&txn, &nss)));
+    BSONObjBuilder builder2;
+    expr2->toBSON(&builder2);
+
+    ASSERT_NE(builder1.obj(), builder2.obj());
+}
+
+TEST(ExpressionWhere, WhereExpressionsWithSameScopeAreEquivalent) {
+    OperationContextImpl txn;
+    const char code[] = "function(){ return a; }";
+
+    BSONObj query1 = BSON("$where" << BSONCodeWScope(code, BSON("a" << true)));
+    auto expr1 = unittest::assertGet(
+        MatchExpressionParser::parse(query1, ExtensionsCallbackReal(&txn, &nss)));
+
+    BSONObj query2 = BSON("$where" << BSONCodeWScope(code, BSON("a" << true)));
+    auto expr2 = unittest::assertGet(
+        MatchExpressionParser::parse(query2, ExtensionsCallbackReal(&txn, &nss)));
+
+    ASSERT(expr1->equivalent(expr2.get()));
+    ASSERT(expr2->equivalent(expr1.get()));
+}
+
+TEST(ExpressionWhere, WhereExpressionsWithDifferentScopesAreNotEquivalent) {
+    OperationContextImpl txn;
+    const char code[] = "function(){ return a; }";
+
+    BSONObj query1 = BSON("$where" << BSONCodeWScope(code, BSON("a" << true)));
+    auto expr1 = unittest::assertGet(
+        MatchExpressionParser::parse(query1, ExtensionsCallbackReal(&txn, &nss)));
+
+    BSONObj query2 = BSON("$where" << BSONCodeWScope(code, BSON("a" << false)));
+    auto expr2 = unittest::assertGet(
+        MatchExpressionParser::parse(query2, ExtensionsCallbackReal(&txn, &nss)));
+
+    ASSERT_FALSE(expr1->equivalent(expr2.get()));
+    ASSERT_FALSE(expr2->equivalent(expr1.get()));
+}
+
+}  // namespace
+}  // namespace mongo
diff --git a/src/mongo/dbtests/matchertests.cpp b/src/mongo/dbtests/matchertests.cpp
index 694c9cf5553..2d009406e24 100644
--- a/src/mongo/dbtests/matchertests.cpp
+++ b/src/mongo/dbtests/matchertests.cpp
@@ -33,6 +33,7 @@
 
 #include "mongo/db/db_raii.h"
 #include "mongo/db/json.h"
+#include "mongo/db/matcher/extensions_callback_real.h"
 #include "mongo/db/matcher/matcher.h"
 #include "mongo/db/operation_context_impl.h"
 #include "mongo/dbtests/dbtests.h"
diff --git a/src/mongo/s/chunk_manager.cpp b/src/mongo/s/chunk_manager.cpp
index cd5bd4e223d..95fe87de933 100644
--- a/src/mongo/s/chunk_manager.cpp
+++ b/src/mongo/s/chunk_manager.cpp
@@ -39,6 +39,7 @@
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/client/remote_command_targeter.h"
 #include "mongo/db/commands.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/query/index_bounds_builder.h"
 #include "mongo/db/query/query_planner.h"
diff --git a/src/mongo/s/chunk_manager_targeter_test.cpp b/src/mongo/s/chunk_manager_targeter_test.cpp
index c7e870c5391..b811edf87e1 100644
--- a/src/mongo/s/chunk_manager_targeter_test.cpp
+++ b/src/mongo/s/chunk_manager_targeter_test.cpp
@@ -31,6 +31,7 @@
 #include "mongo/platform/basic.h"
 
 #include "mongo/db/json.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/s/chunk_manager.h"
diff --git a/src/mongo/s/commands/cluster_find_cmd.cpp b/src/mongo/s/commands/cluster_find_cmd.cpp
index d2ae3ef6080..f49c4ebd3c6 100644
--- a/src/mongo/s/commands/cluster_find_cmd.cpp
+++ b/src/mongo/s/commands/cluster_find_cmd.cpp
@@ -33,6 +33,7 @@
 #include "mongo/client/read_preference.h"
 #include "mongo/db/auth/authorization_session.h"
 #include "mongo/db/commands.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/query/cursor_response.h"
 #include "mongo/db/stats/counters.h"
 #include "mongo/s/query/cluster_find.h"
diff --git a/src/mongo/s/shard_key_pattern.cpp b/src/mongo/s/shard_key_pattern.cpp
index ae7f569c845..30dbc63ee72 100644
--- a/src/mongo/s/shard_key_pattern.cpp
+++ b/src/mongo/s/shard_key_pattern.cpp
@@ -34,6 +34,7 @@
 #include "mongo/db/field_ref_set.h"
 #include "mongo/db/hasher.h"
 #include "mongo/db/index_names.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/ops/path_support.h"
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/util/mongoutils/str.h"
diff --git a/src/mongo/s/strategy.cpp b/src/mongo/s/strategy.cpp
index 911c23971ea..9534192381b 100644
--- a/src/mongo/s/strategy.cpp
+++ b/src/mongo/s/strategy.cpp
@@ -45,6 +45,7 @@
 #include "mongo/db/commands.h"
 #include "mongo/db/max_time.h"
 #include "mongo/db/server_parameters.h"
+#include "mongo/db/matcher/extensions_callback_noop.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/query/lite_parsed_query.h"
 #include "mongo/db/query/getmore_request.h"