SERVER-12180 Clean up dependency tracking code

Behavior changes (none effect semantics of pipeline, just implementation):
* We now track what we know about fields and metadata separately. This allows
  us to prove that we won't need the text score if we see a $group or $out.
* If we don't need any fields from the source document we now use a projection
  that will return an empty document, or just the text score if it is needed.
  We used to use {_id: 0} which returned all other fields.

Code organization changes:
* Dependencies are now tracked using a dedicated struct rather than a
  set<string> with some magic strings.
* ParsedDeps is now a proper class rather than a typedef.
* Removed ExpressionFieldPath::_baseVar since its former role is fulfilled
  better by _variable.

16 files changed, 481 insertions, 331 deletions

diff --git a/src/mongo/SConscript b/src/mongo/SConscript
index 6b5d99e5fa6..78e41bbf7c9 100644
--- a/src/mongo/SConscript
+++ b/src/mongo/SConscript
@@ -417,6 +417,7 @@ env.Library("coredb", [
         "db/pipeline/accumulator_min_max.cpp",
         "db/pipeline/accumulator_push.cpp",
         "db/pipeline/accumulator_sum.cpp",
+        "db/pipeline/dependencies.cpp",
         "db/pipeline/document.cpp",
         "db/pipeline/document_source.cpp",
         "db/pipeline/document_source_bson_array.cpp",
diff --git a/src/mongo/db/pipeline/dependencies.cpp b/src/mongo/db/pipeline/dependencies.cpp
new file mode 100644
index 00000000000..bed2332549d
--- /dev/null
+++ b/src/mongo/db/pipeline/dependencies.cpp
@@ -0,0 +1,175 @@
+/**
+*    Copyright (C) 2014 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/pch.h"
+
+#include "mongo/db/jsobj.h"
+#include "mongo/db/pipeline/dependencies.h"
+#include "mongo/db/pipeline/field_path.h"
+#include "mongo/util/mongoutils/str.h"
+
+namespace mongo {
+    namespace str = mongoutils::str;
+
+    BSONObj DepsTracker::toProjection() const {
+        BSONObjBuilder bb;
+
+        if (needTextScore)
+            bb.append(Document::metaFieldTextScore, BSON("$meta" << "textScore"));
+
+        if (needWholeDocument)
+            return bb.obj();
+
+        if (fields.empty()) {
+            // Projection language lacks good a way to say no fields needed. This fakes it.
+            bb.append("_id", 0);
+            bb.append("$noFieldsNeeded", 1);
+            return bb.obj();
+        }
+
+        bool needId = false;
+        string last;
+        for (set<string>::const_iterator it(fields.begin()), end(fields.end()); it!=end; ++it) {
+            if (str::startsWith(*it, "_id") && (it->size() == 3 || (*it)[3] == '.')) {
+                // _id and subfields are handled specially due in part to SERVER-7502
+                needId = true;
+                continue;
+            }
+
+            if (!last.empty() && str::startsWith(*it, last)) {
+                // we are including a parent of *it so we don't need to include this field
+                // explicitly. In fact, due to SERVER-6527 if we included this field, the parent
+                // wouldn't be fully included.  This logic relies on on set iterators going in
+                // lexicographic order so that a string is always directly before of all fields it
+                // prefixes.
+                continue;
+            }
+
+            last = *it + '.';
+            bb.append(*it, 1);
+        }
+
+        if (needId) // we are explicit either way
+            bb.append("_id", 1);
+        else
+            bb.append("_id", 0);
+
+        return bb.obj();
+    }
+
+    // ParsedDeps::_fields is a simple recursive look-up table. For each field:
+    //      If the value has type==Bool, the whole field is needed
+    //      If the value has type==Object, the fields in the subobject are needed
+    //      All other fields should be missing which means not needed
+    boost::optional<ParsedDeps> DepsTracker::toParsedDeps() const {
+        MutableDocument md;
+
+        if (needWholeDocument || needTextScore) {
+            // can't use ParsedDeps in this case
+            return boost::none;
+        }
+
+        string last;
+        for (set<string>::const_iterator it(fields.begin()), end(fields.end()); it!=end; ++it) {
+            if (!last.empty() && str::startsWith(*it, last)) {
+                // we are including a parent of *it so we don't need to include this field
+                // explicitly. In fact, if we included this field, the parent wouldn't be fully
+                // included.  This logic relies on on set iterators going in lexicographic order so
+                // that a string is always directly before of all fields it prefixes.
+                continue;
+            }
+            last = *it + '.';
+            md.setNestedField(*it, Value(true));
+        }
+
+        return ParsedDeps(md.freeze());
+    }
+
+namespace {
+    // Mutually recursive with arrayHelper
+    Document documentHelper(const BSONObj& bson, const Document& neededFields);
+
+    // Handles array-typed values for ParsedDeps::extractFields
+    Value arrayHelper(const BSONObj& bson, const Document& neededFields) {
+        BSONObjIterator it(bson);
+
+        vector<Value> values;
+        while (it.more()) {
+            BSONElement bsonElement(it.next());
+            if (bsonElement.type() == Object) {
+                Document sub = documentHelper(bsonElement.embeddedObject(), neededFields);
+                values.push_back(Value(sub));
+            }
+
+            if (bsonElement.type() == Array) {
+                values.push_back(arrayHelper(bsonElement.embeddedObject(), neededFields));
+            }
+        }
+
+        return Value::consume(values);
+    }
+
+    // Handles object-typed values including the top-level for ParsedDeps::extractFields
+    Document documentHelper(const BSONObj& bson, const Document& neededFields) {
+        MutableDocument md(neededFields.size());
+
+        BSONObjIterator it(bson);
+        while (it.more()) {
+            BSONElement bsonElement (it.next());
+            StringData fieldName = bsonElement.fieldNameStringData();
+            Value isNeeded = neededFields[fieldName];
+
+            if (isNeeded.missing())
+                continue;
+
+            if (isNeeded.getType() == Bool) {
+                md.addField(fieldName, Value(bsonElement));
+                continue;
+            }
+
+            dassert(isNeeded.getType() == Object);
+
+            if (bsonElement.type() == Object) {
+                Document sub = documentHelper(bsonElement.embeddedObject(), isNeeded.getDocument());
+                md.addField(fieldName, Value(sub));
+            }
+
+            if (bsonElement.type() == Array) {
+                md.addField(fieldName, arrayHelper(bsonElement.embeddedObject(),
+                                                   isNeeded.getDocument()));
+            }
+        }
+
+        return md.freeze();
+    }
+} // namespace
+
+    Document ParsedDeps::extractFields(const BSONObj& input) const {
+        return documentHelper(input, _fields);
+    }
+}
diff --git a/src/mongo/db/pipeline/dependencies.h b/src/mongo/db/pipeline/dependencies.h
new file mode 100644
index 00000000000..47f8f46c432
--- /dev/null
+++ b/src/mongo/db/pipeline/dependencies.h
@@ -0,0 +1,77 @@
+/**
+ * Copyright (c) 2014 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 <boost/optional.hpp>
+#include <set>
+#include <string>
+
+#include "mongo/db/pipeline/document.h"
+
+namespace mongo {
+    class ParsedDeps;
+
+    /**
+     * This struct allows components in an agg pipeline to report what they need from their input.
+     */
+    struct DepsTracker {
+        DepsTracker()
+            : needWholeDocument(false)
+            , needTextScore(false)
+        {}
+
+        /**
+         * Returns a projection object covering the dependencies tracked by this class.
+         */
+        BSONObj toProjection() const;
+
+        boost::optional<ParsedDeps> toParsedDeps() const;
+
+        std::set<std::string> fields; // names of needed fields in dotted notation
+        bool needWholeDocument; // if true, ignore fields and assume the whole document is needed
+        bool needTextScore;
+    };
+
+    /**
+     * This class is designed to quickly extract the needed fields from a BSONObj into a Document.
+     * It should only be created by a call to DepsTracker::ParsedDeps
+     */
+    class ParsedDeps {
+    public:
+        Document extractFields(const BSONObj& input) const;
+
+    private:
+        friend struct DepsTracker; // so it can call constructor
+        explicit ParsedDeps(const Document& fields)
+            : _fields(fields)
+        {}
+
+        Document _fields;
+    };
+}
diff --git a/src/mongo/db/pipeline/document_source.cpp b/src/mongo/db/pipeline/document_source.cpp
index f07739479e3..d4c21fca2fd 100644
--- a/src/mongo/db/pipeline/document_source.cpp
+++ b/src/mongo/db/pipeline/document_source.cpp
@@ -59,8 +59,6 @@ namespace mongo {
 
     void DocumentSource::dispose() {
         if ( pSource ) {
-            // This is required for the DocumentSourceCursor to release its read lock, see
-            // SERVER-6123.
             pSource->dispose();
         }
     }
@@ -71,140 +69,4 @@ namespace mongo {
             array.push_back(entry);
         }
     }
-
-    BSONObj DocumentSource::depsToProjection(const set<string>& deps) {
-        BSONObjBuilder bb;
-
-        bool needId = false;
-
-        string last;
-        for (set<string>::const_iterator it(deps.begin()), end(deps.end()); it!=end; ++it) {
-            if (str::startsWith(*it, "_id") && (it->size() == 3 || (*it)[3] == '.')) {
-                // _id and subfields are handled specially due in part to SERVER-7502
-                needId = true;
-                continue;
-            }
-
-            if (str::startsWith(*it, '$')) {
-                if (*it == "$textScore") {
-                    // textScore metadata
-                    bb.append(Document::metaFieldTextScore, BSON("$meta" << "textScore"));
-                    continue;
-                }
-            }
-
-            if (!last.empty() && str::startsWith(*it, last)) {
-                // we are including a parent of *it so we don't need to include this field
-                // explicitly. In fact, due to SERVER-6527 if we included this field, the parent
-                // wouldn't be fully included.  This logic relies on on set iterators going in
-                // lexicographic order so that a string is always directly before of all fields it
-                // prefixes.
-                continue;
-            }
-
-            last = *it + '.';
-            bb.append(*it, 1);
-        }
-
-        if (needId) // we are explicit either way
-            bb.append("_id", 1);
-        else
-            bb.append("_id", 0);
-
-        return bb.obj();
-    }
-
-    // Taken as a whole, these three functions should produce the same output document given the
-    // same deps set as mongo::Projection::transform would on the output of depsToProjection. The
-    // only exceptions are that we correctly handle the case where no fields are needed and we don't
-    // need to work around the above mentioned bug with subfields of _id (SERVER-7502). This is
-    // tested in a DEV block in DocumentSourceCursor::findNext().
-    //
-    // Output from this function is input for the next two
-    //
-    // ParsedDeps is a simple recursive look-up table. For each field in a ParsedDeps:
-    //      If the value has type==Bool, the whole field is needed
-    //      If the value has type==Object, the fields in the subobject are needed
-    //      All other fields should be missing which means not needed
-    DocumentSource::ParsedDeps DocumentSource::parseDeps(const set<string>& deps) {
-        MutableDocument md;
-
-        string last;
-        for (set<string>::const_iterator it(deps.begin()), end(deps.end()); it!=end; ++it) {
-            if (str::startsWith(*it, '$')) {
-                // documentFromBsonWithDeps doesn't handle meta data
-                if (*it == "$textScore")
-                    return ParsedDeps();
-            }
-
-            if (!last.empty() && str::startsWith(*it, last)) {
-                // we are including a parent of *it so we don't need to include this field
-                // explicitly. In fact, if we included this field, the parent wouldn't be fully
-                // included.  This logic relies on on set iterators going in lexicographic order so
-                // that a string is always directly before of all fields it prefixes.
-                continue;
-            }
-            last = *it + '.';
-            md.setNestedField(*it, Value(true));
-        }
-
-        return md.freeze();
-    }
-
-    // Helper for next function
-    static Value arrayHelper(const BSONObj& bson, const DocumentSource::ParsedDeps& neededFields) {
-        BSONObjIterator it(bson);
-
-        vector<Value> values;
-        while (it.more()) {
-            BSONElement bsonElement(it.next());
-            if (bsonElement.type() == Object) {
-                Document sub = DocumentSource::documentFromBsonWithDeps(
-                                                    bsonElement.embeddedObject(),
-                                                    neededFields);
-                values.push_back(Value(sub));
-            }
-
-            if (bsonElement.type() == Array) {
-                values.push_back(arrayHelper(bsonElement.embeddedObject(), neededFields));
-            }
-        }
-
-        return Value::consume(values);
-    }
-
-    Document DocumentSource::documentFromBsonWithDeps(const BSONObj& bson,
-                                                      const ParsedDeps& neededFields) {
-        MutableDocument md(neededFields.size());
-
-        BSONObjIterator it(bson);
-        while (it.more()) {
-            BSONElement bsonElement (it.next());
-            StringData fieldName = bsonElement.fieldNameStringData();
-            Value isNeeded = neededFields[fieldName];
-
-            if (isNeeded.missing())
-                continue;
-
-            if (isNeeded.getType() == Bool) {
-                md.addField(fieldName, Value(bsonElement));
-                continue;
-            }
-
-            dassert(isNeeded.getType() == Object);
-
-            if (bsonElement.type() == Object) {
-                Document sub = documentFromBsonWithDeps(bsonElement.embeddedObject(),
-                                                        isNeeded.getDocument());
-                md.addField(fieldName, Value(sub));
-            }
-
-            if (bsonElement.type() == Array) {
-                md.addField(fieldName, arrayHelper(bsonElement.embeddedObject(),
-                                                   isNeeded.getDocument()));
-            }
-        }
-
-        return md.freeze();
-    }
 }
diff --git a/src/mongo/db/pipeline/document_source.h b/src/mongo/db/pipeline/document_source.h
index 604b3117a16..a6bd0e8727b 100644
--- a/src/mongo/db/pipeline/document_source.h
+++ b/src/mongo/db/pipeline/document_source.h
@@ -38,6 +38,7 @@
 #include "mongo/db/jsobj.h"
 #include "mongo/db/matcher.h"
 #include "mongo/db/pipeline/document.h"
+#include "mongo/db/pipeline/dependencies.h"
 #include "mongo/db/pipeline/expression_context.h"
 #include "mongo/db/pipeline/expression.h"
 #include "mongo/db/pipeline/value.h"
@@ -128,33 +129,20 @@ namespace mongo {
         virtual void optimize();
 
         enum GetDepsReturn {
-            NOT_SUPPORTED, // This means the set should be ignored and the full object is required.
-            EXHAUSTIVE, // This means that everything needed should be in the set
-            SEE_NEXT, // Add the next Source's deps to the set
+            NOT_SUPPORTED = 0x0, // The full object and all metadata may be required
+            SEE_NEXT = 0x1, // Later stages could need either fields or metadata
+            EXHAUSTIVE_FIELDS = 0x2, // Later stages won't need more fields from input
+            EXHAUSTIVE_META = 0x4, // Later stages won't need more metadata from input
+            EXHAUSTIVE_ALL = EXHAUSTIVE_FIELDS | EXHAUSTIVE_META, // Later stages won't need either
         };
 
-        /** Get the fields this operation needs to do its job.
-         *  Deps should be in "a.b.c" notation
-         *  An empty string in deps means the whole document is needed.
-         *
-         *  @param deps results are added here. NOT CLEARED
+        /**
+         * Get the dependencies this operation needs to do its job.
          */
-        virtual GetDepsReturn getDependencies(set<string>& deps) const {
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const {
             return NOT_SUPPORTED;
         }
 
-        /** This takes dependencies from getDependencies and
-         *  returns a projection that includes all of them
-         */
-        static BSONObj depsToProjection(const set<string>& deps);
-
-        /** These functions take the same input as depsToProjection but are able to
-         *  produce a Document from a BSONObj with the needed fields much faster.
-         */
-        typedef Document ParsedDeps; // See implementation for structure
-        static ParsedDeps parseDeps(const set<string>& deps);
-        static Document documentFromBsonWithDeps(const BSONObj& object, const ParsedDeps& deps);
-
         /**
          * In the default case, serializes the DocumentSource and adds it to the vector<Value>.
          *
@@ -408,12 +396,9 @@ namespace mongo {
          *
          * @param projection A projection specification describing the fields needed by the rest of
          *                   the pipeline.
-         * @param deps The output of DocumentSource::parseDeps.
-         * @param projectionInQuery True if the underlying cursor will handle the projection for us.
+         * @param deps The output of DepsTracker::toParsedDeps
          */
-        void setProjection(const BSONObj& projection,
-                           const ParsedDeps& deps,
-                           bool projectionInQuery);
+        void setProjection(const BSONObj& projection, const boost::optional<ParsedDeps>& deps);
 
         /// returns -1 for no limit
         long long getLimit() const;
@@ -432,9 +417,7 @@ namespace mongo {
         BSONObj _query;
         BSONObj _sort;
         BSONObj _projection;
-        bool _haveDeps;
-        ParsedDeps _dependencies;
-        bool _projectionInQuery;
+        boost::optional<ParsedDeps> _dependencies;
         intrusive_ptr<DocumentSourceLimit> _limit;
         long long _docsAddedToBatches; // for _limit enforcement
 
@@ -450,7 +433,7 @@ namespace mongo {
         virtual boost::optional<Document> getNext();
         virtual const char *getSourceName() const;
         virtual void optimize();
-        virtual GetDepsReturn getDependencies(set<string>& deps) const;
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const;
         virtual void dispose();
         virtual Value serialize(bool explain = false) const;
 
@@ -687,6 +670,7 @@ namespace mongo {
         virtual boost::optional<Document> getNext();
         virtual const char *getSourceName() const;
         virtual Value serialize(bool explain = false) const;
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const;
 
         // Virtuals for SplittableDocumentSource
         virtual intrusive_ptr<DocumentSource> getShardSource() { return NULL; }
@@ -735,7 +719,7 @@ namespace mongo {
         virtual void optimize();
         virtual Value serialize(bool explain = false) const;
 
-        virtual GetDepsReturn getDependencies(set<string>& deps) const;
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const;
 
         /**
           Create a new projection DocumentSource from BSON.
@@ -809,7 +793,7 @@ namespace mongo {
         virtual bool coalesce(const intrusive_ptr<DocumentSource> &pNextSource);
         virtual void dispose();
 
-        virtual GetDepsReturn getDependencies(set<string>& deps) const;
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const;
 
         virtual intrusive_ptr<DocumentSource> getShardSource();
         virtual intrusive_ptr<DocumentSource> getMergeSource();
@@ -923,7 +907,7 @@ namespace mongo {
         virtual bool coalesce(const intrusive_ptr<DocumentSource> &pNextSource);
         virtual Value serialize(bool explain = false) const;
 
-        virtual GetDepsReturn getDependencies(set<string>& deps) const {
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const {
             return SEE_NEXT; // This doesn't affect needed fields
         }
 
@@ -979,7 +963,7 @@ namespace mongo {
         virtual bool coalesce(const intrusive_ptr<DocumentSource> &pNextSource);
         virtual Value serialize(bool explain = false) const;
 
-        virtual GetDepsReturn getDependencies(set<string>& deps) const {
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const {
             return SEE_NEXT; // This doesn't affect needed fields
         }
 
@@ -1033,7 +1017,7 @@ namespace mongo {
         virtual const char *getSourceName() const;
         virtual Value serialize(bool explain = false) const;
 
-        virtual GetDepsReturn getDependencies(set<string>& deps) const;
+        virtual GetDepsReturn getDependencies(DepsTracker* deps) const;
 
         /**
           Create a new projection DocumentSource from BSON.
diff --git a/src/mongo/db/pipeline/document_source_cursor.cpp b/src/mongo/db/pipeline/document_source_cursor.cpp
index bdc76a1f516..6be57a990d3 100644
--- a/src/mongo/db/pipeline/document_source_cursor.cpp
+++ b/src/mongo/db/pipeline/document_source_cursor.cpp
@@ -97,8 +97,8 @@ namespace mongo {
         BSONObj obj;
         Runner::RunnerState state;
         while ((state = runner->getNext(&obj, NULL)) == Runner::RUNNER_ADVANCED) {
-            if (_haveDeps && !_projectionInQuery) {
-                _currentBatch.push_back(documentFromBsonWithDeps(obj, _dependencies));
+            if (_dependencies) {
+                _currentBatch.push_back(_dependencies->extractFields(obj));
             }
             else {
                 _currentBatch.push_back(Document::fromBsonWithMetaData(obj));
@@ -255,7 +255,6 @@ namespace {
                                                CursorId cursorId,
                                                const intrusive_ptr<ExpressionContext> &pCtx)
         : DocumentSource(pCtx)
-        , _haveDeps(false)
         , _docsAddedToBatches(0)
         , _ns(ns)
         , _cursorId(cursorId)
@@ -270,11 +269,8 @@ namespace {
 
     void DocumentSourceCursor::setProjection(
             const BSONObj& projection,
-            const ParsedDeps& deps,
-            bool projectionInQuery) {
+            const boost::optional<ParsedDeps>& deps) {
         _projection = projection;
         _dependencies = deps;
-        _projectionInQuery = projectionInQuery;
-        _haveDeps = true;
     }
 }
diff --git a/src/mongo/db/pipeline/document_source_group.cpp b/src/mongo/db/pipeline/document_source_group.cpp
index 7e7e0bb9e2b..b5350f61fa5 100644
--- a/src/mongo/db/pipeline/document_source_group.cpp
+++ b/src/mongo/db/pipeline/document_source_group.cpp
@@ -153,7 +153,7 @@ namespace mongo {
         return Value(DOC(getSourceName() << insides.freeze()));
     }
 
-    DocumentSource::GetDepsReturn DocumentSourceGroup::getDependencies(set<string>& deps) const {
+    DocumentSource::GetDepsReturn DocumentSourceGroup::getDependencies(DepsTracker* deps) const {
         // add the _id
         pIdExpression->addDependencies(deps);
 
@@ -163,7 +163,7 @@ namespace mongo {
             vpExpression[i]->addDependencies(deps);
         }
 
-        return EXHAUSTIVE;
+        return EXHAUSTIVE_ALL;
     }
 
     intrusive_ptr<DocumentSourceGroup> DocumentSourceGroup::create(
diff --git a/src/mongo/db/pipeline/document_source_out.cpp b/src/mongo/db/pipeline/document_source_out.cpp
index b347e52d3e2..2fc597d7e9c 100644
--- a/src/mongo/db/pipeline/document_source_out.cpp
+++ b/src/mongo/db/pipeline/document_source_out.cpp
@@ -180,4 +180,9 @@ namespace mongo {
 
         return Value(DOC(getSourceName() << _outputNs.coll()));
     }
+
+    DocumentSource::GetDepsReturn DocumentSourceOut::getDependencies(DepsTracker* deps) const {
+        deps->needWholeDocument = true;
+        return EXHAUSTIVE_ALL;
+    }
 }
diff --git a/src/mongo/db/pipeline/document_source_project.cpp b/src/mongo/db/pipeline/document_source_project.cpp
index c6708524f45..8ef3e1c6433 100644
--- a/src/mongo/db/pipeline/document_source_project.cpp
+++ b/src/mongo/db/pipeline/document_source_project.cpp
@@ -131,19 +131,19 @@ namespace mongo {
 
 #if defined(_DEBUG)
         if (exprObj->isSimple()) {
-            set<string> deps;
+            DepsTracker deps;
             vector<string> path;
-            exprObj->addDependencies(deps, &path);
-            pProject->_simpleProjection.init(depsToProjection(deps));
+            exprObj->addDependencies(&deps, &path);
+            pProject->_simpleProjection.init(deps.toProjection());
         }
 #endif
 
         return pProject;
     }
 
-    DocumentSource::GetDepsReturn DocumentSourceProject::getDependencies(set<string>& deps) const {
+    DocumentSource::GetDepsReturn DocumentSourceProject::getDependencies(DepsTracker* deps) const {
         vector<string> path; // empty == top-level
         pEO->addDependencies(deps, &path);
-        return EXHAUSTIVE;
+        return EXHAUSTIVE_FIELDS;
     }
 }
diff --git a/src/mongo/db/pipeline/document_source_sort.cpp b/src/mongo/db/pipeline/document_source_sort.cpp
index c75feb629ce..f25e5fd65e5 100644
--- a/src/mongo/db/pipeline/document_source_sort.cpp
+++ b/src/mongo/db/pipeline/document_source_sort.cpp
@@ -129,7 +129,7 @@ namespace mongo {
         return keyObj.freeze();
     }
 
-    DocumentSource::GetDepsReturn DocumentSourceSort::getDependencies(set<string>& deps) const {
+    DocumentSource::GetDepsReturn DocumentSourceSort::getDependencies(DepsTracker* deps) const {
         for(size_t i = 0; i < vSortKey.size(); ++i) {
             vSortKey[i]->addDependencies(deps);
         }
diff --git a/src/mongo/db/pipeline/document_source_unwind.cpp b/src/mongo/db/pipeline/document_source_unwind.cpp
index 890214c4118..f7c28fa8ec4 100644
--- a/src/mongo/db/pipeline/document_source_unwind.cpp
+++ b/src/mongo/db/pipeline/document_source_unwind.cpp
@@ -143,8 +143,8 @@ namespace mongo {
         return Value(DOC(getSourceName() << _unwindPath->getPath(true)));
     }
 
-    DocumentSource::GetDepsReturn DocumentSourceUnwind::getDependencies(set<string>& deps) const {
-        deps.insert(_unwindPath->getPath(false));
+    DocumentSource::GetDepsReturn DocumentSourceUnwind::getDependencies(DepsTracker* deps) const {
+        deps->fields.insert(_unwindPath->getPath(false));
         return SEE_NEXT;
     }
 
diff --git a/src/mongo/db/pipeline/expression.cpp b/src/mongo/db/pipeline/expression.cpp
index 449360ec36c..82d5c69cbea 100644
--- a/src/mongo/db/pipeline/expression.cpp
+++ b/src/mongo/db/pipeline/expression.cpp
@@ -587,7 +587,7 @@ namespace {
         return intrusive_ptr<Expression>(this);
     }
 
-    void ExpressionCoerceToBool::addDependencies(set<string>& deps, vector<string>* path) const {
+    void ExpressionCoerceToBool::addDependencies(DepsTracker* deps, vector<string>* path) const {
         pExpression->addDependencies(deps);
     }
 
@@ -782,7 +782,7 @@ namespace {
         return intrusive_ptr<Expression>(this);
     }
 
-    void ExpressionConstant::addDependencies(set<string>& deps, vector<string>* path) const {
+    void ExpressionConstant::addDependencies(DepsTracker* deps, vector<string>* path) const {
         /* nothing to do */
     }
 
@@ -901,13 +901,13 @@ namespace {
         return true;
     }
 
-    void ExpressionObject::addDependencies(set<string>& deps, vector<string>* path) const {
+    void ExpressionObject::addDependencies(DepsTracker* deps, vector<string>* path) const {
         string pathStr;
         if (path) {
             if (path->empty()) {
                 // we are in the top level of a projection so _id is implicit
                 if (!_excludeId)
-                    deps.insert("_id");
+                    deps->fields.insert("_id");
             }
             else {
                 FieldPath f (*path);
@@ -930,7 +930,7 @@ namespace {
                 uassert(16407, "inclusion not supported in objects nested in $expressions",
                         path);
 
-                deps.insert(pathStr + it->first);
+                deps->fields.insert(pathStr + it->first);
             }
         }
     }
@@ -1201,9 +1201,6 @@ namespace {
     ExpressionFieldPath::ExpressionFieldPath(const string& theFieldPath, Variables::Id variable)
         : _fieldPath(theFieldPath)
         , _variable(variable)
-        , _baseVar(_fieldPath.getFieldName(0) == "CURRENT" ? CURRENT :
-                   _fieldPath.getFieldName(0) == "ROOT" ?    ROOT :
-                                                             OTHER)
     {}
 
     intrusive_ptr<Expression> ExpressionFieldPath::optimize() {
@@ -1211,13 +1208,12 @@ namespace {
         return intrusive_ptr<Expression>(this);
     }
 
-    void ExpressionFieldPath::addDependencies(set<string>& deps, vector<string>* path) const {
-        // TODO consider state of variables
-        if (_baseVar == ROOT || _baseVar == CURRENT) {
+    void ExpressionFieldPath::addDependencies(DepsTracker* deps, vector<string>* path) const {
+        if (_variable == Variables::ROOT_ID) { // includes CURRENT when it is equivalent to ROOT.
             if (_fieldPath.getPathLength() == 1) {
-                deps.insert(""); // need full doc if just "$$ROOT" or "$$CURRENT"
+                deps->needWholeDocument = true; // need full doc if just "$$ROOT"
             } else {
-                deps.insert(_fieldPath.tail().getPath(false));
+                deps->fields.insert(_fieldPath.tail().getPath(false));
             }
         }
     }
@@ -1383,7 +1379,7 @@ namespace {
         return _subExpression->evaluateInternal(vars);
     }
 
-    void ExpressionLet::addDependencies(set<string>& deps, vector<string>* path) const {
+    void ExpressionLet::addDependencies(DepsTracker* deps, vector<string>* path) const {
         for (VariableMap::const_iterator it=_variables.begin(), end=_variables.end();
                 it != end; ++it) {
             it->second.expression->addDependencies(deps);
@@ -1500,7 +1496,7 @@ namespace {
         return Value::consume(output);
     }
 
-    void ExpressionMap::addDependencies(set<string>& deps, vector<string>* path) const {
+    void ExpressionMap::addDependencies(DepsTracker* deps, vector<string>* path) const {
         _input->addDependencies(deps);
         _each->addDependencies(deps);
     }
@@ -1531,8 +1527,8 @@ namespace {
                 : Value();
     }
 
-    void ExpressionMeta::addDependencies(set<string>& deps, vector<string>* path) const {
-        deps.insert("$textScore");
+    void ExpressionMeta::addDependencies(DepsTracker* deps, vector<string>* path) const {
+        deps->needTextScore = true;
     }
 
     /* ------------------------- ExpressionMillisecond ----------------------------- */
@@ -1782,7 +1778,7 @@ namespace {
         return this;
     }
 
-    void ExpressionNary::addDependencies(set<string>& deps, vector<string>* path) const {
+    void ExpressionNary::addDependencies(DepsTracker* deps, vector<string>* path) const {
         for(ExpressionVector::const_iterator i(vpOperand.begin());
             i != vpOperand.end(); ++i) {
             (*i)->addDependencies(deps);
diff --git a/src/mongo/db/pipeline/expression.h b/src/mongo/db/pipeline/expression.h
index 99121ed1d55..31a0171ecc2 100644
--- a/src/mongo/db/pipeline/expression.h
+++ b/src/mongo/db/pipeline/expression.h
@@ -30,6 +30,7 @@
 
 #include "mongo/pch.h"
 
+#include "mongo/db/pipeline/dependencies.h"
 #include "mongo/db/pipeline/document.h"
 #include "mongo/db/pipeline/field_path.h"
 #include "mongo/db/pipeline/value.h"
@@ -176,7 +177,7 @@ namespace mongo {
          *             where {a:1} inclusion objects aren't allowed, they get
          *             NULL.
          */
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const = 0;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const = 0;
 
         /** simple expressions are just inclusion exclusion as supported by ExpressionObject */
         virtual bool isSimple() { return false; }
@@ -292,7 +293,7 @@ namespace mongo {
         // virtuals from Expression
         virtual intrusive_ptr<Expression> optimize();
         virtual Value serialize(bool explain) const;
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
 
         /*
           Add an operand to the n-ary expression.
@@ -398,7 +399,7 @@ namespace mongo {
     public:
         // virtuals from ExpressionNary
         virtual intrusive_ptr<Expression> optimize();
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
         virtual Value evaluateInternal(Variables* vars) const;
         virtual Value serialize(bool explain) const;
 
@@ -470,7 +471,7 @@ namespace mongo {
     public:
         // virtuals from Expression
         virtual intrusive_ptr<Expression> optimize();
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
         virtual Value evaluateInternal(Variables* vars) const;
         virtual const char *getOpName() const;
         virtual Value serialize(bool explain) const;
@@ -530,7 +531,7 @@ namespace mongo {
     public:
         // virtuals from Expression
         virtual intrusive_ptr<Expression> optimize();
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
         virtual Value evaluateInternal(Variables* vars) const;
         virtual Value serialize(bool explain) const;
 
@@ -577,16 +578,8 @@ namespace mongo {
         // Helper for evaluatePath to handle Array case
         Value evaluatePathArray(size_t index, const Value& input) const;
 
-        // A cache of string comparison of _fieldPath.getFieldName(0)
-        enum BaseVar {
-            CURRENT,
-            ROOT,
-            OTHER,
-        };
-
         const FieldPath _fieldPath;
         const Variables::Id _variable;
-        const BaseVar _baseVar; // TODO remove
     };
 
 
@@ -612,7 +605,7 @@ namespace mongo {
         virtual intrusive_ptr<Expression> optimize();
         virtual Value serialize(bool explain) const;
         virtual Value evaluateInternal(Variables* vars) const;
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
 
         static intrusive_ptr<Expression> parse(
             BSONElement expr,
@@ -645,7 +638,7 @@ namespace mongo {
         virtual intrusive_ptr<Expression> optimize();
         virtual Value serialize(bool explain) const;
         virtual Value evaluateInternal(Variables* vars) const;
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
 
         static intrusive_ptr<Expression> parse(
             BSONElement expr,
@@ -668,7 +661,7 @@ namespace mongo {
         // virtuals from Expression
         virtual Value serialize(bool explain) const;
         virtual Value evaluateInternal(Variables* vars) const;
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
 
         static intrusive_ptr<Expression> parse(
             BSONElement expr,
@@ -729,7 +722,7 @@ namespace mongo {
         // virtuals from Expression
         virtual intrusive_ptr<Expression> optimize();
         virtual bool isSimple();
-        virtual void addDependencies(set<string>& deps, vector<string>* path=NULL) const;
+        virtual void addDependencies(DepsTracker* deps, vector<string>* path=NULL) const;
         /** Only evaluates non inclusion expressions.  For inclusions, use addToDocument(). */
         virtual Value evaluateInternal(Variables* vars) const;
         virtual Value serialize(bool explain) const;
diff --git a/src/mongo/db/pipeline/pipeline_d.cpp b/src/mongo/db/pipeline/pipeline_d.cpp
index 0578f2ac5aa..20fabe2a4e7 100644
--- a/src/mongo/db/pipeline/pipeline_d.cpp
+++ b/src/mongo/db/pipeline/pipeline_d.cpp
@@ -101,45 +101,51 @@ namespace {
         }
 
 
-        /* Look for an initial simple project; we'll avoid constructing Values
-         * for fields that won't make it through the projection.
-         */
-
-        bool haveProjection = false;
-        bool needQueryProjection = false; // true if we need to send the project to query system
-        BSONObj projection;
-        DocumentSource::ParsedDeps dependencies;
+
+        // Find the set of fields in the source documents depended on by this pipeline.
+        DepsTracker deps; // should be considered const after the following block.
         {
-            const bool isTextQuery = DocumentSourceMatch::isTextQuery(queryObj);
-            needQueryProjection = isTextQuery;
-
-            set<string> deps;
-            DocumentSource::GetDepsReturn status = DocumentSource::SEE_NEXT;
-            for (size_t i=0; i < sources.size() && status == DocumentSource::SEE_NEXT; i++) {
-                status = sources[i]->getDependencies(deps);
-                if (deps.count(string())) // empty string means we need the full doc
-                    status = DocumentSource::NOT_SUPPORTED;
-            }
+            bool knowAllFields = false;
+            bool knowAllMeta = false;
+            for (size_t i=0; i < sources.size() && !(knowAllFields && knowAllMeta); i++) {
+                DepsTracker localDeps;
+                DocumentSource::GetDepsReturn status = sources[i]->getDependencies(&localDeps);
+
+                if (status == DocumentSource::NOT_SUPPORTED) {
+                    // Assume this stage needs everything. We may still know something about our
+                    // dependencies if an earlier stage returned either EXHAUSTIVE_FIELDS or
+                    // EXHAUSTIVE_META.
+                    break;
+                }
 
-            // If doing a text query, assume we need score since we can't prove we don't.
-            // Edge cases that make this tricky:
-            // * Need to propagate score from shards to merger even if nothing on shard needs score.
-            // * Stages that are EXHAUSTIVE for field dependencies still propagate metadata.
-            if (isTextQuery)
-                deps.insert("$textScore");
-
-            if (status == DocumentSource::EXHAUSTIVE) {
-                projection = DocumentSource::depsToProjection(deps);
-                dependencies = DocumentSource::parseDeps(deps);
-                haveProjection = true;
-            }
-            else if (isTextQuery) {
-                // We still need score even if we don't know what actual fields are needed.
-                projection = BSON(Document::metaFieldTextScore << BSON("$meta" << "textScore"));
-                haveProjection = true;
+                if (!knowAllFields) {
+                    deps.fields.insert(localDeps.fields.begin(), localDeps.fields.end());
+                    if (localDeps.needWholeDocument)
+                        deps.needWholeDocument = true;
+                    knowAllFields = status & DocumentSource::EXHAUSTIVE_FIELDS;
+                }
+
+                if (!knowAllMeta) {
+                    if (localDeps.needTextScore)
+                        deps.needTextScore = true;
+
+                    knowAllMeta = status & DocumentSource::EXHAUSTIVE_META;
+                }
             }
+
+            if (!knowAllFields)
+                deps.needWholeDocument = true; // don't know all fields we need
+
+            // If doing a text query, assume we need the score if we can't prove we don't.
+            if (!knowAllMeta && DocumentSourceMatch::isTextQuery(queryObj))
+                deps.needTextScore = true;
         }
 
+        // Passing query an empty projection since it is faster to use ParsedDeps::extractFields().
+        // This will need to change to support covering indexes (SERVER-12015). There is an
+        // exception for textScore since that can only be retrieved by a query projection.
+        const BSONObj projectionForQuery = deps.needTextScore ? deps.toProjection() : BSONObj();
+
         /*
           Look for an initial sort; we'll try to add this to the
           Cursor we create.  If we're successful in doing that (further down),
@@ -201,13 +207,11 @@ namespace {
         bool sortInRunner = false;
         if (sortStage) {
             CanonicalQuery* cq;
-            // Passing an empty projection since it is faster to use documentFromBsonWithDeps.
-            // This will need to change to support covering indexes (SERVER-12015).
             Status status =
                 CanonicalQuery::canonicalize(pExpCtx->ns,
                                              queryObj,
                                              sortObj,
-                                             needQueryProjection ? projection : BSONObj(),
+                                             projectionForQuery,
                                              &cq);
             Runner* rawRunner;
             if (status.isOK() && getRunner(cq, &rawRunner, runnerOptions).isOK()) {
@@ -230,7 +234,7 @@ namespace {
                 CanonicalQuery::canonicalize(pExpCtx->ns,
                                              queryObj,
                                              noSort,
-                                             needQueryProjection ? projection : BSONObj(),
+                                             projectionForQuery,
                                              &cq));
 
             Runner* rawRunner;
@@ -258,9 +262,7 @@ namespace {
         if (sortInRunner)
             pSource->setSort(sortObj);
 
-        if (haveProjection) {
-            pSource->setProjection(projection, dependencies, needQueryProjection);
-        }
+        pSource->setProjection(deps.toProjection(), deps.toParsedDeps());
 
         while (!sources.empty() && pSource->coalesce(sources.front())) {
             sources.pop_front();
diff --git a/src/mongo/dbtests/documentsourcetests.cpp b/src/mongo/dbtests/documentsourcetests.cpp
index 221fb13511d..48d13049d9e 100644
--- a/src/mongo/dbtests/documentsourcetests.cpp
+++ b/src/mongo/dbtests/documentsourcetests.cpp
@@ -33,6 +33,7 @@
 #include <boost/thread/thread.hpp>
 
 #include "mongo/db/interrupt_status_mongod.h"
+#include "mongo/db/pipeline/dependencies.h"
 #include "mongo/db/pipeline/document_source.h"
 #include "mongo/db/pipeline/expression_context.h"
 #include "mongo/db/query/get_runner.h"
@@ -42,6 +43,7 @@
 namespace DocumentSourceTests {
 
     static const char* const ns = "unittests.documentsourcetests";
+    static const BSONObj metaTextScore = BSON("$meta" << "textScore");
     static DBDirectClient client;
 
     BSONObj toBson( const intrusive_ptr<DocumentSource>& source ) {
@@ -74,38 +76,72 @@ namespace DocumentSourceTests {
             void run() {
                 {
                     const char* array[] = {"a", "b"}; // basic
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("a" << 1 << "b" << 1 << "_id" << 0));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("a" << 1 << "b" << 1 << "_id" << 0));
                 }
                 {
                     const char* array[] = {"a", "ab"}; // prefixed but not subfield
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("a" << 1 << "ab" << 1 << "_id" << 0));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("a" << 1 << "ab" << 1 << "_id" << 0));
                 }
                 {
                     const char* array[] = {"a", "b", "a.b"}; // a.b included by a
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("a" << 1 << "b" << 1 << "_id" << 0));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("a" << 1 << "b" << 1 << "_id" << 0));
                 }
                 {
                     const char* array[] = {"a", "_id"}; // _id now included
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("a" << 1 << "_id" << 1));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("a" << 1 << "_id" << 1));
                 }
                 {
                     const char* array[] = {"a", "_id.a"}; // still include whole _id (SERVER-7502)
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("a" << 1 << "_id" << 1));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("a" << 1 << "_id" << 1));
                 }
                 {
                     const char* array[] = {"a", "_id", "_id.a"}; // handle both _id and subfield
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("a" << 1 << "_id" << 1));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("a" << 1 << "_id" << 1));
                 }
                 {
                     const char* array[] = {"a", "_id", "_id_a"}; // _id prefixed but non-subfield
-                    BSONObj proj = DocumentSource::depsToProjection(arrayToSet(array));
-                    ASSERT_EQUALS(proj, BSON("_id_a" << 1 << "a" << 1 << "_id" << 1));
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    ASSERT_EQUALS(deps.toProjection(), BSON("_id_a" << 1 << "a" << 1 << "_id" << 1));
+                }
+                {
+                    const char* array[] = {"a"}; // fields ignored with needWholeDocument
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    deps.needWholeDocument = true;
+                    ASSERT_EQUALS(deps.toProjection(), BSONObj());
+                }
+                {
+                    const char* array[] = {"a"}; // needTextScore with needWholeDocument
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    deps.needWholeDocument = true;
+                    deps.needTextScore = true;
+                    ASSERT_EQUALS(
+                        deps.toProjection(),
+                        BSON(Document::metaFieldTextScore << metaTextScore));
+                }
+                {
+                    const char* array[] = {"a"}; // needTextScore without needWholeDocument
+                    DepsTracker deps;
+                    deps.fields = arrayToSet(array);
+                    deps.needTextScore = true;
+                    ASSERT_EQUALS(deps.toProjection(),
+                                  BSON(Document::metaFieldTextScore << metaTextScore
+                                    << "a" << 1
+                                    << "_id" << 0));
                 }
             }
         };
@@ -408,9 +444,11 @@ namespace DocumentSourceTests {
         public:
             void run() {
                 createLimit( 1 );
-                set<string> dependencies;
-                ASSERT_EQUALS( DocumentSource::SEE_NEXT, limit()->getDependencies( dependencies ) );
-                ASSERT_EQUALS( 0U, dependencies.size() );
+                DepsTracker dependencies;
+                ASSERT_EQUALS( DocumentSource::SEE_NEXT, limit()->getDependencies(&dependencies) );
+                ASSERT_EQUALS( 0U, dependencies.fields.size() );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
 
@@ -855,16 +893,18 @@ namespace DocumentSourceTests {
         public:
             void run() {
                 createGroup( fromjson( "{_id:'$x',a:{$sum:'$y.z'},b:{$avg:{$add:['$u','$v']}}}" ) );
-                set<string> dependencies;
-                ASSERT_EQUALS( DocumentSource::EXHAUSTIVE,
-                               group()->getDependencies( dependencies ) );
-                ASSERT_EQUALS( 4U, dependencies.size() );
+                DepsTracker dependencies;
+                ASSERT_EQUALS( DocumentSource::EXHAUSTIVE_ALL,
+                               group()->getDependencies( &dependencies ) );
+                ASSERT_EQUALS( 4U, dependencies.fields.size() );
                 // Dependency from _id expression.
-                ASSERT_EQUALS( 1U, dependencies.count( "x" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "x" ) );
                 // Dependencies from accumulator expressions.
-                ASSERT_EQUALS( 1U, dependencies.count( "y.z" ) );
-                ASSERT_EQUALS( 1U, dependencies.count( "u" ) );
-                ASSERT_EQUALS( 1U, dependencies.count( "v" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "y.z" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "u" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "v" ) );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
 
@@ -1027,20 +1067,23 @@ namespace DocumentSourceTests {
         class Dependencies : public Base {
         public:
             void run() {
-                createProject( fromjson( "{a:true,x:'$b',y:{$and:['$c','$d']}}" ) );
-                set<string> dependencies;
-                ASSERT_EQUALS( DocumentSource::EXHAUSTIVE,
-                               project()->getDependencies( dependencies ) );
-                ASSERT_EQUALS( 5U, dependencies.size() );
+                createProject(fromjson(
+                    "{a:true,x:'$b',y:{$and:['$c','$d']}, z: {$meta:'textScore'}}"));
+                DepsTracker dependencies;
+                ASSERT_EQUALS( DocumentSource::EXHAUSTIVE_FIELDS,
+                               project()->getDependencies( &dependencies ) );
+                ASSERT_EQUALS( 5U, dependencies.fields.size() );
                 // Implicit _id dependency.
-                ASSERT_EQUALS( 1U, dependencies.count( "_id" ) );                
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "_id" ) );
                 // Inclusion dependency.
-                ASSERT_EQUALS( 1U, dependencies.count( "a" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "a" ) );
                 // Field path expression dependency.
-                ASSERT_EQUALS( 1U, dependencies.count( "b" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "b" ) );
                 // Nested expression dependencies.
-                ASSERT_EQUALS( 1U, dependencies.count( "c" ) );
-                ASSERT_EQUALS( 1U, dependencies.count( "d" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "c" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "d" ) );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( true, dependencies.needTextScore );
             }
         };
         
@@ -1368,11 +1411,13 @@ namespace DocumentSourceTests {
         public:
             void run() {
                 createSort( BSON( "a" << 1 << "b.c" << -1 ) );
-                set<string> dependencies;
-                ASSERT_EQUALS( DocumentSource::SEE_NEXT, sort()->getDependencies( dependencies ) );
-                ASSERT_EQUALS( 2U, dependencies.size() );
-                ASSERT_EQUALS( 1U, dependencies.count( "a" ) );
-                ASSERT_EQUALS( 1U, dependencies.count( "b.c" ) );
+                DepsTracker dependencies;
+                ASSERT_EQUALS( DocumentSource::SEE_NEXT, sort()->getDependencies( &dependencies ) );
+                ASSERT_EQUALS( 2U, dependencies.fields.size() );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "a" ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "b.c" ) );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
         
@@ -1629,11 +1674,13 @@ namespace DocumentSourceTests {
         public:
             void run() {
                 createUnwind( "$x.y.z" );
-                set<string> dependencies;
+                DepsTracker dependencies;
                 ASSERT_EQUALS( DocumentSource::SEE_NEXT,
-                               unwind()->getDependencies( dependencies ) );
-                ASSERT_EQUALS( 1U, dependencies.size() );
-                ASSERT_EQUALS( 1U, dependencies.count( "x.y.z" ) );
+                               unwind()->getDependencies( &dependencies ) );
+                ASSERT_EQUALS( 1U, dependencies.fields.size() );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "x.y.z" ) );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
 
diff --git a/src/mongo/dbtests/expressiontests.cpp b/src/mongo/dbtests/expressiontests.cpp
index 3b2307855ff..ab4cf9c4479 100644
--- a/src/mongo/dbtests/expressiontests.cpp
+++ b/src/mongo/dbtests/expressiontests.cpp
@@ -521,10 +521,12 @@ namespace ExpressionTests {
             void run() {
                 intrusive_ptr<Expression> nested = ExpressionFieldPath::create( "a.b" );
                 intrusive_ptr<Expression> expression = ExpressionCoerceToBool::create( nested );
-                set<string> dependencies;
-                expression->addDependencies( dependencies );
-                ASSERT_EQUALS( 1U, dependencies.size() );
-                ASSERT_EQUALS( 1U, dependencies.count( "a.b" ) );
+                DepsTracker dependencies;
+                expression->addDependencies( &dependencies );
+                ASSERT_EQUALS( 1U, dependencies.fields.size() );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "a.b" ) );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
 
@@ -924,9 +926,11 @@ namespace ExpressionTests {
             void run() {
                 intrusive_ptr<Expression> expression =
                         ExpressionConstant::create( Value( 5 ) );
-                set<string> dependencies;
-                expression->addDependencies( dependencies );
-                ASSERT_EQUALS( 0U, dependencies.size() );
+                DepsTracker dependencies;
+                expression->addDependencies( &dependencies );
+                ASSERT_EQUALS( 0U, dependencies.fields.size() );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
 
@@ -990,10 +994,12 @@ namespace ExpressionTests {
         public:
             void run() {
                 intrusive_ptr<Expression> expression = ExpressionFieldPath::create( "a.b" );
-                set<string> dependencies;
-                expression->addDependencies( dependencies );
-                ASSERT_EQUALS( 1U, dependencies.size() );
-                ASSERT_EQUALS( 1U, dependencies.count( "a.b" ) );
+                DepsTracker dependencies;
+                expression->addDependencies( &dependencies );
+                ASSERT_EQUALS( 1U, dependencies.fields.size() );
+                ASSERT_EQUALS( 1U, dependencies.fields.count( "a.b" ) );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }
         };
 
@@ -1282,14 +1288,17 @@ namespace ExpressionTests {
         private:
             void assertDependencies( const BSONArray& expectedDependencies,
                                      const intrusive_ptr<Expression>& expression ) {
-                set<string> dependencies;
-                expression->addDependencies( dependencies );
+                DepsTracker dependencies;
+                expression->addDependencies( &dependencies );
                 BSONArrayBuilder dependenciesBson;
-                for( set<string>::const_iterator i = dependencies.begin(); i != dependencies.end();
-                     ++i ) {
+                for( set<string>::const_iterator i = dependencies.fields.begin();
+                        i != dependencies.fields.end();
+                        ++i ) {
                     dependenciesBson << *i;
                 }
                 ASSERT_EQUALS( expectedDependencies, dependenciesBson.arr() );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }                
         };
 
@@ -1450,15 +1459,18 @@ namespace ExpressionTests {
             void assertDependencies( const BSONArray& expectedDependencies,
                                      const intrusive_ptr<ExpressionObject>& expression,
                                      bool includePath = true ) const {
-                set<string> dependencies;
                 vector<string> path;
-                expression->addDependencies( dependencies, includePath ? &path : 0 );
+                DepsTracker dependencies;
+                expression->addDependencies( &dependencies, includePath ? &path : 0 );
                 BSONArrayBuilder bab;
-                for( set<string>::const_iterator i = dependencies.begin(); i != dependencies.end();
-                    ++i ) {
+                for( set<string>::const_iterator i = dependencies.fields.begin();
+                        i != dependencies.fields.end();
+                        ++i ) {
                     bab << *i;
                 }
                 ASSERT_EQUALS( expectedDependencies, bab.arr() );
+                ASSERT_EQUALS( false, dependencies.needWholeDocument );
+                ASSERT_EQUALS( false, dependencies.needTextScore );
             }            
         };
 
@@ -2098,9 +2110,9 @@ namespace ExpressionTests {
                 intrusive_ptr<ExpressionObject> expression = ExpressionObject::createRoot();
                 expression->includePath( "a" );
                 assertDependencies( BSON_ARRAY( "_id" << "a" ), expression, true );
-                set<string> unused;
+                DepsTracker unused;
                 // 'path' must be provided for inclusion expressions.
-                ASSERT_THROWS( expression->addDependencies( unused ), UserException );
+                ASSERT_THROWS( expression->addDependencies( &unused ), UserException );
             }
         };