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.

1 files changed, 0 insertions, 138 deletions

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();
-    }
 }