SERVER-7174 Implement $inc on new update framework

4 files changed, 750 insertions, 0 deletions

diff --git a/src/mongo/db/ops/SConscript b/src/mongo/db/ops/SConscript
index 4c35518a886..ccd175ff2c6 100644
--- a/src/mongo/db/ops/SConscript
+++ b/src/mongo/db/ops/SConscript
@@ -39,6 +39,7 @@ env.CppUnitTest(
 env.StaticLibrary(
     target='update',
     source=[
+        'modifier_inc.cpp',
         'modifier_set.cpp',
         'modifier_unset.cpp',
     ],
@@ -48,6 +49,15 @@ env.StaticLibrary(
 )
 
 env.CppUnitTest(
+    target='modifier_inc_test',
+    source='modifier_inc_test.cpp',
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/mutable_bson_test_utils',
+        'update',
+    ],
+)
+
+env.CppUnitTest(
     target='modifier_set_test',
     source='modifier_set_test.cpp',
     LIBDEPS=[
diff --git a/src/mongo/db/ops/modifier_inc.cpp b/src/mongo/db/ops/modifier_inc.cpp
new file mode 100644
index 00000000000..00a773f6329
--- /dev/null
+++ b/src/mongo/db/ops/modifier_inc.cpp
@@ -0,0 +1,266 @@
+/**
+ *    Copyright (C) 2013 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/>.
+ */
+
+#include "mongo/db/ops/modifier_inc.h"
+
+#include "mongo/base/error_codes.h"
+#include "mongo/bson/mutable/document.h"
+#include "mongo/db/ops/field_checker.h"
+#include "mongo/db/ops/path_support.h"
+#include "mongo/util/mongoutils/str.h"
+
+namespace mongo {
+
+    using mongoutils::str::stream;
+
+    struct ModifierInc::PreparedState {
+
+        PreparedState(mutablebson::Document& doc)
+            : doc(doc)
+            , idxFound(0)
+            , elemFound(doc.end())
+            , boundDollar("")
+            , newValue()
+            , inPlace(false)
+            , noOp(false) {
+        }
+
+        // Document that is going to be changed.
+        mutablebson::Document& doc;
+
+        // Index in _fieldRef for which an Element exist in the document.
+        int32_t idxFound;
+
+        // Element corresponding to _fieldRef[0.._idxFound].
+        mutablebson::Element elemFound;
+
+        // Value to bind to a $-positional field, if one is provided.
+        std::string boundDollar;
+
+        // Value to be applied
+        SafeNum newValue;
+
+        // This $inc is in-place?
+        bool inPlace;
+
+        // This $inc is a no-op?
+        bool noOp;
+    };
+
+    ModifierInc::ModifierInc()
+        : ModifierInterface ()
+        , _fieldRef()
+        , _posDollar(0)
+        , _val() {
+    }
+
+    ModifierInc::~ModifierInc() {
+    }
+
+    Status ModifierInc::init(const BSONElement& modExpr) {
+
+        //
+        // field name analysis
+        //
+
+        // Perform standard field name and updateable checks.
+        _fieldRef.parse(modExpr.fieldName());
+        Status status = fieldchecker::isUpdatable(_fieldRef);
+        if (! status.isOK()) {
+            return status;
+        }
+
+        // If a $-positional operator was used, get the index in which it occurred.
+        fieldchecker::isPositional(_fieldRef, &_posDollar);
+
+        //
+        // value analysis
+        //
+
+        if (!modExpr.isNumber()) {
+            // TODO: Context for mod error messages would be helpful
+            // include mod code, etc.
+            return Status(ErrorCodes::BadValue,
+                          "Cannot increment with non-numeric argument");
+        }
+
+        _val = modExpr;
+        dassert(_val.isValid());
+
+        return Status::OK();
+    }
+
+    Status ModifierInc::prepare(mutablebson::Element root,
+                                const StringData& matchedField,
+                                ExecInfo* execInfo) {
+
+        _preparedState.reset(new PreparedState(root.getDocument()));
+
+        // If we have a $-positional field, it is time to bind it to an actual field part.
+        if (_posDollar) {
+            if (matchedField.empty()) {
+                return Status(ErrorCodes::BadValue, "matched field not provided");
+            }
+            _preparedState->boundDollar = matchedField.toString();
+            _fieldRef.setPart(_posDollar, _preparedState->boundDollar);
+        }
+
+        // Locate the field name in 'root'. Note that we may not have all the parts in the path
+        // in the doc -- which is fine. Our goal now is merely to reason about whether this mod
+        // apply is a noOp or whether is can be in place. The remaining path, if missing, will
+        // be created during the apply.
+        Status status = pathsupport::findLongestPrefix(_fieldRef,
+                                                       root,
+                                                       &_preparedState->idxFound,
+                                                       &_preparedState->elemFound);
+
+        // FindLongestPrefix may say the path does not exist at all, which is fine here, or
+        // that the path was not viable or otherwise wrong, in which case, the mod cannot
+        // proceed.
+        if (status.code() == ErrorCodes::NonExistentPath) {
+            _preparedState->elemFound = root.getDocument().end();
+        }
+        else if (!status.isOK()) {
+            return status;
+        }
+
+        // We register interest in the field name. The driver needs this info to sort out if
+        // there is any conflict among mods.
+        execInfo->fieldRef[0] = &_fieldRef;
+
+        // Capture the value we are going to write. At this point, there may not be a value
+        // against which to operate, so the result will be simply _val.
+        _preparedState->newValue = _val;
+
+        //
+        // in-place and no-op logic
+        //
+        // If the field path is not fully present, then this mod cannot be in place, nor is a
+        // noOp.
+        if (!_preparedState->elemFound.ok() ||
+            _preparedState->idxFound < static_cast<int32_t>(_fieldRef.numParts() - 1)) {
+            return Status::OK();
+        }
+
+        // If the value being $inc'ed is the same as the one already in the doc, than this is a
+        // noOp.
+        if (!_preparedState->elemFound.isNumeric())
+            return Status(ErrorCodes::BadValue,
+                          "invalid attempt to increment a non-numeric field");
+
+        const SafeNum currentValue = _preparedState->elemFound.getValueSafeNum();
+
+        // TODO: Is it possible for the current value to be EOO?
+
+        // Update newValue w.r.t to the current value of the found element.
+        _preparedState->newValue += currentValue;
+
+        // If the result of the addition is invalid, we must return an error.
+        if (!_preparedState->newValue.isValid())
+            return Status(ErrorCodes::BadValue,
+                          "Failed to increment current value");
+
+        // If the values are identical (same type, same value), then this is a no-op, and
+        // therefore in-place as well.
+        if (_preparedState->newValue.isIdentical(currentValue)) {
+            _preparedState->noOp = execInfo->noOp = true;
+            _preparedState->inPlace = execInfo->inPlace = true;
+            return Status::OK();
+        }
+
+        // If the types are the same, this can be done in place.
+        //
+        // TODO: Potentially, cases where $inc results in a mixed type of the same size could
+        // be in-place as well, but we don't currently handle them.
+        if (_preparedState->newValue.type() == currentValue.type()) {
+            _preparedState->inPlace = execInfo->inPlace = true;
+        }
+
+        return Status::OK();
+    }
+
+    Status ModifierInc::apply() const {
+        dassert(_preparedState->noOp == false);
+
+        // If there's no need to create any further field part, the $inc is simply a value
+        // assignment.
+        if (_preparedState->elemFound.ok() &&
+            _preparedState->idxFound == static_cast<int32_t>(_fieldRef.numParts() - 1)) {
+            return _preparedState->elemFound.setValueSafeNum(_preparedState->newValue);
+        }
+
+        dassert(_preparedState->inPlace == false);
+
+        //
+        // Complete document path logic
+        //
+
+        // Creates the final element that's going to be $set in 'doc'.
+        mutablebson::Document& doc = _preparedState->doc;
+        StringData lastPart = _fieldRef.getPart(_fieldRef.numParts() - 1);
+        mutablebson::Element elemToSet = doc.makeElementSafeNum(lastPart, _preparedState->newValue);
+        if (!elemToSet.ok()) {
+            return Status(ErrorCodes::InternalError, "can't create new element");
+        }
+
+        // Now, we can be in two cases here, as far as attaching the element being set goes:
+        // (a) none of the parts in the element's path exist, or (b) some parts of the path
+        // exist but not all.
+        if (!_preparedState->elemFound.ok()) {
+            _preparedState->elemFound = doc.root();
+            _preparedState->idxFound = 0;
+        }
+        else {
+            _preparedState->idxFound++;
+        }
+
+        // createPathAt() will complete the path and attach 'elemToSet' at the end of it.
+        return pathsupport::createPathAt(_fieldRef,
+                                         _preparedState->idxFound,
+                                         _preparedState->elemFound,
+                                         elemToSet);
+    }
+
+    Status ModifierInc::log(mutablebson::Element logRoot) const {
+
+        // We'd like to create an entry such as {$set: {<fieldname>: <value>}} under 'logRoot'.
+        // We start by creating the {$set: ...} Element.
+        mutablebson::Document& doc = logRoot.getDocument();
+        mutablebson::Element setElement = doc.makeElementObject("$set");
+        if (!setElement.ok()) {
+            return Status(ErrorCodes::InternalError, "cannot append log entry for $set mod");
+        }
+
+        // Then we create the {<fieldname>: <value>} Element.
+        mutablebson::Element logElement = doc.makeElementSafeNum(
+            _fieldRef.dottedField(),
+            _preparedState->newValue);
+
+        if (!logElement.ok()) {
+            return Status(ErrorCodes::InternalError, "cannot append details for $set mod");
+        }
+
+        // Now, we attach the {<fieldname>: <value>} Element under the {$set: ...} one.
+        Status status = setElement.pushBack(logElement);
+        if (!status.isOK()) {
+            return status;
+        }
+
+        // And attach the result under the 'logRoot' Element provided.
+        return logRoot.pushBack(setElement);
+    }
+
+} // namespace mongo
diff --git a/src/mongo/db/ops/modifier_inc.h b/src/mongo/db/ops/modifier_inc.h
new file mode 100644
index 00000000000..5dc9f8fae95
--- /dev/null
+++ b/src/mongo/db/ops/modifier_inc.h
@@ -0,0 +1,73 @@
+/**
+ *    Copyright (C) 2013 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/>.
+ */
+
+#pragma once
+
+#include <boost/scoped_ptr.hpp>
+#include <string>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/bson/mutable/element.h"
+#include "mongo/db/field_ref.h"
+#include "mongo/db/ops/modifier_interface.h"
+
+namespace mongo {
+
+    class ModifierInc : public ModifierInterface {
+        MONGO_DISALLOW_COPYING(ModifierInc);
+
+    public:
+
+        ModifierInc();
+        virtual ~ModifierInc();
+
+        /**
+         * A 'modExpr' is a BSONElement {<fieldname>: <value>} coming from a $inc mod such as
+         * {$inc: {<fieldname: <value>}}. init() extracts the field name and the value to be
+         * assigned to it from 'modExpr'. It returns OK if successful or a status describing
+         * the error.
+         */
+        virtual Status init(const BSONElement& modExpr);
+
+        /** Evaluates the validity of applying $inc to the identified node, and computes
+         *  effects, handling upcasting and overflow as necessary.
+         */
+        virtual Status prepare(mutablebson::Element root,
+                               const StringData& matchedField,
+                               ExecInfo* execInfo);
+
+        /** Updates the node passed in prepare with the results of the $inc */
+        virtual Status apply() const;
+
+        /** Converts the result of the $inc into an equivalent $set under logRoot */
+        virtual Status log(mutablebson::Element logRoot) const;
+
+    private:
+
+        // Access to each component of fieldName that's the target of this mod.
+        FieldRef _fieldRef;
+
+        // 0 or index for $-positional in _fieldRef.
+        size_t _posDollar;
+
+        // Element of the $set expression.
+        SafeNum _val;
+
+        struct PreparedState;
+        scoped_ptr<PreparedState> _preparedState;
+    };
+
+} // namespace mongo
diff --git a/src/mongo/db/ops/modifier_inc_test.cpp b/src/mongo/db/ops/modifier_inc_test.cpp
new file mode 100644
index 00000000000..ad78567cbdf
--- /dev/null
+++ b/src/mongo/db/ops/modifier_inc_test.cpp
@@ -0,0 +1,401 @@
+/**
+ *    Copyright (C) 2013 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/>.
+ */
+
+
+#include "mongo/db/ops/modifier_inc.h"
+
+#include "mongo/base/status.h"
+#include "mongo/base/string_data.h"
+#include "mongo/bson/mutable/algorithm.h"
+#include "mongo/bson/mutable/document.h"
+#include "mongo/bson/mutable/mutable_bson_test_utils.h"
+#include "mongo/db/jsobj.h"
+#include "mongo/db/json.h"
+#include "mongo/platform/cstdint.h"
+#include "mongo/unittest/unittest.h"
+
+namespace {
+
+    using mongo::BSONObj;
+    using mongo::ModifierInc;
+    using mongo::ModifierInterface;
+    using mongo::NumberInt;
+    using mongo::Status;
+    using mongo::StringData;
+    using mongo::fromjson;
+    using mongo::mutablebson::checkDoc;
+    using mongo::mutablebson::ConstElement;
+    using mongo::mutablebson::Document;
+    using mongo::mutablebson::Element;
+    using mongo::mutablebson::countChildren;
+
+    /** Helper to build and manipulate a $inc mod. */
+    class Mod {
+    public:
+        Mod() : _mod() {}
+
+        explicit Mod(BSONObj modObj)
+            : _modObj(modObj)
+            , _mod() {
+            ASSERT_OK(_mod.init(_modObj["$inc"].embeddedObject().firstElement()));
+        }
+
+        Status prepare(Element root,
+                       const StringData& matchedField,
+                       ModifierInterface::ExecInfo* execInfo) {
+            return _mod.prepare(root, matchedField, execInfo);
+        }
+
+        Status apply() const {
+            return _mod.apply();
+        }
+
+        Status log(Element logRoot) const {
+            return _mod.log(logRoot);
+        }
+
+        ModifierInc& mod() { return _mod; }
+
+    private:
+        BSONObj _modObj;
+        ModifierInc _mod;
+    };
+
+    TEST(Init, FailToInitWithInvalidValue) {
+        BSONObj modObj;
+        ModifierInc mod;
+
+        // String is an invalid increment argument
+        modObj = fromjson("{ $inc : { a : '' } }");
+        ASSERT_NOT_OK(mod.init(modObj["$inc"].embeddedObject().firstElement()));
+
+        // Object is an invalid increment argument
+        modObj = fromjson("{ $inc : { a : {} } }");
+        ASSERT_NOT_OK(mod.init(modObj["$inc"].embeddedObject().firstElement()));
+
+        // Array is an invalid increment argument
+        modObj = fromjson("{ $inc : { a : [] } }");
+        ASSERT_NOT_OK(mod.init(modObj["$inc"].embeddedObject().firstElement()));
+    }
+
+    TEST(Init, InitParsesNumberInt) {
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<int>(1))));
+    }
+
+    TEST(Init, InitParsesNumberLong) {
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<long long>(1))));
+    }
+
+    TEST(Init, InitParsesNumberDouble) {
+        Mod incMod(BSON("$inc" << BSON("a" << 1.0)));
+    }
+
+    TEST(SimpleMod, PrepareSimpleOK) {
+        Document doc(fromjson("{ a : 1 }"));
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+
+        ASSERT_EQUALS(execInfo.fieldRef[0]->dottedField(), "a");
+        ASSERT_TRUE(execInfo.inPlace);
+        ASSERT_FALSE(execInfo.noOp);
+    }
+
+    TEST(SimpleMod, PrepareSimpleNonNumericObject) {
+        Document doc(fromjson("{ a : {} }"));
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_NOT_OK(incMod.prepare(doc.root(), "", &execInfo));
+    }
+
+    TEST(SimpleMod, PrepareSimpleNonNumericArray) {
+
+        Document doc(fromjson("{ a : [] }"));
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_NOT_OK(incMod.prepare(doc.root(), "", &execInfo));
+    }
+
+    TEST(SimpleMod, PrepareSimpleNonNumericString) {
+        Document doc(fromjson("{ a : '' }"));
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_NOT_OK(incMod.prepare(doc.root(), "", &execInfo));
+    }
+
+    TEST(SimpleMod, ApplyAndLogEmptyDocument) {
+        Document doc(fromjson("{}"));
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.inPlace);
+        ASSERT_FALSE(execInfo.noOp);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : 1 }")));
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { a : 1 } }")));
+    }
+
+    TEST(SimpleMod, ApplyAndLogSimpleDocument) {
+        Document doc(fromjson("{ a : 2 }"));
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.inPlace);
+        ASSERT_FALSE(execInfo.noOp);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : 3 }")));
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { a : 3 } }")));
+    }
+
+    TEST(DottedMod, ApplyAndLogSimpleDocument) {
+        Document doc(fromjson("{ a : { b : 2 } }"));
+        Mod incMod(fromjson("{ $inc: { 'a.b' : 1 } }"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.inPlace);
+        ASSERT_FALSE(execInfo.noOp);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : { b : 3 } }")));
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { 'a.b' : 3 } }")));
+    }
+
+    TEST(InPlace, IntToInt) {
+        Document doc(BSON("a" << static_cast<int>(1)));
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<int>(1))));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+    }
+
+    TEST(InPlace, LongToLong) {
+        Document doc(BSON("a" << static_cast<long long>(1)));
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<long long>(1))));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+    }
+
+    TEST(InPlace, DoubleToDouble) {
+        Document doc(BSON("a" << 1.0));
+        Mod incMod(BSON("$inc" << BSON("a" << 1.0 )));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+    }
+
+    TEST(NoOp, Int) {
+        Document doc(BSON("a" << static_cast<int>(1)));
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<int>(0))));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+    }
+
+    TEST(NoOp, Long) {
+        Document doc(BSON("a" << static_cast<long long>(1)));
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<long long>(0))));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+    }
+
+    TEST(NoOp, Double) {
+        Document doc(BSON("a" << 1.0));
+        Mod incMod(BSON("$inc" << BSON("a" << 0.0)));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+    }
+
+    TEST(Upcasting, UpcastIntToLong) {
+        // Checks that $inc : NumberLong(0) turns a NumberInt into a NumberLong and logs it
+        // correctly.
+        Document doc(BSON("a" << static_cast<int>(1)));
+        ASSERT_EQUALS(mongo::NumberInt, doc.root()["a"].getType());
+
+        Mod incMod(BSON("$inc" << BSON("a" << static_cast<long long>(0))));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_FALSE(execInfo.inPlace);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : 1 }")));
+        ASSERT_EQUALS(mongo::NumberLong, doc.root()["a"].getType());
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { a : 1 } }")));
+        ASSERT_EQUALS(mongo::NumberLong, logDoc.root()["$set"]["a"].getType());
+    }
+
+    TEST(Upcasting, UpcastIntToDouble) {
+        // Checks that $inc : 0.0 turns a NumberInt into a NumberDouble and logs it
+        // correctly.
+        Document doc(BSON("a" << static_cast<int>(1)));
+        ASSERT_EQUALS(mongo::NumberInt, doc.root()["a"].getType());
+
+        Mod incMod(fromjson("{ $inc : { a : 0.0 } }"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_FALSE(execInfo.inPlace);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : 1.0 }")));
+        ASSERT_EQUALS(mongo::NumberDouble, doc.root()["a"].getType());
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { a : 1.0 } }")));
+        ASSERT_EQUALS(mongo::NumberDouble, logDoc.root()["$set"]["a"].getType());
+    }
+
+    TEST(Upcasting, UpcastLongToDouble) {
+        // Checks that $inc : 0.0 turns a NumberLong into a NumberDouble and logs it
+        // correctly.
+        Document doc(BSON("a" << static_cast<long long>(1)));
+        ASSERT_EQUALS(mongo::NumberLong, doc.root()["a"].getType());
+
+        Mod incMod(fromjson("{ $inc : { a : 0.0 } }"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_FALSE(execInfo.inPlace);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : 1.0 }")));
+        ASSERT_EQUALS(mongo::NumberDouble, doc.root()["a"].getType());
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { a : 1.0 } }")));
+        ASSERT_EQUALS(mongo::NumberDouble, logDoc.root()["$set"]["a"].getType());
+    }
+
+    TEST(Upcasting, DoublesStayDoubles) {
+        // Checks that $inc : 0 doesn't change a NumberDouble away from double
+        Document doc(fromjson("{ a : 1.0 }"));
+        ASSERT_EQUALS(mongo::NumberDouble, doc.root()["a"].getType());
+
+        Mod incMod(fromjson("{ $inc : { a : 1 } }"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_TRUE(execInfo.inPlace);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, fromjson("{ a : 2.0 }")));
+        ASSERT_EQUALS(mongo::NumberDouble, doc.root()["a"].getType());
+
+        Document logDoc;
+        ASSERT_OK(incMod.log(logDoc.root()));
+        ASSERT_TRUE(checkDoc(logDoc, fromjson("{ $set : { a : 2.0 } }")));
+        ASSERT_EQUALS(mongo::NumberDouble, logDoc.root()["$set"]["a"].getType());
+    }
+
+    // The only interesting overflow cases are int->long via increment: we never overflow to
+    // double, and we never decrease precision on decrement.
+
+    TEST(Spilling, OverflowIntToLong) {
+        const int initial_value = std::numeric_limits<int32_t>::max();
+
+        Document doc(BSON("a" << static_cast<int>(initial_value)));
+        ASSERT_EQUALS(mongo::NumberInt, doc.root()["a"].getType());
+
+        Mod incMod(fromjson("{ $inc : { a : 1 } }"));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_FALSE(execInfo.inPlace);
+
+        const long long target_value = static_cast<long long>(initial_value) + 1;
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, BSON("a" << target_value)));
+    }
+
+    TEST(Spilling, UnderflowIntToLong) {
+        const int initial_value = std::numeric_limits<int32_t>::min();
+
+        Document doc(BSON("a" << static_cast<int>(initial_value)));
+        ASSERT_EQUALS(mongo::NumberInt, doc.root()["a"].getType());
+
+        Mod incMod(fromjson("{ $inc : { a : -1 } }"));
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc.root(), "", &execInfo));
+        ASSERT_FALSE(execInfo.noOp);
+        ASSERT_FALSE(execInfo.inPlace);
+
+        const long long target_value = static_cast<long long>(initial_value) - 1;
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc, BSON("a" << target_value)));
+    }
+
+    TEST(Lifecycle, IncModCanBeReused) {
+        Document doc1(fromjson("{ a : 1 }"));
+        Document doc2(fromjson("{ a : 1 }"));
+
+        Mod incMod(fromjson("{ $inc: { a : 1 }}"));
+
+        ModifierInterface::ExecInfo execInfo;
+        ASSERT_OK(incMod.prepare(doc1.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.inPlace);
+        ASSERT_FALSE(execInfo.noOp);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc1, fromjson("{ a : 2 }")));
+
+        ASSERT_OK(incMod.prepare(doc2.root(), "", &execInfo));
+        ASSERT_TRUE(execInfo.inPlace);
+        ASSERT_FALSE(execInfo.noOp);
+
+        ASSERT_OK(incMod.apply());
+        ASSERT_TRUE(checkDoc(doc2, fromjson("{ a : 2 }")));
+    }
+
+} // namespace