SERVER-48052 Make updates create ExpressionContext with 'explain' field correctly initialized

12 files changed, 123 insertions, 34 deletions

diff --git a/jstests/core/find_and_modify_pipeline_update.js b/jstests/core/find_and_modify_pipeline_update.js
index 781b4d0335d..0340d29bd66 100644
--- a/jstests/core/find_and_modify_pipeline_update.js
+++ b/jstests/core/find_and_modify_pipeline_update.js
@@ -6,6 +6,7 @@
 "use strict";
 
 load("jstests/libs/fixture_helpers.js");  // For isMongos.
+load("jstests/libs/analyze_plan.js");     // For planHasStage().
 
 const coll = db.find_and_modify_pipeline_update;
 coll.drop();
@@ -35,10 +36,52 @@ assert.eq(found, {_id: 2, y: 2});
 found = coll.findAndModify({query: {_id: 3}, update: [{$set: {y: 3}}], fields: {x: 1}, new: true});
 assert.eq(found, {_id: 3, x: 3});
 
-// We skip the following test for sharded fixtures as it will fail as the query for
-// findAndModify must contain the shard key.
+//
+// Tests for explain using findAndModify with an _id equality query.
+//
+{
+    let explain =
+        coll.explain("queryPlanner").findAndModify({query: {_id: 3}, update: [{$set: {y: 999}}]});
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "IDHACK"));
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "UPDATE"));
+
+    // Run explain with execution-level verbosity.
+    explain =
+        coll.explain("executionStats").findAndModify({query: {_id: 3}, update: [{$set: {y: 999}}]});
+    assert.eq(explain.executionStats.nReturned, 1);
+    // UPDATE stage would modify one document.
+    const updateStage = getPlanStage(explain.executionStats.executionStages, "UPDATE");
+    assert.eq(updateStage.nWouldModify, 1);
+
+    // Check that no write was performed.
+    assert.eq(coll.find({y: 999}).count(), 0);
+}
+
+// We skip the following tests for sharded fixtures as it will fail as the query when
+// findAndModify doesn't contain the shard key.
 if (!FixtureHelpers.isMongos(db)) {
+    //
+    // Tests for explain with a query that requires a COLLSCAN.
+    //
+    let explain =
+        coll.explain("queryPlanner").findAndModify({query: {y: 3}, update: [{$set: {y: 999}}]});
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "COLLSCAN"));
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "UPDATE"));
+
+    // Run explain with execution-level verbosity.
+    explain =
+        coll.explain("executionStats").findAndModify({query: {y: 3}, update: [{$set: {y: 999}}]});
+    assert.eq(explain.executionStats.nReturned, 1);
+    // UPDATE stage would modify one document.
+    const updateStage = getPlanStage(explain.executionStats.executionStages, "UPDATE");
+    assert.eq(updateStage.nWouldModify, 1);
+
+    // Check that no write was performed.
+    assert.eq(coll.find({y: 999}).count(), 0);
+
+    //
     // Test that 'sort' works with pipeline-style update.
+    //
     assert(coll.drop());
     assert.commandWorked(
         coll.insert([{_id: 0, x: 'b'}, {_id: 1, x: 'd'}, {_id: 2, x: 'a'}, {_id: 3, x: 'c'}]));
diff --git a/jstests/core/update_pipeline_shell_helpers.js b/jstests/core/update_pipeline_shell_helpers.js
index d8bb7d7eb3d..7a4d2419ad7 100644
--- a/jstests/core/update_pipeline_shell_helpers.js
+++ b/jstests/core/update_pipeline_shell_helpers.js
@@ -10,6 +10,8 @@
 "use strict";
 
 load("jstests/aggregation/extras/utils.js");  // For 'arrayEq'.
+load("jstests/libs/analyze_plan.js");         // For planHasStage().
+load("jstests/libs/fixture_helpers.js");      // For isMongos().
 
 // Make sure that the test collection is empty before starting the test.
 const testColl = db.update_pipeline_shell_helpers_test;
@@ -82,6 +84,46 @@ const findOneAndUpdatePostImage = testColl.findOneAndUpdate(
     {_id: 1}, [{$set: {findOneAndUpdate: true}}], {returnNewDocument: true});
 assert.docEq(findOneAndUpdatePostImage, expectedFindOneAndUpdatePostImage);
 
+//
+// Explain for updates that use an _id lookup query.
+//
+{
+    let explain = testColl.explain("queryPlanner").update({_id: 2}, [{$set: {y: 999}}]);
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "IDHACK"));
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "UPDATE"));
+
+    // Run explain with execution-level verbosity.
+    explain = testColl.explain("executionStats").update({_id: 2}, [{$set: {y: 999}}]);
+    assert.eq(explain.executionStats.totalDocsExamined, 1, explain);
+    // UPDATE stage would modify one document.
+    const updateStage = getPlanStage(explain.executionStats.executionStages, "UPDATE");
+    assert.eq(updateStage.nWouldModify, 1);
+
+    // Check that no write was performed.
+    assert.eq(testColl.find({y: 999}).count(), 0);
+}
+
+//
+// Explain for updates that use a query which requires a COLLSCAN.
+//
+
+// We skip these tests under sharded fixtures, since sharded passthroughs require that FAM queries
+// contain the shard key.
+if (!FixtureHelpers.isMongos(db)) {
+    let explain = testColl.explain("queryPlanner").update({a: 2}, [{$set: {y: 999}}]);
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "COLLSCAN"));
+    assert(planHasStage(db, explain.queryPlanner.winningPlan, "UPDATE"));
+
+    // Run explain with execution-level verbosity.
+    explain = testColl.explain("executionStats").update({a: 2}, [{$set: {y: 999}}]);
+    // UPDATE stage would modify one document.
+    const updateStage = getPlanStage(explain.executionStats.executionStages, "UPDATE");
+    assert.eq(updateStage.nWouldModify, 1);
+
+    // Check that no write was performed.
+    assert.eq(testColl.find({y: 999}).count(), 0);
+}
+
 // Shell helpers for replacement updates should reject pipeline-style updates.
 assert.throws(() => testColl.replaceOne({_id: 1}, [{$replaceWith: {}}]));
 assert.throws(() => testColl.findOneAndReplace({_id: 1}, [{$replaceWith: {}}]));
diff --git a/src/mongo/db/commands/find_and_modify.cpp b/src/mongo/db/commands/find_and_modify.cpp
index 2c86f93243d..40ab8129ec2 100644
--- a/src/mongo/db/commands/find_and_modify.cpp
+++ b/src/mongo/db/commands/find_and_modify.cpp
@@ -121,7 +121,7 @@ boost::optional<BSONObj> advanceExecutor(OperationContext* opCtx,
 
 void makeUpdateRequest(OperationContext* opCtx,
                        const FindAndModifyRequest& args,
-                       bool explain,
+                       boost::optional<ExplainOptions::Verbosity> explain,
                        UpdateRequest* requestOut) {
     requestOut->setQuery(args.getQuery());
     requestOut->setProj(args.getFields());
@@ -291,8 +291,7 @@ public:
         } else {
             auto request = UpdateRequest();
             request.setNamespaceString(nsString);
-            const bool isExplain = true;
-            makeUpdateRequest(opCtx, args, isExplain, &request);
+            makeUpdateRequest(opCtx, args, verbosity, &request);
 
             const ExtensionsCallbackReal extensionsCallback(opCtx, &request.getNamespaceString());
             ParsedUpdate parsedUpdate(opCtx, &request, extensionsCallback);
@@ -385,8 +384,8 @@ public:
                 for (;;) {
                     auto request = UpdateRequest();
                     request.setNamespaceString(nsString);
-                    const bool isExplain = false;
-                    makeUpdateRequest(opCtx, args, isExplain, &request);
+                    const auto verbosity = boost::none;
+                    makeUpdateRequest(opCtx, args, verbosity, &request);
 
                     if (opCtx->getTxnNumber()) {
                         request.setStmtId(stmtId);
diff --git a/src/mongo/db/commands/write_commands/write_commands.cpp b/src/mongo/db/commands/write_commands/write_commands.cpp
index 9228fa50fb5..6d1ea157c21 100644
--- a/src/mongo/db/commands/write_commands/write_commands.cpp
+++ b/src/mongo/db/commands/write_commands/write_commands.cpp
@@ -419,7 +419,7 @@ private:
                 _batch.getRuntimeConstants().value_or(Variables::generateRuntimeConstants(opCtx)));
             updateRequest.setLetParameters(_batch.getLet());
             updateRequest.setYieldPolicy(PlanExecutor::YIELD_AUTO);
-            updateRequest.setExplain();
+            updateRequest.setExplain(verbosity);
 
             const ExtensionsCallbackReal extensionsCallback(opCtx,
                                                             &updateRequest.getNamespaceString());
diff --git a/src/mongo/db/exec/update_stage.cpp b/src/mongo/db/exec/update_stage.cpp
index dd7f405115e..8e8c6694865 100644
--- a/src/mongo/db/exec/update_stage.cpp
+++ b/src/mongo/db/exec/update_stage.cpp
@@ -250,7 +250,7 @@ BSONObj UpdateStage::transformAndUpdate(const Snapshotted<BSONObj>& oldObj, Reco
         RecordId newRecordId;
         CollectionUpdateArgs args;
 
-        if (!request->isExplain()) {
+        if (!request->explain()) {
             args.stmtId = request->getStmtId();
             args.update = logObj;
             if (isUserInitiatedWrite) {
@@ -272,7 +272,7 @@ BSONObj UpdateStage::transformAndUpdate(const Snapshotted<BSONObj>& oldObj, Reco
         }
 
         if (inPlace) {
-            if (!request->isExplain()) {
+            if (!request->explain()) {
                 newObj = oldObj.value();
                 const RecordData oldRec(oldObj.value().objdata(), oldObj.value().objsize());
 
@@ -302,7 +302,7 @@ BSONObj UpdateStage::transformAndUpdate(const Snapshotted<BSONObj>& oldObj, Reco
                                   << BSONObjMaxUserSize,
                     newObj.objsize() <= BSONObjMaxUserSize);
 
-            if (!request->isExplain()) {
+            if (!request->explain()) {
                 if (_shouldCheckForShardKeyUpdate && checkUpdateChangesShardKeyFields(oldObj) &&
                     !args.preImageDoc) {
                     args.preImageDoc = oldObj.value().getOwned();
@@ -336,7 +336,7 @@ BSONObj UpdateStage::transformAndUpdate(const Snapshotted<BSONObj>& oldObj, Reco
 
     // Only record doc modifications if they wrote (exclude no-ops). Explains get
     // recorded as if they wrote.
-    if (docWasModified || request->isExplain()) {
+    if (docWasModified || request->explain()) {
         _specificStats.nModified++;
     }
 
diff --git a/src/mongo/db/exec/upsert_stage.cpp b/src/mongo/db/exec/upsert_stage.cpp
index dc81610bb96..5860ccfb1cf 100644
--- a/src/mongo/db/exec/upsert_stage.cpp
+++ b/src/mongo/db/exec/upsert_stage.cpp
@@ -91,7 +91,7 @@ PlanStage::StageState UpsertStage::doWork(WorkingSetID* out) {
     _specificStats.objInserted = _produceNewDocumentForInsert();
 
     // If this is an explain, skip performing the actual insert.
-    if (!_params.request->isExplain()) {
+    if (!_params.request->explain()) {
         _performInsert(_specificStats.objInserted);
     }
 
diff --git a/src/mongo/db/ops/parsed_update.cpp b/src/mongo/db/ops/parsed_update.cpp
index 18285ed37d5..34458e1f8dd 100644
--- a/src/mongo/db/ops/parsed_update.cpp
+++ b/src/mongo/db/ops/parsed_update.cpp
@@ -45,11 +45,15 @@ ParsedUpdate::ParsedUpdate(OperationContext* opCtx,
                            const ExtensionsCallback& extensionsCallback)
     : _opCtx(opCtx),
       _request(request),
-      _expCtx(make_intrusive<ExpressionContext>(opCtx,
-                                                nullptr,
-                                                _request->getNamespaceString(),
-                                                _request->getRuntimeConstants(),
-                                                _request->getLetParameters())),
+      _expCtx(make_intrusive<ExpressionContext>(
+          opCtx,
+          nullptr,
+          _request->getNamespaceString(),
+          _request->getRuntimeConstants(),
+          _request->getLetParameters(),
+          true,  // mayDbProfile. We pass 'true' here conservatively. In the future we may
+          // change this.
+          request->explain())),
       _driver(_expCtx),
       _canonicalQuery(),
       _extensionsCallback(extensionsCallback) {}
@@ -124,7 +128,7 @@ Status ParsedUpdate::parseQueryToCQ() {
     auto qr = std::make_unique<QueryRequest>(_request->getNamespaceString());
     qr->setFilter(_request->getQuery());
     qr->setSort(_request->getSort());
-    qr->setExplain(_request->isExplain());
+    qr->setExplain(static_cast<bool>(_request->explain()));
     qr->setHint(_request->getHint());
 
     // We get the collation off the ExpressionContext because it may contain a collection-default
diff --git a/src/mongo/db/ops/update.cpp b/src/mongo/db/ops/update.cpp
index 62e88d71e2e..c065f670167 100644
--- a/src/mongo/db/ops/update.cpp
+++ b/src/mongo/db/ops/update.cpp
@@ -57,7 +57,7 @@ UpdateResult update(OperationContext* opCtx, Database* db, const UpdateRequest&
     invariant(db);
 
     // Explain should never use this helper.
-    invariant(!request.isExplain());
+    invariant(!request.explain());
 
     const NamespaceString& nsString = request.getNamespaceString();
     invariant(opCtx->lockState()->isCollectionLockedForMode(nsString, MODE_IX));
diff --git a/src/mongo/db/ops/update_request.h b/src/mongo/db/ops/update_request.h
index 6404b5dcd70..d5bbbd4bdcc 100644
--- a/src/mongo/db/ops/update_request.h
+++ b/src/mongo/db/ops/update_request.h
@@ -196,12 +196,12 @@ public:
         return _fromOplogApplication;
     }
 
-    void setExplain(bool value = true) {
-        _isExplain = value;
+    void setExplain(boost::optional<ExplainOptions::Verbosity> verbosity) {
+        _explain = verbosity;
     }
 
-    bool isExplain() const {
-        return _isExplain;
+    boost::optional<ExplainOptions::Verbosity> explain() const {
+        return _explain;
     }
 
     void setReturnDocs(ReturnDocOption value) {
@@ -277,7 +277,7 @@ public:
         builder << " multi: " << isMulti();
         builder << " fromMigration: " << _fromMigration;
         builder << " fromOplogApplication: " << _fromOplogApplication;
-        builder << " isExplain: " << _isExplain;
+        builder << " isExplain: " << static_cast<bool>(_explain);
         return builder.str();
     }
 
@@ -314,8 +314,9 @@ private:
     // True if this update was triggered by the application of an oplog entry.
     bool _fromOplogApplication = false;
 
-    // Whether or not we are requesting an explained update. Explained updates are read-only.
-    bool _isExplain = false;
+    // Whether or not we are requesting an explained update, and if so, which type. Explained
+    // updates may involve executing stages, but they will not perform writes.
+    boost::optional<ExplainOptions::Verbosity> _explain;
 
     // Specifies which version of the documents to return, if any.
     //
diff --git a/src/mongo/db/pipeline/expression_context.cpp b/src/mongo/db/pipeline/expression_context.cpp
index 8625cf80903..f33d6a16e06 100644
--- a/src/mongo/db/pipeline/expression_context.cpp
+++ b/src/mongo/db/pipeline/expression_context.cpp
@@ -134,8 +134,10 @@ ExpressionContext::ExpressionContext(OperationContext* opCtx,
                                      const NamespaceString& nss,
                                      const boost::optional<RuntimeConstants>& runtimeConstants,
                                      const boost::optional<BSONObj>& letParameters,
-                                     bool mayDbProfile)
-    : ns(nss),
+                                     bool mayDbProfile,
+                                     boost::optional<ExplainOptions::Verbosity> explain)
+    : explain(explain),
+      ns(nss),
       opCtx(opCtx),
       mongoProcessInterface(std::make_shared<StubMongoProcessInterface>()),
       timeZoneDatabase(opCtx && opCtx->getServiceContext()
diff --git a/src/mongo/db/pipeline/expression_context.h b/src/mongo/db/pipeline/expression_context.h
index d3a491119d3..6cd1bba4f3b 100644
--- a/src/mongo/db/pipeline/expression_context.h
+++ b/src/mongo/db/pipeline/expression_context.h
@@ -142,7 +142,8 @@ public:
                       const NamespaceString& ns,
                       const boost::optional<RuntimeConstants>& runtimeConstants = boost::none,
                       const boost::optional<BSONObj>& letParameters = boost::none,
-                      bool mayDbProfile = true);
+                      bool mayDbProfile = true,
+                      boost::optional<ExplainOptions::Verbosity> explain = boost::none);
 
     /**
      * Used by a pipeline to check for interrupts so that killOp() works. Throws a UserAssertion if
diff --git a/src/mongo/db/query/get_executor.cpp b/src/mongo/db/query/get_executor.cpp
index b1bae642936..c27145180ac 100644
--- a/src/mongo/db/query/get_executor.cpp
+++ b/src/mongo/db/query/get_executor.cpp
@@ -915,7 +915,7 @@ StatusWith<unique_ptr<PlanExecutor, PlanExecutor::Deleter>> getExecutorUpdate(
     // the collection prior to calling this method. Explain, however, will never do
     // collection or database creation.
     if (!collection && request->isUpsert()) {
-        invariant(request->isExplain());
+        invariant(request->explain());
     }
 
     // If the parsed update does not have a user-specified collation, set it from the collection
@@ -1002,9 +1002,6 @@ StatusWith<unique_ptr<PlanExecutor, PlanExecutor::Deleter>> getExecutorUpdate(
     // This is the regular path for when we have a CanonicalQuery.
     unique_ptr<CanonicalQuery> cq(parsedUpdate->releaseParsedQuery());
 
-    // Transfer the explain verbosity level into the expression context.
-    cq->getExpCtx()->explain = verbosity;
-
     std::unique_ptr<projection_ast::Projection> projection;
     if (!request->getProj().isEmpty()) {
         invariant(request->shouldReturnAnyDocs());