SERVER-29935 Clarify SingleDocumentTransformation's explain.

It's slightly different than that on DocumentSource, which should be
more obvious.

10 files changed, 50 insertions, 44 deletions

diff --git a/src/mongo/db/pipeline/document_source_replace_root.cpp b/src/mongo/db/pipeline/document_source_replace_root.cpp
index b5def20495e..089ff2d9c98 100644
--- a/src/mongo/db/pipeline/document_source_replace_root.cpp
+++ b/src/mongo/db/pipeline/document_source_replace_root.cpp
@@ -80,7 +80,7 @@ public:
         _newRoot->optimize();
     }
 
-    Document serialize(boost::optional<ExplainOptions::Verbosity> explain) const final {
+    Document serializeStageOptions(boost::optional<ExplainOptions::Verbosity> explain) const final {
         return Document{{"newRoot", _newRoot->serialize(static_cast<bool>(explain))}};
     }
 
diff --git a/src/mongo/db/pipeline/document_source_single_document_transformation.cpp b/src/mongo/db/pipeline/document_source_single_document_transformation.cpp
index df363f8fde2..e425699e80a 100644
--- a/src/mongo/db/pipeline/document_source_single_document_transformation.cpp
+++ b/src/mongo/db/pipeline/document_source_single_document_transformation.cpp
@@ -76,7 +76,7 @@ void DocumentSourceSingleDocumentTransformation::doDispose() {
 
 Value DocumentSourceSingleDocumentTransformation::serialize(
     boost::optional<ExplainOptions::Verbosity> explain) const {
-    return Value(Document{{getSourceName(), _parsedTransform->serialize(explain)}});
+    return Value(Document{{getSourceName(), _parsedTransform->serializeStageOptions(explain)}});
 }
 
 Pipeline::SourceContainer::iterator DocumentSourceSingleDocumentTransformation::doOptimizeAt(
diff --git a/src/mongo/db/pipeline/document_source_single_document_transformation.h b/src/mongo/db/pipeline/document_source_single_document_transformation.h
index 108a13aa161..ee2141a2c8d 100644
--- a/src/mongo/db/pipeline/document_source_single_document_transformation.h
+++ b/src/mongo/db/pipeline/document_source_single_document_transformation.h
@@ -62,11 +62,17 @@ public:
         virtual Document applyTransformation(const Document& input) = 0;
         virtual TransformerType getType() const = 0;
         virtual void optimize() = 0;
-        virtual Document serialize(boost::optional<ExplainOptions::Verbosity> explain) const = 0;
         virtual DocumentSource::GetDepsReturn addDependencies(DepsTracker* deps) const = 0;
         virtual GetModPathsReturn getModifiedPaths() const = 0;
 
         /**
+         * Returns the document describing this stage, not including the stage name. For example,
+         * should return just {_id: 0, x: 1} for the stage parsed from {$project: {_id: 0, x: 1}}.
+         */
+        virtual Document serializeStageOptions(
+            boost::optional<ExplainOptions::Verbosity> explain) const = 0;
+
+        /**
          * Returns true if this transformer is an inclusion projection and is a subset of
          * 'proj', which must be a valid projection specification. For example, if this
          * TransformerInterface represents the inclusion projection
diff --git a/src/mongo/db/pipeline/parsed_add_fields.h b/src/mongo/db/pipeline/parsed_add_fields.h
index e0d60822ba3..f5e53284357 100644
--- a/src/mongo/db/pipeline/parsed_add_fields.h
+++ b/src/mongo/db/pipeline/parsed_add_fields.h
@@ -71,7 +71,7 @@ public:
      */
     void parse(const BSONObj& spec) final;
 
-    Document serialize(boost::optional<ExplainOptions::Verbosity> explain) const final {
+    Document serializeStageOptions(boost::optional<ExplainOptions::Verbosity> explain) const final {
         MutableDocument output;
         _root->serialize(&output, explain);
         return output.freeze();
diff --git a/src/mongo/db/pipeline/parsed_add_fields_test.cpp b/src/mongo/db/pipeline/parsed_add_fields_test.cpp
index 9a39b54ae8a..289e8eb1f33 100644
--- a/src/mongo/db/pipeline/parsed_add_fields_test.cpp
+++ b/src/mongo/db/pipeline/parsed_add_fields_test.cpp
@@ -175,13 +175,13 @@ TEST(ParsedAddFieldsSerialize, SerializesToCorrectForm) {
         fromjson("{a: {$add: [\"$a\", {$const: 2}]}, b: {d: {$const: 3}}, x: {y: {$const: 4}}}"));
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecStats));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 // Verify that serialize treats the _id field as any other field: including when explicity included.
@@ -194,13 +194,13 @@ TEST(ParsedAddFieldsSerialize, AddsIdToSerializeWhenExplicitlyIncluded) {
     auto expectedSerialization = Document(fromjson("{_id: {$const: false}}"));
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecStats));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 // Verify that serialize treats the _id field as any other field: excluded when not explicitly
@@ -216,13 +216,13 @@ TEST(ParsedAddFieldsSerialize, OmitsIdFromSerializeWhenNotIncluded) {
     auto expectedSerialization = Document(fromjson("{a: {$const: true}}"));
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecStats));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 // Verify that the $addFields stage optimizes expressions into simpler forms when possible.
@@ -234,13 +234,13 @@ TEST(ParsedAddFieldsOptimize, OptimizesTopLevelExpressions) {
     auto expectedSerialization = Document{{"a", Document{{"$const", 3}}}};
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecStats));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 // Verify that the $addFields stage optimizes expressions even when they are nested.
@@ -252,13 +252,13 @@ TEST(ParsedAddFieldsOptimize, ShouldOptimizeNestedExpressions) {
     auto expectedSerialization = Document{{"a", Document{{"b", Document{{"$const", 3}}}}}};
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, addition.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecStats));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       addition.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       addition.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 //
diff --git a/src/mongo/db/pipeline/parsed_exclusion_projection.cpp b/src/mongo/db/pipeline/parsed_exclusion_projection.cpp
index b4d52ef77ed..7eca645c314 100644
--- a/src/mongo/db/pipeline/parsed_exclusion_projection.cpp
+++ b/src/mongo/db/pipeline/parsed_exclusion_projection.cpp
@@ -135,7 +135,7 @@ void ExclusionNode::addModifiedPaths(std::set<std::string>* modifiedPaths) const
 // ParsedExclusionProjection.
 //
 
-Document ParsedExclusionProjection::serialize(
+Document ParsedExclusionProjection::serializeStageOptions(
     boost::optional<ExplainOptions::Verbosity> explain) const {
     return _root->serialize();
 }
diff --git a/src/mongo/db/pipeline/parsed_exclusion_projection.h b/src/mongo/db/pipeline/parsed_exclusion_projection.h
index de371df0ccd..3de597910bc 100644
--- a/src/mongo/db/pipeline/parsed_exclusion_projection.h
+++ b/src/mongo/db/pipeline/parsed_exclusion_projection.h
@@ -104,7 +104,7 @@ public:
         return TransformerType::kExclusionProjection;
     }
 
-    Document serialize(boost::optional<ExplainOptions::Verbosity> explain) const final;
+    Document serializeStageOptions(boost::optional<ExplainOptions::Verbosity> explain) const final;
 
     /**
      * Parses the projection specification given by 'spec', populating internal data structures.
diff --git a/src/mongo/db/pipeline/parsed_exclusion_projection_test.cpp b/src/mongo/db/pipeline/parsed_exclusion_projection_test.cpp
index a79950a13b3..348044018e9 100644
--- a/src/mongo/db/pipeline/parsed_exclusion_projection_test.cpp
+++ b/src/mongo/db/pipeline/parsed_exclusion_projection_test.cpp
@@ -87,7 +87,7 @@ TEST(ExclusionProjection, ShouldSerializeToEquivalentProjection) {
 
     // Converts numbers to bools, converts dotted paths to nested documents. Note order of excluded
     // fields is subject to change.
-    auto serialization = exclusion.serialize(boost::none);
+    auto serialization = exclusion.serializeStageOptions(boost::none);
     ASSERT_EQ(serialization.size(), 4UL);
     ASSERT_VALUE_EQ(serialization["a"], Value(false));
     ASSERT_VALUE_EQ(serialization["_id"], Value(false));
diff --git a/src/mongo/db/pipeline/parsed_inclusion_projection.h b/src/mongo/db/pipeline/parsed_inclusion_projection.h
index c42acc75e85..e93aa0fe736 100644
--- a/src/mongo/db/pipeline/parsed_inclusion_projection.h
+++ b/src/mongo/db/pipeline/parsed_inclusion_projection.h
@@ -199,7 +199,7 @@ public:
     /**
      * Serialize the projection.
      */
-    Document serialize(boost::optional<ExplainOptions::Verbosity> explain) const final {
+    Document serializeStageOptions(boost::optional<ExplainOptions::Verbosity> explain) const final {
         MutableDocument output;
         if (_idExcluded) {
             output.addField("_id", Value(false));
diff --git a/src/mongo/db/pipeline/parsed_inclusion_projection_test.cpp b/src/mongo/db/pipeline/parsed_inclusion_projection_test.cpp
index 4c1395504cd..ef77bb03943 100644
--- a/src/mongo/db/pipeline/parsed_inclusion_projection_test.cpp
+++ b/src/mongo/db/pipeline/parsed_inclusion_projection_test.cpp
@@ -138,13 +138,13 @@ TEST(InclusionProjection, ShouldSerializeToEquivalentProjection) {
         "{_id: true, a: {$add: [\"$a\", {$const: 2}]}, b: {d: true}, x: {y: {$const: 4}}}"));
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecStats));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 TEST(InclusionProjection, ShouldSerializeExplicitExclusionOfId) {
@@ -156,13 +156,13 @@ TEST(InclusionProjection, ShouldSerializeExplicitExclusionOfId) {
     auto expectedSerialization = Document{{"_id", false}, {"a", true}};
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecStats));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 
@@ -176,13 +176,13 @@ TEST(InclusionProjection, ShouldOptimizeTopLevelExpressions) {
     auto expectedSerialization = Document{{"_id", true}, {"a", Document{{"$const", 3}}}};
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecStats));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 TEST(InclusionProjection, ShouldOptimizeNestedExpressions) {
@@ -196,13 +196,13 @@ TEST(InclusionProjection, ShouldOptimizeNestedExpressions) {
         Document{{"_id", true}, {"a", Document{{"b", Document{{"$const", 3}}}}}};
 
     // Should be the same if we're serializing for explain or for internal use.
-    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serialize(boost::none));
+    ASSERT_DOCUMENT_EQ(expectedSerialization, inclusion.serializeStageOptions(boost::none));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kQueryPlanner));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kQueryPlanner));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecStats));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecStats));
     ASSERT_DOCUMENT_EQ(expectedSerialization,
-                       inclusion.serialize(ExplainOptions::Verbosity::kExecAllPlans));
+                       inclusion.serializeStageOptions(ExplainOptions::Verbosity::kExecAllPlans));
 }
 
 TEST(InclusionProjection, ShouldReportThatAllExceptIncludedFieldsAreModified) {