SERVER-54925 Move away from using Bson_serialization_type “any”

17 files changed, 920 insertions, 153 deletions

diff --git a/buildscripts/idl/idl_check_compatibility.py b/buildscripts/idl/idl_check_compatibility.py
index 120a42d5a4f..77a187857ae 100644
--- a/buildscripts/idl/idl_check_compatibility.py
+++ b/buildscripts/idl/idl_check_compatibility.py
@@ -50,6 +50,7 @@ from idl.compiler import CompilerImportResolver
 from idl_compatibility_errors import IDLCompatibilityContext, IDLCompatibilityErrorCollection, dump_errors
 
 ALLOW_ANY_TYPE_LIST: List[str] = [
+    # This list if only used in unit-tests.
     "commandAllowedAnyTypes",
     "commandAllowedAnyTypes-param-anyTypeParam",
     "commandAllowedAnyTypes-reply-anyTypeField",
@@ -69,6 +70,12 @@ ALLOW_ANY_TYPE_LIST: List[str] = [
     "replyFieldCppTypeNotEqual-reply-cppTypeNotEqualReplyField",
     "commandCppTypeNotEqual",
     "commandParameterCppTypeNotEqual-param-cppTypeNotEqualParam",
+    "replyFieldSerializerNotEqual-reply-serializerNotEqualReplyField",
+    "commandSerializerNotEqual",
+    "commandParameterSerializerNotEqual-param-serializerNotEqualParam",
+    "replyFieldDeserializerNotEqual-reply-deserializerNotEqualReplyField",
+    "commandDeserializerNotEqual",
+    "commandParameterDeserializerNotEqual-param-deserializerNotEqualParam",
     "newlyAddedReplyFieldTypeBsonAnyAllowed-reply-newlyAddedBsonSerializationTypeAnyReplyField",
     "replyFieldTypeBsonAnyWithVariantUnstable-reply-bsonSerializationTypeWithVariantAnyUnstableReplyField",
     "newlyAddedParamBsonAnyAllowList-param-newlyAddedBsonAnyAllowListParam",
@@ -78,6 +85,12 @@ ALLOW_ANY_TYPE_LIST: List[str] = [
     "commandParameterCppTypeNotEqualUnstable-param-cppTypeNotEqualParam",
     "replyFieldCppTypeNotEqualUnstable-reply-cppTypeNotEqualReplyUnstableField",
     "commandCppTypeNotEqualUnstable",
+    "commandParameterSerializerNotEqualUnstable-param-serializerNotEqualParam",
+    "replyFieldSerializerNotEqualUnstable-reply-serializerNotEqualReplyUnstableField",
+    "commandSerializerNotEqualUnstable",
+    "commandParameterDeserializerNotEqualUnstable-param-deserializerNotEqualParam",
+    "replyFieldDeserializerNotEqualUnstable-reply-deserializerNotEqualReplyUnstableField",
+    "commandDeserializerNotEqualUnstable",
 
     # TODO (SERVER-54956): Decide what to do with commands: (create, createIndexes).
     'create-param-backwards',
@@ -93,8 +106,17 @@ ALLOW_ANY_TYPE_LIST: List[str] = [
     'saslContinue-param-payload',
     'saslContinue-reply-payload',
 
-    # TODO (SERVER-54925): Decide what to do with commands:
-    # (aggregate, find, update, delete, findAndModify, explain).
+    # These commands (aggregate, find, update, delete, findAndModify, explain) might contain some
+    # fields with type `any`. Currently, it's not possible to avoid the `any` type in those cases.
+    # Instead, here are the preventive measures in-place to catch unintentional breaking changes:
+    # 1- Added comments on top of custom serializers/deserializers (related to these fields) to
+    #    let the future developers know that their modifications to these methods might lead to
+    #    a breaking change in the API.
+    # 2- Added proper unit-tests to catch accidental changes to the custom serializers/deserializers
+    #    by over-fitting on the current implementation of these custom serializers/deserializers.
+    # 3- Added further checks to the current script (idl_check_compatibility.py) to check for
+    #    changing a custom serializer/deserializer and considering it as a potential breaking
+    #    change.
     'aggregate-param-pipeline',
     'aggregate-param-explain',
     'aggregate-param-allowDiskUse',
@@ -289,10 +311,21 @@ def check_reply_field_type_recursive(ctxt: IDLCompatibilityContext,
                 cmd_name, field_name, old_field_type.name, old_field.idl_file_path)
             return
 
+        # If cpp_type is changed, it's a potential breaking change.
         if old_field_type.cpp_type != new_field_type.cpp_type:
             ctxt.add_reply_field_cpp_type_not_equal_error(cmd_name, field_name, new_field_type.name,
                                                           new_field.idl_file_path)
 
+        # If serializer is changed, it's a potential breaking change.
+        if (not old_field.unstable) and old_field_type.serializer != new_field_type.serializer:
+            ctxt.add_reply_field_serializer_not_equal_error(
+                cmd_name, field_name, new_field_type.name, new_field.idl_file_path)
+
+        # If deserializer is changed, it's a potential breaking change.
+        if (not old_field.unstable) and old_field_type.deserializer != new_field_type.deserializer:
+            ctxt.add_reply_field_deserializer_not_equal_error(
+                cmd_name, field_name, new_field_type.name, new_field.idl_file_path)
+
     if isinstance(old_field_type, syntax.VariantType):
         # If the new type is not variant just check the single type.
         new_variant_types = new_field_type.variant_types if isinstance(
@@ -542,10 +575,21 @@ def check_param_or_command_type_recursive(ctxt: IDLCompatibilityContext,
                 cmd_name, old_type.name, old_field.idl_file_path, param_name, is_command_parameter)
             return
 
+        # If cpp_type is changed, it's a potential breaking change.
         if old_type.cpp_type != new_type.cpp_type:
             ctxt.add_command_or_param_cpp_type_not_equal_error(
                 cmd_name, new_type.name, new_field.idl_file_path, param_name, is_command_parameter)
 
+        # If serializer is changed, it's a potential breaking change.
+        if (not old_field.unstable) and old_type.serializer != new_type.serializer:
+            ctxt.add_command_or_param_serializer_not_equal_error(
+                cmd_name, new_type.name, new_field.idl_file_path, param_name, is_command_parameter)
+
+        # If deserializer is changed, it's a potential breaking change.
+        if (not old_field.unstable) and old_type.deserializer != new_type.deserializer:
+            ctxt.add_command_or_param_deserializer_not_equal_error(
+                cmd_name, new_type.name, new_field.idl_file_path, param_name, is_command_parameter)
+
     if isinstance(old_type, syntax.VariantType):
         if not isinstance(new_type, syntax.VariantType):
             if not old_field.unstable:
diff --git a/buildscripts/idl/idl_compatibility_errors.py b/buildscripts/idl/idl_compatibility_errors.py
index dc5c30a2105..02961c50ccf 100644
--- a/buildscripts/idl/idl_compatibility_errors.py
+++ b/buildscripts/idl/idl_compatibility_errors.py
@@ -112,6 +112,12 @@ ERROR_ID_ADDED_ACCESS_CHECK_FIELD = "ID0067"
 ERROR_ID_COMMAND_STRICT_TRUE_ERROR = "ID0068"
 ERROR_ID_GENERIC_ARGUMENT_REMOVED = "ID0069"
 ERROR_ID_GENERIC_ARGUMENT_REMOVED_REPLY_FIELD = "ID0070"
+ERROR_ID_COMMAND_PARAMETER_SERIALIZER_NOT_EQUAL = "ID0071"
+ERROR_ID_COMMAND_SERIALIZER_NOT_EQUAL = "ID0072"
+ERROR_ID_REPLY_FIELD_SERIALIZER_NOT_EQUAL = "ID0073"
+ERROR_ID_COMMAND_DESERIALIZER_NOT_EQUAL = "ID0074"
+ERROR_ID_COMMAND_PARAMETER_DESERIALIZER_NOT_EQUAL = "ID0075"
+ERROR_ID_REPLY_FIELD_DESERIALIZER_NOT_EQUAL = "ID0076"
 
 # TODO (SERVER-55203): Remove SKIPPED_COMMANDS logic.
 # Any breaking changes added to API V1 before releasing 5.0 should be added to SKIPPED_COMMANDS to
@@ -730,6 +736,22 @@ class IDLCompatibilityContext(object):
                          "that is not equal in the old and new versions.") %
                         (command_name, field_name, type_name), file)
 
+    def add_reply_field_serializer_not_equal_error(self, command_name: str, field_name: str,
+                                                   type_name: str, file: str) -> None:
+        """Add an error about the old and new reply field serializer not being equal."""
+        self._add_error(ERROR_ID_REPLY_FIELD_SERIALIZER_NOT_EQUAL, command_name,
+                        ("'%s' has a reply field or sub-field '%s' of type '%s' that has "
+                         "serializer that is not equal in the old and new versions.") %
+                        (command_name, field_name, type_name), file)
+
+    def add_reply_field_deserializer_not_equal_error(self, command_name: str, field_name: str,
+                                                     type_name: str, file: str) -> None:
+        """Add an error about the old and new reply field deserializer not being equal."""
+        self._add_error(ERROR_ID_REPLY_FIELD_DESERIALIZER_NOT_EQUAL, command_name,
+                        ("'%s' has a reply field or sub-field '%s' of type '%s' that has "
+                         "deserializer that is not equal in the old and new versions.") %
+                        (command_name, field_name, type_name), file)
+
     def add_new_reply_field_type_not_enum_error(self, command_name: str, field_name: str,
                                                 new_field_type: str, old_field_type: str,
                                                 file: str) -> None:
@@ -864,6 +886,38 @@ class IDLCompatibilityContext(object):
                 ("'%s' or its sub-struct has command type '%s' that has cpp_type "
                  "that is not equal in the old and new versions") % (command_name, type_name), file)
 
+    def add_command_or_param_serializer_not_equal_error(self, command_name: str, type_name: str,
+                                                        file: str, field_name: Optional[str],
+                                                        is_command_parameter: bool) -> None:
+        # pylint: disable=too-many-arguments,invalid-name
+        """Add an error about the old and new command or param serializer not being equal."""
+        if is_command_parameter:
+            self._add_error(ERROR_ID_COMMAND_PARAMETER_SERIALIZER_NOT_EQUAL, command_name,
+                            ("'%s' has field or sub-field '%s' of type '%s' that has  "
+                             "serializer that is not equal in the old and new versions") %
+                            (command_name, field_name, type_name), file)
+        else:
+            self._add_error(
+                ERROR_ID_COMMAND_SERIALIZER_NOT_EQUAL, command_name,
+                ("'%s' or its sub-struct has command type '%s' that has serializer "
+                 "that is not equal in the old and new versions") % (command_name, type_name), file)
+
+    def add_command_or_param_deserializer_not_equal_error(self, command_name: str, type_name: str,
+                                                          file: str, field_name: Optional[str],
+                                                          is_command_parameter: bool) -> None:
+        # pylint: disable=too-many-arguments,invalid-name
+        """Add an error about the old and new command or param deserializer not being equal."""
+        if is_command_parameter:
+            self._add_error(ERROR_ID_COMMAND_PARAMETER_DESERIALIZER_NOT_EQUAL, command_name,
+                            ("'%s' has field or sub-field '%s' of type '%s' that has  "
+                             "deserializer that is not equal in the old and new versions") %
+                            (command_name, field_name, type_name), file)
+        else:
+            self._add_error(
+                ERROR_ID_COMMAND_DESERIALIZER_NOT_EQUAL, command_name,
+                ("'%s' or its sub-struct has command type '%s' that has deserializer "
+                 "that is not equal in the old and new versions") % (command_name, type_name), file)
+
     def add_old_reply_field_bson_any_error(self, command_name: str, field_name: str,
                                            old_field_type: str, file: str) -> None:
         """
diff --git a/buildscripts/idl/tests/compatibility_test_fail/new/compatibility_test_fail_new.idl b/buildscripts/idl/tests/compatibility_test_fail/new/compatibility_test_fail_new.idl
index b92612556a8..01da70b3e8c 100644
--- a/buildscripts/idl/tests/compatibility_test_fail/new/compatibility_test_fail_new.idl
+++ b/buildscripts/idl/tests/compatibility_test_fail/new/compatibility_test_fail_new.idl
@@ -41,7 +41,7 @@ types:
         description: "The bson_serialization_type changes from int in the old command's reply
                       field type to [int, string] in the new command's reply field type"
         cpp_type: "std::int32_t"
-    
+
     intStringToIntStringBool:
         bson_serialization_type:
                                 - int
@@ -57,7 +57,7 @@ types:
                                 - int
         description: "The old bson_serialization_type contains 'any'"
         cpp_type: "std::int32_t"
-    
+
     newBsonSerializationTypeAny:
         bson_serialization_type:
                                 - int
@@ -79,6 +79,24 @@ types:
         description: "The old and new bson_serialization_type contains 'any'"
         cpp_type: "std::int32_t"
 
+    bsonSerializationTypeAnySerializerNotEqual:
+        bson_serialization_type:
+                                - int
+                                - any
+        description: "The old and new bson_serialization_type contains 'any'. The 'serializer'
+                      field value here is different from the one defined in old."
+        cpp_type: "std::int64_t"
+        serializer: ::mongo::newSerializer
+
+    bsonSerializationTypeAnyDeserializerNotEqual:
+        bson_serialization_type:
+                                - int
+                                - any
+        description: "The old and new bson_serialization_type contains 'any' The 'deserializer'
+                      field value here is different from the one defined in old."
+        cpp_type: "std::int64_t"
+        deserializer: ::mongo::newDeserializer
+
     intStringBoolToIntString:
         bson_serialization_type:
                                 - int
@@ -97,7 +115,7 @@ types:
 
 enums:
     NewReplyFieldEnumNotSubset:
-        description: "The new reply type is an enum that is not a subset of the old reply type's 
+        description: "The new reply type is an enum that is not a subset of the old reply type's
                       enum values"
         type: string
         values:
@@ -123,7 +141,7 @@ structs:
             unstableNewField:
                 type: string
                 unstable: true
-    
+
     OptionalNewFieldReply:
         description: "This reply contains a field that is required in the old command but is
                       optional in the new command."
@@ -131,11 +149,11 @@ structs:
             optionalNewField:
                 type: string
                 optional: true
-    
+
     MissingNewFieldReply:
         description: "This reply contains a field that exists in the old command but is
                       missing in the new command."
-    
+
     RequiredNewField:
         description: "This struct contains a field that is optional in the old command but is
                       required in the new command."
@@ -223,12 +241,28 @@ structs:
                     variant: [array<oldBsonSerializationTypeAny>, array<newBsonSerializationTypeAny>]
 
     CppTypeNotEqualReply:
-        description: "This reply contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' and the cpp_types are not equal"
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the cpp_types are not equal"
         fields:
             cppTypeNotEqualReplyField:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    SerializerNotEqualReply:
+        description: "This reply contains a field whose old and new type
+                        have a bson_serialization_type that contains 'any'
+                        and the serializers are not equal"
+        fields:
+            serializerNotEqualReplyField:
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    DeserializerNotEqualReply:
+        description: "This reply contains a field whose old and new type have
+                        a bson_serialization_type that contains 'any' and the
+                        deserializers are not equal"
+        fields:
+            deserializerNotEqualReplyField:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     NewlyAddedBsonSerializationTypeAnyReply:
         description: "This reply contains a newly added field whose type has a bson_serialization_type
                         that contains 'any' that is not explicitly allowed"
@@ -270,13 +304,29 @@ structs:
                     variant: [oldBsonSerializationTypeAny, newBsonSerializationTypeAny]
 
     CppTypeNotEqualUnstableReply:
-        description: "This reply contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' and the cpp_types are not equal and where the old field
-                      is unstable"
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the cpp_types are
+                        not equal and where the old field is unstable"
         fields:
             cppTypeNotEqualReplyUnstableField:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    SerializerNotEqualUnstableReply:
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the serializers are
+                        not equal and where the old field is unstable"
+        fields:
+            serializerNotEqualReplyUnstableField:
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    DeserializerNotEqualUnstableReply:
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the deserializers are
+                        not equal and where the old field is unstable"
+        fields:
+            deserializerNotEqualReplyUnstableField:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     NewlyAddedBsonSerializationTypeAnyStruct:
         description: "This struct contains a newly added field whose type has a bson_serialization_type
                         that contains 'any' that is not explicitly allowed"
@@ -323,41 +373,59 @@ structs:
                     variant: [oldBsonSerializationTypeAny, newBsonSerializationTypeAny]
 
     CppTypeNotEqualUnstableStruct:
-        description: "This struct contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' and the cpp_types are not equal and where the old field
-                      is unstable"
+        description: "This struct contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the cpp_types are
+                        not equal and where the old field is unstable"
         fields:
             cppTypeNotEqualStructUnstableField:
                 optional: true
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    SerializerNotEqualUnstableStruct:
+        description: "This struct contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the serializers are
+                        not equal and where the old field is unstable"
+        fields:
+            serializerNotEqualStructUnstableField:
+                optional: true
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    DeserializerNotEqualUnstableStruct:
+        description: "This struct contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the deserializers are
+                        not equal and where the old field is unstable"
+        fields:
+            deserializerNotEqualStructUnstableField:
+                optional: true
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     StructFieldTypeRecursiveReplyOne:
-        description: "This reply contains a field whose new type is a struct that is not 
+        description: "This reply contains a field whose new type is a struct that is not
                       compatible with the old field type"
         fields:
             structReplyField:
                 type: UnstableNewFieldReply
-    
+
     StructFieldTypeRecursiveReplyTwo:
-        description: "This reply contains a field whose new type is a struct that is not 
+        description: "This reply contains a field whose new type is a struct that is not
                       compatible with the old field type"
         fields:
             structReplyField:
                 type: StructType
 
     StructType:
-        description: "This struct contains a field whose new type is incompatible with the 
+        description: "This struct contains a field whose new type is incompatible with the
                       old field type"
         fields:
             fieldOne:
                 type: BsonNotSubsetReply
-    
+
     NewVariantTypeReply:
         description: "This reply contains a new field that has a variant type while the old field
                       is not a variant type"
         fields:
             newVariantTypeReplyField:
-                type: 
+                type:
                     variant: [int, string]
 
     NewVariantNotSubsetReply:
@@ -365,7 +433,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSubsetReplyField:
-                type: 
+                type:
                     variant: [int, bool, string]
 
     NewVariantNotSubsetReplyWithArray:
@@ -373,7 +441,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSubsetReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<bool>, array<string>]
 
     NewVariantNotSubsetReplyTwo:
@@ -381,7 +449,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSubsetReplyFieldTwo:
-                type: 
+                type:
                     variant: [int, bool, string, double]
 
     NewVariantNotSubsetReplyTwoWithArray:
@@ -389,15 +457,15 @@ structs:
                       of the old variant types"
         fields:
             variantNotSubsetReplyFieldTwo:
-                type: 
+                type:
                     variant: [array<int>, array<bool>, array<string>, array<double>]
-   
+
     VariantRecursiveReply:
         description: "This reply contains a field that has a new variant type that is not
                       compatible with the old variant type"
         fields:
             variantRecursiveReplyField:
-                type: 
+                type:
                     variant: [int, intStringToIntStringBool]
 
     VariantRecursiveReplyWithArray:
@@ -405,15 +473,15 @@ structs:
                       compatible with the old variant type"
         fields:
             variantRecursiveReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<intStringToIntStringBool>]
-    
+
     NewVariantStructNotSubsetReply:
         description: "This reply contains a field whose new variant types are not a subset
                       of the old variant types"
         fields:
             variantStructNotSubsetReplyField:
-                type: 
+                type:
                     variant: [int, string, StructType]
 
     NewVariantStructNotSubsetReplyWithArray:
@@ -421,23 +489,23 @@ structs:
                       of the old variant types"
         fields:
             variantStructNotSubsetReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<string>, array<StructType>]
-    
+
     VariantStructRecursiveReply:
         description: "This reply contains a field that has a new variant struct type that is not
                       compatible with the old variant struct type"
         fields:
             variantStructRecursiveReplyField:
-                type: 
+                type:
                     variant: [int, StructFieldTypeRecursiveReplyTwo]
-    
+
     VariantStructRecursiveReplyWithArray:
         description: "This reply contains a field that has a new variant struct type that is not
                       compatible with the old variant struct type"
         fields:
             variantStructRecursiveReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<StructFieldTypeRecursiveReplyTwo>]
 
     CommandParamStructRecursiveOne:
@@ -507,7 +575,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetField:
-                type: 
+                type:
                     variant: [int, bool]
 
     VariantNotSupersetStructWithArray:
@@ -515,7 +583,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetField:
-                type: 
+                type:
                     variant: [array<int>, array<bool>]
 
     VariantNotSupersetStructTwo:
@@ -523,7 +591,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetFieldTwo:
-                type: 
+                type:
                     variant: [int, bool]
 
     VariantNotSupersetStructTwoWithArray:
@@ -531,7 +599,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetFieldTwo:
-                type: 
+                type:
                     variant: [array<int>, array<bool>]
 
     NewTypeNotVariantStruct:
@@ -546,7 +614,7 @@ structs:
                       compatible with the old variant types"
         fields:
             variantRecursiveField:
-                type: 
+                type:
                     variant: [int, intStringBoolToIntString]
 
     VariantRecursiveStructWithArray:
@@ -554,7 +622,7 @@ structs:
                       compatible with the old variant types"
         fields:
             variantRecursiveField:
-                type: 
+                type:
                     variant: [array<int>, array<intStringBoolToIntString>]
 
     VariantStructNotSupersetStruct:
@@ -562,7 +630,7 @@ structs:
                       while the new one does not"
         fields:
             variantStructNotSupersetField:
-                type: 
+                type:
                     variant: [int, string]
 
     VariantStructNotSupersetStructWithArray:
@@ -570,7 +638,7 @@ structs:
                       while the new one does not"
         fields:
             variantStructNotSupersetField:
-                type: 
+                type:
                     variant: [array<int>, array<string>]
 
     VariantStructRecursiveStruct:
@@ -637,7 +705,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-    
+
     removedCommandParameter:
         description: "parameter will be removed from command in compatibility_test_fail/new
                       which results in an error"
@@ -784,6 +852,34 @@ commands:
             cppTypeNotEqualParam:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    commandParameterSerializerNotEqual:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the serializers
+                      are not equal"
+        command_name: commandParameterSerializerNotEqual
+        namespace: ignored
+        cpp_name: commandParameterSerializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            serializerNotEqualParam:
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    commandParameterDeserializerNotEqual:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the deserializers
+                      are not equal"
+        command_name: commandParameterDeserializerNotEqual
+        namespace: ignored
+        cpp_name: commandParameterDeserializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            deserializerNotEqualParam:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     oldCommandParamTypeBsonAnyUnstable:
         description: "old command fails because it has a parameter type that has a
                       bson_serialization_type that contains 'any' and the old param is unstable"
@@ -842,6 +938,36 @@ commands:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
                 optional: true
 
+    commandParameterSerializerNotEqualUnstable:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the serializers
+                      are not equal"
+        command_name: commandParameterSerializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: commandParameterSerializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            serializerNotEqualParam:
+                type: bsonSerializationTypeAnySerializerNotEqual
+                optional: true
+
+    commandParameterDeserializerNotEqualUnstable:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the deserializers
+                      are not equal"
+        command_name: commandParameterDeserializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: commandParameterDeserializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            deserializerNotEqualParam:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+                optional: true
+
     parameterFieldTypeBsonAnyWithVariantUnstable:
         description: "command fails when its paramter field variant types have bson_serialization_type
                       'any' that is not compatible with each other"
@@ -1040,7 +1166,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: UnstableNewFieldReply
-    
+
     newReplyFieldOptional:
         description: "new command fails because it contains an optional reply field that is
                       required in the corresponding old command"
@@ -1211,8 +1337,8 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-        fields: 
-            variantAnyField: 
+        fields:
+            variantAnyField:
                 type: BsonSerializationTypeWithVariantAnyStruct
 
     parameterFieldTypeBsonAnyWithVariantWithArray:
@@ -1224,8 +1350,8 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-        fields: 
-            variantAnyField: 
+        fields:
+            variantAnyField:
                 type: BsonSerializationTypeWithVariantAnyStructWithArray
 
     commandTypeBsonAnyWithVariant:
@@ -1260,6 +1386,26 @@ commands:
         api_version: "1"
         reply_type: CppTypeNotEqualReply
 
+    replyFieldSerializerNotEqual:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the serializers are not equal"
+        command_name: replyFieldSerializerNotEqual
+        namespace: ignored
+        cpp_name: replyFieldSerializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: SerializerNotEqualReply
+
+    replyFieldDeserializerNotEqual:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the deserializers are not equal"
+        command_name: replyFieldDeserializerNotEqual
+        namespace: ignored
+        cpp_name: replyFieldDeserializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: DeserializerNotEqualReply
+
     newReplyFieldTypeStructRecursiveOne:
         description: "new command fails because its reply field type is a struct that is
                       incompatible with the old reply field type struct"
@@ -1385,6 +1531,28 @@ commands:
         api_version: "1"
         reply_type: OkReply
 
+    commandSerializerNotEqual:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the serializers are not equal"
+        command_name: commandSerializerNotEqual
+        namespace: type
+        type: bsonSerializationTypeAnySerializerNotEqual
+        cpp_name: commandSerializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
+    commandDeserializerNotEqual:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the deserializers are not equal"
+        command_name: commandDeserializerNotEqual
+        namespace: type
+        type: bsonSerializationTypeAnyDeserializerNotEqual
+        cpp_name: commandDeserializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
     oldTypeBsonAnyUnstable:
         description: "old command fails because its type has a bson_serialization_type
                       that contains 'any' and the old type field is unstable"
@@ -1420,7 +1588,8 @@ commands:
 
     commandCppTypeNotEqualUnstable:
         description: "command fails because its type has a bson_serialization_type
-                      that contains 'any' and the cpp_types are not equal and the old type field is unstable"
+                      that contains 'any' and the cpp_types are not equal and the
+                      old type field is unstable"
         command_name: commandCppTypeNotEqualUnstable
         namespace: type
         type: CppTypeNotEqualUnstableStruct
@@ -1429,6 +1598,30 @@ commands:
         api_version: "1"
         reply_type: OkReply
 
+    commandSerializerNotEqualUnstable:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the serializers are not equal and the
+                      old type field is unstable"
+        command_name: commandSerializerNotEqualUnstable
+        namespace: type
+        type: SerializerNotEqualUnstableStruct
+        cpp_name: commandSerializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
+    commandDeserializerNotEqualUnstable:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the deserializers are not equal and the
+                      old type field is unstable"
+        command_name: commandDeserializerNotEqualUnstable
+        namespace: type
+        type: DeserializerNotEqualUnstableStruct
+        cpp_name: commandDeserializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
     commandTypeBsonAnyWithVariantUnstable:
         description: "command fails when its variant types have bson_serialization_type
                       'any' that is not compatible with each other and the old type field is unstable"
@@ -1581,7 +1774,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: NewVariantTypeReply
-    
+
     newReplyFieldVariantNotSubset:
         description: "new command fails because its reply field type is a variant type that is not
                       a subset of the old reply field variant types"
@@ -1661,7 +1854,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: NewVariantStructNotSubsetReplyWithArray
-    
+
     replyFieldVariantStructRecursive:
         description: "new command fails because its reply field type has a variant
                       struct type that is not compatible with the old reply field variant
@@ -1672,7 +1865,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: VariantStructRecursiveReply
-    
+
     replyFieldVariantStructRecursiveWithArray:
         description: "new command fails because its reply field type has a variant
                       struct type that is not compatible with the old reply field variant
@@ -1695,7 +1888,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParam:
-                type: 
+                type:
                     variant: [int, bool]
 
     newParamVariantNotSupersetWithArray:
@@ -1709,7 +1902,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParam:
-                type: 
+                type:
                     variant: [array<int>, array<bool>]
 
     newParamVariantNotSupersetTwo:
@@ -1723,7 +1916,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParamTwo:
-                type: 
+                type:
                     variant: [int, string]
 
     newParamVariantNotSupersetTwoWithArray:
@@ -1737,7 +1930,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParamTwo:
-                type: 
+                type:
                     variant: [array<int>, array<string>]
 
     newParamTypeNotVariant:
@@ -1764,7 +1957,7 @@ commands:
         reply_type: OkReply
         fields:
             variantRecursiveParam:
-                type: 
+                type:
                     variant: [int, intStringBoolToIntString]
 
     newParamVariantRecursiveWithArray:
@@ -1778,7 +1971,7 @@ commands:
         reply_type: OkReply
         fields:
             variantRecursiveParam:
-                type: 
+                type:
                     variant: [array<int>, array<intStringBoolToIntString>]
 
     newParamVariantStructNotSuperset:
@@ -1792,7 +1985,7 @@ commands:
         reply_type: OkReply
         fields:
             variantStructNotSupersetParam:
-                type: 
+                type:
                     variant: [int, string]
 
     newParamVariantStructNotSupersetWithArray:
@@ -1806,7 +1999,7 @@ commands:
         reply_type: OkReply
         fields:
             variantStructNotSupersetParam:
-                type: 
+                type:
                     variant: [array<int>, array<string>]
 
     newParamVariantStructRecursive:
@@ -2120,7 +2313,7 @@ commands:
             none: true
 
     complexChecksNotSubset:
-        description: "new command fails because the complex checks are not a subset of the 
+        description: "new command fails because the complex checks are not a subset of the
                       old complex checks"
         command_name: complexChecksNotSubset
         namespace: ignored
@@ -2134,7 +2327,7 @@ commands:
                 - check: checkOne
 
     complexChecksNotSubsetTwo:
-        description: "new command fails because the complex checks are not a subset of the 
+        description: "new command fails because the complex checks are not a subset of the
                       old complex checks"
         command_name: complexChecksNotSubsetTwo
         namespace: ignored
@@ -2289,7 +2482,8 @@ commands:
 
     replyFieldCppTypeNotEqualUnstable:
         description: "command fails because its reply field type has a bson_serialization_type
-                      that contains 'any', and the cpp_types are not equal and the old reply field is unstable"
+                      that contains 'any', and the cpp_types are not equal and
+                      the old reply field is unstable"
         command_name: replyFieldCppTypeNotEqualUnstable
         namespace: ignored
         cpp_name: replyFieldCppTypeNotEqualUnstable
@@ -2297,6 +2491,28 @@ commands:
         api_version: "1"
         reply_type: CppTypeNotEqualUnstableReply
 
+    replyFieldSerializerNotEqualUnstable:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the serializers are not equal and
+                      the old reply field is unstable"
+        command_name: replyFieldSerializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: replyFieldSerializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: SerializerNotEqualUnstableReply
+
+    replyFieldDeserializerNotEqualUnstable:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the deserializers are not equal and
+                      the old reply field is unstable"
+        command_name: replyFieldDeserializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: replyFieldDeserializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: DeserializerNotEqualUnstableReply
+
     newlyAddedReplyFieldTypeBsonAnyNotAllowed:
         description: "command fails because it has a newly added reply field type has a bson_serialization_type
                       that contains 'any' that is not explicitly allowed"
diff --git a/buildscripts/idl/tests/compatibility_test_fail/old/compatibility_test_fail_old.idl b/buildscripts/idl/tests/compatibility_test_fail/old/compatibility_test_fail_old.idl
index 4d29cdfe451..dabaeccbddc 100644
--- a/buildscripts/idl/tests/compatibility_test_fail/old/compatibility_test_fail_old.idl
+++ b/buildscripts/idl/tests/compatibility_test_fail/old/compatibility_test_fail_old.idl
@@ -61,7 +61,7 @@ types:
                                 - int
         description: "The new bson_serialization_type contains 'any'"
         cpp_type: "std::int32_t"
-    
+
     bsonSerializationTypeAny:
         bson_serialization_type:
                                 - int
@@ -76,6 +76,24 @@ types:
         description: "The old and new bson_serialization_type contains 'any'"
         cpp_type: "std::int64_t"
 
+    bsonSerializationTypeAnySerializerNotEqual:
+        bson_serialization_type:
+                                - int
+                                - any
+        description: "The old and new bson_serialization_type contains 'any'. The 'serializer'
+                      field value here is different from the one defined in new."
+        cpp_type: "std::int64_t"
+        serializer: ::mongo::oldSerializer
+
+    bsonSerializationTypeAnyDeserializerNotEqual:
+        bson_serialization_type:
+                                - int
+                                - any
+        description: "The old and new bson_serialization_type contains 'any'. The 'deserializer'
+                      field value here is different from the one defined in new."
+        cpp_type: "std::int64_t"
+        deserializer: ::mongo::oldDeserializer
+
     intStringBoolToIntString:
         bson_serialization_type:
                                 - int
@@ -96,13 +114,13 @@ types:
 
 enums:
     NewReplyFieldEnumNotSubset:
-        description: "The new reply type is an enum that is not a subset of the old reply type's 
+        description: "The new reply type is an enum that is not a subset of the old reply type's
                       enum values"
         type: string
         values:
             valueOne: "one"
             valueTwo: "two"
-    
+
     EnumNotSuperset:
         description: "The new enum is not a superset of the old enum values"
         type: string
@@ -128,7 +146,7 @@ structs:
         fields:
             optionalNewField:
                 type: string
-    
+
     RequiredNewField:
         description: "This struct contains a field that is optional in the old command but is
                       required in the new command."
@@ -136,7 +154,7 @@ structs:
             requiredNewField:
                 type: string
                 optional: true
-    
+
     MissingNewFieldReply:
         description: "This reply contains a field that exists in the old command but is
                       missing in the new command."
@@ -204,15 +222,15 @@ structs:
                 type: newBsonSerializationTypeAny
 
     BsonSerializationTypeAnyReply:
-        description: "This reply contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' that is not explicitly allowed"
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' that is not explicitly allowed"
         fields:
             bsonSerializationTypeAnyReplyField:
                 type: bsonSerializationTypeAny
 
     NewlyAddedBsonSerializationTypeAnyReply:
-        description: "This reply contains a newly added field whose type has a bson_serialization_type
-                        that contains 'any' that is not explicitly allowed"
+        description: "This reply contains a newly added field whose type has a
+                        bson_serialization_type that contains 'any' that is not explicitly allowed"
 
     OldBsonSerializationTypeAnyUnstableReply:
         description: "This reply contains a field that is unstable in the old version
@@ -242,8 +260,9 @@ structs:
                 unstable: true
 
     BsonSerializationTypeWithVariantAnyUnstableReply:
-        description: "This reply contains a field whose old and new variant types have a bson_serialization_type
-                        that contains 'any' that is not compatible and where the old field is unstable"
+        description: "This reply contains a field whose old and new variant types have a
+                        bson_serialization_type that contains 'any' that is not compatible
+                        and where the old field is unstable"
         fields:
             bsonSerializationTypeWithVariantAnyUnstableReplyField:
                 type:
@@ -251,17 +270,35 @@ structs:
                 unstable: true
 
     CppTypeNotEqualUnstableReply:
-        description: "This reply contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' and the cpp_types are not equal and where the old field
-                      is unstable"
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the cpp_types are
+                        not equal and where the old field is unstable"
         fields:
             cppTypeNotEqualReplyUnstableField:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
                 unstable: true
 
+    SerializerNotEqualUnstableReply:
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the serializers are
+                        not equal and where the old field is unstable"
+        fields:
+            serializerNotEqualReplyUnstableField:
+                type: bsonSerializationTypeAnySerializerNotEqual
+                unstable: true
+
+    DeserializerNotEqualUnstableReply:
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the deserializers are
+                        not equal and where the old field is unstable"
+        fields:
+            deserializerNotEqualReplyUnstableField:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+                unstable: true
+
     NewlyAddedBsonSerializationTypeAnyStruct:
-        description: "This struct contains a newly added field whose type has a bson_serialization_type
-                        that contains 'any' that is not explicitly allowed"
+        description: "This struct contains a newly added field whose type has a
+                        bson_serialization_type that contains 'any' that is not explicitly allowed"
         fields:
             newlyAddedBsonSerializationTypeAnyStructField:
                 unstable: true
@@ -305,17 +342,35 @@ structs:
                     variant: [oldBsonSerializationTypeAny, newBsonSerializationTypeAny]
 
     CppTypeNotEqualUnstableStruct:
-        description: "This struct contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' and the cpp_types are not equal and where the old field
-                      is unstable"
+        description: "This struct contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the cpp_types are
+                        not equal and where the old field is unstable"
         fields:
             cppTypeNotEqualStructUnstableField:
                 unstable: true
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    SerializerNotEqualUnstableStruct:
+        description: "This struct contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the serializers are
+                        not equal and where the old field is unstable"
+        fields:
+            serializerNotEqualStructUnstableField:
+                unstable: true
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    DeserializerNotEqualUnstableStruct:
+        description: "This struct contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the deserializers are
+                        not equal and where the old field is unstable"
+        fields:
+            deserializerNotEqualStructUnstableField:
+                unstable: true
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     BsonSerializationTypeWithVariantAnyStruct:
-        description: "This struct contains a field whose old and new variant types have a bson_serialization_type
-                        that contains 'any' that is not compatible"
+        description: "This struct contains a field whose old and new variant types have a
+                        bson_serialization_type that contains 'any' that is not compatible"
         fields:
             bsonSerializationTypeAnyStructField:
                 type:
@@ -331,28 +386,44 @@ structs:
                               array<newBsonSerializationTypeAny>]
 
     CppTypeNotEqualReply:
-        description: "This reply contains a field whose old and new type have a bson_serialization_type
-                        that contains 'any' and the cpp_types are not equal"
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and the cpp_types are not equal"
         fields:
             cppTypeNotEqualReplyField:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    SerializerNotEqualReply:
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and
+                        the serializers are not equal"
+        fields:
+            serializerNotEqualReplyField:
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    DeserializerNotEqualReply:
+        description: "This reply contains a field whose old and new type have a
+                        bson_serialization_type that contains 'any' and
+                        the deserializers are not equal"
+        fields:
+            deserializerNotEqualReplyField:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     StructFieldTypeRecursiveReplyOne:
-        description: "This reply contains a field whose new type is a struct that is not 
+        description: "This reply contains a field whose new type is a struct that is not
                       compatible with the old field type"
         fields:
             structReplyField:
                 type: UnstableNewFieldReply
-    
+
     StructFieldTypeRecursiveReplyTwo:
-        description: "This reply contains a field whose new type is a struct that is not 
+        description: "This reply contains a field whose new type is a struct that is not
                       compatible with the old field type"
         fields:
             structReplyField:
                 type: StructType
 
     StructType:
-        description: "This struct contains a field whose new type is incompatible with the 
+        description: "This struct contains a field whose new type is incompatible with the
                       old field type"
         fields:
             fieldOne:
@@ -370,23 +441,23 @@ structs:
                       of the old variant types"
         fields:
             variantNotSubsetReplyField:
-                type: 
+                type:
                     variant: [int, string]
-    
+
     NewVariantNotSubsetReplyWithArray:
         description: "This reply contains a field whose new variant types are not a subset
                       of the old variant types"
         fields:
             variantNotSubsetReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<string>]
-    
+
     NewVariantNotSubsetReplyTwo:
         description: "This reply contains a field whose new variant types are not a subset
                       of the old variant types"
         fields:
             variantNotSubsetReplyFieldTwo:
-                type: 
+                type:
                     variant: [int, string]
 
     NewVariantNotSubsetReplyTwoWithArray:
@@ -394,7 +465,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSubsetReplyFieldTwo:
-                type: 
+                type:
                     variant: [array<int>, array<string>]
 
     VariantRecursiveReply:
@@ -402,15 +473,15 @@ structs:
                       compatible with the old variant type"
         fields:
             variantRecursiveReplyField:
-                type: 
+                type:
                     variant: [int, intStringToIntStringBool]
-    
+
     VariantRecursiveReplyWithArray:
         description: "This reply contains a field that has a new variant type that is not
                       compatible with the old variant type"
         fields:
             variantRecursiveReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<intStringToIntStringBool>]
 
     NewVariantStructNotSubsetReply:
@@ -418,7 +489,7 @@ structs:
                       of the old variant types"
         fields:
             variantStructNotSubsetReplyField:
-                type: 
+                type:
                     variant: [int, string]
 
     NewVariantStructNotSubsetReplyWithArray:
@@ -426,7 +497,7 @@ structs:
                       of the old variant types"
         fields:
             variantStructNotSubsetReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<string>]
 
     VariantStructRecursiveReply:
@@ -434,7 +505,7 @@ structs:
                       compatible with the old variant struct type"
         fields:
             variantStructRecursiveReplyField:
-                type: 
+                type:
                     variant: [int, StructFieldTypeRecursiveReplyTwo]
 
     VariantStructRecursiveReplyWithArray:
@@ -442,7 +513,7 @@ structs:
                       compatible with the old variant struct type"
         fields:
             variantStructRecursiveReplyField:
-                type: 
+                type:
                     variant: [array<int>, array<StructFieldTypeRecursiveReplyTwo>]
 
     CommandParamStructRecursiveOne:
@@ -501,7 +572,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetField:
-                type: 
+                type:
                     variant: [int, bool, string]
 
     VariantNotSupersetStructWithArray:
@@ -509,7 +580,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetField:
-                type: 
+                type:
                     variant: [array<int>, array<bool>, array<string>]
 
     VariantNotSupersetStructTwo:
@@ -517,7 +588,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetFieldTwo:
-                type: 
+                type:
                     variant: [int, bool, string, double]
 
     VariantNotSupersetStructTwoWithArray:
@@ -525,7 +596,7 @@ structs:
                       of the old variant types"
         fields:
             variantNotSupersetFieldTwo:
-                type: 
+                type:
                     variant: [array<int>, array<bool>, array<string>, array<double>]
 
     NewTypeNotVariantStruct:
@@ -533,7 +604,7 @@ structs:
                       old one is"
         fields:
             variantField:
-                type: 
+                type:
                     variant: [int, bool]
 
     VariantRecursiveStruct:
@@ -541,7 +612,7 @@ structs:
                       compatible with the old variant types"
         fields:
             variantRecursiveField:
-                type: 
+                type:
                     variant: [int, intStringBoolToIntString]
 
     VariantRecursiveStructWithArray:
@@ -549,7 +620,7 @@ structs:
                       compatible with the old variant types"
         fields:
             variantRecursiveField:
-                type: 
+                type:
                     variant: [array<int>, array<intStringBoolToIntString>]
 
     VariantStructNotSupersetStruct:
@@ -557,7 +628,7 @@ structs:
                       while the new one does not"
         fields:
             variantStructNotSupersetField:
-                type: 
+                type:
                     variant: [int, string, StructCommandParameterType]
 
     VariantStructNotSupersetStructWithArray:
@@ -565,7 +636,7 @@ structs:
                       while the new one does not"
         fields:
             variantStructNotSupersetField:
-                type: 
+                type:
                     variant: [array<int>, array<string>, array<StructCommandParameterType>]
 
     VariantStructRecursiveStruct:
@@ -611,7 +682,7 @@ commands:
         reply_type: OkReply
 
     removedCommand:
-        description: "command will be removed from compatibility_test_fail/new which results 
+        description: "command will be removed from compatibility_test_fail/new which results
                       in an error"
         command_name: removedCommand
         namespace: ignored
@@ -775,6 +846,34 @@ commands:
             cppTypeNotEqualParam:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
 
+    commandParameterSerializerNotEqual:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the serializers
+                      are not equal"
+        command_name: commandParameterSerializerNotEqual
+        namespace: ignored
+        cpp_name: commandParameterSerializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            serializerNotEqualParam:
+                type: bsonSerializationTypeAnySerializerNotEqual
+
+    commandParameterDeserializerNotEqual:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the deserializers
+                      are not equal"
+        command_name: commandParameterDeserializerNotEqual
+        namespace: ignored
+        cpp_name: commandParameterDeserializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            deserializerNotEqualParam:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+
     oldCommandParamTypeBsonAnyUnstable:
         description: "old command fails because it has a parameter type that has a
                       bson_serialization_type that contains 'any' and the old param is unstable"
@@ -833,6 +932,36 @@ commands:
                 type: bsonSerializationTypeAnyCppTypeNotEqual
                 unstable: true
 
+    commandParameterSerializerNotEqualUnstable:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the serializers
+                      are not equal"
+        command_name: commandParameterSerializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: commandParameterSerializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            serializerNotEqualParam:
+                type: bsonSerializationTypeAnySerializerNotEqual
+                unstable: true
+
+    commandParameterDeserializerNotEqualUnstable:
+        description: "command fails because it has a parameter type that has a
+                      bson_serialization_type that contains 'any' and where the deserializers
+                      are not equal"
+        command_name: commandParameterDeserializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: commandParameterDeserializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+        fields:
+            deserializerNotEqualParam:
+                type: bsonSerializationTypeAnyDeserializerNotEqual
+                unstable: true
+
     parameterFieldTypeBsonAnyWithVariantUnstable:
         description: "command fails when its paramter field variant types have bson_serialization_type
                       'any' that is not compatible with each other"
@@ -895,7 +1024,7 @@ commands:
         fields:
             newParamNotStruct:
                 type: StructCommandParameterType
-    
+
     newCommandParameterTypeEnumOrStructOne:
         description: "new command fails because its parameter type is an enum while the
                       parameter type in the old command is an non-enum or non-struct"
@@ -1025,7 +1154,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: UnstableNewFieldReply
-    
+
     newReplyFieldOptional:
         description: "new command fails because it contains an optional reply field that is
                       required in the corresponding old command"
@@ -1045,7 +1174,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: MissingNewFieldReply
-    
+
     importedReplyCommand:
         description: "reply is imported and should fail"
         command_name: importedReplyCommand
@@ -1196,8 +1325,8 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-        fields: 
-            variantAnyField: 
+        fields:
+            variantAnyField:
                 type: BsonSerializationTypeWithVariantAnyStruct
 
     parameterFieldTypeBsonAnyWithVariantWithArray:
@@ -1209,8 +1338,8 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-        fields: 
-            variantAnyField: 
+        fields:
+            variantAnyField:
                 type: BsonSerializationTypeWithVariantAnyStructWithArray
 
     commandTypeBsonAnyWithVariant:
@@ -1234,7 +1363,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-       
+
     replyFieldCppTypeNotEqual:
         description: "command fails because its reply field type has a bson_serialization_type
                       that contains 'any', and the cpp_types are not equal"
@@ -1245,6 +1374,26 @@ commands:
         api_version: "1"
         reply_type: CppTypeNotEqualReply
 
+    replyFieldSerializerNotEqual:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the serializers are not equal"
+        command_name: replyFieldSerializerNotEqual
+        namespace: ignored
+        cpp_name: replyFieldSerializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: SerializerNotEqualReply
+
+    replyFieldDeserializerNotEqual:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the deserializers are not equal"
+        command_name: replyFieldDeserializerNotEqual
+        namespace: ignored
+        cpp_name: replyFieldDeserializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: DeserializerNotEqualReply
+
     oldReplyFieldTypeBsonAnyUnstable:
         description: "old command fails when its reply field type has a bson_serialization_type
                       that contains 'any' and the old reply field is unstable"
@@ -1287,7 +1436,8 @@ commands:
 
     replyFieldCppTypeNotEqualUnstable:
         description: "command fails because its reply field type has a bson_serialization_type
-                      that contains 'any', and the cpp_types are not equal and the old reply field is unstable"
+                      that contains 'any', and the cpp_types are not equal and
+                      the old reply field is unstable"
         command_name: replyFieldCppTypeNotEqualUnstable
         namespace: ignored
         cpp_name: replyFieldCppTypeNotEqualUnstable
@@ -1295,9 +1445,31 @@ commands:
         api_version: "1"
         reply_type: CppTypeNotEqualUnstableReply
 
+    replyFieldSerializerNotEqualUnstable:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the serializers are not equal and
+                      the old reply field is unstable"
+        command_name: replyFieldSerializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: replyFieldSerializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: SerializerNotEqualUnstableReply
+
+    replyFieldDeserializerNotEqualUnstable:
+        description: "command fails because its reply field type has a bson_serialization_type
+                      that contains 'any', and the deserializers are not equal and
+                      the old reply field is unstable"
+        command_name: replyFieldDeserializerNotEqualUnstable
+        namespace: ignored
+        cpp_name: replyFieldDeserializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: DeserializerNotEqualUnstableReply
+
     newlyAddedReplyFieldTypeBsonAnyNotAllowed:
-        description: "command fails because it has a newly added reply field type has a bson_serialization_type
-                      that contains 'any' that is not explicitly allowed"
+        description: "command fails because it has a newly added reply field type has a
+                      bson_serialization_type that contains 'any' that is not explicitly allowed"
         command_name: newlyAddedReplyFieldTypeBsonAnyNotAllowed
         namespace: ignored
         cpp_name: newlyAddedReplyFieldTypeBsonAnyNotAllowed
@@ -1430,6 +1602,28 @@ commands:
         api_version: "1"
         reply_type: OkReply
 
+    commandSerializerNotEqual:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the serializers are not equal"
+        command_name: commandSerializerNotEqual
+        namespace: type
+        type: bsonSerializationTypeAnySerializerNotEqual
+        cpp_name: commandSerializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
+    commandDeserializerNotEqual:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the deserializers are not equal"
+        command_name: commandDeserializerNotEqual
+        namespace: type
+        type: bsonSerializationTypeAnyDeserializerNotEqual
+        cpp_name: commandDeserializerNotEqual
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
     oldTypeBsonAnyUnstable:
         description: "old command fails because its type has a bson_serialization_type
                       that contains 'any' and the old type field is unstable"
@@ -1465,7 +1659,8 @@ commands:
 
     commandCppTypeNotEqualUnstable:
         description: "command fails because its type has a bson_serialization_type
-                      that contains 'any' and the cpp_types are not equal and the old type field is unstable"
+                      that contains 'any' and the cpp_types are not equal and
+                      the old type field is unstable"
         command_name: commandCppTypeNotEqualUnstable
         namespace: type
         type: CppTypeNotEqualUnstableStruct
@@ -1474,9 +1669,34 @@ commands:
         api_version: "1"
         reply_type: OkReply
 
+    commandSerializerNotEqualUnstable:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the serializers are not equal and
+                      the old type field is unstable"
+        command_name: commandSerializerNotEqualUnstable
+        namespace: type
+        type: SerializerNotEqualUnstableStruct
+        cpp_name: commandSerializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
+    commandDeserializerNotEqualUnstable:
+        description: "command fails because its type has a bson_serialization_type
+                      that contains 'any' and the deserializers are not equal and
+                      the old type field is unstable"
+        command_name: commandDeserializerNotEqualUnstable
+        namespace: type
+        type: DeserializerNotEqualUnstableStruct
+        cpp_name: commandDeserializerNotEqualUnstable
+        strict: true
+        api_version: "1"
+        reply_type: OkReply
+
     commandTypeBsonAnyWithVariantUnstable:
         description: "command fails when its variant types have bson_serialization_type
-                      'any' that is not compatible with each other and the old type field is unstable"
+                      'any' that is not compatible with each other and
+                      the old type field is unstable"
         command_name: commandTypeBsonAnyWithVariantUnstable
         namespace: type
         type: BsonSerializationTypeWithVariantAnyUnstableStruct
@@ -1594,7 +1814,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: OkReply
-    
+
     newTypeFieldAddedRequired:
         description: "new command fails because it has an added type field that is required
                       when it should be optional"
@@ -1626,7 +1846,7 @@ commands:
         strict: true
         api_version: "1"
         reply_type: NewVariantTypeReply
-    
+
     newReplyFieldVariantNotSubset:
         description: "new command fails because its reply field type is a variant type that is not
                       a subset of the old reply field variant types"
@@ -1740,7 +1960,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParam:
-                type: 
+                type:
                     variant: [int, bool, string]
 
     newParamVariantNotSupersetWithArray:
@@ -1754,7 +1974,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParam:
-                type: 
+                type:
                     variant: [array<int>, array<bool>, array<string>]
 
     newParamVariantNotSupersetTwo:
@@ -1768,7 +1988,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParamTwo:
-                type: 
+                type:
                     variant: [int, bool, string, double]
 
     newParamVariantNotSupersetTwoWithArray:
@@ -1782,7 +2002,7 @@ commands:
         reply_type: OkReply
         fields:
             variantNotSupersetParamTwo:
-                type: 
+                type:
                     variant: [array<int>, array<bool>, array<string>, array<double>]
 
     newParamTypeNotVariant:
@@ -1796,7 +2016,7 @@ commands:
         reply_type: OkReply
         fields:
             variantParam:
-                type: 
+                type:
                     variant: [int, bool]
 
     newParamVariantRecursive:
@@ -1810,7 +2030,7 @@ commands:
         reply_type: OkReply
         fields:
             variantRecursiveParam:
-                type: 
+                type:
                     variant: [int, intStringBoolToIntString]
 
     newParamVariantRecursiveWithArray:
@@ -1824,7 +2044,7 @@ commands:
         reply_type: OkReply
         fields:
             variantRecursiveParam:
-                type: 
+                type:
                     variant: [array<int>, array<intStringBoolToIntString>]
 
     newParamVariantStructNotSuperset:
@@ -1838,7 +2058,7 @@ commands:
         reply_type: OkReply
         fields:
             variantStructNotSupersetParam:
-                type: 
+                type:
                     variant: [int, string, StructCommandParameterType]
 
     newParamVariantStructNotSupersetWithArray:
@@ -1852,7 +2072,7 @@ commands:
         reply_type: OkReply
         fields:
             variantStructNotSupersetParam:
-                type: 
+                type:
                     variant: [array<int>, array<string>, array<StructCommandParameterType>]
 
     newParamVariantStructRecursive:
@@ -2167,7 +2387,7 @@ commands:
                 - check: checkOne
 
     complexChecksNotSubset:
-        description: "new command fails because the complex checks are not a subset of the 
+        description: "new command fails because the complex checks are not a subset of the
                       old complex checks"
         command_name: complexChecksNotSubset
         namespace: ignored
@@ -2181,7 +2401,7 @@ commands:
                 - check: checkTwo
 
     complexChecksNotSubsetTwo:
-        description: "new command fails because the complex checks are not a subset of the 
+        description: "new command fails because the complex checks are not a subset of the
                       old complex checks"
         command_name: complexChecksNotSubsetTwo
         namespace: ignored
diff --git a/buildscripts/idl/tests/test_compatibility.py b/buildscripts/idl/tests/test_compatibility.py
index 89a4e6130c6..56cf3e68408 100644
--- a/buildscripts/idl/tests/test_compatibility.py
+++ b/buildscripts/idl/tests/test_compatibility.py
@@ -92,7 +92,7 @@ class TestIDLCompatibilityChecker(unittest.TestCase):
             path.join(dir_path, "compatibility_test_fail/new"), ["src"])
 
         self.assertTrue(error_collection.has_errors())
-        self.assertTrue(error_collection.count() == 164)
+        self.assertEqual(error_collection.count(), 170)
 
         invalid_api_version_new_error = error_collection.get_error_by_command_name(
             "invalidAPIVersionNew")
@@ -212,6 +212,21 @@ class TestIDLCompatibilityChecker(unittest.TestCase):
         self.assertRegex(
             str(command_parameter_cpp_type_not_equal_error), "commandParameterCppTypeNotEqual")
 
+        command_parameter_serializer_not_equal_error = error_collection.get_error_by_command_name(
+            "commandParameterSerializerNotEqual")
+        self.assertEqual(command_parameter_serializer_not_equal_error.error_id,
+                         idl_compatibility_errors.ERROR_ID_COMMAND_PARAMETER_SERIALIZER_NOT_EQUAL)
+        self.assertRegex(
+            str(command_parameter_serializer_not_equal_error), "commandParameterSerializerNotEqual")
+
+        command_parameter_deserializer_not_equal_error = error_collection.get_error_by_command_name(
+            "commandParameterDeserializerNotEqual")
+        self.assertTrue(command_parameter_deserializer_not_equal_error.error_id ==
+                        idl_compatibility_errors.ERROR_ID_COMMAND_PARAMETER_DESERIALIZER_NOT_EQUAL)
+        self.assertRegex(
+            str(command_parameter_deserializer_not_equal_error),
+            "commandParameterDeserializerNotEqual")
+
         old_command_parameter_type_bson_any_unstable_error = error_collection.get_error_by_command_name(
             "oldCommandParamTypeBsonAnyUnstable")
         self.assertTrue(
@@ -612,6 +627,20 @@ class TestIDLCompatibilityChecker(unittest.TestCase):
                         idl_compatibility_errors.ERROR_ID_REPLY_FIELD_CPP_TYPE_NOT_EQUAL)
         self.assertRegex(str(reply_field_cpp_type_not_equal_error), "replyFieldCppTypeNotEqual")
 
+        reply_field_serializer_not_equal_error = error_collection.get_error_by_command_name(
+            "replyFieldSerializerNotEqual")
+        self.assertTrue(reply_field_serializer_not_equal_error.error_id ==
+                        idl_compatibility_errors.ERROR_ID_REPLY_FIELD_SERIALIZER_NOT_EQUAL)
+        self.assertRegex(
+            str(reply_field_serializer_not_equal_error), "replyFieldSerializerNotEqual")
+
+        reply_field_deserializer_not_equal_error = error_collection.get_error_by_command_name(
+            "replyFieldDeserializerNotEqual")
+        self.assertTrue(reply_field_deserializer_not_equal_error.error_id ==
+                        idl_compatibility_errors.ERROR_ID_REPLY_FIELD_DESERIALIZER_NOT_EQUAL)
+        self.assertRegex(
+            str(reply_field_deserializer_not_equal_error), "replyFieldDeserializerNotEqual")
+
         new_reply_field_type_struct_one_error = error_collection.get_error_by_command_name(
             "newReplyFieldTypeStructRecursiveOne")
         self.assertTrue(new_reply_field_type_struct_one_error.error_id ==
@@ -687,6 +716,18 @@ class TestIDLCompatibilityChecker(unittest.TestCase):
                         idl_compatibility_errors.ERROR_ID_COMMAND_CPP_TYPE_NOT_EQUAL)
         self.assertRegex(str(command_cpp_type_not_equal_error), "commandCppTypeNotEqual")
 
+        command_serializer_not_equal_error = error_collection.get_error_by_command_name(
+            "commandSerializerNotEqual")
+        self.assertTrue(command_serializer_not_equal_error.error_id ==
+                        idl_compatibility_errors.ERROR_ID_COMMAND_SERIALIZER_NOT_EQUAL)
+        self.assertRegex(str(command_serializer_not_equal_error), "commandSerializerNotEqual")
+
+        command_deserializer_not_equal_error = error_collection.get_error_by_command_name(
+            "commandDeserializerNotEqual")
+        self.assertTrue(command_deserializer_not_equal_error.error_id ==
+                        idl_compatibility_errors.ERROR_ID_COMMAND_DESERIALIZER_NOT_EQUAL)
+        self.assertRegex(str(command_deserializer_not_equal_error), "commandDeserializerNotEqual")
+
         old_type_bson_any_unstable_error = error_collection.get_error_by_command_name(
             "oldTypeBsonAnyUnstable")
         self.assertTrue(old_type_bson_any_unstable_error.error_id == idl_compatibility_errors.
diff --git a/src/mongo/db/ops/write_ops.cpp b/src/mongo/db/ops/write_ops.cpp
index 8e00f19713a..f69ad8844bb 100644
--- a/src/mongo/db/ops/write_ops.cpp
+++ b/src/mongo/db/ops/write_ops.cpp
@@ -79,6 +79,10 @@ void checkOpCountForCommand(const T& op, size_t numOps) {
 
 namespace write_ops {
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 bool readMultiDeleteProperty(const BSONElement& limitElement) {
     // Using a double to avoid throwing away illegal fractional portion. Don't want to accept 0.5
     // here
@@ -90,6 +94,10 @@ bool readMultiDeleteProperty(const BSONElement& limitElement) {
     return limit == 0;
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void writeMultiDeleteProperty(bool isMulti, StringData fieldName, BSONObjBuilder* builder) {
     builder->append(fieldName, isMulti ? 0 : 1);
 }
@@ -328,6 +336,10 @@ write_ops::UpdateModification::UpdateModification(const BSONObj& update, Classic
 write_ops::UpdateModification::UpdateModification(std::vector<BSONObj> pipeline)
     : _update{PipelineUpdate{std::move(pipeline)}} {}
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 write_ops::UpdateModification write_ops::UpdateModification::parseFromBSON(BSONElement elem) {
     return UpdateModification(elem);
 }
@@ -363,6 +375,10 @@ write_ops::UpdateModification::Type write_ops::UpdateModification::type() const
         _update);
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void write_ops::UpdateModification::serializeToBSON(StringData fieldName,
                                                     BSONObjBuilder* bob) const {
 
diff --git a/src/mongo/db/ops/write_ops_parsers.h b/src/mongo/db/ops/write_ops_parsers.h
index 20b9f543bc7..900740b271b 100644
--- a/src/mongo/db/ops/write_ops_parsers.h
+++ b/src/mongo/db/ops/write_ops_parsers.h
@@ -51,11 +51,17 @@ constexpr int kRetryableAndTxnBatchWriteBSONSizeOverhead =
 /**
  * Parses the 'limit' property of a delete entry, which has inverted meaning from the 'multi'
  * property of an update.
+ *
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
  */
 bool readMultiDeleteProperty(const BSONElement& limitElement);
 
 /**
  * Writes the 'isMulti' value as a limit property.
+ *
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
  */
 void writeMultiDeleteProperty(bool isMulti, StringData fieldName, BSONObjBuilder* builder);
 
@@ -100,8 +106,16 @@ public:
 
     /**
      * These methods support IDL parsing of the "u" field from the update command and OP_UPDATE.
+     *
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
      */
     static UpdateModification parseFromBSON(BSONElement elem);
+
+    /**
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
+     */
     void serializeToBSON(StringData fieldName, BSONObjBuilder* bob) const;
 
     // When parsing from legacy OP_UPDATE messages, we receive the "u" field as an object. When an
diff --git a/src/mongo/db/pipeline/aggregation_request_helper.cpp b/src/mongo/db/pipeline/aggregation_request_helper.cpp
index 133e151dae6..5bfa4b7c2a3 100644
--- a/src/mongo/db/pipeline/aggregation_request_helper.cpp
+++ b/src/mongo/db/pipeline/aggregation_request_helper.cpp
@@ -241,6 +241,10 @@ PlanExecutorPipeline::ResumableScanType getResumableScanType(const AggregateComm
 
 // Custom serializers/deserializers for AggregateCommandRequest.
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 boost::optional<mongo::ExplainOptions::Verbosity> parseExplainModeFromBSON(
     const BSONElement& explainElem) {
     uassert(ErrorCodes::TypeMismatch,
@@ -254,6 +258,10 @@ boost::optional<mongo::ExplainOptions::Verbosity> parseExplainModeFromBSON(
     return boost::none;
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeExplainToBSON(const mongo::ExplainOptions::Verbosity& explain,
                             StringData fieldName,
                             BSONObjBuilder* builder) {
@@ -264,6 +272,10 @@ void serializeExplainToBSON(const mongo::ExplainOptions::Verbosity& explain,
     return;
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 mongo::SimpleCursorOptions parseAggregateCursorFromBSON(const BSONElement& cursorElem) {
     if (cursorElem.eoo()) {
         SimpleCursorOptions cursor;
@@ -284,6 +296,10 @@ mongo::SimpleCursorOptions parseAggregateCursorFromBSON(const BSONElement& curso
     return cursor;
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeAggregateCursorToBSON(const mongo::SimpleCursorOptions& cursor,
                                     StringData fieldName,
                                     BSONObjBuilder* builder) {
diff --git a/src/mongo/db/pipeline/aggregation_request_helper.h b/src/mongo/db/pipeline/aggregation_request_helper.h
index 631fd87a278..bb447712f7f 100644
--- a/src/mongo/db/pipeline/aggregation_request_helper.h
+++ b/src/mongo/db/pipeline/aggregation_request_helper.h
@@ -131,23 +131,40 @@ PlanExecutorPipeline::ResumableScanType getResumableScanType(const AggregateComm
 
 /**
  * Custom serializers/deserializers for AggregateCommandRequest.
+ *
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
  */
-
 boost::optional<mongo::ExplainOptions::Verbosity> parseExplainModeFromBSON(
     const BSONElement& explainElem);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeExplainToBSON(const mongo::ExplainOptions::Verbosity& explain,
                             StringData fieldName,
                             BSONObjBuilder* builder);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 mongo::SimpleCursorOptions parseAggregateCursorFromBSON(const BSONElement& cursorElem);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeAggregateCursorToBSON(const SimpleCursorOptions& cursor,
                                     StringData fieldName,
                                     BSONObjBuilder* builder);
 
 /**
  * Parse an aggregation pipeline definition from 'pipelineElem'.
+ *
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
  */
 static std::vector<BSONObj> parsePipelineFromBSON(const BSONElement& pipelineElem) {
     std::vector<BSONObj> pipeline;
diff --git a/src/mongo/db/pipeline/aggregation_request_test.cpp b/src/mongo/db/pipeline/aggregation_request_test.cpp
index 66bac44423c..947764892b7 100644
--- a/src/mongo/db/pipeline/aggregation_request_test.cpp
+++ b/src/mongo/db/pipeline/aggregation_request_test.cpp
@@ -554,6 +554,23 @@ TEST(AggregationRequestTest, ShouldRejectNoCursorNoExplain) {
         aggregation_request_helper::parseFromBSONForTests(nss, cursorRequest.done()).getStatus());
 }
 
+TEST(AggregationRequestTest, ShouldRejectNonObjectCursor) {
+    NamespaceString nss("a.collection");
+    const BSONObj validRequest = fromjson(
+        "{aggregate: 'collection',"
+        "pipeline: [{$match: {a: 'abc'}}],"
+        "cursor: {},"
+        "isMapReduceCommand: true,"
+        "$db: 'a'}");
+    const BSONObj nonObjCursorCommand = fromjson("{cursor: 1}");
+    aggregationRequestParseFailureHelper(
+        nss, validRequest, nonObjCursorCommand, ErrorCodes::TypeMismatch);
+
+    const BSONObj arrayCursorCommand = fromjson("{cursor: []}");
+    aggregationRequestParseFailureHelper(
+        nss, validRequest, arrayCursorCommand, ErrorCodes::TypeMismatch);
+}
+
 TEST(AggregationRequestTest, ShouldRejectExplainTrueWithSeparateExplainArg) {
     NamespaceString nss("a.collection");
     const BSONObj validRequest = fromjson(
diff --git a/src/mongo/db/query/hint_parser.cpp b/src/mongo/db/query/hint_parser.cpp
index d1372d86f55..1de75b84f82 100644
--- a/src/mongo/db/query/hint_parser.cpp
+++ b/src/mongo/db/query/hint_parser.cpp
@@ -33,6 +33,10 @@
 
 namespace mongo {
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 BSONObj parseHint(const BSONElement& element) {
     if (element.type() == BSONType::String) {
         return BSON("$hint" << element.valueStringData());
@@ -44,6 +48,10 @@ BSONObj parseHint(const BSONElement& element) {
     MONGO_UNREACHABLE;
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeHintToBSON(const BSONObj& hint, StringData fieldName, BSONObjBuilder* builder) {
     if (hint.isEmpty())
         return;
diff --git a/src/mongo/db/query/max_time_ms_parser.cpp b/src/mongo/db/query/max_time_ms_parser.cpp
index 7f2c84f07ad..054b2b76ead 100644
--- a/src/mongo/db/query/max_time_ms_parser.cpp
+++ b/src/mongo/db/query/max_time_ms_parser.cpp
@@ -62,6 +62,10 @@ StatusWith<int> parseMaxTimeMS(BSONElement maxTimeMSElt) {
     return StatusWith<int>(static_cast<int>(maxTimeMSLongLong));
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 int32_t parseMaxTimeMSForIDL(BSONElement maxTimeMSElt) {
     return static_cast<int32_t>(uassertStatusOK(parseMaxTimeMS(maxTimeMSElt)));
 }
diff --git a/src/mongo/db/query/max_time_ms_parser.h b/src/mongo/db/query/max_time_ms_parser.h
index 1e5ec985c77..d111b480599 100644
--- a/src/mongo/db/query/max_time_ms_parser.h
+++ b/src/mongo/db/query/max_time_ms_parser.h
@@ -56,6 +56,10 @@ static constexpr auto kMaxTimeMSOpOnlyMaxPadding = 100LL;
  */
 StatusWith<int> parseMaxTimeMS(BSONElement maxTimeMSElt);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 int32_t parseMaxTimeMSForIDL(BSONElement maxTimeMSElt);
 
 }  // namespace mongo
diff --git a/src/mongo/db/query/query_request_test.cpp b/src/mongo/db/query/query_request_test.cpp
index e60a04ff79e..8518c0e4661 100644
--- a/src/mongo/db/query/query_request_test.cpp
+++ b/src/mongo/db/query/query_request_test.cpp
@@ -1194,36 +1194,74 @@ TEST(QueryRequestTest, ParseFromCommandForbidExtraOption) {
 
 TEST(QueryRequestTest, ParseMaxTimeMSStringValueFails) {
     BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << "foo");
-    ASSERT_NOT_OK(parseMaxTimeMS(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]));
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
+}
+
+TEST(QueryRequestTest, ParseMaxTimeMSBoolValueFails) {
+    BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << true);
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
+}
+
+TEST(QueryRequestTest, ParseMaxTimeMSNullValueFails) {
+    BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << BSONNULL);
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
+}
+
+TEST(QueryRequestTest, ParseMaxTimeMSUndefinedValueFails) {
+    BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << BSONUndefined);
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
+}
+
+TEST(QueryRequestTest, ParseMaxTimeMSEmptyObjectValueFails) {
+    const auto emptyObj = BSONObjBuilder().obj();
+    BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << emptyObj);
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
 }
 
 TEST(QueryRequestTest, ParseMaxTimeMSNonIntegralValueFails) {
     BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << 100.3);
-    ASSERT_NOT_OK(parseMaxTimeMS(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]));
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
 }
 
 TEST(QueryRequestTest, ParseMaxTimeMSOutOfRangeDoubleFails) {
     BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << 1e200);
-    ASSERT_NOT_OK(parseMaxTimeMS(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]));
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
 }
 
 TEST(QueryRequestTest, ParseMaxTimeMSNegativeValueFails) {
     BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << -400);
-    ASSERT_NOT_OK(parseMaxTimeMS(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]));
+    ASSERT_THROWS_CODE(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]),
+                       DBException,
+                       ErrorCodes::BadValue);
 }
 
 TEST(QueryRequestTest, ParseMaxTimeMSZeroSucceeds) {
     BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << 0);
-    auto maxTime = parseMaxTimeMS(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]);
-    ASSERT_OK(maxTime);
-    ASSERT_EQ(maxTime.getValue(), 0);
+    ASSERT_EQ(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]), 0);
+}
+
+TEST(QueryRequestTest, ParseMaxTimeMSEmptyElementSucceeds) {
+    const auto emptyElem = BSONElement();
+    ASSERT_EQ(parseMaxTimeMSForIDL(emptyElem), 0);
 }
 
 TEST(QueryRequestTest, ParseMaxTimeMSPositiveInRangeSucceeds) {
     BSONObj maxTimeObj = BSON(query_request_helper::cmdOptionMaxTimeMS << 300);
-    auto maxTime = parseMaxTimeMS(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]);
-    ASSERT_OK(maxTime);
-    ASSERT_EQ(maxTime.getValue(), 300);
+    ASSERT_EQ(parseMaxTimeMSForIDL(maxTimeObj[query_request_helper::cmdOptionMaxTimeMS]), 300);
 }
 
 TEST(QueryRequestTest, ConvertToAggregationSucceeds) {
diff --git a/src/mongo/idl/basic_types.h b/src/mongo/idl/basic_types.h
index c02366d3c5f..62e191a9bf5 100644
--- a/src/mongo/idl/basic_types.h
+++ b/src/mongo/idl/basic_types.h
@@ -47,6 +47,10 @@ namespace mongo {
  */
 class OptionalBool {
 public:
+    /**
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
+     */
     static OptionalBool parseFromBSON(BSONElement element) {
         uassert(ErrorCodes::TypeMismatch,
                 str::stream() << "Field '" << element.fieldNameStringData()
@@ -76,6 +80,9 @@ public:
 
     /**
      * Serialize this object as a field in a document. If _value is empty, omit the field.
+     *
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
      */
     void serializeToBSON(StringData fieldName, BSONObjBuilder* builder) const {
         if (_value) {
@@ -85,6 +92,9 @@ public:
 
     /**
      * Serialize this object as an element of a BSON array. If _value is empty, omit the entry.
+     *
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
      */
     void serializeToBSON(BSONArrayBuilder* builder) const {
         if (_value) {
@@ -112,6 +122,10 @@ private:
  */
 class IDLAnyType {
 public:
+    /**
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
+     */
     static IDLAnyType parseFromBSON(const BSONElement& element) {
         return IDLAnyType(element);
     }
@@ -119,10 +133,18 @@ public:
     IDLAnyType() = default;
     IDLAnyType(const BSONElement& element) : _element(element) {}
 
+    /**
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
+     */
     void serializeToBSON(StringData fieldName, BSONObjBuilder* builder) const {
         builder->appendAs(_element, fieldName);
     }
 
+    /**
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
+     */
     void serializeToBSON(BSONArrayBuilder* builder) const {
         builder->append(_element);
     }
@@ -141,6 +163,10 @@ protected:
  */
 class IDLAnyTypeOwned : public IDLAnyType {
 public:
+    /**
+     * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+     * break because of it.
+     */
     static IDLAnyTypeOwned parseFromBSON(const BSONElement& element) {
         return IDLAnyTypeOwned(element);
     }
diff --git a/src/mongo/idl/idl_parser.cpp b/src/mongo/idl/idl_parser.cpp
index 9cad14bffca..de0ffd40852 100644
--- a/src/mongo/idl/idl_parser.cpp
+++ b/src/mongo/idl/idl_parser.cpp
@@ -341,14 +341,26 @@ std::vector<std::vector<std::uint8_t>> transformVector(const std::vector<ConstDa
     return output;
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void noOpSerializer(bool, StringData fieldName, BSONObjBuilder* bob) {}
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeBSONWhenNotEmpty(BSONObj obj, StringData fieldName, BSONObjBuilder* bob) {
     if (!obj.isEmpty()) {
         bob->append(fieldName, obj);
     }
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 BSONObj parseOwnedBSON(BSONElement element) {
     uassert(ErrorCodes::TypeMismatch,
             str::stream() << "Expected field " << element.fieldNameStringData()
@@ -357,6 +369,10 @@ BSONObj parseOwnedBSON(BSONElement element) {
     return element.Obj().getOwned();
 }
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 bool parseBoolean(BSONElement element) {
     uassert(ErrorCodes::TypeMismatch,
             str::stream() << "Expected field " << element.fieldNameStringData()
diff --git a/src/mongo/idl/idl_parser.h b/src/mongo/idl/idl_parser.h
index 47096c0d117..316ccd06c7e 100644
--- a/src/mongo/idl/idl_parser.h
+++ b/src/mongo/idl/idl_parser.h
@@ -289,12 +289,28 @@ std::vector<std::string> transformVector(const std::vector<StringData>& input);
 std::vector<ConstDataRange> transformVector(const std::vector<std::vector<std::uint8_t>>& input);
 std::vector<std::vector<std::uint8_t>> transformVector(const std::vector<ConstDataRange>& input);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void noOpSerializer(bool, StringData fieldName, BSONObjBuilder* bob);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 void serializeBSONWhenNotEmpty(BSONObj obj, StringData fieldName, BSONObjBuilder* bob);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 BSONObj parseOwnedBSON(BSONElement element);
 
+/**
+ * IMPORTANT: The method should not be modified, as API version input/output guarantees could
+ * break because of it.
+ */
 bool parseBoolean(BSONElement element);
 
 }  // namespace mongo