SERVER-43964 UUID etc need not befriend IDL types

7 files changed, 108 insertions, 128 deletions

diff --git a/buildscripts/idl/idl/cpp_types.py b/buildscripts/idl/idl/cpp_types.py
index d4066af197f..bb7ec7d0a22 100644
--- a/buildscripts/idl/idl/cpp_types.py
+++ b/buildscripts/idl/idl/cpp_types.py
@@ -56,24 +56,6 @@ def is_primitive_scalar_type(cpp_type):
     ]
 
 
-def get_primitive_scalar_type_default_value(cpp_type):
-    # type: (str) -> str
-    """
-    Return a default value for a primitive scalar type.
-
-    Assumes the IDL generated code verifies the user sets the value before serialization.
-    """
-    # pylint: disable=invalid-name
-    assert is_primitive_scalar_type(cpp_type)
-    if cpp_type == 'bool':
-        return 'false'
-    # TODO (SERVER-50101): Remove 'FeatureCompatibility::Version' once IDL supports a command
-    # cpp_type of C++ enum.
-    if cpp_type == 'ServerGlobalParams::FeatureCompatibility::Version':
-        return 'ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault44Behavior'
-    return '-1'
-
-
 def is_primitive_type(cpp_type):
     # type: (str) -> bool
     """Return True if a cpp_type is a primitive type and should not be returned as reference."""
diff --git a/buildscripts/idl/idl/generator.py b/buildscripts/idl/idl/generator.py
index 34747fd6d24..3dc643b5075 100644
--- a/buildscripts/idl/idl/generator.py
+++ b/buildscripts/idl/idl/generator.py
@@ -1580,13 +1580,12 @@ class _CppSourceFileWriter(_CppFileWriterBase):
         if default_init:
             for field in struct.fields:
                 needs_init = (field.type and field.type.cpp_type and not field.type.is_array
-                              and cpp_types.is_primitive_scalar_type(field.type.cpp_type))
-
-                if _is_required_serializer_field(field) and needs_init:
+                              and _is_required_serializer_field(field)
+                              and field.cpp_name != 'dbName')
+                if needs_init:
                     initializers.append(
-                        '%s(%s)' % (_get_field_member_name(field),
-                                    cpp_types.get_primitive_scalar_type_default_value(
-                                        field.type.cpp_type)))
+                        '%s(mongo::idl::preparsedValue<decltype(%s)>())' %
+                        (_get_field_member_name(field), _get_field_member_name(field)))
 
         # Serialize the _dbName field second
         initializes_db_name = False
@@ -1760,13 +1759,13 @@ class _CppSourceFileWriter(_CppFileWriterBase):
 
                     if struct.command_field.type.cpp_type and cpp_types.is_primitive_scalar_type(
                             struct.command_field.type.cpp_type):
-                        self._writer.write_line('%s localCmdType(%s);' %
-                                                (cpp_type_info.get_storage_type(),
-                                                 cpp_types.get_primitive_scalar_type_default_value(
-                                                     struct.command_field.type.cpp_type)))
+                        self._writer.write_line(
+                            'auto localCmdType = mongo::idl::preparsedValue<%s>();' %
+                            (cpp_type_info.get_storage_type()))
                     else:
                         self._writer.write_line(
-                            '%s localCmdType;' % (cpp_type_info.get_storage_type()))
+                            'auto localCmdType = mongo::idl::preparsedValue<%s>();' %
+                            (cpp_type_info.get_storage_type()))
                     self._writer.write_line(
                         '%s object(localCmdType);' % (common.title_case(struct.cpp_name)))
                 elif struct.namespace in (common.COMMAND_NAMESPACE_CONCATENATE_WITH_DB,
@@ -1777,7 +1776,8 @@ class _CppSourceFileWriter(_CppFileWriterBase):
                 else:
                     assert False, "Missing case"
             else:
-                self._writer.write_line('%s object;' % common.title_case(struct.cpp_name))
+                self._writer.write_line('auto object = mongo::idl::preparsedValue<%s>();' %
+                                        common.title_case(struct.cpp_name))
 
             self._writer.write_line(method_info.get_call('object'))
             self._writer.write_line('return object;')
diff --git a/src/mongo/db/s/migration_destination_manager.cpp b/src/mongo/db/s/migration_destination_manager.cpp
index 7e5a9fbe72f..3c62eaa932d 100644
--- a/src/mongo/db/s/migration_destination_manager.cpp
+++ b/src/mongo/db/s/migration_destination_manager.cpp
@@ -701,7 +701,7 @@ MigrationDestinationManager::getCollectionOptions(OperationContext* opCtx,
     fromOptionsBob.append(info["uuid"]);
     fromOptions = fromOptionsBob.obj();
 
-    return {fromOptions, fromUUID};
+    return {fromOptions, UUID::fromCDR(fromUUID)};
 }
 
 void MigrationDestinationManager::_dropLocalIndexesIfNecessary(
@@ -918,7 +918,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
           "fromShard"_attr = _fromShard,
           "epoch"_attr = _epoch,
           "sessionId"_attr = *_sessionId,
-          "migrationId"_attr = _migrationId.toBSON());
+          "migrationId"_attr = _migrationId->toBSON());
 
     MoveTimingHelper timing(
         outerOpCtx, "to", _nss.ns(), _min, _max, 6 /* steps */, &_errmsg, _toShard, _fromShard);
@@ -928,7 +928,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
     if (initialState == ABORT) {
         LOGV2_ERROR(22013,
                     "Migration abort requested before the migration started",
-                    "migrationId"_attr = _migrationId.toBSON());
+                    "migrationId"_attr = _migrationId->toBSON());
         return;
     }
 
@@ -965,7 +965,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
                   "scheduled for deletion",
                   "namespace"_attr = _nss.ns(),
                   "range"_attr = redact(range.toString()),
-                  "migrationId"_attr = _migrationId.toBSON());
+                  "migrationId"_attr = _migrationId->toBSON());
 
             auto status = CollectionShardingRuntime::waitForClean(
                 outerOpCtx, _nss, donorCollectionOptionsAndIndexes.uuid, range);
@@ -979,7 +979,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
         }
 
         // Insert a pending range deletion task for the incoming range.
-        RangeDeletionTask recipientDeletionTask(_migrationId,
+        RangeDeletionTask recipientDeletionTask(*_migrationId,
                                                 _nss,
                                                 donorCollectionOptionsAndIndexes.uuid,
                                                 _fromShard,
@@ -1099,7 +1099,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
                             LOGV2_WARNING(
                                 22011,
                                 "secondaryThrottle on, but doc insert timed out; continuing",
-                                "migrationId"_attr = _migrationId.toBSON());
+                                "migrationId"_attr = _migrationId->toBSON());
                         } else {
                             uassertStatusOK(replStatus.status);
                         }
@@ -1177,7 +1177,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
                 if (getState() == ABORT) {
                     LOGV2(22002,
                           "Migration aborted while waiting for replication at catch up stage",
-                          "migrationId"_attr = _migrationId.toBSON());
+                          "migrationId"_attr = _migrationId->toBSON());
                     return;
                 }
 
@@ -1190,7 +1190,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
                 if (i > 100) {
                     LOGV2(22003,
                           "secondaries having hard time keeping up with migrate",
-                          "migrationId"_attr = _migrationId.toBSON());
+                          "migrationId"_attr = _migrationId->toBSON());
                 }
 
                 sleepmillis(20);
@@ -1212,12 +1212,12 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
 
         LOGV2(22004,
               "Waiting for replication to catch up before entering critical section",
-              "migrationId"_attr = _migrationId.toBSON());
+              "migrationId"_attr = _migrationId->toBSON());
         LOGV2_DEBUG_OPTIONS(4817411,
                             2,
                             {logv2::LogComponent::kShardMigrationPerf},
                             "Starting majority commit wait on recipient",
-                            "migrationId"_attr = _migrationId.toBSON());
+                            "migrationId"_attr = _migrationId->toBSON());
 
         runWithoutSession(outerOpCtx, [&] {
             auto awaitReplicationResult =
@@ -1229,12 +1229,12 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
 
         LOGV2(22005,
               "Chunk data replicated successfully.",
-              "migrationId"_attr = _migrationId.toBSON());
+              "migrationId"_attr = _migrationId->toBSON());
         LOGV2_DEBUG_OPTIONS(4817412,
                             2,
                             {logv2::LogComponent::kShardMigrationPerf},
                             "Finished majority commit wait on recipient",
-                            "migrationId"_attr = _migrationId.toBSON());
+                            "migrationId"_attr = _migrationId->toBSON());
     }
 
     {
@@ -1274,7 +1274,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* outerOpCtx) {
             if (getState() == ABORT) {
                 LOGV2(22006,
                       "Migration aborted while transferring mods",
-                      "migrationId"_attr = _migrationId.toBSON());
+                      "migrationId"_attr = _migrationId->toBSON());
                 return;
             }
 
@@ -1407,7 +1407,7 @@ bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
                     "reloaded remote document",
                     "localDoc"_attr = redact(localDoc),
                     "remoteDoc"_attr = redact(updatedDoc),
-                    "migrationId"_attr = _migrationId.toBSON());
+                    "migrationId"_attr = _migrationId->toBSON());
             }
 
             // We are in write lock here, so sure we aren't killing
@@ -1438,7 +1438,7 @@ bool MigrationDestinationManager::_flushPendingWrites(OperationContext* opCtx,
                   "chunkMin"_attr = redact(_min),
                   "chunkMax"_attr = redact(_max),
                   "lastOpApplied"_attr = op,
-                  "migrationId"_attr = _migrationId.toBSON());
+                  "migrationId"_attr = _migrationId->toBSON());
         }
         return false;
     }
@@ -1449,7 +1449,7 @@ bool MigrationDestinationManager::_flushPendingWrites(OperationContext* opCtx,
           "namespace"_attr = _nss.ns(),
           "chunkMin"_attr = redact(_min),
           "chunkMax"_attr = redact(_max),
-          "migrationId"_attr = _migrationId.toBSON());
+          "migrationId"_attr = _migrationId->toBSON());
 
     return true;
 }
diff --git a/src/mongo/db/s/migration_destination_manager.h b/src/mongo/db/s/migration_destination_manager.h
index 761f8c9c4ef..b90a56f52f1 100644
--- a/src/mongo/db/s/migration_destination_manager.h
+++ b/src/mongo/db/s/migration_destination_manager.h
@@ -234,7 +234,7 @@ private:
 
     stdx::thread _migrateThreadHandle;
 
-    UUID _migrationId;
+    boost::optional<UUID> _migrationId;
     LogicalSessionId _lsid;
     TxnNumber _txnNumber{kUninitializedTxnNumber};
     NamespaceString _nss;
diff --git a/src/mongo/idl/idl_parser.h b/src/mongo/idl/idl_parser.h
index 316ccd06c7e..17d7c803586 100644
--- a/src/mongo/idl/idl_parser.h
+++ b/src/mongo/idl/idl_parser.h
@@ -37,6 +37,7 @@
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/bson/bsontypes.h"
 #include "mongo/db/namespace_string.h"
+#include "mongo/stdx/type_traits.h"
 
 namespace mongo {
 
@@ -70,6 +71,69 @@ void idlSerialize(BSONObjBuilder* builder, StringData fieldName, std::vector<T>
     }
 }
 
+/**
+ * A few overloads of `idlPreparsedValue` are built into IDL. See
+ * `preparsedValue` below. They are placed into a tiny private
+ * namespace which defines no types to isolate them.
+ */
+namespace preparsed_value_adl_barrier {
+
+/**
+ * This is the fallback for `idlPreparsedValue`. It value-initializes a `T`
+ * with a forwarded argument list in the usual way.
+ */
+template <typename T, typename... A>
+auto idlPreparsedValue(stdx::type_identity<T>, A&&... a) {
+    return T(std::forward<A>(a)...);
+}
+
+/**
+ * The value -1 is a conspicuous "uninitialized" value for integers.
+ * The integral type `bool` is exempt from this convention, however.
+ */
+template <typename T, std::enable_if_t<std::is_integral_v<T> && !std::is_same_v<bool, T>, int> = 0>
+auto idlPreparsedValue(stdx::type_identity<T>) {
+    return static_cast<T>(-1);
+}
+
+/**
+ * Define a default Feature Compatibility Version enum value for use in parsed
+ * ServerGlobalParams.
+ * TODO(SERVER-50101): Remove 'FeatureCompatibility::Version' once IDL supports
+ * a command cpp_type of C++ enum.
+ */
+inline auto idlPreparsedValue(
+    stdx::type_identity<ServerGlobalParams::FeatureCompatibility::Version>) {
+    return ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault44Behavior;
+}
+
+}  // namespace preparsed_value_adl_barrier
+
+/**
+ * Constructs an instance of `T(args...)` for use in idl parsing. The way the
+ * IDL generator currently writes C++ parse functions, it makes an instance of
+ * a field of type `T` and then mutates it. `preparsedValue<T>()` is used to
+ * construct those objects. This convention allows an extension hook whereby a
+ * type can select a custom initializer for such pre-parsed objects,
+ * particularly for types that shouldn't have a public default constructor.
+ *
+ * The extension hook is implemented via ADL on the name `idlPreparsedValue`.
+ *
+ * `idlPreparsedValue` takes a `type_identity<T>` and then some forwarded
+ * constructor arguments optionally (the IDL generator doesn't currently
+ * provide any such arguments but could conceivably do so in the future). A
+ * type `T` is deduced from this `type_identity<T>` argument.
+ *
+ * There are other ways to implement this extension mechanism, but this
+ * phrasing allows argument-dependent lookup to search the namespaces
+ * associated with `T`, since `T` is a template parameter of the
+ * `type_identity<T>` argument.
+ */
+template <typename T, typename... A>
+T preparsedValue(A&&... args) {
+    using preparsed_value_adl_barrier::idlPreparsedValue;
+    return idlPreparsedValue(stdx::type_identity<T>{}, std::forward<A>(args)...);
+}
 
 }  // namespace idl
 
diff --git a/src/mongo/s/catalog/type_chunk.h b/src/mongo/s/catalog/type_chunk.h
index 425edb9c4e2..1de86691f20 100644
--- a/src/mongo/s/catalog/type_chunk.h
+++ b/src/mongo/s/catalog/type_chunk.h
@@ -39,6 +39,7 @@
 #include "mongo/s/chunk_version.h"
 #include "mongo/s/shard_id.h"
 #include "mongo/s/shard_key_pattern.h"
+#include "mongo/stdx/type_traits.h"
 
 namespace mongo {
 
@@ -123,17 +124,14 @@ public:
     ChunkRange unionWith(ChunkRange const& other) const;
 
 private:
-    // For use with IDL parsing - limited to friend access only.
-    ChunkRange() = default;
-
-    // Make the IDL generated parser a friend
-    friend class RangeDeletionTask;
-    friend class MigrationCoordinatorDocument;
-
     BSONObj _minKey;
     BSONObj _maxKey;
 };
 
+inline ChunkRange idlPreparsedValue(stdx::type_identity<ChunkRange>) {
+    return ChunkRange{{}, {}};
+}
+
 class ChunkHistory : public ChunkHistoryBase {
 public:
     ChunkHistory() : ChunkHistoryBase() {}
diff --git a/src/mongo/util/uuid.h b/src/mongo/util/uuid.h
index a5e259a3c9a..eade27480d6 100644
--- a/src/mongo/util/uuid.h
+++ b/src/mongo/util/uuid.h
@@ -40,83 +40,20 @@
 #include "mongo/bson/bsonmisc.h"
 #include "mongo/bson/bsonobj.h"
 #include "mongo/logv2/log_attr.h"
+#include "mongo/stdx/type_traits.h"
 
 namespace mongo {
 
-namespace repl {
-class CollectionInfo;
-class OplogEntryBase;
-class DurableReplOperation;
-class InitialSyncIdDocument;
-}  // namespace repl
-
-namespace idl {
-namespace import {
-class One_UUID;
-}  // namespace import
-}  // namespace idl
-
 /**
  * A UUID is a 128-bit unique identifier, per RFC 4122, v4, using
  * a secure random number generator.
  */
 class UUID {
-    using UUIDStorage = std::array<unsigned char, 16>;
-
-    // Make the IDL generated parser a friend
-    friend class ConfigsvrShardCollectionResponse;
-    friend class CommonReshardingMetadata;
-    friend class DonorAbortMigration;
-    friend class DonorStartMigration;
-    friend class DonorWaitForMigrationToCommit;
-    friend class DonorForgetMigration;
-    friend class DonorStateMachine;
-    friend class DatabaseVersion;
-    friend class DbCheckOplogCollection;
-    friend class EncryptionPlaceholder;
-    friend class ExternalKeysCollectionDocument;
-    friend class idl::import::One_UUID;
-    friend class IndexBuildEntry;
-    friend class KeyStoreRecord;
-    friend class ListCollectionsReplyInfo;
-    friend class LogicalSessionId;
-    friend class LogicalSessionToClient;
-    friend class LogicalSessionIdToClient;
-    friend class LogicalSessionFromClient;
-    friend class MigrationCoordinatorDocument;
-    friend class MigrationDestinationManager;
-    friend class MigrationRecipientCommonData;
-    friend class RangeDeletionTask;
-    friend class ResolvedKeyId;
-    friend class repl::CollectionInfo;
-    friend class repl::OplogEntryBase;
-    friend class repl::DurableReplOperation;
-    friend class repl::InitialSyncIdDocument;
-    friend class RecipientForgetMigration;
-    friend class RecipientSyncData;
-    friend class ReshardingDonorDocument;
-    friend class ReshardingSourceId;
-    friend class ResumeIndexInfo;
-    friend class ResumeTokenInternal;
-    friend class ShardCollectionTypeBase;
-    friend class ShardsvrCleanupReshardCollection;
-    friend class ShardsvrShardCollectionResponse;
-    friend class ShardsvrRenameCollection;
-    friend class TenantMigrationDonorDocument;
-    friend class TenantMigrationRecipientDocument;
-    friend class TestReshardCloneCollection;
-    friend class TypeCollectionRecipientFields;
-    friend class TypeCollectionReshardingFields;
-    friend class VoteCommitIndexBuild;
-    friend class ImportCollectionOplogEntry;
-    friend class VoteCommitImportCollection;
-
-
 public:
     /**
      * The number of bytes contained in a UUID.
      */
-    static constexpr int kNumBytes = sizeof(UUIDStorage);
+    static constexpr int kNumBytes = 16;
 
     /**
      * Generate a new random v4 UUID per RFC 4122.
@@ -143,7 +80,7 @@ public:
     static UUID parse(const BSONObj& obj);
 
     static UUID fromCDR(ConstDataRange cdr) {
-        UUID uuid;
+        UUID uuid{UUIDStorage{}};
         invariant(cdr.length() == uuid._uuid.size());
         memcpy(uuid._uuid.data(), cdr.data(), uuid._uuid.size());
         return uuid;
@@ -242,19 +179,18 @@ public:
     }
 
 private:
-    UUID(const UUIDStorage& uuid) : _uuid(uuid) {}
+    using UUIDStorage = std::array<unsigned char, kNumBytes>;
 
-    /**
-     *  Should never be used, as the resulting UUID will not be unique.
-     *  The exception is in code generated by the IDL compiler, which itself ensures
-     *  such an invalid value cannot propagate.
-     */
-    friend class LogicalSessionId;
-    UUID() = default;
+    UUID(const UUIDStorage& uuid) : _uuid(uuid) {}
 
     UUIDStorage _uuid{};  // UUID in network byte order
 };
 
+/** Allow IDL-generated parsers to define uninitialized UUID objects. */
+inline auto idlPreparsedValue(stdx::type_identity<UUID>) {
+    return UUID::fromCDR(std::array<unsigned char, 16>{});
+}
+
 inline std::ostream& operator<<(std::ostream& s, const UUID& uuid) {
     return (s << uuid.toString());
 }