CSHARP-6007: Mark Server version 4.2 as EOL from driver's PoV (Min server version as 4.4, minWireVersion as 9) by sanych-sun · Pull Request #2016 · mongodb/mongo-csharp-driver

sanych-sun · 2026-05-28T20:28:30Z

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Pull request overview

Raises the driver's minimum supported MongoDB server version from 4.2 to 4.4 (minimum wire version 8 → 9), and removes/cleans up feature gates, tests, and CI matrix entries that targeted the now-unsupported 4.2 era. Several pre-4.4 code paths and helpers (e.g. FindProjectionChecker, CompatibilityLevel-driven projection fallback, pre-4.4 connection-pool-clearing behaviour, transactions-feature gating) are removed.

Changes:

Bump WireVersion.__supportedWireVersionRange from Server42 to Server44, update derived tests, and remove pre-4.4 Feature.*Supports(...) test requirements throughout the test suite.
Delete FindProjectionChecker and simplify FindOperation / FindOneAnd*Operation / LinqProviderAdapter / CoreSession.EnsureTransactionsAreSupported / Server.ShouldClearConnectionPoolForChannelException / DefaultAuthenticator to drop 4.2-era branches; mark HintForFindAndModifyFeature obsolete and introduce a new (currently only test-consumed) HintForFindAndModifyOperations feature.
Remove MongoDB 4.2 (and Ubuntu 18.04) variants from evergreen/evergreen.yml, including CSFLE, OData and compression matrices.

Reviewed changes

Copilot reviewed 89 out of 89 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/MongoDB.Driver/Core/Misc/WireVersion.cs	Raises min supported wire version to `Server44`.
src/MongoDB.Driver/Core/Misc/Feature.cs	Marks `HintForFindAndModifyFeature` obsolete; adds new `HintForFindAndModifyOperations`; removes `[Obsolete]` from `HintForUpdateAndReplaceOperations`.
src/MongoDB.Driver/Core/Misc/HintForFindAndModifyFeature.cs	Marks class `[Obsolete]`.
src/MongoDB.Driver/Core/Operations/FindProjectionChecker.cs	Deleted; pre-4.4 projection check no longer needed.
src/MongoDB.Driver/Core/Operations/FindOperation.cs	Drops `FindProjectionChecker` call.
src/MongoDB.Driver/Core/Operations/FindOneAndDeleteOperation.cs / FindOneAndReplaceOperation.cs / FindOneAndUpdateOperation.cs	Drop `FindProjectionChecker`; wrap remaining obsolete hint check with pragmas + TODO (CSHARP-6061).
src/MongoDB.Driver/Core/Servers/Server.cs / DefaultServer.cs / LoadBalancedServer.cs	Remove `maxWireVersion` parameter and pre-4.4 state-change pool-clear behavior.
src/MongoDB.Driver/Core/Bindings/CoreSession.cs	Simplifies `EnsureTransactionsAreSupported` to only reject standalone.
src/MongoDB.Driver/Authentication/DefaultAuthenticator.cs	Removes `ScramSha256Authentication` gating for saslSupportedMechs hello.
src/MongoDB.Driver/Linq/LinqProviderAdapter.cs	Removes pre-4.4 client-side projection fallback.
src/MongoDB.Driver/ProjectionDefinitionBuilder.cs	Removes unused `PositionalOperatorProjectionDefinition` class.
tests/MongoDB.Driver.TestHelpers/Core/XunitExtensions/RequireServer.cs	Drops CSFLE wire-version precondition in CSFLE requirement check.
tests/MongoDB.Driver.Tests/Specifications/server-selection/ServerSelectionTestHelpers.cs	Default max wire version 8→9, default server version 4.2→4.4.
tests/.../WireVersionTests.cs, ClusterTests.cs, ServerDescriptionTests.cs	Update expected supported wire range / compatibility test data to `9..29`.
tests/.../ConnectionInitializerTests.cs, AuthenticationHelperTests.cs, MongoDBX509AuthenticatorTests.cs, CSharp3173Tests.cs	Update hello max wire versions from `Server42`/`Server36` to `Server44`.
tests/.../WritableServerSelectorTests.cs	Replaces `Server42` secondary with `Server44`.
tests/.../CoreSessionTests.cs	Simplifies transaction-support test to only standalone rejection.
tests/.../ConnectionsSurvivePrimaryStepDownTests.cs	Removes pool-clear branches tied to `KeepConnectionPoolWhenNotPrimaryConnectionException`.
tests/.../BulkUpdateOperationTests.cs, BulkMixedWriteOperationTests.cs, RetryableUpdateCommandOperationTests.cs	Drop dead `HintForUpdateAndReplaceOperations` branches in hint-not-supported tests.
tests/.../FindOneAnd*OperationTests.cs	Switch to `HintForFindAndModifyOperations.FirstSupportedWireVersion`; remove `Execute_with_hint_should_throw_when_hint_is_not_supported` tests.
tests/.../ChangeStreamCursorTests.cs	Remove pre-PBRT branches.
tests/.../AsyncCursorTests.cs	Remove pre-4.4 getMore-comment test.
tests/.../AggregateToCollectionOperationTests.cs	Remove `AggregateMerge` requirement.
tests/.../EncryptionTestHelper.cs, ClientEncryptionTests.cs, AutoEncryptionTests.cs, ClientEncryptionProseTests.cs, ClientEncryptionExamples.cs, ExplicitEncryptionExamples.cs	Drop CSFLE feature requirements / early return.
tests/.../AuthenticationTests.cs	Drop `ScramSha256Authentication` precondition.
tests/.../ListDatabasesTests.cs, IFindFluentExtensionsTests.cs, OfTypeMongoCollectionTests.cs, PinnedShardRouterTests.cs, RetryableWritesTests.cs, ClusterTests.cs, ConnectionsSurvivePrimaryStepDownTests.cs, IFindFluentExtensionsTests.cs, MqlToHashedIndexKeyTests.cs	Drop now-unconditionally-supported feature requirements.
tests/.../Linq3Implementation/Jira/CSharpTests.cs and Linq3ImplementationWithLinq2Tests/.cs	Drop `Feature.*` requirements (projection, ToString, ToConversionOperators, SetStage, TrigOperators, etc.) and remove `CompatibilityLevel` plumbing.
tests/.../CSharp4734Tests.cs	Remove fallback assertions for pre-4.4 `NotSupportedException` from find projection.
tests/.../Sessions/SessionsProseTests.cs, retryable-reads/RetryableReadsProseTests.cs, retryable-writes prose tests, CrudProseTests.cs, AggregateTest.cs	Drop FailPointsFailCommand[ForSharded] / FailPointsBlockConnection / ClientSideEncryption / Transactions requirements.
tests/MongoDB.Driver.Examples/*	Drop ClientSideEncryption / Transactions feature requirements in example tests.
evergreen/evergreen.yml	Remove 4.2 + Ubuntu 18.04 variants; adjust OData/CSFLE matrices.

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+
        /// <summary>
        /// Gets the hint for update and replace operations feature.
        /// </summary>


+        /// Gets the hint for find and modify operations feature.
+        /// </summary>
+        public static Feature HintForFindAndModifyOperations => __hintForFindAndModifyOperations;
+
        /// <summary>


sanych-sun · 2026-05-28T20:47:55Z

+            // TODO: Investigate and remove code below in scope of https://jira.mongodb.org/browse/CSHARP-6061
+#pragma warning disable CS0618 // Type or member is obsolete
            if (Feature.HintForFindAndModifyFeature.DriverMustThrowIfNotSupported(wireVersion) || (WriteConcern != null && !WriteConcern.IsAcknowledged))
+#pragma warning restore CS0618 // Type or member is obsolete


Yes, but we have a discrepancy in CSharp implementation and CRUD spec which we want to investigate and fix separately . I've decided not to remove this feature check now to reduce the noise around the code. This will be addressed as a part of https://jira.mongodb.org/browse/CSHARP-6061

…rver version as 4.4, minWireVersion as 9)

BorisDog

LGTM!

Copilot AI review requested due to automatic review settings May 28, 2026 20:28

sanych-sun requested a review from a team as a code owner May 28, 2026 20:28

sanych-sun requested a review from ajcvickers May 28, 2026 20:28

Copilot started reviewing on behalf of sanych-sun May 28, 2026 20:28 View session

sanych-sun requested a review from BorisDog May 28, 2026 20:29

sanych-sun added the maintenance Non-code maintenance (deps, docs, configs, etc.). label May 28, 2026

Copilot AI reviewed May 28, 2026

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ajcvickers approved these changes May 29, 2026

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BorisDog requested changes May 29, 2026

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Comment thread src/MongoDB.Driver/Core/Misc/Feature.cs Outdated

Comment thread src/MongoDB.Driver/Core/Misc/Feature.cs Outdated

Comment thread src/MongoDB.Driver/Core/Misc/Feature.cs Outdated

sanych-sun added 4 commits May 29, 2026 12:46

CSHARP-6007: Mark Server version 4.2 as EOL from driver's PoV (Min se…

f18b7d6

…rver version as 4.4, minWireVersion as 9)

pr

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pr

eeb1961

Fix after rebase

48bb4b3

sanych-sun force-pushed the CSHARP-6007 branch from bedf887 to 48bb4b3 Compare May 29, 2026 19:55

sanych-sun requested a review from BorisDog May 29, 2026 19:58

BorisDog approved these changes May 29, 2026

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CSHARP-6007: Mark Server version 4.2 as EOL from driver's PoV (Min server version as 4.4, minWireVersion as 9)#2016

CSHARP-6007: Mark Server version 4.2 as EOL from driver's PoV (Min server version as 4.4, minWireVersion as 9)#2016
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