Added Scala 3 support by rozza · Pull Request #1904 · mongodb/mongo-java-driver

rozza · 2026-03-03T13:04:54Z

Added Macro support for Scala 3
Split Scala code to Scala 2 and Scala 3 specific code Updated evergreen to test Scala 3
Updated spotless Scala configuration to default to Scala 2 Added custom spotless Scala configuration for Scala 3 in bson-scala Updated test code work both with Scala 2 and Scala 3

JAVA-5261

rozza · 2026-03-03T16:20:06Z

Evergreen Scala build: https://spruce.corp.mongodb.com/version/69a7062cea6cf30007b219da/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

Added Macro support for Scala 3 Split Scala code to Scala 2 and Scala 3 specific code Updated evergreen to test Scala 3 Updated spotless Scala configuration to default to Scala 2 Added custom spotless Scala configuration for Scala 3 in bson-scala Updated test code work both with Scala 2 and Scala 3 JAVA-5261

rozza · 2026-03-04T09:48:48Z

.evergreen/.evg.yml

      - name: "scala-test-task"

+  - matrix_name: "scala-tests-3"
+    matrix_spec: { auth: "noauth", ssl: "nossl", jdk: [ "jdk17", "jdk21" ], version: [ "8.0" ], topology: "replicaset",


Scala 3 currently supports Java 8.

However, with Java 8 some of the test Models caused scalatest-Junit to fail with invalid class name.

Unfortunately, the fix is to upgrade scalatest but doing that limits the base version of the SDK - so I opted not test against Java 8, rather than set a hard base of 17.

rozza · 2026-03-04T09:51:53Z

bom/build.gradle.kts


 scalaVersions?.forEach { version ->
-    require(version.matches(Regex("\\d\\.\\d{2}"))) { "Scala version '$version' must be in the format X.YY" }
+    require(version.matches(Regex("^[23].*"))) { "Scala version '$version' not supported." }


This is to ensure the bom is correctly configured.

Where as Scala 2.11, 2.12, 2.13 are all major releases. Scala 3 has gone for the traditional Major.Minor.Patch formatting.

This means the postfix for artifacts for scala 3 is just _3 where as Scala 2 variants are _2.11, _2.12 etc. eg: mongo-scala-driver_2.11

rozza · 2026-03-04T09:52:40Z

bson-scala/src/main/scala-2/org/mongodb/scala/bson/codecs/macrocodecs/MacroCodec.scala

      case BsonType.DOCUMENT => readDocument(reader, decoderContext, clazz, typeArgs)
      case BsonType.ARRAY    => readArray(reader, decoderContext, clazz, typeArgs)
-      case BsonType.NULL =>
+      case BsonType.NULL     =>


Scalafmt changes only and a move to scala2 source directory

rozza · 2026-03-04T09:54:33Z

bson-scala/src/main/scala-3/org/mongodb/scala/bson/codecs/macrocodecs/CaseClassCodec.scala

+ *
+ * @see [[MacroCodec]] for the runtime base trait that the generated codec extends.
+ */
+private[bson] object CaseClassCodec {


This is the core of the CaseClassCodec Macro. It follows the same patterns as the Scala 2 version.

Scala 3 totally rewrote the Macros in a non compatible way. So this version is updated for the new Scala 3 macros and compile time reflection.

rozza · 2026-03-04T09:55:37Z

bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/immutable/Document.scala

@@ -0,0 +1,141 @@
+/*


Scala 3 versions of Document and BaseBsonDocument using Scala 3 specific classes.

Much the same as the Scala 2.13 version. But I didn't want to split out joint Scala 2.13 & Scala 3 code as the source directories are confusing enough.

rozza · 2026-03-04T10:02:41Z

buildSrc/src/main/kotlin/conventions/spotless.gradle.kts

    scala {
        target("**/*.scala")
-        scalafmt().configFile(rootProject.file("config/scala/scalafmt.conf"))
+        targetExclude("**/scala-3/**")


The default excludes all scala-3 code.

rozza · 2026-03-04T10:03:14Z

buildSrc/src/main/kotlin/project/scala.gradle.kts

    // ============================================
    val compileOptions = mutableListOf("-target:jvm-1.8")
    when (scalaVersion) {
+        "3" -> {


This adds the Scala 3 code base with its own specific sourcesets.

rozza · 2026-03-04T10:08:02Z

...grationTest/scala/org/mongodb/scala/documentation/DocumentationChangeStreamExampleSpec.scala


 package org.mongodb.scala.documentation

-import java.util.concurrent.CountDownLatch


All these test changes were needed to ensure the tests work in both Scala 2 and Scala 3.

Implicit conversions now have to be explicitly imported in Scala 3. Some Scala 3 language based implicits where previously used (eg maxTime auto conversion to Duration). This is now explicit so that it can work across versions.

Partial functions are required to be ( varname: Type) => where as previously they could be without parenthesis.

Functions that are defined with parenthesis, must include them in Scala 3 eg: collection.watch was fine in Scala 2, but now must be collection.watch().

rozza · 2026-03-04T10:10:07Z

driver-scala/src/test/scala/org/mongodb/scala/BaseSpec.scala


-abstract class BaseSpec extends AnyFlatSpec with Matchers {}
+abstract class BaseSpec extends AnyFlatSpec with Matchers {
+  val DEFAULT_EXCLUSIONS: Set[String] =


I DRY'd up the default exclusions. Depending on the version of Scala depends on the name of some of the auto added methods to java / scala classes when relfecting on the methods in the API.

rozza · 2026-03-04T10:10:29Z

gradle.properties

 org.gradle.jvmargs=-Dfile.encoding=UTF-8 -Duser.country=US -Duser.language=en
 ## NOTE: This property is also used to generate scala compile versions in BOM.
-supportedScalaVersions=2.13,2.12,2.11
+supportedScalaVersions=3,2.13,2.12,2.11


driver-scala/README.md

bson-scala/src/main/scala-2/org/mongodb/scala/bson/codecs/macrocodecs/CaseClassCodec.scala

buildSrc/src/main/kotlin/project/scala.gradle.kts

driver-scala/src/test/scala/org/mongodb/scala/model/BucketGranularitySpec.scala

driver-scala/README.md

Copilot

Pull request overview

This PR adds Scala 3 support across the Scala driver and BSON Scala modules, including Scala 3 macro-based codecs, version-specific source set wiring, updated formatting (Spotless/scalafmt) configuration, and Evergreen CI coverage.

Changes:

Add Scala 3 as a supported build/test target (Gradle properties, BOM validation, Evergreen matrix).
Split Scala sources/tests into Scala 2 vs Scala 3 source sets and update Scala build wiring/dependencies.
Add Scala 3 macro codec implementation + Scala 3-specific BSON collection code and tests.

Reviewed changes

Copilot reviewed 79 out of 87 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
gradle/libs.versions.toml	Adds Scala 3 library/test coordinates and bumps tool/test versions.
gradle.properties	Adds Scala 3 to supportedScalaVersions.
driver-scala/src/test/scala/org/mongodb/scala/model/ValidationLevelSpec.scala	Uses shared DEFAULT_EXCLUSIONS for reflection-based API parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/ValidationActionSpec.scala	Uses shared DEFAULT_EXCLUSIONS for reflection-based API parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/ProjectionsSpec.scala	Adjusts method invocation to be Scala 3-compatible.
driver-scala/src/test/scala/org/mongodb/scala/model/MergeOptionsSpec.scala	Updates exclusions for Scala 3 method synthesis differences.
driver-scala/src/test/scala/org/mongodb/scala/model/FiltersSpec.scala	Updates exclusions for Scala 3 compiler-synthesized methods.
driver-scala/src/test/scala/org/mongodb/scala/model/CollationStrengthSpec.scala	Uses shared DEFAULT_EXCLUSIONS for parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/CollationSpec.scala	Uses shared DEFAULT_EXCLUSIONS for parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/CollationMaxVariableSpec.scala	Uses shared DEFAULT_EXCLUSIONS for parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/CollationCaseFirstSpec.scala	Uses shared DEFAULT_EXCLUSIONS for parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/CollationAlternateSpec.scala	Uses shared DEFAULT_EXCLUSIONS for parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/BucketGranularitySpec.scala	Uses shared DEFAULT_EXCLUSIONS for parity test.
driver-scala/src/test/scala/org/mongodb/scala/model/AggregatesSpec.scala	Adds import to support Scala 3 compilation changes.
driver-scala/src/test/scala/org/mongodb/scala/internal/ScalaObservableSpec.scala	Tweaks syntax/class definitions for Scala 3 compatibility.
driver-scala/src/test/scala/org/mongodb/scala/internal/FlatMapObservableTest.scala	Fixes Promise completion call signature for Scala 3.
driver-scala/src/test/scala/org/mongodb/scala/internal/CollectObservableTest.scala	Adds ObservableFuture import for Scala 3 compilation.
driver-scala/src/test/scala/org/mongodb/scala/connection/ConnectionSpec.scala	Updates builder invocation style for Scala 3.
driver-scala/src/test/scala/org/mongodb/scala/ReadPreferenceSpec.scala	Updates exclusions and formatting for Scala 3.
driver-scala/src/test/scala/org/mongodb/scala/ReadConcernSpec.scala	Uses DEFAULT_EXCLUSIONS for Scala 3 compiler methods.
driver-scala/src/test/scala/org/mongodb/scala/ReadConcernLevelSpec.scala	Uses DEFAULT_EXCLUSIONS for Scala 3 compiler methods.
driver-scala/src/test/scala/org/mongodb/scala/ObservableImplicitsToGridFSUploadPublisherUnitSpec.scala	Adds explicit type to satisfy Scala 3 inference.
driver-scala/src/test/scala/org/mongodb/scala/MongoDriverInformationSpec.scala	Consolidates exclusions via DEFAULT_EXCLUSIONS.
driver-scala/src/test/scala/org/mongodb/scala/DistinctObservableSpec.scala	Refactors exclusions to include DEFAULT_EXCLUSIONS.
driver-scala/src/test/scala/org/mongodb/scala/CreateIndexCommitQuorumSpec.scala	Excludes Scala 3 synthetic methods via DEFAULT_EXCLUSIONS.
driver-scala/src/test/scala/org/mongodb/scala/BaseSpec.scala	Introduces DEFAULT_EXCLUSIONS shared by multiple tests.
driver-scala/src/test/scala-2/org/mongodb/scala/ApiAliasAndCompanionSpec.scala	Formatting tweak for Scala 2 specific tests.
driver-scala/src/integrationTest/scala/tour/QuickTourCaseClass.scala	Updates find/first call chain for Scala 3 compatibility.
driver-scala/src/integrationTest/scala/tour/QuickTour.scala	Updates find/first call chain and lambda syntax for Scala 3.
driver-scala/src/integrationTest/scala/tour/Helpers.scala	Updates toJson invocation for Scala 3.
driver-scala/src/integrationTest/scala/tour/ClientSideEncryptionExplicitEncryptionOnlyTour.scala	Updates find/first call chain for Scala 3.
driver-scala/src/integrationTest/scala/tour/ClientSideEncryptionExplicitEncryptionAndDecryptionTour.scala	Updates find/first call chain for Scala 3.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncMongoIterable.scala	Import ordering cleanup.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncMongoDatabase.scala	Adapts timeouts to Duration-based APIs.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncMongoCursor.scala	Import ordering and minor match formatting.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncMongoCollection.scala	Adds futures imports used by updated APIs.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncMongoCluster.scala	Adds futures import for updated APIs.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncMapReduceIterable.scala	Adapts maxTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncListSearchIndexesIterable.scala	Adapts maxTime and explain signatures for Scala 3 typing.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncListIndexesIterable.scala	Adapts maxTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncListDatabasesIterable.scala	Adapts maxTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncListCollectionsIterable.scala	Adapts maxTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncFindIterable.scala	Adapts maxTime/maxAwaitTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncDistinctIterable.scala	Adapts maxTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncClientSession.scala	Import ordering cleanup.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncClientEncryption.scala	Adds conversion import for updated BSON APIs.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncChangeStreamIterable.scala	Adapts maxAwaitTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/syncadapter/SyncAggregateIterable.scala	Adapts maxTime/maxAwaitTime to Duration-based API.
driver-scala/src/integrationTest/scala/org/mongodb/scala/gridfs/GridFSObservableSpec.scala	Scala 3 syntax adjustments (type params, class defs).
driver-scala/src/integrationTest/scala/org/mongodb/scala/documentation/DocumentationTransactionsExampleSpec.scala	Updates helper invocation style for Scala 3.
driver-scala/src/integrationTest/scala/org/mongodb/scala/documentation/DocumentationExampleSpec.scala	Updates helpers, watch() invocation, observer class for Scala 3.
driver-scala/src/integrationTest/scala/org/mongodb/scala/documentation/DocumentationChangeStreamExampleSpec.scala	Updates watch() invocation and lambda syntax for Scala 3.
driver-scala/src/integrationTest/scala/org/mongodb/scala/TestMongoClientHelper.scala	Converts helpers to explicit nullary methods + local WAIT_DURATION.
driver-scala/src/integrationTest/scala/org/mongodb/scala/RequiresMongoDBISpec.scala	Updates helper calls/signatures for Scala 3.
driver-scala/README.md	Documents Scala version support, source layout, Spotless, and testing flags.
config/scala/scalafmt-3.conf	Adds Scala 3-specific scalafmt configuration.
config/scala/scalafmt-2.conf	Updates Scala 2 scalafmt version.
buildSrc/src/main/kotlin/project/scala.gradle.kts	Adds Scala 3 dependency wiring and source set configuration.
buildSrc/src/main/kotlin/conventions/spotless.gradle.kts	Defaults Spotless to Scala 2 config and excludes scala-3 paths.
bson-scala/src/test/scala/org/mongodb/scala/bson/collections/MutableDocumentSpec.scala	Formatting adjustments for Scala 3 compatibility.
bson-scala/src/test/scala/org/mongodb/scala/bson/collections/ImmutableDocumentSpec.scala	Formatting adjustments for Scala 3 compatibility.
bson-scala/src/test/scala/org/mongodb/scala/bson/codecs/MutableDocumentCodecSpec.scala	Formatting adjustments for Scala 3 compatibility.
bson-scala/src/test/scala/org/mongodb/scala/bson/codecs/ImmutableDocumentCodecSpec.scala	Formatting adjustments for Scala 3 compatibility.
bson-scala/src/test/scala-3/org/mongodb/scala/bson/codecs/Models.scala	Adds Scala 3 test models for macro codec coverage.
bson-scala/src/test/scala-3/org/mongodb/scala/bson/codecs/MacrosSpec.scala	Adds Scala 3 macro codec spec suite.
bson-scala/src/test/scala-2/org/mongodb/scala/bson/codecs/MacrosSpec.scala	Import/order formatting tweaks for Scala 2 suite.
bson-scala/src/main/scala/org/mongodb/scala/bson/codecs/IterableCodec.scala	Minor formatting update.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/package.scala	Scala 3 package object for collection Document alias.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/mutable/Document.scala	Scala 3 mutable Document implementation.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/immutable/Document.scala	Scala 3 immutable Document implementation.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/BaseDocument.scala	Scala 3 BaseDocument implementation.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/codecs/macrocodecs/MacroCodec.scala	Scala 3 runtime macro codec base implementation.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/codecs/macrocodecs/CaseClassProvider.scala	Scala 3 macro entry point for codec providers.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/codecs/macrocodecs/CaseClassCodec.scala	Scala 3 macro that generates codecs.
bson-scala/src/main/scala-3/org/mongodb/scala/bson/codecs/Macros.scala	Scala 3 public macro API (inline/quoted) surface.
bson-scala/src/main/scala-2/org/mongodb/scala/bson/collection/package.scala	Scala 2 package object for collection Document alias.
bson-scala/src/main/scala-2/org/mongodb/scala/bson/collection/BaseDocument.scala	Scala 2 BaseDocument implementation.
bson-scala/src/main/scala-2/org/mongodb/scala/bson/codecs/macrocodecs/MacroCodec.scala	Scala 2 macro codec runtime tweaks/formatting.
bson-scala/src/main/scala-2/org/mongodb/scala/bson/codecs/macrocodecs/CaseClassProvider.scala	Scala 2 macro provider wiring changes.
bson-scala/src/main/scala-2/org/mongodb/scala/bson/codecs/macrocodecs/CaseClassCodec.scala	Scala 2 macro codec formatting tweak.
bson-scala/src/main/scala-2/org/mongodb/scala/bson/codecs/Macros.scala	Scala 2 public macro API surface (macro defs).
bson-scala/src/main/scala-2.13/org/mongodb/scala/bson/collection/mutable/Document.scala	Scala 2.13 mutable Document implementation.
bson-scala/src/main/scala-2.13/org/mongodb/scala/bson/collection/immutable/Document.scala	Scala 2.13 immutable Document implementation.
bson-scala/build.gradle.kts	Adds Scala-version-aware Spotless override for scala-3 sources.
bson-scala/README.md	Documents Scala 3 support and module build/layout details.
bom/build.gradle.kts	Updates Scala version validation to accept Scala 3.
.evergreen/.evg.yml	Adds Scala 3 axis and build variants for Scala 3 testing.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/mutable/Document.scala

bson-scala/README.md

driver-scala/src/test/scala/org/mongodb/scala/model/FiltersSpec.scala

buildSrc/src/main/kotlin/project/scala.gradle.kts

bson-scala/src/test/scala-3/org/mongodb/scala/bson/codecs/MacrosSpec.scala

driver-scala/src/test/scala/org/mongodb/scala/BaseSpec.scala

bson-scala/src/main/scala-3/org/mongodb/scala/bson/collection/immutable/Document.scala

rozza · 2026-03-11T13:55:08Z

@copilot open a new pull request to apply changes based on the comments in this thread

OK that didn't happen (might be a config issue on the org) So manually did the changes.

rozza force-pushed the JAVA-5261 branch 6 times, most recently from 6dd3f40 to 71cab33 Compare March 3, 2026 16:03

rozza force-pushed the JAVA-5261 branch from 71cab33 to f8535e1 Compare March 4, 2026 09:25

rozza requested a review from strogiyotec March 4, 2026 09:26

rozza commented Mar 4, 2026

View reviewed changes

rozza marked this pull request as ready for review March 4, 2026 10:11

rozza requested a review from a team as a code owner March 4, 2026 10:11

strogiyotec requested changes Mar 11, 2026

View reviewed changes

PR updates

346bc7b

rozza requested review from Copilot and strogiyotec March 11, 2026 10:49

Copilot started reviewing on behalf of rozza March 11, 2026 11:15 View session

Copilot AI reviewed Mar 11, 2026

View reviewed changes

copilot review updates

6c5ffb3

strogiyotec approved these changes Mar 11, 2026

View reviewed changes


		package org.mongodb.scala.documentation

		import java.util.concurrent.CountDownLatch

Conversation

rozza commented Mar 3, 2026

Uh oh!

rozza commented Mar 3, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

rozza commented Mar 11, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

rozza commented Mar 11, 2026 •

edited

Loading